DIY Tesla Impulse Turbine

[Toymaker]

Yes, it is a common design of Engineering connection. Easy to assemble correctly, dismantle and re-assemble. I use Gas fittings - "Calor gas" used to use Butane at cylinder pressure - using 1/8in bore copper pipe and 1/8" BSP fittings. Now use LOW pressure butane or propane (via a regulator) to 1/4" BSP fittings... for caravans, etc. But I now use copper brake pipe for my steam as the "common" pipework, with 1/8" BSP fittings, or 5/16" x 32 M.E. to suit Model Engineering commercial fittings.
Pre-assemble olives onto pre-shaped pipes, using a fitting in a vice or similar, rather than using "the job" for the first tightening of the nut onto the olive. Then use the pipe assembly on the proper job.
K2

Thanks for the feedback K2. Your instructions closely match one of the how-to YouTube videos I've watched; the only addition to your instructions was to hand tighten the nut until snug, then turn the nut an additional 1/2 turn using a wrench, no more. I believe I may have initially over-tightened the nut, and the threads are now stripped from my attempts to stop the leaking. I've ordered replacement parts, but of course this means more waiting for those parts to arrive. :-(

 

[Steamchick]

You can add a single wrap of PTFE plumbers tape around an olive before assembling the joint. But I have never found that necessary if I pre-assemble olives onto the pipe. I have heard of some people apllying grease instead of PTFE TAPE. BUT I assemble dry and clean. Then you only need a nip to make a water -tight and pressure proof joint when you fit the pipe assembly to the job. Too much torque strips threads.
Take care. You don't want overstressed threads failing when you have pressure on the boiler.
K2

 

[Toymaker]

Problem solved,...no more leaks !!! After waiting 2 weeks for replacement parts, the new connections leaked almost as bad as the old ones; the difference being the new connections don't start leaking until a bit over 100 psi.

I had already decided that if the new connectors also leaked, I would move on to plan-B, which was to braze the 3mm copper tube to the brass fitting. This method makes diss-assembly and re-assembly a bit more difficult, but this method doesn't leak; I hydrostatically tested the fittings up to 450 psi with no problems.

 

[Steamchick]

Intended to be good for 6 bar NWP, = 12 bar hydro test without leak. I do use olives, but never see leaks. Possibly as I don't see >6bar...
K2

 

[Toymaker]

Intended to be good for 6 bar NWP, = 12 bar hydro test without leak. I do use olives, but never see leaks. Possibly as I don't see >6bar...
K2

The package of parts shown in post #339 was ordered from AliExpress, from China, and came with no instructions, no pressure ratings, not even a brand name. Both fittings began leaking at about 8 bar, so they didn't even make it to 12 bar without leaks.

12 bar max huh?,....Guess it's a good thing I brazed the tube to the fitting

 

[Steamchick]

I say "12bar" - because on the copper tube that is the highest test pressure I can speculate it will see. But there may be applications for these nuts and olives on thicker walled copper tube that see much higher hydraulic pressures.... I simply don't know. You bought stuff planned for car oil pressure systems - typically 80psi normal pressure, = 160psi "test" pressure. My experience is these fittings used for Butane at cylinder pressure - 15psi at 20 deg.C. - but must be capable of a couple of hundred psi for test.. I haven't got a reference document for that...
I do know however, that everything has an upper WORKING limit, much below where it fails. Maybe you should consult an Hydraulic component manufacturer to understand what is recommended for your pressure? Maybe Steel nuts to take the stresses of your higher pressure? - even steel pipework and brazed olives - or deformed/swaged steel ends such as used on Car Brake pipework? (That is a system you NEVER expect to fail at hydraulic pressures. - But I don't know what those pressures are...). >1500N force on the brake pedal (When a big strong guy is pressing in an emergency?) x the mechanical advantage of the lever, Plus the added SERVO generated load onto the piston of whatever area = pressure in the pipework.
I'm sure you can do the sums on your system - to be sure to be safe. - I GUESS that as this is on the water feed side, if a Pressure gauge fitting blew off during service, then the boiler would instantly discharge whatever steam was in the heater coil, then just melt-down, without any further drama? - The feed water being pumped out of an open tube would act as a quench to the outside of the boiler?
K2

