# Ambitious ORC Turbine



## Toymaker (Jan 30, 2022)

For the past year I've been slowly designing and building pieces of a rather ambitious "steam" engine project.  I'm retired so I have the luxury of taking as much time as I want, or need, to complete this project, and like most folks here, this is my hobby, not my job.

My goal is to build the smallest, lightest turbine possible that develops around 200 HP (150 kW) with the best fuel efficiency that I can achieve, and the entire system must also be mobile.

With those requirements in mind, I set out to build an ORC (Organic Rankine Cycle) turbine engine.  I've already posted a few pics of some of the parts in the General Engine Discussion  forum and the Boilers forum, but I'll start from the beginning in this forum as this project is still incomplete.  

I started by making a list of all the various parts I would need, then sketched out a system diagram and finally drew up a CAD drawing which made making changes easier.  Keep in mind that the below drawing is still in flux and incomplete, but I believe it represents at least 95% of the finished system.  






For several reasons I decided to use a 3 stage axial flow turbine.  This is a closed system which constantly re-cycles the working fluid, which in this case is not water, but an organic liquid instead.  Below is a rough sketch of the turbine and other parts, to be discussed later.   I've left out a lot of detail, which I will discuss if asked.





Turbines can be tricky to regulate, especially small ones.  They can over-rev in the blink of an eye.   Also, I've chosen to use a supercritical boiler with high flow and heated with a forced air burner with high flow rate.   For safety and for best control, I decided to use a microcontroller along with sensors and servo motors to take full control of the entire system.  These on-board computers are often referred to as a FADEC, for Full Authority Digital Electronic Control.   Below is the FADEC system I will be using.




This was my starting point and continues to be my guide for what still needs to be accomplished.  
Again, please keep in mind that these drawings are still in a state of flux, and can be changed and added to as needed.  

Next, I'll post a few pics and videos of the actual parts I've managed to make thus far.


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## Toymaker (Jan 30, 2022)

One of the advantages of using an organic working fluid instead of water is that the turbine can be made with only 1 to 3 stages and still be quite efficient.  I chose to build a 3 stage axial flow turbine with most parts made from 6061 aluminum, including the blades.  The center shaft, or spindle, is steel and both bearings are ceramic; (The bearing shown in the pick below is standard Stainless Steel, but it has already been replaced with a full ceramic thrust bearing).






The pic below shows the outside of the turbine housing.  Those 8 large threaded holes drilled at a 45 degree angle are where the "steam" flows into the steam chest and from there through the nozzle vanes.  The 4 socket head screws penetrate through the housing and hold the nozzle in place.  






The 3rd and largest _*Blisk *_(Bladed Disk) is just over 3.5" in diameter while the 1st stage blisk is 2.36" in diameter.  All three blisks slide onto the splined spindle.  Below are the 2nd and 3rd row blisks and the second set of stator blades.






The pic below shows how the boiler output "steam" is routed through eight 8mm tubes into the turbine housing.
Eight additional 8mm aluminum tubes will be brazed into the holes you see in the uppermost oddly shaped block and then wound around in a spiral pattern forming the super critical section of the boiler.


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## Toymaker (Jan 30, 2022)

The burner uses as cordless leaf blower to force air through the combustion chamber.  The design is similar to the burner section of a jet engine, and the burners inside of "torpedo space heaters" and burns standard diesel fuel.  
The fuel nozzle is a siphon type that uses low pressure air to suck in the fuel and atomize it into a fine mist; at 6 psi air pressure, the nozzle is rated at 14 liters/hour.  My manual testing has shown the burner to work well up to 7psi.  The video below shows the burner running at near Maximum fuel burn.  That no black smoke is seen from the exhaust indicates 100% clean fuel burn, or at least very close to 100%.  14 liters/h = 148 kWh = 200 HP-hours. 




Your browser is not able to display this video.


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## Toymaker (Jan 31, 2022)

The burner is made from two different sizes of stainless steel cups which are widely available here in Thailand.  The handles are removed with my shop grinder and bottoms are cut out on my lathe.  One cup has swirl vanes cut into the bottom along with holes to mount the fuel nozzle.  





Two rings of swirl vanes, like the one shown below, are added to help force the fresh air to swirl around the outer surface of the inner burner cans to keep them cool and help guide the fresh air into the combustion chamber in a swirling pattern.  The swirling tornado-like flames stay inside the combustion chamber just a bit longer, allowing for greater fuel-air mixing and more complete combustion of all the fuel.   The last pick in this row shows all three outer shell cans stacked together.  The silicone tubes carry low pressure air and siphoned fuel into the nozzle.  








This last pic shows how the inner burner cans fit inside the outer shell cans.  The two sets of swirl vanes keep the inner cans in alignment as they expand and contract during heating and cooling.  

Now before someone asks, "why didn't I just use a couple of stainless steel tubes or even rolled stainless sheet",...the answer is that I've had to learn to use what's available while living in Thailand.  Stainless tubes and sheet are both very hard to acquire where I live, so I use what I can get.  But as an un-planned benefit, turns out that the separate cans make disassembly and re-assembly very easy.  

Finally, here's a pic showing the small cordless leaf blower mounted onto the burner where it blows fresh air into the combustion area.  The battery is removed from the blower and it's electric motor is powered by a PWM motor speed control which allows me to manually increase or decrease air flow into the burner.  

This last pic also shows the two white porcelain electrodes for the high voltage spark ignitor.


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## Toymaker (Jan 31, 2022)

In preparation for using a FADEC to control the engine, I modified the manual pressure regulator I'm using to control fuel flow, by adding a stepper motor and electronics to drive the motor.  The manual regulator is on the left while the FADEC controlled version is on the right.  Same regulator and gauge in both pics, just added some automation goodies to the right pic.


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## ddmckee54 (Jan 31, 2022)

This looks too well thought out to be an impulse build.  What are you planning on doing with this thing? Nice looking machine work, especially on the blisks.  What did you use to cut the internal splines?


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## Toymaker (Jan 31, 2022)

ddmckee54 said:


> This looks too well thought out to be an impulse build.  What are you planning on doing with this thing? Nice looking machine work, especially on the blisks.  What did you use to cut the internal splines?



Thanks for the compliments on the machine work,...it's all done on my DIY CNC Lathe and Mill.  I think it's been about 8 or 9 years ago that I built my CNC Milling machine, and with that and a CNC rotor tool I also built, I'm able to machine most everything I need, including those internal splines.  Here's a link to a YouTube video I made months ago on how I did it: *Cutting Internal Splines*.

You're right about this project not being an impulse build, the engine has a very specific purpose.  Most folks look at the hot flames coming out of a jet engine and believe it's all those hot gases that make the thrust, and that is true, but a jet engine's exhaust doesn't need to be hot in order to produce thrust, the gases just need to be moving and have mass.  F=ma governs how much static thrust a jet engine produces; the mass of the exhaust gases times it's acceleration is how thrust is calculated,....and it's the compressor inside the engine that is doing all the work to produce that thrust.  Essentially, jet engines are just big air compressors that direct their compressed air out of the back of the engine.

It really doesn't matter what type of motor drives a jet engine's compressor, as long as that motor has adequate power and can spin the compressor at the required rpm the compressor will produce thrust. 

So that's my first step; determine how much thrust a steam turbine can produce.  If all goes as I hope it will, that's the first step in an even larger project.


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## ddmckee54 (Feb 1, 2022)

What kind of rpm's are you aiming/hoping for from the turbine?  Have you done any dynamic balancing on it? (Or maybe just haven't gotten that far yet?)


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## Toymaker (Feb 1, 2022)

ddmckee54 said:


> What kind of rpm's are you aiming/hoping for from the turbine?  Have you done any dynamic balancing on it? (Or maybe just haven't gotten that far yet?)



Planned max RPM is 70,000.

Currently, static balancing only.  I did find an interesting technique for dynamic balancing using a standard smart phone:  I haven't used *Dynamic Balance App*  but it was written to help drone owners balance the motors on their drones but I should be able to use it tell me if I need to balance my rotor or if it's close enough I needn't worry. 

If you know of any good methods for dynamic balancing, please do let me know. 

Two methods of static balancing that have worked very well for me in the past:  One method requires both shaft ends of the rotor to be placed on knife edges which must be perfectly horizontal.   The heavy part of the rotor will slowly roll to the bottom.  The second method replaces the knife edges with very clean ceramic bearings, with no lubrication.  I've found this works equally well and without the need to align the two knife edges perfectly horizontal.


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## skyline1 (Feb 2, 2022)

Toymaker said:


> One method requires both shaft ends of the rotor to be placed on knife edges which must be perfectly horizontal. The heavy part of the rotor will slowly roll to the bottom.



I use exactly the same method to balance the rotors on my little DeLaval's (see avatar) and have found that, although simple, it works really well

Best Regards Mark


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## mu38&Bg# (Feb 2, 2022)

The phone apps are not doing dynamic (dual plane) balancing.

Static balance is acceptable when the shaft is short or is a single disk.


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## ddmckee54 (Feb 2, 2022)

Are you building a refrigeration unit?  The system looks similar, though a lot smaller, to the old steam heated chillers that were used in some of the buildings that I worked in - many... many... moons ago. (mid-80's)


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## ddmckee54 (Feb 2, 2022)

Toymaker said:


> If you know of any good methods for dynamic balancing, please do let me know.



I remember watching a video of a guy building a small gas turbine.  I think he machined his own compressor wheel and then dynamically balanced it.  If it's the guy I'm thinking of, he builds some fairly high-tech projects and then gets into the science and engineering behind them.  I'll see if I can find it again.


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## HMEL (Feb 2, 2022)

Toymaker said:


> Thanks for the compliments on the machine work,...it's all done on my DIY CNC Lathe and Mill.  I think it's been about 8 or 9 years ago that I built my CNC Milling machine, and with that and a CNC rotor tool I also built, I'm able to machine most everything I need, including those internal splines.  Here's a link to a YouTube video I made months ago on how I did it: *Cutting Internal Splines*.
> 
> You're right about this project not being an impulse build, the engine has a very specific purpose.  Most folks look at the hot flames coming out of a jet engine and believe it's all those hot gases that make the thrust, and that is true, but a jet engine's exhaust doesn't need to be hot in order to produce thrust, the gases just need to be moving and have mass.  F=ma governs how much static thrust a jet engine produces; the mass of the exhaust gases times it's acceleration is how thrust is calculated,....and it's the compressor inside the engine that is doing all the work to produce that thrust.  Essentially, jet engines are just big air compressors that direct their compressed air out of the back of the engine.
> 
> ...


What you have in mind to build is called a combined cycle plant.  Now as a technical point the jet engine compressor is designed to take the working fluid (air ) to a higher Pressure in a combustion can. Here fuel is added and the combustion products with even higher pressure are exhausted out the exit nozzle which yields a thrust.  If the compressor is driven by a motor you do not need the driving blades on the shaft to power the compressor.  Almost 70% of a turbine developed power drives the compressor.  Its a pressure drop that determines the power. All of this can be calculated.  In a combined cycle the hot gas from the turbine is dropped into the furnace of the steam boiler at about 1500 degree F.  To calculate the steam turbine take the inlet pressure and calculate the drop in the condenser and that yields the horsepower theoretical number.  The actual number will be less by some efficiency number. A basic textbook in thermodynamics will demonstrate the proper technique to determine what is called Pressure Volume work. For examples you might look at the guys who fly model airplanes with jet engines.  They will not have the steam cycle attached but they have everything else. Its actually amazing how small they can make these things.


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## Toymaker (Feb 2, 2022)

ddmckee54 said:


> Are you building a refrigeration unit?  The system looks similar, though a lot smaller, to the old steam heated chillers that were used in some of the buildings that I worked in - many... many... moons ago. (mid-80's)



No, the system is not for refrigeration.  Once the turbine, boiler, condenser, etc are all working well together I will connect a centrifugal compressor (the same you'll find on automotive turbo chargers) directly to the turbine's output shaft which will compress large volumes of air to about 50 to 60 psi.


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## Toymaker (Feb 2, 2022)

HMEL said:


> Now as a technical point the jet engine compressor is designed to take the working fluid (air ) to a higher Pressure in a combustion can. Here fuel is added and the combustion products with even higher pressure are exhausted out the exit nozzle which yields a thrust.



Your explanation of how a jet engine works is mostly correct, but with one small mistake: during normal operation, the combustion chamber and the combustion gases are always at a slightly lower pressure then the compressor outlet.  The temperature of the combustions gases are clearly much higher, but the pressure is always a few psi lower.  When pressures inside the combustion chamber or it's exhaust inadvertently reach a higher pressure then the compressor outlet the combustion gases flow backwards through the compressor and is one cause of what's known as a "compressor stall".  



HMEL said:


> If the compressor is driven by a motor you do not need the driving blades on the shaft to power the compressor.  Almost 70% of a turbine developed power drives the compressor.  Its a pressure drop that determines the power. All of this can be calculated.  In a combined cycle the hot gas from the turbine is dropped into the furnace of the steam boiler at about 1500 degree F.  To calculate the steam turbine take the inlet pressure and calculate the drop in the condenser and that yields the horsepower theoretical number.  The actual number will be less by some efficiency number. A basic textbook in thermodynamics will demonstrate the proper technique to determine what is called Pressure Volume work. For examples you might look at the guys who fly model airplanes with jet engines.  They will not have the steam cycle attached but they have everything else. Its actually amazing how small they can make these things.



I'm not using the exhaust of a small jet engine as my heat source, though I do admit that the burner exhaust in the video  I posted above does look and sound a lot like a jet engine, it is just a diesel fuel burner with a "leaf blower" forcing high speed air through the burner.  

