# DIY Tesla Impulse Turbine

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I have been considering adding a spare superheater to the boiler - which uses one of the under-tubes as a steam heater, but really hardly more than a steam drier. I am also thinking of a stainless steel superheater in the firebox, when I have made a much bugger burner for the boiler. Lots to do! Maybe I'll start a thread on it, but it just seemed like a useful addition to Toymaker's thread on Tesla turbine technology.
Thanks for suggestions.
K2

An alternative would be to use it as an air blower/compressor - then use the air for running another engine?
I don't know how to calculate the expected power output from a Tesla turbine.... any clues? Possibly in one of the papers already posted that I haven't read yet?
K2

Hi Nerd,
I wonder when you suggest using multiple stages of the Tesla turbine, if one of us doesn't understand it properly? (I.E. Me?).
An impulse turbine can develop about 50% of tractive energy - per rotor - I think? (something due to geometry when the gas stream turns 90degrees from input to exhaust direction against each blade? ). But maybe it was "half-speed" (1/4 kinetic energy remaining?). So multiple rotors each extracting 50% of energy (or is that velocity??) leave a lot to be collected by a later stage (I think?), as the exhaust from the first stage can give 50% to the second, then 50% to the third... etc. so the shaft accumulates 50% + 25% + 12.5% etc. thus achieving high efficiencies?
But the whole principle I think Tesla achieved was a single stage obtaining ~80~90% of the energy, so the exhaust contained too little to make a further stage useful? (back then!).
Also, in the Tesla mode the helix is very fine (e.g. there are smoke demos to show this on Utube?). It starts as a coarse helix at lower speeds, but when the turbine achieves true Tesla mode the helix manages to make thousands of rotations from the outer high velocity zone to the centre "near rotor speed at exhaust ports" - which was maybe 1/10th of the initial speed. And energy is proportional to Vsquared... so necessarily Tesla was right in the possible efficiency he could predict - and achieved. All in a single stage. Or maybe I missed something and got it all wrong? (I often do!!). It is all due to the progressive slowing of the gas stream per revolution that the gas stream makes, as it slows it naturally finds a slower surface - which is at a smaller radius - thus generating the helix, naturally. So the exhaust outflow from the Tesla turbine is very slow (and low pressure, and cool, having lost the energy). You can't get enough velocity, pressure or temperature from the Tesla turbine to power another stage. - I think? - but I really am unsure now, with your suggestion.
An impulse turbine does a Momentum exchange, by turning the gas stream through 90degrees, it needs a force to turn the gas stream, reacted on the blade (like any aerofoil works?), so the reaction force turns the turbine wheel. But the gas stream still contains a lot of energy. Hence the Parson's turbine multi-stage approach?
The idea that Toymaker is using seems interesting: Useing an impulse turbine to extract "half" the energy at a lowish turbine speed, then let the remaining gas stream pass through a Tesla type array of disc-slots, to extract more energy... But I fear the impulse momentum exchange will direct the gas stream "backwards" (and inwards?) from the tips, so rotating in the wrong direction, and thus effectively extracting some energy from the discs... lowering the efficiency? Or maybe simply going in the right direction, but so slowly so as to make very little difference? I.E> after the impulse outer ring, the gas simply transits directly to the exhaust holes in the middle, without any "Tesla" style input to the rotor. But I don't know! - SO I am watching the thread to find out and learn..
Cheers!
K2
In an impulse turbine (and the Tesla turbine is one, as there is no change in pressure within the rotor) all of the change in enthalpy happens in the nozzles. Essentially, the nozzle expands and cools the gas, which results in an increase in the tangential component of the gas velocity. The rotor then extracts momentum from the high velocity gas stream, giving you your mechanical work.

I think you should be with me up to here.

The Tesla turbine does a good job of extracting momentum from the gas. It might even be over 90% efficient at that, certainly a good DeLaval rotor can be over 85% efficient at that task and a Tesla turbine at the right speed could surpass it. However to do this, it has to match the gas velocity.

Remember how the nozzles are doing the job of changing heat in the steam into kinetic energy? The more enthalpy we take from the gas, the greater the pressure drop and the higher the velocity at which the gas emerges from the nozzle. ou know, the Tesla rotor has to rotate at close to that speed to efficiently exchange momentum with the gas.