 

[Toymaker]

I say "12bar" - because on the copper tube that is the highest test pressure I can speculate it will see. But there may be applications for these nuts and olives on thicker walled copper tube that see much higher hydraulic pressures.... I simply don't know. You bought stuff planned for car oil pressure systems - typically 80psi normal pressure, = 160psi "test" pressure. My experience is these fittings used for Butane at cylinder pressure - 15psi at 20 deg.C. - but must be capable of a couple of hundred psi for test.. I haven't got a reference document for that...
I do know however, that everything has an upper WORKING limit, much below where it fails. Maybe you should consult an Hydraulic component manufacturer to understand what is recommended for your pressure? Maybe Steel nuts to take the stresses of your higher pressure? - even steel pipework and brazed olives - or deformed/swaged steel ends such as used on Car Brake pipework? (That is a system you NEVER expect to fail at hydraulic pressures. - But I don't know what those pressures are...). >1500N force on the brake pedal (When a big strong guy is pressing in an emergency?) x the mechanical advantage of the lever, Plus the added SERVO generated load onto the piston of whatever area = pressure in the pipework.
I'm sure you can do the sums on your system - to be sure to be safe. - I GUESS that as this is on the water feed side, if a Pressure gauge fitting blew off during service, then the boiler would instantly discharge whatever steam was in the heater coil, then just melt-down, without any further drama? - The feed water being pumped out of an open tube would act as a quench to the outside of the boiler?
K2

The coper tube is 3mm (0.118") OD with a 0.053" ID, making the wall thickness a bit under 1mm, at 0.0325".
Using Barlow’s formula: P = 2*T*S/D and a copper yield strength of 11,000 psi, results in 6,059 psi,....which is 12 times my working pressure of 500 psi.

Now that I've brazed the copper tube to the brass fittings, thereby eliminating the flare-less connections, I believe the boiler tubes will fail before the newly installed 3mm pressure guage tube fails.

 

[Toymaker]

Today's Tesla Turbine test results. Big win as my epoxy resin spider (part of the coupler) held up. But only a tiny increase in power output; up to 47 watts from 36 previously. Sadly, my digital tachometer chose today to stop working, so I do not know turbine RPM. Per the gauges, steam flow rate into the turbine was about 0.7 LPM at about 20 psi.

I had to stop testing early because I started to smell burnt rubber which I suspect is coming from the throw-rugs I placed around the boiler as noise suppression.

 

[Steamchick]

Fun! What plan to check everything, before increasing the steam pressure and flow?
I find 20psi instantly becomes "wet" with expansion (A lot of condensation, not a lot of power), so I am sure higher steam temperatures (superheating) are needed to get turbines working properly. But then I have only a little experience of 1 Tesla turbine. (Lots of reciprocating engines though). So you are more expert, than I.
With a crude calculation, I have decided I need 3 times the superheater normally fitted to a Proprietary boiler. Loco users always appreciate a loco with large superheaters, more than one with less.
I guess your flash (tube) boiler should provide superheating in the final coils? What temperature of steam do you have at the point of entry to the turbine? (As the steam expands down the feed pipe some condenses to water becoming wet steam - I cannot see your feed-pipe - Is it well lagged to prevent excess heat loss and further condensation before the turbine?). I lag my stem pipes with Cotton string wound around the pipe, then painted with white paint. But on 2 boilers the superheating is so good it chars the cotton for a bit , leaving bare pipe. I must get some "proper" heat resistant string!
I suspect a lot of noise is coming from the boiler exhaust? An absorption silencer may be needed if noise is a problem. - That is 2 concentric tubes, with stainless wire wool between them and the inner one perforated. E.g.:

https://www.ebay.co.uk/itm/28374707...7779&msclkid=80f1e2f96318165516ba85a2936848c6
The Roar from your burner will mostly be white noise, so this is the most suitable silencer design for you, IMHO. (With NO restriction on the exhaust).
K2