I have not yet measured the exhaust gas temperature of my burner but since I'm not adding any cooling air to the exhaust, as is done with all jet engines, I suspect Adiabatic flame temperatures of around 2100C (3800F)


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## Steamchick (Feb 3, 2022)

Hi Toymaker. An impressive project. I am trying to understand your boiler concept.... it looks like a flash boiler? Liquid injected at one end and superheated vapour extracted at the other? One point to research.... you may have done it already? I.E.  The corrosion resistance of aluminium at the expected max temperature of your organic fluid. Please can you post more drawings of the boiler?
K2


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## Steamchick (Feb 4, 2022)

Hi Toymaker, I was looking at bearings - considering something for a turbine that I have some parts and ideas about. I read about these bearings: 
KLNJ R Series 2RS C3 Rubber Sealed High Speed Imperial Bearings - High Quality 
"High speed" means 35,000rpm. for class C3. Apparently they are "slack" to permit the balls to expand when they get hot at speed...
So for higher speeds, we need special bearings, that I have not found yet.
What class/material of bearings do you plan to use? ( - for planned 70,000rpm max speed? (Your turbine is bigger than I am looking at). I'm sure it is in the post - all I have seen is "full ceramic thrust bearing..." ).
Ta,
K2.


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## Toymaker (Feb 4, 2022)

Steamchick said:


> Hi Toymaker. An impressive project. I am trying to understand your boiler concept.... it looks like a flash boiler? Liquid injected at one end and superheated vapour extracted at the other?



I have struggled to draw a 3D approximation of what my boiler should look like,  and although I've managed to sketch out a few pencil and paper drawings, they're all so bad that I'm the only person that can interpret them.  The best I can do for now is to describe the 2D drawing below.  

All the small green circles represent 5/16 (8mm) OD boiler tubes, except that I got lazy and didn't show all of them, so in the areas you see green circles, imagine that space is filled with boiler tubes.  Flames from the burner are forced to flow around the tubes turning 180 degrees and flow out the Exhaust.  Sheet metal baffles not shown will direct the combustion gases to take a spiral path around the outside of the burner, thereby maximizing the time the gases are in contact with the boiler tubes.  





The boiler starts out as a mono-tube boiler having a single inlet tube for high pressure Freon from the Boiler Feed Pump, but soon branches out into 2 tubes, then 4 tubes, and finally into the 8 separate tubes which directly connect to the turbine.  Many small tubes provide a much larger surface area and smaller diameter, both of which increase heat transfer from the combustion gases to the "steam".   This drawing is a "schematic", it is not to scale, nor does it show the actual placement of the boiler tubes.  




Do we call this a "Flash Boiler"?  Some will say yes, others will say no,...I'll let the reader decide.  
It will however be a Supercritical Boiler as I intend to keep pressure and temperature nearest the boiler outlet just above the critical point of the working fluid, thereby keeping the working fluid in a liquid state until it exits the steam nozzles inside the turbine.  This serves several purposes: liquids conduct heat better than gases, so by keeping the working fluid in it's liquid state inside the boiler tubes, the fluid is able to absorb heat from the combustion gases faster and transport that heat out of the boiler faster.  Second, the boiler tubes are Aluminum and will quickly be melted by the combustion gases if they are not kept cool by the working fluid carrying away the heat quickly enough. Finally, supplying the convergent-divergent nozzles with a liquid on the supply side allows that liquid to flash into a vapor on the exit side resulting in the highest possible gas velocity flowing into the turbine blades.  



Steamchick said:


> One point to research.... you may have done it already? I.E.  The corrosion resistance of aluminium at the expected max temperature of your organic fluid. Please can you post more drawings of the boiler?
> K2



Thanks for the safety advice,...it's always welcome.  
As much as possible, I'm trying to chose a working fluid that isn't corrosive to aluminum at higher temperatures.  My current first choice is R-123, which has been used successfully in other ORC engines.   However, the critical point is 184C and at temperatures above 250C it can decompose into hydrochloric acid, hydrofluoric acid, and carbonyl halides.   Since the combustion gases will likely be at 2100C (3800F) I do not know if any of the R-123 molecules will be decomposed as they contact the tube's inner walls.  Unless someone here knows the answer, this is something I will need to determine experimentally.


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## Toymaker (Feb 4, 2022)

Steamchick said:


> Hi Toymaker, I was looking at bearings - considering something for a turbine that I have some parts and ideas about. I read about these bearings:
> KLNJ R Series 2RS C3 Rubber Sealed High Speed Imperial Bearings - High Quality
> "High speed" means 35,000rpm. for class C3. Apparently they are "slack" to permit the balls to expand when they get hot at speed...
> So for higher speeds, we need special bearings, that I have not found yet.
> ...



I'm using a 6000 (10 x 26 x 8mm) on the front end of the turbine shaft and a 6201 (12 x 32 x 10mm)  on the back end of the shaft.  Both are full ceramic bearings and are made by "Mochu", which I believe is a Chinese company.  Neither bearing was overly expensive so I doubt they're the very best quality, but at least until I'm more confident that my ORC engine has good potential, I'm unwilling to invest $150 per bearing for _ABEC 7 _hi quality bearings.  

I'm not familiar with the term, "class C3".  What I see used by bearing retailers and manufactures is the ABEC scoring system, where ABEC 1 is the lowest quality and ABEC 7 is the highest.  

What I learned about ceramic bearings while I was still in the working world has left me fairly confident with using even lower quality ceramic bearings.  Some 15 years ago Lockheed Martin hired an outside company specializing in long term failure analysis; their job was to continuously spin a rather heavy gyroscope while putting it through extremely hot & cold cycles.  They did this for 6 months, at which time the bearings were disassembled and inspected for signs of wear.  There was absolutely zero wear,...and the bearings had been run the entire 6 months with no lubrication,...they were run dry.  So as long as the bearings I have are of reasonably good quality and don't induce unwanted vibration, I'm rather confident they'll last for a very long time, even at RPMs well beyond their rating.

Also, don't flood your hi rpm bearings with lots of oil, instead find a way to spray the bearing with an oil mist.


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## ddmckee54 (Feb 4, 2022)

Toymaker:

I'm familiar with centrifugal compressors, 5-6 years ago I did the electrical installation design work for a 900Hp centrifugal air compressor, it pumps out 4000cfm at 90psi.  That was a 900Hp 480V electric motor by the way.  It was a trick to get that motor started without tripping out the main breaker on the sub-station.  That pig of a motor wanted to pull 5400 amps for almost 30 seconds when starting.

Don


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## Steamchick (Feb 4, 2022)

Hi Toymaker. Respecting your knowledge, but recognising your admitted gaps, I think there is a big risk of breakdown of the molecules at high temperature. Also, I doubt the temperature of the flame you predict, but that is mainly irrelevant.
I am not a chemist, so may be completely wrong about this, but I understand the chemical bonds are fixed energy level bonds (Quantum mechanics of electron energy levels). Hit them with more energy (temperature) than the "bond energy" (Critical temperature) and they come apart. Hence, at over the critical temperature, the chemistry will break down into horribly corrosive and toxic stuff, as you explain. Please don't risk it until an expert explains why it will be OK. In my book it will be a disaster! We don't want you to have a toxic gas accident.
I suggest you will be much safer with steam? Yes, it corrodes aluminium above 400C. Yes it can kill (drowning, dehydration, high temperature, air displacement suffocation, etc.) But chemically it won't break down until 400C when the aluminium will take the oxygen and leave very explosive hydrogen. That's what blew up 4 Japanese nuclear power stations! But 1 whiff of hydrofluoric acid vapour and your lungs will bleed you to drowning inside. If you live, you'll be blind, brain damaged and struggling to breathe for the remainder of your survival. Please don't risk that! Life is too precious.
Take care,
K2


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## Toymaker (Feb 4, 2022)

Steamchick said:


> Hi Toymaker. Respecting your knowledge, but recognising your admitted gaps, I think there is a big risk of breakdown of the molecules at high temperature. Also, I doubt the temperature of the flame you predict, but that is mainly irrelevant.



The combustion temperatures of many different substances, including kerosene, can be found here: *adiabatic flame temperature*



Steamchick said:


> I am not a chemist, so may be completely wrong about this, but I understand the chemical bonds are fixed energy level bonds (Quantum mechanics of electron energy levels). Hit them with more energy (temperature) than the "bond energy" (Critical temperature) and they come apart. Hence, at over the critical temperature, the chemistry will break down into horribly corrosive and toxic stuff, as you explain. Please don't risk it until an expert explains why it will be OK. In my book it will be a disaster! We don't want you to have a toxic gas accident.



I'm no chemist either, but I think your explanation of how substances break down is mostly correct, although I think you're miss-using the term "Critical temperature".  The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.   I think you mean _Decomposition temperature_ which is where chemical bonds begin to break down; for R-123 that's 250°C. 



Steamchick said:


> I suggest you will be much safer with steam? Yes, it corrodes aluminium above 400°C. Yes it can kill (drowning, dehydration, high temperature, air displacement suffocation, etc.) But chemically it won't break down until 400C when the aluminium will take the oxygen and leave very explosive hydrogen. That's what blew up 4 Japanese nuclear power stations! But 1 whiff of hydrofluoric acid vapour and your lungs will bleed you to drowning inside. If you live, you'll be blind, brain damaged and struggling to breathe for the remainder of your survival. Please don't risk that! Life is too precious.
> Take care,
> K2



Again, I appreciate your concerns for my safety.  All I can do is assure you that I don't take unnecessary risks.  

Of course steam is a safer working fluid than most Freons, but in my application it simply wont work very well.   Two properties of steam make it undesirable for my application.   First, at the low steam temperatures I need to use, steam tends to be a "wet" vapor; meaning the steam contains some percentage of liquid water suspended in the steam vapor.  Wet steam is not a problem for piston engines, but it is a problem for turbines as the suspended liquid water erodes the high rpm metal blades.  Second, without getting into the thermodynamics,  steam expands much, much more than any Freon or other organic working fluid, which is why steam turbines need many rows of blades, or stages, to efficiently convert the heat energy into mechanical energy.   All those turbine stages add weight and complexity.  Freons don't expand nearly as much as water-steam and are very efficient using one, two, three turbine stages.  If I use steam in my 3 stage turbine the exhaust steam would still contain an enormous amount of heat energy that would require a very large condenser, or I would need to use an open cycle design and vent the used steam into the atmosphere.  Neither of these two approaches are good.

I would love to use water as my working fluid, but for my application, water is pour choice.

I still want to discuss the thermodynamics of heat transfer from those hot combustion gases into the working fluid flowing through the aluminum tubes, and some of safety measures I will be using during my testing phase, but I'll do that in a separate reply.


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## Toymaker (Feb 5, 2022)

Steamchick said:


> I think there is a big risk of breakdown of the molecules at high temperature.



First, my disclaimer: I'm an old retired Electronics Engineer.  The only formal education I have on the subject of  thermodynamics is that when electronic components get too hot they emit smoke and stop working    So don't take any of my following comments as being factual,...they're just my assumptions based on my observations.

Let me explain how a few of the experiences I've had guide my understanding of how heat is transferred from combustion gasses, through an aluminum tube, and into a liquid flowing inside the tube.  I still recall an experiment my high school physics class did which demonstrated several thermodynamic properties.   Students constructed a small squarish shaped cup from a single sheet of notebook paper, filled the cup with water,  placed the cup above a Bunsen burner, and proceeded to boil the water in the paper cup without burning the very thin notebook paper.  The flame from a Bunsen burner is typically around 1,500°C, well above the temperature needed to ignite the paper, and yet the paper remained un-damaged.   The water keeps the entire surface and thickness of the paper below the ignition temperature of the paper.

A second example: a propane torch will very quickly melt the walls of an empty aluminum soda can, but fill the soda can with water and you wont be able to melt the aluminum until nearly all the water is gone.  This demonstrates that the thin walls of the aluminum can rapidly distribute the 1500°C  temperature from the torch into the lower temperature water, and prevents the aluminum from melting.  So even though the torch is bathing the outer surface of the Aluminum can in 1500°C gasses, the aluminum wall of the can remains at a much lower temperature.  

I believe we can infer that as long as boiler tubes are filled with a rapidly flowing liquid or gaseous working fluid, that the aluminum tubes will remain at, or very close to, the temperature of the working fluid inside the tube, which will not only prevent the aluminum tubes from melting but also prevent the working fluid from reaching decomposition temperatures. 

Your thoughts?