So if we want to reduce rotor speed, we have to lower the velocity of the steam jet from the nozzle. The only way to do this is to reduce the change in pressure across the nozzle (ok you could also make the nozzle less efficient, but we don't want that). So if we didn't change the steam supply pressure, the pressure at the nozzle outlet will now be higher. Being an impulse turbine, the Tesla turbine will not alter this pressure, it will be the same at the exhaust as it is at the nozzle outlet. So we now have an exhaust stream which still has pressure we could use in a second stage. Also the turbine is delivering less power, so we need the second stage to make up for it!

Parson's turbines are different, they are combined impulse and reaction turbines. Essentially the rotor is designed such that it is also a nozzle, and the jet thrust from expansion of the gas through the rotating nozzles contributes 50% of the work done (the other 50% comes from fixed nozzles and doing the same thing seen in a pure impulse turbine)

Can anyone who has run an actual turbine comment on the observed change in air tempurature across the turbine?

Ie. Do physical observations back it's possible use as a gas expander?

In an impulse turbine (and the Tesla turbine is one, as there is no change in pressure within the rotor) all of the change in enthalpy happens in the nozzles. Essentially, the nozzle expands and cools the gas, which results in an increase in the tangential component of the gas velocity. The rotor then extracts momentum from the high velocity gas stream, giving you your mechanical work.

I think you should be with me up to here.

The Tesla turbine does a good job of extracting momentum from the gas. It might even be over 90% efficient at that, certainly a good DeLaval rotor can be over 85% efficient at that task and a Tesla turbine at the right speed could surpass it. However to do this, it has to match the gas velocity.

Remember how the nozzles are doing the job of changing heat in the steam into kinetic energy? The more enthalpy we take from the gas, the greater the pressure drop and the higher the velocity at which the gas emerges from the nozzle. ou know, the Tesla rotor has to rotate at close to that speed to efficiently exchange momentum with the gas.

So if we want to reduce rotor speed, we have to lower the velocity of the steam jet from the nozzle. The only way to do this is to reduce the change in pressure across the nozzle (ok you could also make the nozzle less efficient, but we don't want that). So if we didn't change the steam supply pressure, the pressure at the nozzle outlet will now be higher. Being an impulse turbine, the Tesla turbine will not alter this pressure, it will be the same at the exhaust as it is at the nozzle outlet. So we now have an exhaust stream which still has pressure we could use in a second stage. Also the turbine is delivering less power, so we need the second stage to make up for it!

Parson's turbines are different, they are combined impulse and reaction turbines. Essentially the rotor is designed such that it is also a nozzle, and the jet thrust from expansion of the gas through the rotating nozzles contributes 50% of the work done (the other 50% comes from fixed nozzles and doing the same thing seen in a pure impulse turbine)

There are a number of papers I see on multi stage tesla turbines... but just spit balling, using a off the shelf centrifugal expander wheel after the tesla might give better low end power conversion as well as expanding converted power at higher flow rates.

A hybrid.

Maybe an expander wheel from one of those 100\$ turbo kits. Just toss the compressor, shaft and bearings but use the expander casing and wheel mounted on a common shaft to the tesla turbine.

Thanks Nerd. I think I follow this. Can't imagine how the Toymaker arrangement will work though.
K2

On you tube, Tom Stanton has just put up a video with some air turbine blade testing that might be of interest.

Thanks Nerd. I think I follow this. Can't imagine how the Toymaker arrangement will work though.
K2

You've seen the video I posted showing my turbine directly driving a water pump,... my turbine is already running on compressed air . The design is primarily an impulse turbine which directs the mostly spent steam inwards, where the steam is allowed to continue to expand and hopefully add some small amount of energy to the discs.

In an impulse turbine (and the Tesla turbine is one, as there is no change in pressure within the rotor) all of the change in enthalpy happens in the nozzles. Essentially, the nozzle expands and cools the gas, which results in an increase in the tangential component of the gas velocity. The rotor then extracts momentum from the high velocity gas stream, giving you your mechanical work.

I've read several papers explaining how steam continues to expand between Tesla discs as it spirals inwards through the discs; this expansion results in additional steam momentum being produced long after the steam has exited the nozzle.
Consider the length of a typical industrial multi-stage steam turbine. Steam from the nozzles is expanding through the entire length of the turbine. That expansion converts the enthalpy of the steam into momentum which the many rows of turbine blades convert to mechanical energy. We can calculate the pressure and temperature drop from on stage to the next to determine how much energy is available from each stage.