 

[Steamchick]

Another thought - as you have a "HOT" exterior to the boiler... Wrap some crinkly aluminium foil around the boiler. Even a few layers making an "air trap" and "radiant heat reflector".
On one boiler, the surface temperature of the (conventional) boiler was measured at 135C, but when we placed a crinkly foil cover on the boiler the external temperature went to less than 50C on the non-contact thermometer, (warm to the touch) and the turbine increased speed a little, I guess with improved boiler temperature (2 or 3 degrees?) measured on the un-insulated boiler front.
Just ideas that may help, and become more significant as the pressure rises...
K2

 

[Toymaker]

Fun! What plan to check everything, before increasing the steam pressure and flow?

Since I stopped mid-way into my gradual power increase, I will start back at idle power and once again gradually increase burner-boiler power output, and the next time I can hopefully reach higher pressure into the Tesla turbine.

I guess your flash (tube) boiler should provide superheating in the final coils?

At least for now, I'm playing it safe and will limit steam pressure to 400 psi at to 231 C (448 F).

What temperature of steam do you have at the point of entry to the turbine?

Good question,...there's no easy way to measure steam temperature at that point. However, considering my feed line is only 1 meter long, I suspect minimal temperature drop between boiler out and turbine in.

(As the steam expands down the feed pipe some condenses to water becoming wet steam - I cannot see your feed-pipe - Is it well lagged to prevent excess heat loss and further condensation before the turbine?). I lag my stem pipes with Cotton string wound around the pipe, then painted with white paint. But on 2 boilers the superheating is so good it chars the cotton for a bit , leaving bare pipe. I must get some "proper" heat resistant string!
I suspect a lot of noise is coming from the boiler exhaust? An absorption silencer may be needed if noise is a problem. - That is 2 concentric tubes, with stainless wire wool between them and the inner one perforated. E.g.:

K2

The stainless steel braided tube in the photo below is the steam feed pipe. It's sold for use with steam and air at working pressures up to 1500 psi.

 

[Steamchick]

That's a fantastic bit of hose! But for a final installation I guess you'll fix everything together, so could easily insulate the steam connection then. The pressure drop of just a few psi of steam that is not superheated will cause condensation droplets. Also to push the steam along the pipe takes a few psi. Thus the outlet of the delivery Pipe is always a small pressure drop below the inlet. A Tesla turbine is pretty much immune to damage from droplets. Bladed turbines damage badly with water drops. Either way, super heating really helps get dry steam into the turbine, with more energy than wet steak of the same temperature. Your coil flash boiler naturally will give a degree of superheating. "How much" should be measured to understand how the system is performing. So can you arrange some temperature measurents? Even with a non- contact temperature of fitting on the pipework will hive you an idea.
I hope the boiler gives you lots of steam and lots of superheat. That mean's LOTS of power!
K2

 

[Toymaker]

That's a fantastic bit of hose! But for a final installation I guess you'll fix everything together, so could easily insulate the steam connection then. The pressure drop of just a few psi of steam that is not superheated will cause condensation droplets. Also to push the steam along the pipe takes a few psi. Thus the outlet of the delivery Pipe is always a small pressure drop below the inlet. A Tesla turbine is pretty much immune to damage from droplets. Bladed turbines damage badly with water drops. Either way, super heating really helps get dry steam into the turbine, with more energy than wet steak of the same temperature. Your coil flash boiler naturally will give a degree of superheating. "How much" should be measured to understand how the system is performing. So can you arrange some temperature measurents?

I already have a temperature sensor (RTD: Resistance Temperature Device) mounted on the steam output side of the boiler; eliminating electrical noise so it reads accurately has not been a priority up to this point, as "ball-park" values have been good enough.

Even with a non- contact temperature of fitting on the pipework will hive you an idea.

I have a non-contact laser infrared thermometer which I can use to check steam-hose fitting temperatures at both ends of the hose,....that will happen after I get everything else running and stable.