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## Steamchick (Feb 5, 2022)

Hi Toymaker. Thanks for your clear reply #23. I understand now about the "decomposition temperature", versus "Critical temperature".
I feel I disagree (without technical backing) about "wet steam" versus "dry steam". But that is from a real lack of technical data. Should you use Steam at a pressure of (say) 6 barg. (90psi) = 166C, and superheat to (say) 300C. before expanding through the turbine to (say) 20psi, before entering a condenser, and returning to the boiler coils via a pump, I would _guess _the steam is still dry? > 126C.? But I'll let you work out the thermodynamics, as it is beyond my expertise.... (Sorry). I am Not sure what efficiency (expansion/pressure drop?) you expect at each stage? Equally, if the steam will become "wet" due to expansion, adiabatic cooling and pressure drop, then surely your gas will have similar changes of state, as energy is removed and the latent heat (energy) is drawn from the fluid? I understand that in power stations, Parson's turbines have "economisers" - to pre-heat the boiler feed water, but also as the first stage of pressure reduction from dry steam to wet steam, before the condenser? These then maintain the turbine outlet at dry steam temperatures and pressures? Forgive me for not "knowing", and lambasting you with lots of questions.
Not a criticism, just something I don't understand about Parson's turbines. (But I have sailed a few yachts!). It appears to me that your design, for whatever reason, has few blades at each stage. I am aware that as a momentum exchange the entering gas is intended to exit at 90degrees from the entering incident angle, so the pressure on the back of the blade transfers energy by velocity/momentum exchange. (Like a Pelton wheel?). I think this means that the gas can only transfer up to 50% of its momentum to the wheel (in the mathematical extreme case). But I also thought that the Parson's turbine used the aerodynamics of the gas forced through a narrow gap, especially around a curved (convex) shape, would create a pressure drop across that surface. Thus - when sailing - the "slot width" is critical to get extra power "from the wind" by accelerating the air through the slot (from a leading aerofoil onto the next aerofoil) and gaining the consequential lower pressure on the leading surface? (Aerodynamic "lift" on the aerofoil). Ergo, the gas ensuing from a fixed slot will have a layer of high velocity gas that will cause "lift" (lower pressure) across the face of the next moving blade...? If there is no blade (because of a large gap) both this "lift" and the momentum exchange of the "pushing" gas is lost..? Sorry if my explanation is a bit squiffy, I am fumbling with notions I don't fully understand here. Your "large slot" (few blades) design appears to me to be losing some power transfer at each stage by the low number of blades? (compared to pictures of conventional "parson's turbines"?). I.E. the large gaps between power blades means the "jets" of gas from the fixed blades "waste" a lot of flow before the next blade comes along? - But maybe that is the intent , or due to manufacturing limitations? Can you advise , please? - I am trying to learn before I make a turbine that doesn't work (effectively, that is!). I have seen many models consume huge amounts of steam and hardly any output - except a whizzing noise! They need high pressures to start, and high gas flows to do anything.
I'll reply to #24 next.
K2


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## Steamchick (Feb 5, 2022)

Hi again - reply to #24. I recognise your theory of flame temperature versus heat flow into a liquid through walls of a container. 
My understanding - not the text book or any other "known" theory, just what I have picked up along the way....
We know that in the combustion of hydrocarbons (is that politically correct nowadays?) the gases change from Hydrocarbons to ions of hydrogen and carbon: The hydrogen burns very quickly with O2 from the air to make water molecules (the light blue cone of the bunsen burner). The carbon ions combine with O2 to make CO - similarly quickly in the earlier stages of the flame. Actually, in your flame, there are free carbons that are glowing yellow with the heat of surrounding combustion, as there is a shortage of O2 (air) to get this to "blue flame". The CO, and free C ions then combine with any remaining O ions, in the dark blue flame of the bunsen burner, so there is no free C in the exhaust. (I think you will have some residual C smoke?). IF this mixture of water molecules, nitrogen (from the air), CO2 (from completed combustion of C/CO) and CO and C cools below around 300~350C, (Local temperature around the ions - pressure also affects this I think?), then the gas mixture ceases combustion. And we are left with unburnt CO and C (soot). Not smelly (BUT CO kills!). I have avoided any inclusion of NOx formation as we are talking of combustion around atmospheric pressure. (NOx form in the high pressure of ICE engines at over 900C.).
So we have "hot gas" below 300C. 
To have a flame impinge upon a "cool" surface, the heat is transferred to the surface by conduction form the gas, plus radiant heat from anywhere in the flame (e.g. the yellow glowing particles of C smoke, even the infra-red from the combusting gas being hot!). The radiant heat is taken up by the cooler surface according to Stefan's law of the t-4th power - of the difference of temperatures and the reflectivity of the surface. The conduction of heat from the "hot-zone" of the flame to the cooler surface relies upon the temperature difference and the thermal conductivity of the gas mixture. (very poor). Then there is a temperature difference across the thickness of the surface, so the outside is hotter than the inside (at fluid temperature) to force the heat flow through the surface. Effectively, the non-combusting gas mixture at the surface is insulating the material surface from "flame" temperatures, so the surface cannot get above around 300C anyway. Actually, in a boiler that has some significant scale, there may only be 10~30C temperature difference across the surface, so "in extremis" we can use a surface temperature of (say) 20C higher than the "cooling fluid" temperature as the surface temperature of the metal tubes. - This means that in the paper cup experiment, the paper remains below char temperature. 3 thicknesses of paper may however not work, as the outer layer chars and weakens the container. - Did you do that one? I remember a "trainee teacher" trying it and wetting the bench when the outer paper went up in flames and the whole thing collapsed. We (Kids) collapsed laughing as well!
But practically, you can calculate the heat flow into the pipes, and therefore the rise of temperature of the liquid within, to determine the flow required to keep it from boiling. (Pretty standard calculations for all heat exchangers - I'm sure you'll find the calcs on the web). For water-tube boilers, fired like yours, we should expect to be able to generate steam of 5 ~ 6.5cu.in per 100 sq.in of surface are - according to the old text book. Considering the arrangement of tubes around the flame from your burner, some part of the surfaces will get radiant heat from the flames, but other parts of tubes will be in shadow, so only get "gas conducted" heating. Again there are some tubes that will see more turbulent gases on the surface, and at higher temperatures than other areas that are further along the cooling path of exhaust gases. So perhaps you need to consider the "extreme" tube surface temperature of around 300C where flames are licking, down to the exhaust pipe temperature of gases which will be only as cool as the pipes with cooling fluid at the exhaust exit point. It is worth noting, (for model steam) that one cannot get the exhaust cooler than the boiler temperature, unless you have a cold water boiler feed pre-heater. (Very few do so). People are often amazed how inefficient their boilers are, due to the "hottest" pipes being at (only!) 300C (or less!) and the coolest at the same temperature as the steam! They "want" to calculate based on "flame temperature" as the hottest, and below steam temperature as the lowest! Thermodynamics won't do that. - An example: Someone suggested to me that his tall, heavy copper tube exhaust chimney on a vertical boiler conducted heat from the exhaust gases (as the gases were cooled by the heat flowing into the walls of the chimney - below steam temperature) back into the boiler.... not realising the chimney was a great big conductive cooler for the boiler! Heat MUST flow from the boiler (hotter than the chimney) to the cooler (chimney!). I engineer a break between these parts so to stop heat being dragged out of the boiler by the chimney tube. It also means that transport is easier with a removable chimney!
Keep up the good work,
K2


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## raveney (Feb 5, 2022)

Beautiful machine work, and intriguing concept. Please consider material choices for the boiler tubes. ASME section II has tables for boiler tube and pressure part requirements. As a reality check, in an actual combined cycle gas turbine exhaust temperature is 1200 F. The leading row finned boiler tubes in the Heat Recovery Steam Generators, HRSG, are A335-T91 and have steam temperatures around 1050 F at 2000 psig. The piping to the turbine is also P91 as well as valves. The designers may opt to use a lower alloy such as T-22, but the wall thickness needs to increase accordingly and heat transfer is reduced impacting efficiency. I cannot Imagine using aluminum.


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## Toymaker (Feb 5, 2022)

raveney said:


> Beautiful machine work, and intriguing concept. Please consider material choices for the boiler tubes. ASME section II has tables for boiler tube and pressure part requirements. As a reality check, in an actual combined cycle gas turbine exhaust temperature is 1200 F. The leading row finned boiler tubes in the Heat Recovery Steam Generators, HRSG, are A335-T91 and have steam temperatures around 1050 F at 2000 psig. The piping to the turbine is also P91 as well as valves. The designers may opt to use a lower alloy such as T-22, but the wall thickness needs to increase accordingly and heat transfer is reduced impacting efficiency. I cannot Imagine using aluminum.



Hello Raveney, the working fluid in my boiler will be limited to a max temperature of  184°C  (363°F) and 550 psig, so not even close to temperatures inside commercial steam boilers.  Most aluminum alloys retain near full yield strength up to 200°C, so by staying below 200°C and keeping the pressures low, I believe I can easily use aluminum tubing in the boiler.  
I considered using finned boiler tubes but decided to use small diameter, parallel tubes instead, which gives me a large tube surface area and very good heat transfer from the tube walls into the working fluid.


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## Toymaker (Feb 5, 2022)

Steamchick said:


> Hi again - reply to #24. I recognise your theory of flame temperature versus heat flow into a liquid through walls of a container.
> <snip>
> Actually, in your flame, there are free carbons that are glowing yellow with the heat of surrounding combustion, as there is a shortage of O2 (air) to get this to "blue flame".
> <snip>



I think there reasons other than free carbon atoms causing the flame to glow yellow.  Regardless, I need to buy a non-contact IR temperature reader so I can measure the temperature of those flames.



Steamchick said:


> <snip>
> Did you do that one? I remember a "trainee teacher" trying it and wetting the bench when the outer paper went up in flames and the whole thing collapsed. We (Kids) collapsed laughing as well!



Yes, I actually performed the paper cup water boil over a Bunsen burner,....and my cup didn't leak or catch fire  



Steamchick said:


> Considering the arrangement of tubes around the flame from your burner, some part of the surfaces will get radiant heat from the flames, but other parts of tubes will be in shadow, so only get "gas conducted" heating. Again there are some tubes that will see more turbulent gases on the surface, and at higher temperatures than other areas that are further along the cooling path of exhaust gases.
> <snip>
> Keep up the good work,
> K2



Yep, the hottest part of the boiler is located both at the flame front from the burner and the exit point for the boiler tubes.  All the remaining tubing in the boil is there to absorb as much heat energy as possible from the combustion gases before they leave the boiler.  In the old  *SES automotive boiler* this section was called the economizer. 

Thanks for challenging and questioning my design and ideas,...it forces me to take another look and ensure that I'm either right or that I need to re-think something.   And please let me know when you start designing and building your turbine, I will enjoy following your progress.


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## Steamchick (Feb 5, 2022)

Cheers Toymaker. Many of my questions will be the wrong ones, but occasionally I hit a gem. Hence please sift the dross in my witterings,  in case you can find the gem! And shoot me down when (not "if") I am wrong or stupid. That's how I learn!
Just one odd point, you mention "max 184C, at 550 psig" ? Please confirm the pressure? I am not familiar with properties of the fluid you will use, but that is a lot of pressure! Presumably that pressure keeps the fluid liquid, until some expansion point (De Laval nozzle?) when it boils and the hot vapour is used to drive the turbine?
Cheers!
K2


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## Toymaker (Feb 5, 2022)

Steamchick said:


> Cheers Toymaker. Many of my questions will be the wrong ones, but occasionally I hit a gem. Hence please sift the dross in my witterings,  in case you can find the gem! And shoot me down when (not "if") I am wrong or stupid. That's how I learn!
> Just one odd point, you mention "max 184C, at 550 psig" ? Please confirm the pressure? I am not familiar with properties of the fluid you will use, but that is a lot of pressure! Presumably that pressure keeps the fluid liquid, until some expansion point (De Laval nozzle?) when it boils and the hot vapour is used to drive the turbine?
> Cheers!
> K2



You're right !!  I think 550psi is about 10 to 20 psi too high.  I had used this *enthalpy chart* for R123 to get the 550psi value, but upon further Googling I found a much more complete document listing nearly all the thermodynamic properties of R123 (aka HCFC-123):  *thermodynamic properties of R123*  Page 10 shows that at 183°C  the pressure will be 3627 kPa or 526 psi.  

I will try to operate the boiler in the super critical pressure-temperature region for R123, meaning that I need to keep the pressure at or a little above 526 psi, and the temperature at or a little below 183°C, which will keep the R123 in a liquid state.  My goal is keep the working fluid, R123, in it's liquid stated until it reaches the De Laval nozzles (or convergent-divergent nozzles).  As the r123 liquid passes through the nozzles it will flash into a vapor at very high velocity as it impacts the first row of turbine blades.


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## Steamchick (Feb 6, 2022)

Well... I am surprised I am right, that must be a rare event like the confluence of Mercury and Jupiter!
Next (stupid?) Question.... How have you designed the nozzle profiles? (Possibly a MATHCAD or other programme?). Working with such a different fluid (instead of the common use of steam that is) the calculations will be "standard" but with the factors for the R123 instead of steam?
Cheers!
K2


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## raveney (Feb 6, 2022)

Hello Toymaker,
I misunderstood your burner to be a model combustion turbine when I posted above. Understand better after rereading. Aluminum is an excellent conductor, as well as easily bent, machined etc. So the tubing is 0.313" OD and assuming seamless T-6061. UNS A96061 has an upper limit of 400 F, and useable yield stress of 4.5 KSI at that temperature. Seems a lot more reasonable IF you can control the temperature on tubing OD inside the burner. A few well intended questions as you appear to be in design stage at the moment.

Could you insulate the burner exhaust where the tubes are to be placed, and measure temperature with a thermocouple at various points?
This empirical data may serve as your design (maximum) temperature.
What is the plan on controlling steam turbine overspeed? This is a critical question for generator protection as well.
Not familiar at all with R123 properties, but there must be some over pressurization (relief valves) protection to keep things safe. Can R123 be released safely?
Have you taken into account pressure loss after the pump, tubing, fittings and nozzles?

Again, very nice work, and thank you for sharing


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## Toymaker (Feb 6, 2022)

Steamchick said:


> Well... I am surprised I am right, that must be a rare event like the confluence of Mercury and Jupiter!
> Next (stupid?) Question.... How have you designed the nozzle profiles? (Possibly a MATHCAD or other programme?). Working with such a different fluid (instead of the common use of steam that is) the calculations will be "standard" but with the factors for the R123 instead of steam?
> Cheers!
> K2



If you look at the nozzles on existing turbines using a Freon, you'll see there's no difference from those found in steam turbines.   Also, solid fuel rockets use convergent-divergent nozzles that look very similar to those in a steam turbine, so I'm left with an opinion that the exact shape of a convergent-divergent nozzle isn't all that critical.  I believe the more crucial aspect is the total area of all the nozzles combined.  It's that value that will determine the max volume of working fluid that can pass through the turbine.


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## Toymaker (Feb 6, 2022)

raveney said:


> Hello Toymaker,
> I misunderstood your burner to be a model combustion turbine when I posted above. Understand better after rereading. Aluminum is an excellent conductor, as well as easily bent, machined etc. So the tubing is 0.313" OD and assuming seamless T-6061. UNS A96061 has an upper limit of 400 F, and useable yield stress of 4.5 KSI at that temperature. Seems a lot more reasonable IF you can control the temperature on tubing OD inside the burner. A few well intended questions as you appear to be in design stage at the moment.
> 
> Could you insulate the burner exhaust where the tubes are to be placed, and measure temperature with a thermocouple at various points?
> ...