Steam in a Tesla turbine also expands over that same long distance, but that distance is a spiral shape, not linear.

I've read several papers explaining how steam continues to expand between Tesla discs as it spirals inwards through the discs; this expansion results in additional steam momentum being produced long after the steam has exited the nozzle.
Consider the length of a typical industrial multi-stage steam turbine. Steam from the nozzles is expanding through the entire length of the turbine. That expansion converts the enthalpy of the steam into momentum which the many rows of turbine blades convert to mechanical energy. We can calculate the pressure and temperature drop from on stage to the next to determine how much energy is available from each stage.

Steam in a Tesla turbine also expands over that same long distance, but that distance is a spiral shape, not linear.
Could you link the papers? I'm having trouble conceptualising how the Tesla turbine can act as a reaction turbine.

Could you link the papers? I'm having trouble conceptualising how the Tesla turbine can act as a reaction turbine.

I will look for those papers, but for now; I didn't mean to imply that a Tesla turbine acted in any way like a reaction turbine, as it doesn't. What I'm trying to convey is that steam continues to expand as it flows through and between the discs of a Tesla turbine,... expansion which results in momentum which is imparted to the discs via laminar flow on the disc surface.

Could you link the papers? I'm having trouble conceptualising how the Tesla turbine can act as a reaction turbine.

Here's a quote from this linked Scientific American article: "the particles of the fluid complete a number of turns around the shaft before reaching the exhaust, covering in the meantime a lineal path some 12 to 16 feet in length. During its progress from inlet to exhaust, the velocity and pressure of the steam are reduced until it leaves the exhaust at 1 or 2 pounds gage pressure."

I will look for those papers, but for now; I didn't mean to imply that a Tesla turbine acted in any way like a reaction turbine, as it doesn't. What I'm trying to convey is that steam continues to expand as it flows through and between the discs of a Tesla turbine,... expansion which results in momentum which is imparted to the discs via laminar flow on the disc surface.
If there is pressure drop across the rotor that is doing work on the shaft there is reaction occurring, though it might be happening via a different mechanism from a parsons turbine.

https://scholar.google.com/scholar_...e#d=gs_qabs&t=1716694264253&u=#p=t3DQCJ_3CCIJ

This paper is a good source on the operation of a Tesla turbine, often cited by others. They say you can in principle operate them entirely in reaction mode (I still don't understand how this works, but apparently it does) but practical designs are mostly impulse. Notably they recreated Tesla's original model and found it to be effectively a pure impulse machine. Their optimised model is mostly impulse but has some reaction.

For those who are interested in checking my working (I make no guarantees that I'm not a big old dummy making stupid mistakes), here's my steam turbine spreadsheet. A few notes:
1. Superheating is not considered, the turbine is assumed to be running on wet steam.
2. At present, it only does a complete parameterisation for single or two stage Rateau turbines. You can copy the blocks that work out the nozzle sizes to do more stages, but spreadsheet software being spreadsheet software this will mess up various things I haven't correctly 'locked in.' If the maths is confirmed to be right I might be persuaded to fix this so users can copy out arbitrary numbers of stages.
3. The nozzle outlet size calculation should be ok even if the nozzle is supersonic, but it doesn't calculate how big the throat should be.
4. The pressures in each stage are approximate, because the conditions are determined by lookup table.

Somebody who is actually good at thermodynamics please help me!

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• Turbine design.zip
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If there is pressure drop across the rotor that is doing work on the shaft there is reaction occurring, though it might be happening via a different mechanism from a parsons turbine.

https://scholar.google.com/scholar_lookup?title=An analytical and experimental investigation of multiple-disk turbines&publication_year=1965&author=W. Rice#d=gs_qabs&t=1716694264253&u=#p=t3DQCJ_3CCIJ

This paper is a good source on the operation of a Tesla turbine, often cited by others. They say you can in principle operate them entirely in reaction mode (I still don't understand how this works, but apparently it does) but practical designs are mostly impulse. Notably they recreated Tesla's original model and found it to be effectively a pure impulse machine. Their optimised model is mostly impulse but has some reaction.

I'm not member of ASME and therefore cannot access the linked article :-(

As to how Tesla turbines work:
The transfer of steam's momentum energy into Tesla discs is accomplished entirely due to boundary layer effect. Remember your high school chemistry or physics class on the topic of adhesive and cohesive forces? Adhesion is a property that nearly all fluids (both liquids and gases) posses. The Adhesive property of water is the reason water "wets" most surfaces. Adhesive force is also the reason water or coffee slightly climbs up the wall of a glass or cup and forms a meniscus at the contact points.

