Ambitious ORC Turbine

[ddmckee54]

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

 

[Steamchick]

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

 

[Toymaker]

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

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.

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.

 

[Toymaker]

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?

 

[Steamchick]

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

 

[Steamchick]

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

 

[raveney]

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.

 

[Toymaker]

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.

 

[Toymaker]

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.

<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

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.

 

[Steamchick]

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

 

[Toymaker]

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.

 

[Steamchick]

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

 

[raveney]

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

 

[Toymaker]

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.

 

[Toymaker]

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

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.

 

[Bentwings]

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

 

[Bentwings]

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.

 

[Steamchick]

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

1. I agree the total CSA of the combined set of nozzles (throat CSA) determines the total flow, subject to pressure difference across the throat.
2. I do not know how to design the converging nozzle.
3. 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

 

[HMEL]

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?

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.

 

[Bentwings]

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

1. I agree the total CSA of the combined set of nozzles (throat CSA) determines the total flow, subject to pressure difference across the throat.
2. I do not know how to design the converging nozzle.
3. 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

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 .