Before I start winding the boiler's aluminum tubes I plan to first test a theory I have.  I will run a single, short length of aluminum tube, bent into a "U" shape, and place it directly in the hottest part of the burner flames.  Using only water supplied from my house, I will run a continuous flow through the tube.  I'm betting the tube will not melt under those conditions.  Next step will be to slow the water flow rate down to a point at which steam is coming out of the open end; again I'm betting that the tube will remain undamaged.  Final step, place an orifice onto the open end of the tube which restricts steam flowing out of the tube.  Monitor the tube & steam temperatures using a non-contact thermometer and allow those temperatures to reach 400°F.  Again, I'm betting the tubing remains undamaged even when exposed to the burner's hottest exhaust gases.  As this point, I will be confident that my aluminum tube boiler will work as designed.  

After the boiler is physically finished, the first few tests will be using water, not R123. 

Safety relief valves on the boiler will vent the excess vapors into the condenser, not out into the open air.  Only if condenser pressures get too high will R123 be vented into the air.  

If you'll go back to the first post, you will find a schematic block diagram showing all the pressures and temperatures and RPM sensor which the FADEC (aka on-board computer) will be monitoring and controlling. 

Since I'm not designing this engine with any pre-determined output power levels, I really don't have a need to worry about various pressure losses,...Whatever power I get will make me happy.


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## Bentwings (Feb 6, 2022)

Steamchick said:


> Hi Toymaker. An impressive project. I am trying to understand your boiler concept.... it looks like a flash boiler? Liquid injected at one end and superheated vapour extracted at the other? One point to research.... you may have done it already? I.E.  The corrosion resistance of aluminium at the expected max temperature of your organic fluid. Please can you post more drawings of the boiler?
> K2


im going to post assembly Pictish whe it ready to pu together . I’ve go three magnesium anodes tat r similar to what bird on m big boat I also have  3 scre in Andes that I’ll scre in eithe on the en cos o i can  just install them on t he tube bulkheads at assembly the tapped holes wil be available either way I don’t really think the boiler will be capable of super heat  I think I may have misled as I did not know  what to call the internal heat tubes these ar not connected   heated waterwill flo from hot t cold I just got a nice industrial temp gage with enough fittings to make a s iPhone tube. I haven’t decided on h boiler lines yet. I found 1/4” copper tube fitting used  in AC work so 1/4” copper lines could be made I also have access to 
Stainless steel lines and fittings so I may use that. In any case I ant to be able to service any part as required. This  comes from auto racing we constantly take things apart to inspect them so serviceability is important . I don’t like bending lines . If it’s necessary I’ll use Teflon braided hose . There is heat and pressure rated stuff that’s far beyond what I anticipate. I have dual electrical timers so I can have max run time pre set once I get a handle on how the boiler heats I’ll be able to set an operating limit.

spell check is already giving me fits . I just got word the engine frames will be delivered Tuesday so I can start assembly of the engines pretty exciting for me now.
 Hope spell check doesn’t make too big of mess I’ve gone over his a couple times


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## Bentwings (Feb 6, 2022)

Toymaker said:


> If you look at the nozzles on existing turbines using a Freon, you'll see there's no difference from those found in steam turbines.   Also, solid fuel rockets use convergent-divergent nozzles that look very similar to those in a steam turbine, so I'm left with an opinion that the exact shape of a convergent-divergent nozzle isn't all that critical.  I believe the more crucial aspect is the total area of all the nozzles combined.  It's that value that will determine the max volume of working fluid that can pass through the turbine.


I’ve got 2 single stage turbines mostly just to experiment with . Before I get into turbines I want to get his project operational I have a number of generator motor  things I want to try out.


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## Steamchick (Feb 6, 2022)

Hi Toymaker, just some clarification of my understanding of De Laval nozzles.

I agree the total CSA of the combined set of nozzles (throat CSA) determines the total flow, subject to pressure difference across the throat.
I do not know how to design the converging nozzle.
I have read about the diverging nozzle with gas mixtures accelerating to  sonic velocities. BUT the sonic limit (speed of sound) varies as the pressure and density of fluid (gas mixture). In rocketry, the diverging nozzle is different for an atmospheric and vacuum environment, and some nozzles have variable bells to optimise the shape as the rocket passes through the thinning atmosphere with altitude. I think that the nozzle can choke the output (velocity) if the wrong shape. 
As you are sending gas at the orifice from the pressure of the liquid, to a space beyond the nozzle at "some other pressure", I think the divergent nozzle shape is critical, both to the pressures, the density of gas at the end of the nozzle, and also the speed of sound for the gas at the pressure within the chamber at the end of the nozzle.I think that if the nozzle is too wide, you won't develop the velocity of gas that would be achieve with a correct nozzle. I also think that if the nozzle is too long it will choke the flow and reduce performance of the gas stream, both mass and velocity.
Please research this as I am not an expert, just a novice at the early stages of learning these subjects. I am quite likely to be wrong.....
K2


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## HMEL (Feb 6, 2022)

Toymaker said:


> First, my disclaimer: I'm an old retired Electronics Engineer.  The only formal education I have on the subject of  thermodynamics is that when electronic components get too hot they emit smoke and stop working    So don't take any of my following comments as being factual,...they're just my assumptions based on my observations.
> 
> Let me explain how a few of the experiences I've had guide my understanding of how heat is transferred from combustion gasses, through an aluminum tube, and into a liquid flowing inside the tube.  I still recall an experiment my high school physics class did which demonstrated several thermodynamic properties.   Students constructed a small squarish shaped cup from a single sheet of notebook paper, filled the cup with water,  placed the cup above a Bunsen burner, and proceeded to boil the water in the paper cup without burning the very thin notebook paper.  The flame from a Bunsen burner is typically around 1,500°C, well above the temperature needed to ignite the paper, and yet the paper remained un-damaged.   The water keeps the entire surface and thickness of the paper below the ignition temperature of the paper.
> 
> ...


I agree with Steamchick, Heat transfer depends on the working fluid and the velocity in the tube.  It also depends on residence time of the combustion gases and it gets a bit more complicated when radiation is involved not to mention consideration of the approach temps. The examples you cited deal with the latent heat of vaporization in open heaters and are not applicable.


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## Bentwings (Feb 6, 2022)

Steamchick said:


> Hi Toymaker, just some clarification of my understanding of De Laval nozzles.
> 
> I agree the total CSA of the combined set of nozzles (throat CSA) determines the total flow, subject to pressure difference across the throat.
> I do not know how to design the converging nozzle.
> ...


It’s been auto long since I worked it’s high speed gas and liquid flow model rocketry is not my interest. So I can’t help here there is a lot of high physical involved I was in a problem thing. Rules were solve it fast . Very high pressure job  I wish I was paid appropriately. LOL it did no have anything to do with turbines strictly office ugh speed flow with extremely dangerous fluid fortunate there was block house and isolated  area. I was glad we had hearing eye nose protection . It’s a bygone era thankfully . Nobody got hurt I always wanted to be a ilot but knowing what was under the belly  or wings now would be more scary than combat it’s enough working with model steam engines . Turbines will have to take a back seat fo now . . Kk Harry calihan says “ you have o know your limitations “ 

I have enough steam oil to get started I just found that PM Research has quart bottles so I’ll order one that should last a long time . My little engine has terribly inefficient intake and exhaust manifolds by race car standards but I’m not even going there for now. I just want to see things moving smoothly and puffs of steam coming t regularly . All else will be pure enjoyment .


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## Toymaker (Feb 6, 2022)

Steamchick said:


> Hi Toymaker, just some clarification of my understanding of De Laval nozzles.
> 
> I agree the total CSA of the combined set of nozzles (throat CSA) determines the total flow, subject to pressure difference across the throat.
> I do not know how to design the converging nozzle.
> ...



From what I've learned about nozzles, choking is not usually a big problem.  Induced turbulent flow is the biggest concern, which happens when the gases are allowed to expand too quickly, but as long as the nozzle expansion angle stays somewhere close to 15°, there shouldn't be a problem.  Here are couple of images of real existing ORC nozzles. The color images were generated using CFD (Computational Fluid Dynamics) software; notice how the upper portion of the nozzle is not fully complete, but instead relies on the fluid flow from the adjacent nozzle to help shape the flow. The convergent-divergent shape is also obvious, and exists only in 2 dimensions as these nozzles are not round holes.
Also notice how thin the nozzle material becomes at the nozzle exit;  when you actually machine these nozzles you will find that compromises will need to be made as the designed material thickness becomes less than 0.010", which from a practical standpoint, wont work.






In a multi-stage axial flow design, you should also keep the expansion angle of the entire turbine housing close to 15° so as to avoid turbulent flow through the blades and stators.

Also, in the 2 dimensional plan view, notice how both the second stage blades and stators (black & white drwg above)  roughly form convergent-divergent nozzles, the entrance to all the blades and stators is larger then the exit, forcing the gases to accelerate through the blade row.

Finally, here's my nozzle and blading design.  Ignore purple lines as they're only construction lines from my CAD drawing.  The gap between adjacent nozzles is 1.5mm.  Notice the nozzles convergent-divergent geometry.





Added one final pic,...this is my actual nozzle.  It's not easy to see, but if you focus on the root area you can see the convergent-divergent geometry.


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## Toymaker (Feb 6, 2022)

HMEL said:


> I agree with Steamchick, Heat transfer depends on the working fluid and the velocity in the tube.  It also depends on residence time of the combustion gases and it gets a bit more complicated when radiation is involved not to mention consideration of the approach temps. The examples you cited deal with the latent heat of vaporization in open heaters and are not applicable.



Yes, I too agree with Steamchick's assertions concerning heat transfer.  The purpose of my example was only show that so long as the heat transfer from the aluminum into the contained fluid is adequate that the fluid's heat absorption will prevent the aluminum from rising higher then the contained fluid.  The process by which the fluid is absorbing the heat out of the aluminum, thereby keeping it's temperature from rising too high, is not important for the point I'm trying to make.   Whether the heat transfer is due to latent heat of vaporization, or fluid flow rate through the tube,  my point is that the temperature of the aluminum tube will be only slightly higher than the fluid it contains.  If you read post #35 you'll see how I plan to demonstrate this.


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## Steamchick (Feb 7, 2022)

Hi Toymaker. Post #41 is just brilliant! Explained a lot of what I was trying to understand. I am convinced it will work!
K2


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## Toymaker (Feb 7, 2022)

Steamchick said:


> Hi Toymaker.
> I feel I disagree (without technical backing) about "wet steam" versus "dry steam". But that is from a real lack of technical data. Should you use Steam at a pressure of (say) 6 barg. (90psi) = 166C, and superheat to (say) 300C. before expanding through the turbine to (say) 20psi, before entering a condenser, and returning to the boiler coils via a pump, I would _guess _the steam is still dry? > 126C.?



I know that wet steam occurs when saturated steam and condensate water molecules are mixed.  And that sometimes, heat loss in piping causes some of the saturated steam to condense and create a steam/water mix. But quite honestly, I still don't fully understand how steam could possibly condense and form liquid droplets inside a pipe filled with steam.  Why those little suspended water droplet fail to re-vaporize baffles me. 



Steamchick said:


> It appears to me that your design, for whatever reason, has few blades at each stage.
> <snip>
> Your "large slot" (few blades) design appears to me to be losing some power transfer at each stage by the low number of blades? (compared to pictures of conventional "parson's turbines"?). I.E. the large gaps between power blades means the "jets" of gas from the fixed blades "waste" a lot of flow before the next blade comes along?



You're absolutely right that my design has far fewer blades than a typical turbine,...and I would love to have more blades,... but with the small overall size of this turbine the diameter of the blisk at the blade root was also very small and I'm limited to how many blades I can squeeze onto the blisk.  

Below is a short video of an earlier turbine I built and have not yet tested.  The OD of the larger rotor is a bit over 7", more than double the OD of my current turbine.  The larger size gave me enough room to fit in a more standard number of blades.  The potential power of the turbine below scares the crap out of me, which is why I decided to put this one the shelf until I have far more experience with steam turbines  




Your browser is not able to display this video.


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## Henry K (Feb 7, 2022)

R123 is one of the refrigerants that has negative impacts on ozone and CO2. Check Wikipedia or other sources. As a hobby, I would not want to contribute these problems even in a trivial way.


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## Toymaker (Feb 7, 2022)

Henry K said:


> R123 is one of the refrigerants that has negative impacts on ozone and CO2. Check Wikipedia or other sources. As a hobby, I would not want to contribute these problems even in a trivial way.



This single graph from an *R123 Environmental Study *should tell you everything you need to know about the environmental impact of R123.  The impact to both Global Warming and to Ozone Depletion are very nearly zero.  
It's only the poor wording of the Montreal Protocol that may end up banning R123.