I hope the boiler gives you lots of steam and lots of superheat. That mean's LOTS of power!
K2

Thanks for the good wishes

 

[Steamchick]

Great! Have you compared the temperature from the RTD sensor with the saturated steam temperature at the pressure you are delivering? Is it much higher than the saturated steam temperature? - The difference is the superheat... (As you know, but others may not know?).
When using superheat in the engine, you are delivering more heat (energy) in the steam than when it is saturated, for the same pressure. When the steam expands inside the engine, there is therefore less condensed water (droplets) produced during expansion (and cooling) of the steam - which is quite significant to running certain engines. e.g. Large thermal power stations run their turbines COMPLETELY dry, so even the steam exiting the turbine is above the temperature of the saturated steam at the pressure it is leaving the turbine. This ensures the bladed turbines only see a hot gas (Steam), and thus avoid blade damage that would occur if the droplets of water condensed inside the turbine. What comes out of those turbines then passes through economisers (feed-water heat exchangers) and on to the condensers where the steam converts back to water. - Perhaps you'll eventually install an Economiser between the turbine and the condenser? - The hot condensate can then pass through the feed pump, then economiser and on to feed the boiler. Long-term, that's a modification I plan for the Tesla Turbine I can experiment with.
When running the Tesla turbine recently, I noticed that it was pretty immune to "water in the steam", while it was just "white water vapour" blowing into the atmosphere from the exhaust. But initially, more water vapour (condensate) was being generated than could blow out, so the blades were running in a puddle of water, until I drilled a small drain hole at the bottom of the casing to drain the space outside and below the discs... When the casing and internals had heated-up significantly (above water boiling point?) all the water vapour exited the exhaust ports and problems disappeared. I reckon I could improve the efficiency by lagging the casing as well. Otherwise the lost heat is just more fuel wasted before the discs do their work and extract the energy from the steam.
For those that don't know, Steam is an invisible gas - made of water molecules. The white clouds from a kettle or pot-boiling are water vapour = Liquid water in an aerosol I.E. NOT steam.
I am interested to see how you progress?
(Sorry if I prattle-on too much!).
K2

 

[Steamchick]

Just reading your information again... (#353)
Of course:
400 psi at 231 C (448 F). - is the temperature of the saturated steam. = no superheat. BUT will you control to 400psi? - or to 231C? The design of the boiler could develop superheated steam anyway, so at 400psi you'll have a higher temperature at the steam outlet. I guess you'll control the flow of feed water to manage this against the fuel feed setting? I'll not even try to figure out how to control this. You have already done that.
As to "electrical noise" - you'll be managing that as well!
Fascinating engineering!
K2

 

[Toymaker]

Just reading your information again... (#353)
Of course:
400 psi at 231 C (448 F). - is the temperature of the saturated steam. = no superheat. BUT will you control to 400psi? - or to 231C? The design of the boiler could develop superheated steam anyway, so at 400psi you'll have a higher temperature at the steam outlet. I guess you'll control the flow of feed water to manage this against the fuel feed setting? I'll not even try to figure out how to control this. You have already done that.
As to "electrical noise" - you'll be managing that as well!
Fascinating engineering!
K2

The plan is to control pressure while monitoring temperature and limiting temperature to below 232 C. The temperature limitations of Copper limits steam temperature to about 231 C (400 psi (2.758 mP)). Whether or not those numbers put the steam into the superheat region is irrelevant, as those numbers represent the limitations of the copper tube.