Gases or vapors also have adhesive properties and tend to "stick" to most any solid surface it comes into contact with. You might be familiar with the diagram below, which shows how the velocity of air flowing over a surface slows down considerably as the air gets closer to that solid surface. Air, gas, & steam all have adhesive properties and tend to "stick", or adhere to all the solid surfaces they come into contact with. This property is why steam doesn't flow effortlessly through a pipe or tube, but encounters resistance to it's flow.

Surface roughness affects the thickness of the boundary layer, with rough surfaces having thicker layers than polished surfaces. So, grab some 60 grit sandpaper and scratch the surfaces on your Tesla discs, as all those scratches give the steam more "grip" on the discs.

It's the boundary layers between two discs that act as soft, pliant impulse blades in a Tesla turbine.

I'm not member of ASME and therefore cannot access the linked article :-(

As to how Tesla turbines work:
The transfer of steam's momentum energy into Tesla discs is accomplished entirely due to boundary layer effect. Remember your high school chemistry or physics class on the topic of adhesive and cohesive forces? Adhesion is a property that nearly all fluids (both liquids and gases) posses. The Adhesive property of water is the reason water "wets" most surfaces. Adhesive force is also the reason water or coffee slightly climbs up the wall of a glass or cup and forms a meniscus at the contact points.

Gases or vapors also have adhesive properties and tend to "stick" to most any solid surface it comes into contact with. You might be familiar with the diagram below, which shows how the velocity of air flowing over a surface slows down considerably as the air gets closer to that solid surface. Air, gas, & steam all have adhesive properties and tend to "stick", or adhere to all the solid surfaces they come into contact with. This property is why steam doesn't flow effortlessly through a pipe or tube, but encounters resistance to it's flow.
View attachment 156442

Surface roughness affects the thickness of the boundary layer, with rough surfaces having thicker layers than polished surfaces. So, grab some 60 grit sandpaper and scratch the surfaces on your Tesla discs, as all those scratches give the steam more "grip" on the discs.

It's the boundary layers between two discs that act as soft, pliant impulse blades in a Tesla turbine.
Indeed it is viscous drag. Take note of the differences between turbulent and laminar boundary layers too, they will have an impact on the turbine's behaviour. However this doesn't explain how it can be operating as a reaction turbine.
One potential hypothesis that comes to mind is that the fluid flow within the rotor actually acts as a nozzle of sorts, causing the fluid to accelerate tangentially as it spirals inwards and giving extra momentum that can be transferred to the rotor.

Here's a quote from this linked Scientific American article: "the particles of the fluid complete a number of turns around the shaft before reaching the exhaust, covering in the meantime a lineal path some 12 to 16 feet in length. During its progress from inlet to exhaust, the velocity and pressure of the steam are reduced until it leaves the exhaust at 1 or 2 pounds gage pressure."

I think if you look at this mathematically that they are not saying it expands.

Here I suspect that the steam comes out wet and over saturated which means a massive volume reduction and the change in volume is = to work done.

Decreases in fluid velocity and thus increases in volume are assuming Isentropic systems, if I understand the math. Your system is the opposite of isentropic by base design.

Indeed it is viscous drag. Take note of the differences between turbulent and laminar boundary layers too, they will have an impact on the turbine's behaviour. However this doesn't explain how it can be operating as a reaction turbine.
One potential hypothesis that comes to mind is that the fluid flow within the rotor actually acts as a nozzle of sorts, causing the fluid to accelerate tangentially as it spirals inwards and giving extra momentum that can be transferred to the rotor.
I don't think you could get turbulent boundary flow in a tesla turbine assuming the disc spacing is ideal and the disc blade tip geometry is flat or triangular, because there is no room for turbulent eddy shedding stuff between the pairs of blades.

My .02\$

In a combination impulse version, I would expect each Impulse tip blade to generate forced eddy shedding, which the discs would then be forced to rectify, which may increase disc vibration at higher speeds.

@Toymaker what is the plan for power transmission? Hydraulic, mechanical, electric?

@Toymaker what is the plan for power transmission? Hydraulic, mechanical, electric?

I'm building a giant leaf blower

The turbine output shaft will be coupled directly to a centrifugal air compressor, either a standard bladed design, or a Tesla pump, if it proves workable.

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