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## Steamchick (Feb 8, 2022)

Hi Toymaker, Maybe I can fumble my way through an explanation re: "I still don't fully understand how steam could possibly condense and form liquid droplets inside a pipe filled with steam.":- As I see it... If fine spray from the rapid boiling in the  boiler (bubbles bursting) is not separated from the steam then some un-boiled water will pass down the steam pipe at the same temperature as the steam - but not the same phase. I.E. these droplets will need extra latent heat to vapourise... but the steam pipe actually "extracts" a little heat as the steam expands to accelerate down the steam pipe, so there is no "spare heat" to vapourise these droplets. In fact, without extra heat more steam condenses to power the wet steam down the pipe. So water in 2 states hits the turbine. (No good!). The "Obvious" countermeasure, is to have some extra coils in the flue gases to add extra heat to the wet steam, to provide the extra latent heat needed to dry the steam, the elevate the temperature further, so the steam is carrying a lot more energy into the engine. (superheating). That is, so the steam reaching the engine is hotter and still at a higher pressure than the "condensing pressure" (equal or less than the boiler pressure). Flash boilers (like yours = coils in flames/hot exhaust) do this "somewhere" along the pipework in the flames/hot exhaust gases..... Except, with your high pressure (523psi) and temperature controlled pipework (at 183C), you plan to have liquid right up to the nozzles: AT which point, the pressure of the liquid (523psi) and heat therein will expand/cool to a state of lower pressure, that cannot sustain the liquid state and will use some of the energy (temperature) to provide the latent heat to convert the liquid to gas at the lower pressure/same temperature. The worry, is that there won't be the gas pressure at the narrowest point of the nozzles, to make the expansion "sonic". But whatever energy that remains for expansion of the gas - after the latent heat extracted from the pressure/temperature has vapourised the liquid - will start at the lower pressure and then accelerate the gas into the turbine.
Your plan: "I will try to operate the boiler in the super critical pressure-temperature region for R123, meaning that I need to keep the pressure at or a little above 526 psi (3627 kPa ), and the temperature at or a little below 183°C, which will keep the R123 in a liquid state. My goal is keep the working fluid, R123, in it's liquid stated until it reaches the De Laval nozzles (or convergent-divergent nozzles). As the R123 liquid passes through the nozzles it will flash into a vapor at very high velocity as it impacts the first row of turbine blades."
I think the "trick" you will be performing, is in controlling the  pumping of the fluid with enough flow to raise the pressure (against the venting at the nozzles) and keep the temperature at the hottest point of the boiler coils to 183C or below.
Just trying to work this out (My confused brain will probably get this wrong? - But a clever person will correct me!):
Enthalpy of 1kg of R123 at 183C:
Liquid: 422.6Kj/Kg. Latent heat to vapourise to gas = 18.9 kj/kg.
Therefore to change state from liquid to gas without addition of external heat, the gas only has Enthalpy of 422.6-18.9 = 403.7 Kj/Kg.... Thus the temperature of the gas will be at 39C: having taken the heat from the liquid to vapourise to gas. - See table: Thermodynamic Properties of HCFC-123, SI units (frigoristes.fr)
I.E. the gas at 39C will start to expand and accelerate down the expansion nozzle... So then you are in the realms of determining what pressure you can attain at the end of the turbine, so you can see what energy you can extract from the gas (in the perfect 100% efficient case). However, life has its little kick-backs, in that at each stage the gas is expanding (and cooling): but only "half" the stages are dynamic, and extract some heat /velocity from the gas into kinetic energy of the turbine wheel (and some is conducted away to the shaft). At the fixed blades, the heat within the gas is extracted as heat conducted away to the shaft/body, and some to accelerate the gas through the blades with the change of momentum and friction heating the blades in the process. 39C is about the temperature of the human body, and usually a room would be considered to be at 20~25C. So that leaves Enthalpy of 394.9Kj/Kg. at 25C.: you can extract a total of 8.6Kj/Kg. through the turbine. If the efficiency is 25% (a random guess?)- this then becomes 2.15Kj/Kg. converted to shaft energy for the pumps, generator or whatever you will put onto the shaft as the load.
So how many Kgs of gas will you pump per second?
What does this all mean?
K2


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## Steamchick (Feb 8, 2022)

Maybe I was wrong with my thermodynamic calculation...?
Your plan:_ "I will try to operate the boiler in the super critical pressure-temperature region for R123, meaning that I need to keep the pressure at or a little above 526 psi (3627 kPa ), and the temperature at or a little below 183°C, which will keep the R123 in a liquid state. My goal is keep the working fluid, R123, in it's liquid stated until it reaches the De Laval nozzles (or convergent-divergent nozzles). As the R123 liquid passes through the nozzles it will flash into a vapor"_. 
Simply:

Liquid R123 at 183C = pressure 3627kPa, Enthalpy = 422.6Kj/Kg.
Gaseous R123 with Enthalpy = 422.7Kj/Kg is at 71C and pressure = 388kPa. I.E. JUST to make the physical change of state from liquid to gas. - Without any other losses to heat the intake metalwork of the turbine. (More later!). So your starting point cannot be a gas pressure above 388kPa (abs).
If the turbine gas exit  (The point just after the last moving blade) is at 20C, then the gas will be at a pressure of 75kPa (abs) with Enthalpy of 392Kj/Kg. I.E. It will have converted ~30Kj/Kg of Enthalpy into kinetic energy (gas and turbine motion) and heat (friction of gas against fixed and moving blades and walls of housing, bearings, conduction to cooler surfaces, etc.). This is the aspect that determines efficiency. 
For momentum exchange, I understand mathematically you cannot have more than 50% of the momentum transferred from moving fluid to moving component. But considering the thermal losses (Perhaps this will be well lagged?) I guess the losses could be between 20 and 50% of the input heat (Enthalpy of gas). so you could easily have efficiency of 50% x 50% = 25% - or even less? So for the power you need, you only have maybe 25% of 30Kj/Kg = 7.5Kj/Kg.  - so use this to convert to how many Kgs of gas per second you need to pump through the system. (Then working backwards, you can determine how much heat is needed to achieve this?).
You can also work out the condenser size, based on post turbine condensing of the gas at (or below) 75kPa (abs). into liquid.
But there is a catch... 75kPa is sub-atmospheric pressure. So must be generated by the suction side of the pump that converts the gas back to liquid. So you need to do the sums to convert the gas back to liquid considering Enthalpy... temperature and pressure....
More stuff: The liquid has t=o leave the heat source and get to the nozzle point before expanding the gas... but there will be energy (Fluid Enthaply) lost during that phase, buy conduction of heat to pipes - and then lost - and from friction (losses) of the fluid moving in the pipes. Also, there must be some (small) pressure drop to move the fluid along the pipes. So the Pressure at the nozzle (liquid) will be lower as a result, and the starting Enthalpy I have used will be "a perfect number" - not a real one. When you have a flow in Kgs per second, you can do calcs on the pipework to understand the pressure drop in the pipework, to get a better starting Enthalpy.
Sorry to be a damp squib, but I begin to doubt that R123 will work the way you expected? Can you comment? (I may be wrong - as usual! - I am learning thermodynamics from scratch on this one!)
Of course, using steam tables, or for any other medium, you can do the same calculations...
K2


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## HMEL (Feb 8, 2022)

Toymaker said:


> Before I start winding the boiler's aluminum tubes I plan to first test a theory I have.  I will run a single, short length of aluminum tube, bent into a "U" shape, and place it directly in the hottest part of the burner flames.  Using only water supplied from my house, I will run a continuous flow through the tube.  I'm betting the tube will not melt under those conditions.  Next step will be to slow the water flow rate down to a point at which steam is coming out of the open end; again I'm betting that the tube will remain undamaged.  Final step, place an orifice onto the open end of the tube which restricts steam flowing out of the tube.  Monitor the tube & steam temperatures using a non-contact thermometer and allow those temperatures to reach 400°F.  Again, I'm betting the tubing remains undamaged even when exposed to the burner's hottest exhaust gases.  As this point, I will be confident that my aluminum tube boiler will work as designed.
> 
> After the boiler is physically finished, the first few tests will be using water, not R123.
> 
> ...


You should know that aluminum yield strength vs temperature of most aluminum alloys downward descent of what many call the knee starts at 200 degrees C.(392F)  At a temperature of 275C the material has lost over 50% of its strength.  It is for this reason that many codes do not allow aluminum to be placed in a fired system. These numbers come from certified laboratories and testing facilities.  The test you are designing will be performed at atmosphere or 24.7 psia far below what you intend to operate. At 400C degrees there will be little or no strength.  Because of the way you have split the manifold for the heat exchanger the flow will decrease by half as it passes through one of the splitters. In the design of a good safe heat exchanger you need to stay above that knee. Your burner design will easily give you a bulk temperature of over 1600 degree F.  You should redesign your test to replicate your operating conditions.


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## Toymaker (Feb 8, 2022)

HMEL said:


> You should know that aluminum yield strength vs temperature of most aluminum alloys downward descent of what many call the knee starts at 200 degrees C.(392F)  At a temperature of 275C the material has lost over 50% of its strength.  It is for this reason that many codes do not allow aluminum to be placed in a fired system. These numbers come from certified laboratories and testing facilities.



Aluminum's 200°C knee is the main reason I will be keeping boiler temperature below 200°C.  Looking at the temperature to yield strength graph below, my _never exceed_  temperature of 184°C seems reasonable, yes?







HMEL said:


> The test you are designing will be performed at atmosphere or 24.7 psia far below what you intend to operate. At 400C degrees there will be little or no strength.  Because of the way you have split the manifold for the heat exchanger the flow will decrease by half as it passes through one of the splitters. In the design of a good safe heat exchanger you need to stay above that knee. Your burner design will easily give you a bulk temperature of over 1600 degree F.  You should redesign your test to replicate your operating conditions.


 
Part of my working career included testing various parts of airplanes, and our moto was test-like-you-fly,  So I like your idea of a slight redesign of my test,...it shouldn't be too difficult to place a valve and a pressure gauge onto the open end of the boiler tube to restrict flow and increase pressure up operational levels.


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## Toymaker (Feb 8, 2022)

Steamchick said:


> Hi Toymaker, Maybe I can fumble my way through an explanation re: "I still don't fully understand how steam could possibly condense and form liquid droplets inside a pipe filled with steam.":- As I see it... If fine spray from the rapid boiling in the  boiler (bubbles bursting) is not separated from the steam then some un-boiled water will pass down the steam pipe at the same temperature as the steam - but not the same phase. I.E. these droplets will need extra latent heat to vapourise... but the steam pipe actually "extracts" a little heat as the steam expands to accelerate down the steam pipe, so there is no "spare heat" to vapourise these droplets. In fact, without extra heat more steam condenses to power the wet steam down the pipe. So water in 2 states hits the turbine. (No good!). The "Obvious" countermeasure, is to have some extra coils in the flue gases to add extra heat to the wet steam, to provide the extra latent heat needed to dry the steam, the elevate the temperature further, so the steam is carrying a lot more energy into the engine. (superheating). That is, so the steam reaching the engine is hotter and still at a higher pressure than the "condensing pressure" (equal or less than the boiler pressure).



Thank you,...This is one of the best explanations on wet steam I've read.  



Steamchick said:


> Your plan: "I will try to operate the boiler in the super critical pressure-temperature region for R123, meaning that I need to keep the pressure at or a little above 526 psi (3627 kPa ), and the temperature at or a little below 183°C, which will keep the R123 in a liquid state. My goal is keep the working fluid, R123, in it's liquid stated until it reaches the De Laval nozzles (or convergent-divergent nozzles). As the R123 liquid passes through the nozzles it will flash into a vapor at very high velocity as it impacts the first row of turbine blades."
> I think the "trick" you will be performing, is in controlling the  pumping of the fluid with enough flow to raise the pressure (against the venting at the nozzles) and keep the temperature at the hottest point of the boiler coils to 183C or below.



My current design uses a  _pressure washer,_ driven by a DC motor for the boiler feed pump, which allows the FADEC to control motor speed and thereby output pressure and flow rate.  The FADEC also has control of both the air flow into the burner and fuel flow.  By monitoring pressure & temperature of the working fluid at the boilers output and turbine RPM, the FADEC will be able to regulate all three of these parameters by controlling burner output levels and feed pump pressure & flow.  This is all pretty standard process control.  My biggest concern is avoiding feedback induced oscillations.  



Steamchick said:


> Just trying to work this out (My confused brain will probably get this wrong? - But a clever person will correct me!):
> Enthalpy of 1kg of R123 at 183C:
> Liquid: 422.6Kj/Kg. Latent heat to vapourise to gas = 18.9 kj/kg.
> Therefore to change state from liquid to gas without addition of external heat, the gas only has Enthalpy of 422.6-18.9 = 403.7 Kj/Kg.... Thus the temperature of the gas will be at 39C: having taken the heat from the liquid to vapourise to gas. - See table: Thermodynamic Properties of HCFC-123, SI units (frigoristes.fr)
> ...



I don't understand how you arrived at this conclusion, "_Thus the temperature of the gas will be at 39C_"


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## Toymaker (Feb 8, 2022)

Steamchick said:


> <snip>
> 
> Gaseous R123 with Enthalpy = 422.7Kj/Kg is at 71C and pressure = 388kPa. I.E. JUST to make the physical change of state from liquid to gas. -
> <snip>



Where did you get these values?  I'm not following your logic.


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## Steamchick (Feb 9, 2022)

Hi Toymaker, maybe my logic is at fault? I would not be surprised as I am not experienced in thermodynamics. But the tables in the link I posted are much like steam tables. My logic goes like this in post #47.