 

[Toymaker]

Great! Have you compared the temperature from the RTD sensor with the saturated steam temperature at the pressure you are delivering? Is it much higher than the saturated steam temperature? - The difference is the superheat... (As you know, but others may not know?).
When using superheat in the engine, you are delivering more heat (energy) in the steam than when it is saturated, for the same pressure. When the steam expands inside the engine, there is therefore less condensed water (droplets) produced during expansion (and cooling) of the steam - which is quite significant to running certain engines. e.g. Large thermal power stations run their turbines COMPLETELY dry, so even the steam exiting the turbine is above the temperature of the saturated steam at the pressure it is leaving the turbine. This ensures the bladed turbines only see a hot gas (Steam), and thus avoid blade damage that would occur if the droplets of water condensed inside the turbine. What comes out of those turbines then passes through economisers (feed-water heat exchangers) and on to the condensers where the steam converts back to water. - Perhaps you'll eventually install an Economiser between the turbine and the condenser? - The hot condensate can then pass through the feed pump, then economiser and on to feed the boiler. Long-term, that's a modification I plan for the Tesla Turbine I can experiment with.
When running the Tesla turbine recently, I noticed that it was pretty immune to "water in the steam", while it was just "white water vapour" blowing into the atmosphere from the exhaust. But initially, more water vapour (condensate) was being generated than could blow out, so the blades were running in a puddle of water, until I drilled a small drain hole at the bottom of the casing to drain the space outside and below the discs... When the casing and internals had heated-up significantly (above water boiling point?) all the water vapour exited the exhaust ports and problems disappeared. I reckon I could improve the efficiency by lagging the casing as well. Otherwise the lost heat is just more fuel wasted before the discs do their work and extract the energy from the steam.
For those that don't know, Steam is an invisible gas - made of water molecules. The white clouds from a kettle or pot-boiling are water vapour = Liquid water in an aerosol I.E. NOT steam.
I am interested to see how you progress?
(Sorry if I prattle-on too much!).
K2

I didn't have time to gather much data before I was forced to shut down after I smelled burning rubber; the small floor mats I had surrounded the boiler with (as noise suppression) all have a rubber backing which, on one of the mats, was becoming way too hot. Fortunately there was no fire, only slightly melted rubber. The mats failed to suppress much of the noise, so the mats are now gone.

Most of the noise is generated by steam rushing out of the boiler's 5/8" exhaust tube, which quiets down a little when I redirect steam flow through the Tesla turbine. The second loudest source of noise is the centrifugal blower (leaf blower); I've managed to suppress some of that noise by placing a 1 meter long air duct on the input. Finally, the wobble-plate air compressor generates some noise; I've placed a small foam plastic box over the compressor in an attempt to suppress that noise source.

 

[Steamchick]

I like the practical "Copper limits steam temperature to 231C".
I didn't know that, as I follow ASME (even though I am in the UK) and design my boilers to Max 100 psi for Silver Soldered Steam vessels. BUT with a "wet boiler", the Superheater isn't a part of the boiler structural calculation. So can be copper, or stainless steel, etc. as appropriate, for design of the system.
That means I should now get an infra-red or other thermometer to check how hot the exhaust from the superheater actually is, (rather than "VERY HOT!"). - Then modify if too hot for copper. I have melted a soft-soldered joint (On a bought component) with the superheated steam from a small boiler (500cc, 30psi), but assumed it was soldered with electrical solder, = melts less than 200C...
So if I can find a solder that melts around 230C, that may be a good indicator?
Also, I have seen oxidation/tempering colours on the copper tubes of a super-heater... but I think this is always during initial firing, before steam flows through the superheater to cool the tubes. Considering my boilers are limited to 30psi (Because the inspector says that is what he will certify, whatever the calculations say! - And that is adequate for my smaall engines.) - 30psi is only 7 1/2 % of the stress of the 400psi limit, so if I limit superheat temperature to 230C (At pressure) that should be safe.
Thanks for the advice!
K2

 

[Toymaker]