The Enthalpy (the absolute energy contained within, or needed to get to this state...) of liquid R123 at 183C is given in the table. = 422.6Kj/Kg.
So I considered that to get the Enthalpy (energy of latent heat of vaporisation) to vaporise the liquid to gas I should deduct this value from the enthalpy of the liquid. 422.6 - 18.9 = 403.7 Kj/Kg.
Thus the remaining enthalpy (energy within the gas) = 403.7Kj/Kg., would define the gas at a temperature and with the related lower pressure as per the table. Therefore I took that value of enthalpy and from the table for Gas determined the related temperature as 39C.
So in reality, the liquid at 183C has cooled to gas at 39C. With related pressure drop. All the heat required to expend the liquid into gas has come form within the liquid, as it is an adiabatic expansion to create the gas from the liquid. I.E. This is how a refrigerator works to get the cold gas for keeping your foodstuff cold, and ice cream frozen. 
Maybe I am in error by subtracting the latent heat from the enthalpy of the liquid? A proper refrigeration Engineer (NOT a clever and we'll trained fitter who knows how to mend a fridge!) will do these calculations as his job so can teach us all, perhaps? That's why I reconsidered in post#48 by not subtracting the latent heat of vaporisation from the enthalpy of the liquid. And my confusion demonstrates why this needs expert advice, so we can all learn! 
I am sorry I am unclear about some of this, but I find text books blow my mind. So I learn by trying to solve problems, so I can teach myself. However, I do need an expert to say "Good, the right answer", or "Wrong, it should be _______!".
The calculations for steam are basically the same, but use different tables. And I am not an expert with interpreting those either!
Cheers,
K2


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## Toymaker (Feb 9, 2022)

Steamchick said:


> Hi Toymaker, maybe my logic is at fault? I would not be surprised as I am not experienced in thermodynamics. But the tables in the link I posted are much like steam tables. My logic goes like this in post #47.
> 
> The Enthalpy (the absolute energy contained within, or needed to get to this state...) of liquid R123 at 183C is given in the table. = 422.6Kj/Kg.
> So I considered that to get the Enthalpy (energy of latent heat of vaporisation) to vaporise the liquid to gas I should deduct this value from the enthalpy of the liquid. 422.6 - 18.9 = 403.7 Kj/Kg.
> ...



I'm not an expert in thermodynamics either,...I'm just an old retired electronic engineer whom likes to play with turbines. 
Hopefully an expert will chime in and add some much needed clarity.


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## Steamchick (Feb 9, 2022)

My brother has given me some advice. I THINK, my later post #48 is correct, so the gas after expansion is at 71C.
K2


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## Toymaker (Feb 9, 2022)

Steamchick said:


> My brother has given me some advice. I THINK, my later post #48 is correct, so the gas after expansion is at 71C.
> K2



Remember the definition of "latent heat", is the heat required to convert a solid into a liquid or vapor, or a liquid into a vapor, *without change of temperature*.  Table 1 of the the Thermodynamics Properties chart shows us that at 183°C  R123 can be either a liquid or a vapor, the only difference is 18.9 kJ/kg of latent heat.  Even the pressure remains the same in both states.  My point being that I don't believe you can change the temperature of a gas or a liquid by only changing it's latent heat.  

Whether I have a liquid or a vapor on the input side of the nozzle, the biggest nozzle related changes to the working fluid will come as it passes through the nozzle and expands towards the first row of blades; which will be governed by the ideal gas law, _PV_ = _nRT_ .  At the nozzle's most restricted point the total area is 0.22 sqr".  At the face of the first row of blades, the area is 1.185 sqr" giving a 5.38 increase in area and volume.  Using Table 1:  at 183°C the vapor volume is 0.0022.   We now know the vapor will expand 5.38 times as it reaches the first blade row, so 0.0022 x 5.38 = 0.0118.   Again from Table 1, a volume of 0.0118 corresponds to a temperature of 126°C or 127°C.


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## Steamchick (Feb 10, 2022)

Hi Toymaker, I agree with the PV=RT aspect of expansion from nozzle to blades... 
But I think you mis-understand the latent heat bit - If I am right, which may be not so, if I misunderstand it!
But Here goes. (See also post #48?). N.B. Pressures are absolute, Temperatures degrees C. 
The Enthalpy of the liquid is the "energy within" the liquid R123 at 183C and pressure = 3627kPa. So,_* Hf liquid*_ = 422.6Kj/Kg. 
The conversion from liquid to gaseous state is ADIABATIC: I.E. NO ENERGY flows in from outside.
So to achieve the gaseous state needs an energy (from somewhere...) of 18.9Kj/Kg. Being ADIABATIC, the only place this can come from is the energy stored *within *the pressure and temperature of the liquid: I.E. _*Hg liquid*_ = _*E Gaseous*_:  Hence The GASEOUS state has to be at a lower temperature and pressure - I.E.  relating to the Enthalpy of 422.6Kj/Kg. - because there is no energy input of extracted (Enthalpy is constant at an Adiabatic change).
So referring to the tables of GAS Enthalpy of 422.6Kj/Kg. I found the temperature and pressure of the gas after conversion of the physical state =  71C and 388kPa.  

Then the PV = RT from nozzle pressure and temperature of the gas is used as P/T = R/V.. or T/P = V/R, or V = RT/P, or however you wish to calculate what happens to the gas after the conversion of physical state.
It is 46 years since I did any Thermodynamics, except for 3 or 4 boiler calculations, so I am a "beginner", and likely to be wrong... Maybe a refrigeration Engineer or thermodynamics teacher can decide who is right, as I am still not 100% sure! - But it seems to be logical (to me) that this is what it should be...

K2


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## Toymaker (Feb 10, 2022)

Steamchick said:


> Hi Toymaker, I agree with the PV=RT aspect of expansion from nozzle to blades...
> But I think you mis-understand the latent heat bit - If I am right, which may be not so, if I misunderstand it!
> But Here goes. (See also post #48?). N.B. Pressures are absolute, Temperatures degrees C.
> The Enthalpy of the liquid is the "energy within" the liquid R123 at 183C and pressure = 3627kPa. So,_* Hf liquid*_ = 422.6Kj/Kg.
> ...



Hi Steamchick,  If you stop using the supercritical approach of having the working fluid remain a liquid right up to the nozzle exit, and instead do the calculations for a vapor state at the nozzle input and output, then you end up with the calculations I made in post #56 using  _PV_ = _nRT_  and yielding 126°C at a pressure of 1352kPa.

Your calculations which start with the working fluid in a liquid state, result in a much lower temperature and pressure just transitioning from liquid to vapor and without even expanding through the nozzle.  

We cant both be right,...so my money is on _PV_ = _nRT_  yielding the correct answer.


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## solarenergyadventures (Feb 10, 2022)

Hi guys! I've got to jump in here regarding PV=nRT. You cannot use PV=nRT when dealing with a Vapor according to my thermo book. This is why we use the Steam Tables. There is no simple mathematical expression for pressure, volume, and temperature when dealing with vapors. The vapor temperature must be so high above the critical point that the substance takes on the properties of a perfect gas. ONLY Then is PV=nRT valid. The steam tables are derived empirically from extensive laboratory testing of the substance in question, so the enthalpies listed in the tables are actually real-world results of the steam at various temperatures and pressures.  

Regarding nozzle choking in a DeLaval nozzle. You must have choked flow at the narrowest part of the nozzle, otherwise the gas will not accelerate to supersonic velocities.  

I'm also working on ORC engines, so I've done a fair bit of thermo research. 
Cheers M8s


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## Toymaker (Feb 10, 2022)

solarenergyadventures said:


> Hi guys! I've got to jump in here regarding PV=nRT. You cannot use PV=nRT when dealing with a Vapor according to my thermo book. This is why we use the Steam Tables. There is no simple mathematical expression for pressure, volume, and temperature when dealing with vapors. The vapor temperature must be so high above the critical point that the substance takes on the properties of a perfect gas. ONLY Then is PV=nRT valid. The steam tables are derived empirically from extensive laboratory testing of the substance in question, so the enthalpies listed in the tables are actually real-world results of the steam at various temperatures and pressures.
> 
> Regarding nozzle choking in a DeLaval nozzle. You must have choked flow at the narrowest part of the nozzle, otherwise the gas will not accelerate to supersonic velocities.
> 
> ...



Glad you jumped in Solarenergyadventures,...always nice to get input from someone with actual experience with ORC. 

Some 50 years ago I was taught that the Ideal Gas Law, PV=nRT, only works for an _ideal gas_, which doesn't actually exist in the real world,...but that PV=nRT will get you pretty close;  I've never had a reason to doubt that,...until today.  

So, looking a little closer at the thermo tables Steamchick and I have both been using, under the heading, Equations, in the DuPont Suva paper on the *Thermodynamic Properties of HCFC123* it's stated that the Modified Benedict-Webb-Rubin (MBWR) equation of state was used to calculate the tables of thermodynamic properties,...PV=nRT was not used.  

Since I was using the DuPont Suva table to get the values I referenced in posts #56 & #58, I was wrong to state that those values were derived from PV=nRT.  

But, I'm still left with the question: am I using the DuPont Suva table correctly?  I determined the gas volume expanded 5.38 times as it passes through the turbine nozzle.  At the most restricted part of the nozzle, Using Table 1, I find at 183°C the gas volume is 0.0022.  The gas will expand 5.38 times as it passes through the nozzle, so 0.0022 x 5.38 = 0.0118.  Again from Table 1, the new gas volume of 0.0118 corresponds to a temperature of 126°C or 127°C. Therefore, the nozzle will have a temperature drop from 183°C to 126°C.  

If you've used similar thermo charts in your work, I'ld appreciate your feedback.


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## solarenergyadventures (Feb 12, 2022)

Toymaker said:


> Glad you jumped in Solarenergyadventures,...always nice to get input from someone with actual experience with ORC.
> 
> Some 50 years ago I was taught that the Ideal Gas Law, PV=nRT, only works for an _ideal gas_, which doesn't actually exist in the real world,...but that PV=nRT will get you pretty close;  I've never had a reason to doubt that,...until today.
> 
> ...


I looked at the table, and I do believe you are interpreting the volume correctly. Are you planning to superheat above 183 C?  Keep in mind that as the gas expands and cools, it will be dropping into the wet region under the "steam dome." At this point, some of your steam will have started to condense, and turbines don't really like being bead blasted by little liquid droplets. Superheat would move the point that you start your expansion up and to the right allowing your isentropic expansion to mostly avoid the steam dome. Some moisture is okay, but too much can tear things up.  

Looking at previous posts, I see you are planning to use aluminum for your boiler. In my humble opinion, this is not a good idea. Steel pipe is easily available, cheap, roughly three times stronger than aluminum, and, most importantly, does not lose strength at such a low temperature. 
Cheers all!


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## Toymaker (Feb 12, 2022)

solarenergyadventures said:


> I looked at the table, and I do believe you are interpreting the volume correctly. Are you planning to superheat above 183 C?  Keep in mind that as the gas expands and cools, it will be dropping into the wet region under the "steam dome." At this point, some of your steam will have started to condense, and turbines don't really like being bead blasted by little liquid droplets. Superheat would move the point that you start your expansion up and to the right allowing your isentropic expansion to mostly avoid the steam dome. Some moisture is okay, but too much can tear things up.



Always nice to get confirmation from someone who's done this before,...thank you.

Because I want to keep those aluminum boiler tubes from losing too much strength as they get warm, I don't plan to superheat above 183C. 

I dont fully understand why, but I do know that some fluids are classified as "wetting fluids", such as steam, for the reasons you've stated, while others are classified as "drying fluids", meaning they don't tend to form little condensation droplets as the gas cools;  that web page I sent you , *Power from the sun*, talks briefly about this.   As far as I know, R123 falls into the "drying" category.   I wont use a working fluid that is classified as "wetting".   



solarenergyadventures said:


> Looking at previous posts, I see you are planning to use aluminum for your boiler. In my humble opinion, this is not a good idea. Steel pipe is easily available, cheap, roughly three times stronger than aluminum, and, most importantly, does not lose strength at such a low temperature.
> Cheers all!



Yep, I know I'm getting myself into quite a challenge by attempting to use aluminum tubing in the boiler.  I've devised a few simple experiments I'll perform to insure the aluminum tubing, and of equal importance, the aluminum brazing, are both up to the task.  Only if the aluminum cant take the heat will I replace it with steel or copper or perhaps titanium tubing, and even then I will start by replacing only the hottest section, leaving the remaining tubing aluminum.  Boilers are one of the heavier parts of any Steam engine, and one of my goals is to make the entire engine as light as possible.


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## Steamchick (Feb 12, 2022)

Hi Solar-man. I appreciate some expertise joining the discussions. I am only here because it sounds like an interesting project, and while I have little Thermodynamics knowledge -definitely not expert! - I am trying to learn how to work things out using this model. So I'll be very glad of advice from someone who has done the calcs.
K2


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## solarenergyadventures (Feb 12, 2022)

Toymaker said:


> Always nice to get confirmation from someone who's done this before,...thank you.
> 
> Because I want to keep those aluminum boiler tubes from losing too much strength as they get warm, I don't plan to superheat above 183C.
> 
> ...


That makes sense. I was reading through your earlier posts and noticed you are planning to drive a turbocharger compressor with your engine. What happens to all that high volume/ medium pressure air from the turbocharger compressor?


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## Toymaker (Feb 13, 2022)

solarenergyadventures said:


> That makes sense. I was reading through your earlier posts and noticed you are planning to drive a turbocharger compressor with your engine. What happens to all that high volume/ medium pressure air from the turbocharger compressor?



The complete answer to your question gets pretty complicated, but the short answer is:  all that air flow will be the primary thrust producer for a large quadcopter (aka: a drone).  

Much more complicated answer:
Finishing the steam turbine is only the first step in my larger experimental project that involves using the field of fluidics and applying it to propulsive thrust.  If you're not already familiar with the Coanda effect, please watch this short YouTube video on the *Coanda Effect*;  if you're already familiar with the basic aerodynamics of how air flows over a wing, skip ahead in the video to the 4:55 time mark.  The video doesn't mention it, but this is the principle of how the Dyson fan works, and more importantly, it shows how high velocity air can be used to force a much larger volume of air to be added to the thrust producing airflow.  At this point, we need to understand that the overall thrust didn't magickly increase; total thrust is still governed by F=ma and the Coanda effect thruster simply changed a small amount of high velocity air into a much larger volume of lower velocity air, keeping "F" pretty much unchanged.

So if the Coanda effect thruster didn't increase thrust, then why use it at all,...what's the advantage?
In all aircraft, efficiency is greatest when the velocity of the exhaust gases from a jet engine is only slightly higher then the forward velocity of the aircraft.  Applying this fact to an aircraft that's hovering, (zero forward velocity) it's easy to see that we need very large volumes of low velocity air if we want to hover, which is why helicopters have such long blades, and not the smaller propellers found on similar sized airplanes.  

If you're still interested, it's time to watch another short video: *Jetoptera*.  The Jetotera planes are pretty innovative, but they are not the first to use the Coanda effect to augment thrust in an aircraft, as it appears they've borrowed extensively from the *Rockwell XFV-12* built in the late 1970's for the US Navy; this was America's first serious attempt to build a supersonic fighter plane with VTOL capabilities.  Although the XFV-12 program was ultimately cancelled, engineers learned a great deal about fluidics as applied to aircraft.

Referencing the Jetoptera video, my plan is to replace their jet engine, which supplies the airflow into their Coanda effect thrusters, with a steam turbine driving a centrifugal compressor.  Because I'll be supplying my Coanda effect thrusters with relatively cold air, I can use light weight materials such as plastics, carbon fiberglass, and aluminum for their fabrication.  

This is one of the most ambitious projects I've ever taken on, but I'm retired now, and have lots of time to take one vary small step at a time, and then slowly put all those pieces together; it's what I enjoy doing.  

A bit of trivia: whether I succeed or not, I wont be the first person to build a plane powered by a steam engine.  In 1933 the Besler brothers built and flew their *Steam powered Biplane*.  Imagine,...flying a plane powered by a steam driven twin-piston engine!  Just Amazing !


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## Steamchick (Feb 13, 2022)

Wow! Ambitious!
K2


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## Toymaker (Feb 14, 2022)

*Boiler Design  &  online calculator *How much tubing will I need?  

I'm still waiting for an IR thermometer to arrive from an eBay purchase, which allow me to read the actual temperature of the burner's exhaust flames, but for now, based on the bright yellow color of the flame, I'll guess the temperature is between 1200 C to 1400 C.  Since the burner is being fed by a centrifugal air blower (aka leaf blower) I will assume the flame temp will not drop across the hottest section of the boiler tubing.  I will also assume the feed pump is large enough to keep the "steam" moving rapidly through the 8mm OD tubing.

While researching the topic of Heat Transfer, I came across an *online calculator* that I believe can be used to help determine how much tubing will be required.  

If I'm right and I'm using the calculator correctly, I will need less than 1/2 meter length of 8mm OD tubing.  My instincts are telling me that can't be right,...seems way too little.  And maybe I've got this part wrong.  But I will walk through the process and those that have done these calculations before can check my work.
Assume I want to get approx 150 kW output.
If I go with my original plan and use Aluminum tube, the calculator inputs and single output are as follows:  

_ 200         k - thermal conductivity (W/(mK)
 0.0008    A - area (m2)
1200       t1 - temperature 1 C
184         t2 - temperature 2 C
0.001       s - material thickness (m)_
Heat transfer (W): 162560

I only need 0.0008 sqr meters of tube surface.  Even using the ID surface area of an 8mm OD tube, the tube length needed is less than 1/2 meter.  This seems impossibly short, yes ??

If these calculations are accurate, I no longer need to be concerned about the weight of tubing in the hottest section of the boiler, and I can easily use copper or steel tubing instead.

Comments Please.


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## Steamchick (Feb 14, 2022)

I agree with expectations of flame temp from colour....
I haven't checked your calculations, but the simple "tools" (calculations) usually work correctly. 

I should use steel tubing: Safest in case of pump failure, or whatever... "expect the unexpected" - The strongest is always best!
K2


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## Bentwings (Feb 15, 2022)

Toymaker said:


> The complete answer to your question gets pretty complicated, but the short answer is:  all that air flow will be the primary thrust producer for a large quadcopter (aka: a drone).
> 
> Much more complicated answer:
> Finishing the steam turbine is only the first step in my larger experimental project that involves using the field of fluidics and applying it to propulsive thrust.  If you're not already familiar with the Coanda effect, please watch this short YouTube video on the *Coanda Effect*;  if you're already familiar with the basic aerodynamics of how air flows over a wing, skip ahead in the video to the 4:55 time mark.  The video doesn't mention it, but this is the principle of how the Dyson fan works, and more importantly, it shows how high velocity air can be used to force a much larger volume of air to be added to the thrust producing airflow.  At this point, we need to understand that the overall thrust didn't magickly increase; total thrust is still governed by F=ma and the Coanda effect thruster simply changed a small amount of high velocity air into a much larger volume of lower velocity air, keeping "F" pretty much unchanged.
> ...


Look into the Tesla turbines there is a guy making a model that has don some remarkable work with them I think he is building a new one with ceramic bearings so it can rev higher


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## Steamchick (Feb 15, 2022)

150kW is a big engine. - WOW!
K2


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## Toymaker (Feb 15, 2022)

Steamchick said:


> 150kW is a big engine. - WOW!
> K2



I recently calculated the power output of my little 3 stage turbine using the calculated enthalpy drop across each stage and came up 144 kW output.  That's a rough number that doesn't take into account number of blades at each stage, power from impulse & reaction forces of each stage, tip clearance losses, RPM, etc.  But I suspect that number wont drop below 100 kW, nor is it likely to go above 200 kW.  

So spec'ing the boiler at 150 kW seems like a nice place to start.


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## Steamchick (Feb 15, 2022)

Hi Toymaker,
I have been pondering to try and understand all this: As you say earlier, _"I will try to operate the boiler in the super critical pressure-temperature region for R123, meaning that I need to keep the pressure at or a little above 526 psi (3627 kPa ), and the temperature at or a little below 183°C, which will keep the R123 in a liquid state. My goal is keep the working fluid, R123, in it's liquid stated until it reaches the De Laval nozzles (or convergent-divergent nozzles). As the R123 liquid passes through the nozzles it will flash into a vapor"_ I assumed that the liquid state was intended to pass all the way through from the heating coils, the aluminium bent tubes towards the turbine, the conical part and up to the first set of fixed blades - that I understand form the De Laval nozzles... the first part of the first stage of the turbine...?
So at what point do you envisage the Liquid turning to gas, so I can "stop using my supercritical approach" (Sorry, I didn't mean to offend, just try and learn how this works).
I am not "having the working fluid remain a liquid right up to the nozzle exit, and instead do the calculations for a vapor state at the nozzle input and output" but I thought that when you said the "_liquid stated until it reaches the De Laval nozzles" _you meant the narrowest point of the nozzle. It seems logical to me as the expansion starts _at the narrowest point _I think?
Anyway, my point, is simple - I think? If the liquid turns to gas inside the flame heated part of the plumbing then it will absorb the 18.9kJ/kg. of latent heat it needs for the change of state. BUT it the liquid turns to gas OUTSIDE the heated zone, then it must be an adiabatic process, and the pressure and temperature will drop as the Enthalpy change is zero. So the Liquid at 183C and 3627kPa (abs) with Enthaply of 422.6kJ/kg remains the same enthalpy when it becomes gas at 71C and pressure of 388kPa (abs). At least, this is what I understand the thermodynamics to say from the tables Thermodynamic Properties of HCFC-123, SI units (frigoristes.fr) - which I use as I would normally use steam tables. This is still an input to the Laval nozzles in GAS form of 41psi (bar) or 56psi (abs).... I think Absolute pressure is more appropriate, as you will have the suction from the compressor to re-pressurise the gas and liquidise it as it is pumped back to the boiler pipework. Thinking of how the boiler pipework must end in some sort of manifold in order to travel down the aluminium pipes to the turbine, I guess that the liquid will lose pressure slightly there and start to boil and cool, and may be totally gasified by the time it reaches the compression side of the De Laval nozzles... Are these in the hot or cold zone? System diagram in post #1 suggests the cold zone, so adiabatic change of state will more likely occur there, not at the De Laval nozzles.
Have I understood this correctly yet?
Thanks,
K2


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## Steamchick (Feb 15, 2022)

re: post #71. Specifying the boiler for 150kW is a fair sized boiler! As a comparison, a domestic central heating boiler of 30kW sits in my kitchen... so you want a boiler 5 times as big. (That deserved the "Wow!"). 
I know a locomotive boiler that uses 27kW of gas (determined from pressure and jet size), which is on a 5 inch gauge chassis. So 150kW could be the sort of boiler for a loco for a 13inch gauge track (or whatever!). Have you calculated the "fuel-power" you are pumping into your burner? (I may have missed it in an earlier post).

I think (again, not an expert, just a novice learning how to do this) - that you can take the 150kW and translate it into the kgs per second of liquid HCFC123  you need to pump into the boiler to extract the heat, by using the difference in Enthalpy of the HP and cold liquid (post pump) to the Enthalpy of the HP and hot liquid. - Values taken form the table I attached earlier - as the pump power (I think?) does the change of state from LP cold gas to HP liquid...?
Ta,
K2


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## Steamchick (Feb 15, 2022)

I am fascinated by your project. Considering the exhaust from your burner: and the coanda effect nozzles....
The momentum exchange of moving gases reacting on the host vehicle causes thrust. So if the host vehicle generates a lot of low pressure hot gas, made of larger molecules than N2 and O2 in air, then it may be a good idea to inject this gas into the coanda nozzle. The basis is that this gas is initially a part of the vehicle, so when accelerated and ejected from the nozzle will add to the momentum ejected backwards, thus increasing the momentum reaction force forwards....
I think?
If so, perhaps it should be in the form of a De Laval nozzle in the middle of the coanda nozzle, and thus the exhaust gas jet can enhance the mass of air drawn through the coanda nozzle, utilising the last of the heat energy in the exhaust as it expands and cools adiabatically through the nozzle...?
Sorry if this is a crazy idea, but perhaps worth considering?
K2


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## Toymaker (Feb 15, 2022)

Steamchick said:


> Hi Toymaker,
> I have been pondering to try and understand all this: As you say earlier, _"I will try to operate the boiler in the super critical pressure-temperature region for R123, meaning that I need to keep the pressure at or a little above 526 psi (3627 kPa ), and the temperature at or a little below 183°C, which will keep the R123 in a liquid state. My goal is keep the working fluid, R123, in it's liquid stated until it reaches the De Laval nozzles (or convergent-divergent nozzles). As the R123 liquid passes through the nozzles it will flash into a vapor"_



The three most important words out of everything I stated above, are, _I will try  _ I am not at all confident that I can accomplish this.
The only reason for my wanting to operate in the super critical region is because the R-123 would remain in the liquid state, therefore remaining more dense, which means greater contact with the walls of the boiler tubes and therefore capable of carrying away more heat from the Aluminum tubes.  For me, it's only a secondary benefit that the entire engine should operate a bit more efficiently.



Steamchick said:


> I assumed that the liquid state was intended to pass all the way through from the heating coils, the aluminium bent tubes towards the turbine, the conical part and up to the first set of fixed blades - that I understand form the De Laval nozzles... the first part of the first stage of the turbine...?



You got it right all the way up to the nozzle.  The R-123 will flash into a vapor just as it passes through the narrowest section of the nozzle.  If all goes as planned, the gaseous R-123 will greatly accelerate, perhaps reaching Mach 2 as it reaches the entrance to the first row of rotor blades. 



Steamchick said:


> So at what point do you envisage the Liquid turning to gas, so I can "stop using my supercritical approach" (Sorry, I didn't mean to offend, just try and learn how this works).
> I am not "having the working fluid remain a liquid right up to the nozzle exit, and instead do the calculations for a vapor state at the nozzle input and output" but I thought that when you said the "_liquid stated until it reaches the De Laval nozzles" _you meant the narrowest point of the nozzle. It seems logical to me as the expansion starts _at the narrowest point _I think?



Yes, exactly right.



Steamchick said:


> Anyway, my point, is simple - I think? If the liquid turns to gas inside the flame heated part of the plumbing



The only way for that to happen is if my tubing springs a leak and the pressure drops.  Otherwise, the flames will be washing the tubing in 1200 C exhaust gasses, keeping the R-123 firmly in a super critical liquid state,...assuming of course that I can actually attain and keep the super critical condition inside the boiler.



Steamchick said:


> then it will absorb the 18.9kJ/kg. of latent heat it needs for the change of state. BUT it the liquid turns to gas OUTSIDE the heated zone, then it must be an adiabatic process, and the pressure and temperature will drop as the Enthalpy change is zero. So the Liquid at 183C and 3627kPa (abs) with Enthaply of 422.6kJ/kg remains the same enthalpy when it becomes gas at 71C and pressure of 388kPa (abs).



This is where you and I disagree.

I think understanding how the process works will be easier if, for the moment, we step away from using a supercritical fluid  and consider only the gaseous state.   On the input side of the nozzle the gas temp is 183 C, the pressure is 3627.05 kPa and the enthalpy of our R-123 is 441.5 kJ/kg.  The most restricted part of the nozzle has an area of 0.231 sqr inches, and after the R-123 passes through the nozzle openings it expands until it reaches the first rotor blades, where the total area is 1.185 sqr inches.  So the gases have expanded 5.13 times.  From the R-123 properties table we see that the volume of the gas at the smallest part of the nozzle, when it was still at 183 C, is 0.0022 m3/kg.  We just calculated that the volume of the gas expanded 5.13 times.  So 5.13 x 0.0022 m3/kg = 0.01128 m3/kg; this is the new volume we need to look up on our table, and it's at 128 C (not 71 C).



Steamchick said:


> At least, this is what I understand the thermodynamics to say from the tables Thermodynamic Properties of HCFC-123, SI units (frigoristes.fr) - which I use as I would normally use steam tables. This is still an input to the Laval nozzles in GAS form of 41psi (bar) or 56psi (abs).... I think Absolute pressure is more appropriate, as you will have the suction from the compressor to re-pressurise the gas and liquidise it as it is pumped back to the boiler pipework. Thinking of how the boiler pipework must end in some sort of manifold in order to travel down the aluminium pipes to the turbine, I guess that the liquid will lose pressure slightly there and start to boil and cool, and may be totally gasified by the time it reaches the compression side of the De Laval nozzles... Are these in the hot or cold zone? System diagram in post #1 suggests the cold zone, so adiabatic change of state will more likely occur there, not at the De Laval nozzles.
> Have I understood this correctly yet?
> Thanks,
> K2



There is no manifold.  All 8 tubes feeding into the turbine's steam chest have their own separate tube on the inside of the boiler.  All tubes external to the boiler will be covered in insulation to limit heat loss.  Given the high flow rate of 183 C  fluid between the boiler and the nozzle, I suspect all components will heat up to 183 C very quickly, after which there will no longer be any heat loss.