I like the practical "Copper limits steam temperature to 231C".
I didn't know that, as I follow ASME (even though I am in the UK) and design my boilers to Max 100 psi for Silver Soldered Steam vessels. BUT with a "wet boiler", the Superheater isn't a part of the boiler structural calculation. So can be copper, or stainless steel, etc. as appropriate, for design of the system.
That means I should now get an infra-red or other thermometer to check how hot the exhaust from the superheater actually is, (rather than "VERY HOT!"). - Then modify if too hot for copper. I have melted a soft-soldered joint (On a bought component) with the superheated steam from a small boiler (500cc, 30psi), but assumed it was soldered with electrical solder, = melts less than 200C...
So if I can find a solder that melts around 230C, that may be a good indicator?
Also, I have seen oxidation/tempering colours on the copper tubes of a super-heater... but I think this is always during initial firing, before steam flows through the superheater to cool the tubes. Considering my boilers are limited to 30psi (Because the inspector says that is what he will certify, whatever the calculations say! - And that is adequate for my smaall engines.) - 30psi is only 7 1/2 % of the stress of the 400psi limit, so if I limit superheat temperature to 230C (At pressure) that should be safe.
Thanks for the advice!
K2

NOTE: The 231 C number I sighted as a temperature limit for copper is the number I'm using for my specific monotube boiler and is based on what I personally feel is safe for my copper monotube boiler. Other design factors such as wall thickness, boiler diameter, brazing metal used will all play a part in determining a safe working temperature. I arrived at the 231 C (448 F) number in part from calculations I've done and in part from the experience of other monotube builders. Steam car builders whom have posted their experiences on the SACA (Steam Automobile Club of America) forum web pages have demonstrated through multiple builds that copper tube boilers are safe to operate at 440 F at 400 psi.

 

[Steamchick]

Thanks for the qualification Toymaker. I have learned that your information is reliable, and qualified, so trust the 230C as a "Standard" used somewhere, or justifiable someway, so can be trusted if applied correctly.
From my (Inexperienced) understanding of flash boilers, somewhere along the length of the heater tube the change of state occurs from water to steam so after some point extra heat may be gained after all the water is converted to steam. The "dry steam" that follows may rise in temperature if the heating gases still have heat and adequate temperature for this to happen. Thus Flash boilers are designed on principles that consider superheated steam to be generated. I.E. If you are controlling a copper pipe flash boiler to 230C then "heaven help me" if I exceed that wisdom with my superheaters! I.E. it would be folly for me to go beyond your limit without substantial justification.
So I respect your expertise and advice accordingly.
All the boiler books I have mention superheaters, flash boilers, etc. but do not give design information or limits.
My superheaters are either attached to boilers mechanically, or some of the small boilers have a dryer/superheater coil silver soldered at the boiler, then pass through the flues/smoke box or fire-box to gain extra heat. The silver soldered joint is considered a part of the boiler, so shall not exceed 200C (based on ASME limits), but further along the superheater tube it is expected that the temperature can rise above 200C.
The consideration I have is that the small boilers (less than 3 bar-litres) that my inspector will evaluate and certify are generally limited to 2 or 3 bar (because of size and the 3 bar-litre limit). The superheated tube must be adequately strong to withstand the temperature of the environment (e.g. gases in the firebox if it transits the firebox) without any cooling steam until valves are opened and steam passes through to reduce the superheater tube temperature (by extracting heat). Much like the Flash-tube boiler when initially fired-up?
When firing, I normally "bar" the engine as soon as the boiler starts boiling, so some low pressure steam is pumped through the boiler (and superheater tube) before "minimum running pressure" is realised, so any condensate is pumped though and out of the engine to avoid Hydraulic lock. (Damaging to reciprocating engines, but not turbines!). The condensate is from hot steam condensing in a cold engine, but in turn warming the engine, so that by the time working pressure is achieved, the engine is hot enough to run without much condensate that would risk an Hydraulic lock.
Of course the engine cannot be barred until steam is being generated in the boiler, as otherwise it will simply suck excess water into the boiler such that the boiler primes when the water boils.
Should a cold engine be given adequate steam to run, without warming, then it is very likely that it will run-away initially, but produce so much condensate with the cold cylinder, piston expansion, etc. that when the hydraulic lock happens a conrod or bearing will be damaged from the flywheel energy becoming an impulsive shock with the instant deceleration of the piston.
I don't know what could happen with the Tesla turbine - probably nothing? But take care anyway.
K2