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## Bentwings (Feb 15, 2022)

Steamchick said:


> Hi Toymaker,
> I have been pondering to try and understand all this: As you say earlier, _"I will try to operate the boiler in the super critical pressure-temperature region for R123, meaning that I need to keep the pressure at or a little above 526 psi (3627 kPa ), and the temperature at or a little below 183°C, which will keep the R123 in a liquid state. My goal is keep the working fluid, R123, in it's liquid stated until it reaches the De Laval nozzles (or convergent-divergent nozzles). As the R123 liquid passes through the nozzles it will flash into a vapor"_ I assumed that the liquid state was intended to pass all the way through from the heating coils, the aluminium bent tubes towards the turbine, the conical part and up to the first set of fixed blades - that I understand form the De Laval nozzles... the first part of the first stage of the turbine...?
> So at what point do you envisage the Liquid turning to gas, so I can "stop using my supercritical approach" (Sorry, I didn't mean to offend, just try and learn how this works).
> I am not "having the working fluid remain a liquid right up to the nozzle exit, and instead do the calculations for a vapor state at the nozzle input and output" but I thought that when you said the "_liquid stated until it reaches the De Laval nozzles" _you meant the narrowest point of the nozzle. It seems logical to me as the expansion starts _at the narrowest point _I think?
> ...


You are way beyond me here . My experience was more in aerodynamics and orface flow. The poin in orfaces was not exceeding super sonic and reducing turbulence. It’s been many years and I don’t have the sophisticated computer programs that let you see graphically what was happening . I did get to observe what happens to very critical snd dangerously corrosive effects materials that were forced outside the envelope. It resulted in “ extremely rapid decomposition with release of very great pressures “ more commonly called explosions .  It was often said our batteries were more powerful than the ordinance .  Thank goodness we had a nice bunker


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## Bentwings (Feb 15, 2022)

Bentwings said:


> You are way beyond me here . My experience was more in aerodynamics and orface flow. The poin in orfaces was not exceeding super sonic and reducing turbulence. It’s been many years and I don’t have the sophisticated computer programs that let you see graphically what was happening . I did get to observe what happens to very critical snd dangerously corrosive effects materials that were forced outside the envelope. It resulted in “ extremely rapid decomposition with release of very great pressures “ more commonly called explosions .  It was often said our batteries were more powerful than the ordinance .  Thank goodness we had a nice bunker


Pardon my ignorance but what is this 123 you note?  Sounds like a refrigerant or something similar.


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## Steamchick (Feb 15, 2022)

Hi Owen, I appreciate your efforts trying to unscramble my brain, but maybe we had better just leave it there. I was never able to pass my thermodynamics exams, as I seem to have a mental block that gives the "wrong" answers. 
In this case, it is how the fluid gets from the liquid to gaseous state, so you can do you gaseous expansion from nozzle to turbine blades. I think we have to get the 18.6kJ/kg. of latent heat from the liquid enthalpy, (because that's what I have been working on when I use similar tables for water/steam change of state). But I can't see how you manage that bit of the calculation.
No hassle, I'll sort it out in time.
Thanks for your patience.
K2


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## Toymaker (Feb 15, 2022)

Bentwings said:


> Pardon my ignorance but what is this 123 you note?  Sounds like a refrigerant or something similar.



You're correct !!  *R-123* (also known as HCFC-123) was developed as a refrigerant, but has also been used as the working fluid in numerous heat expansion engines.  If you click on *R-123* the link will take you to a pdf document on it's Thermodynamic Properties.


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## Toymaker (Feb 15, 2022)

Steamchick said:


> re: post #71. Specifying the boiler for 150kW is a fair sized boiler!
> <snip>
> Have you calculated the "fuel-power" you are pumping into your burner? (I may have missed it in an earlier post).
> <snip>
> ...



Yes.  My burner uses a siphon type fuel nozzle that's rated to burn 14L/h maximum.  1 liter of Diesel fuel  = 10.6 kWh.   So, 10.6 kWh x 14 L/h = 148.4 kW

The few test runs I've done with the burner have shown that the nozzle will supply a bit more fuel flow than the 14 L/h rating; I'm fairly certain that I can get 15 L/h, giving me 160 kW.


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## Toymaker (Feb 15, 2022)

Steamchick said:


> I am fascinated by your project. Considering the exhaust from your burner: and the coanda effect nozzles....
> The momentum exchange of moving gases reacting on the host vehicle causes thrust. So if the host vehicle generates a lot of low pressure hot gas, made of larger molecules than N2 and O2 in air, then it may be a good idea to inject this gas into the coanda nozzle. The basis is that this gas is initially a part of the vehicle, so when accelerated and ejected from the nozzle will add to the momentum ejected backwards, thus increasing the momentum reaction force forwards....
> I think?
> If so, perhaps it should be in the form of a De Laval nozzle in the middle of the coanda nozzle, and thus the exhaust gas jet can enhance the mass of air drawn through the coanda nozzle, utilising the last of the heat energy in the exhaust as it expands and cools adiabatically through the nozzle...?
> ...



Hmmmm, that's an interesting idea.   As the exhaust gases exit the boiler I could easily rout them into the intake of the large centrifugal compressor, where they would be mixed with a much larger volume of ambient air.  

Your idea of using a De Laval nozzle to shoot high velocity air into the middle of the Coanda nozzle is very similar to what was done on the XFV-12 program; below is a diagram of the Augmenter Geometry they used.  The structure in the top middle of the diagram is a nozzle.  



If you look closely at the first diagram I posted, you'll see a similar set of shapes as the one above, in the upper right portion of my drawing.


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## Toymaker (Feb 15, 2022)

Steamchick said:


> I think (again, not an expert, just a novice learning how to do this) - that you can take the 150kW and translate it into the kgs per second of liquid HCFC123  you need to pump into the boiler to extract the heat, by using the difference in Enthalpy of the HP and cold liquid (post pump) to the Enthalpy of the HP and hot liquid. - Values taken form the table I attached earlier - as the pump power (I think?) does the change of state from LP cold gas to HP liquid...?
> Ta,
> K2



When I did the rough power output calculations for the turbine, I started by determining the maximum mass of R123 that would be flowing through the nozzle.  The nozzle is the most limiting part of the overall engine.  

Gas flow rates through a nozzle cannot exceed the local speed of sound, which for R-123 at the critical point is 78.1 m/s.  Total nozzle area is 0.231 sqr in or 0.000149 sqr meters.  So, 78.1 m/s x 0.000149 sqr meters = 0.0116 cubic meters/sec.  From our favorite thermo properties table, I find the density of R123 at the critical point to be 449 kg/cubic meter, and since I only have 0.0116 cubic meters, my total mass flow is 5.2 kg/s.


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## Steamchick (Feb 16, 2022)

Re: post #81: I think the feeding of the compressor with exhaust gas will have 1 advantage of increasing the density of the compressor gas. But also possibly higher pressure and flow due to pressurising the inlet if the inlet with injected exhaust gas is design as a "gas injector", to draw-in extra air. I make gas burners for small model boilers, and induced air from the gas jet requires a particular geometry (not unlike a Delaval nozzle). I.E. A converging throat to venturi with controlled expansion following. This could sort of supercharge the compressor.... It is all about pressure change to velocity to develop a sub-atmospheric pressure gradient that sucks-in extra air, then slows the mixture to re-develop pressure above atmospheric....
I knew a guy (50 years ago) who increased his engine power on his drag racer by "exhaust gas injection" to induce extra air into the carburettor. It was a permitted "supercharging", as there was no mechanical device forcing the draught. It only worked as the carb was fully open for the drag.... and was re-jetted accordingly.
K2


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## Steamchick (Feb 16, 2022)

I am enjoying this. The Engineering involved : sizing the fuel pump (post #80), then "energy management" (heat flow) through the rest of the system, is a real education for me. 
Thanks Toymaker!
You can write the book when you finish - a text book example of system design!
K2


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## Toymaker (Feb 17, 2022)

Steamchick said:


> I am enjoying this. The Engineering involved : sizing the fuel pump (post #80), then "energy management" (heat flow) through the rest of the system, is a real education for me.
> Thanks Toymaker!
> You can write the book when you finish - a text book example of system design!
> K2



Thanks for the kind words.

There's a pretty good tutorial on how to calculate power output of a two stage steam turbine using the steam tables at: *Engineers Academy*  The speaker does a good job of explaining how enthalpy drop across each stage determines the power output of that stage.  My only complaint is that the example used gives the pressures at both stage outputs, which are unknown values during the initial design.  Maybe that part is explained in a different video I haven't found yet.


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## HMEL (Feb 18, 2022)

Actually the power output is a criteria of the original design specification.  It starts with a mass flow diagram and the pressure and thermodynamic states are laid out to develop a theoretical horsepower or kw/hr design point.  With the turbine itself it starts at the nozzle block control valve then progress downstream to the condenser.  Use of expansion curves and consideration of nozzle design are set before the wheels and blades are assembled.  If extraction points are required as in the case of feed water heaters it is even more important.  If under contract and if the stakes are high as in large utility machines these will be measured and tested to see if they meet specs.  Same for the boiler The manufacture or designer will usually over design to meet this purchase spec called manufactures margin.  So you do not normally build a turbine and see what you get. The design number will determine the heat rate on how much energy per kw is produced.  For smaller turbines probably not as important.  The manufacture will know or should know what the pressure drop his stages will be.  This will depend upon the type of blade impulse , reaction or hybrid of both types. This design process is used on all systems no matter the working fluid Steam, Ammonia,  or Organic Fluids

And buried under all this theory is the practical aspect of how these things are made.  You do not wish to have the blades leave the wheel due to nozzle passing frequency issues, bad root design or over speed.  Over the years I have kept about 8 of these types of blade failures just as souvenirs  of interesting things that can happen.

The average modeler probably doesn't care about all the engineering that goes into it.  If it spins at any rpm and makes a little power he is probably a happy camper.


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## Steamchick (Feb 18, 2022)

Thanks HMEL. Common sense from someone with experience!
My experience doesn't include turbines, so I am a beginner in the learning process, which is why I have been asking lots of questions and challenging Toymaker (a man of great patience!). But I come from a professional background, where we calculated everything before making it. Much easier to change the pencil-on-drawing before cutting metal, than trying to get the metal to do what it cannot! This methodology was new when I joined a certain design office, as most of the work was "drawn first". Then "made and tested and re-designed to fix the faults"..!!! As long as people followed the 3 LARGE BOOKS of the "Design manual" (a list of designs that had worked!) then they didn't need calculations (Ha! Ha!). I joined, having come from a different company, and started design by planning the job, doing calculations _on existing designs_, then changing to improve to get the required performance of my new designs. First parts:  The steel fabrication shop complained because I used "standard steel structural designs" and "it was too awkward to set-up for welding", then "much to light - it will collapse" criticism. Neither of which was true. And after 4 years I left (the writing was on the wall! - "They have been weighed in the balance and found wanting") as they were closing the place down, except for my designs and a couple of others! So I feel justified in blowing my own trumpet as their walls came tumbling down... "New gates" cannot save the city if the walls are collapsing... Here-endeth the lesson..
K2


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## Toymaker (Feb 18, 2022)

HMEL said:


> Actually the power output is a criteria of the original design specification.  It starts with a mass flow diagram and the pressure and thermodynamic states are laid out to develop a theoretical horsepower or kw/hr design point.  With the turbine itself it starts at the nozzle block control valve then progress downstream to the condenser.  Use of expansion curves and consideration of nozzle design are set before the wheels and blades are assembled.  If extraction points are required as in the case of feed water heaters it is even more important.  If under contract and if the stakes are high as in large utility machines these will be measured and tested to see if they meet specs.  Same for the boiler The manufacture or designer will usually over design to meet this purchase spec called manufactures margin.  So you do not normally build a turbine and see what you get. The design number will determine the heat rate on how much energy per kw is produced.  For smaller turbines probably not as important.  The manufacture will know or should know what the pressure drop his stages will be.  This will depend upon the type of blade impulse , reaction or hybrid of both types. This design process is used on all systems no matter the working fluid Steam, Ammonia,  or Organic Fluids
> 
> And buried under all this theory is the practical aspect of how these things are made.  You do not wish to have the blades leave the wheel due to nozzle passing frequency issues, bad root design or over speed.  Over the years I have kept about 8 of these types of blade failures just as souvenirs  of interesting things that can happen.
> 
> The average modeler probably doesn't care about all the engineering that goes into it.  If it spins at any rpm and makes a little power he is probably a happy camper.



Question:
When calculating the power developed by each turbine stage using the change in enthalpy across each stage, as was done in this *Engineers Academy* example, does the term "stage" include both stator and rotor blades, or just the rotor blades?  Since the job of the stator blades is to re-direct the gas flow, and these blades are not moving, the enthalpy drop across the stators results in increasing the steam velocity which will result in greater energy transfer onto the adjacent rotor.  So it seems logical that I should include the enthalpy drop across both stator and rotor blades to find the total power for each turbine stage.   Or, since the stator is not moving, it therefore does not directly contribute any power transferred onto the rotor blades and the enthalpy drop across the stator should be excluded.  

Which is the correct answer ?


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## Steamchick (Feb 18, 2022)

I don't know, but would guess the enthalpy drops across the static and dynamic pair....?
K2


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