Tesla Turbine Efficiency

I was just wondering about that very point earlier today... The question that occured to me was, "Is the boundary-layer effect more efficient in transferring energy to the turbine impeller than the 'old-style' direct-impingement method?" I did see a small video illustrating the concept of the tesla turbine just today, running on compressed air, but really it didn't show anything (even implied) about how well it works...

An unrelated article I saw earlier today was discussing the efficiency of engines and pointed out how sloppily the term is used these days... some were talking about thermal efficiency, some electrical efficiency, some mechanical efficiency... and all seemed to be hinting at (or trying to imply) that the overall efficiency of the system (power in; power out) was what was under discussion.

Although Tesla's turbine has been around, as an idea, for a long time; it seems to me that it's only been recently revived as an experimental thing... So it seems to me quite likely that there is no experimental data of the type we'd like to see-- some of the first-order research that needs doing, I would think, is to build and test models to collect exactly that kind of experiential data.

Let me know if you hear anything on this...

 

I've read everything from 25 to 95% but have found 40-60% to be believeable, based on videos. I scavenged our engineering library on the subject but didn't find anything more than a paragraph related to the subject. Apparently, the efficiency goes down as the rotor spins faster which I imagine is due to the centrifugal force counteracting the corkscrew effect. While researching, keep in mind that these are also referred to as boundary layer turbines and fixed disc turbines. The best resource I have found so far is:http://www.teslaengine.org/

 

Yeah--- that's the kind of numbers I've seen, too; and they strike me as little different than those projections one sees based on the theoretical efficiency of Carnot cycle engines and whatnot--- not much more than a guess, really. I would consider 50% (in the middle of your reasonable range) as an acceptable compromise between optimism and foolishness, until we can get our hands on actual data...

One thought on the speed: after considering for a bit, I think your hypothesis misses the mark--- boundary layer effect is based on friction, and it won't change because of a tangental force... think of rotorcraft or airscrews--- they don't seem to 'throw off' air in the plane of the spinning disc, which they clearly would if this were a true phenomena. So what does explain the decreasing efficiency? Speed alone, I think! Consider; in most systems where you have a differential, like heat differential or what-have-you, as the differential closes, efficiency drops... Like heat engines, less efficient the closer the hot and cold sides' temperatures are.

I'm thinking that, as the speed of the turbine approaches the speed of the stream of working fluid, the boundary layer effect becomes less and less...

Consider: An object is moving at a given speed (100m/s) through air... there is friction, there is a boundary layer effect. Now increase or reduce speed by 1m/s--- what is the result, in terms of boundary layer effect? Negligible, it seems. Take a stationary object and subject it to a 100m/s airstream, and the effect is noticable. I think that might be a more accurate picture of why the efficiency, however high or low it is, changes as the turbine's speed increases.

 

I kinda see what your getting at Isarmann however I don't feel air moving axially through a prop is a good comparison to a fluid corkscrewing radially inward. However, even in the tiny contact time between air and a prop blade, rotorwash does spiral outward due to a tangential component imparted by the prop blades. The boundary layer is a small part of a prop whereas it's everything in the tesla turbine.

Exactly. The centrifugal force disrupts the corkscrew and creates a back pressure to the incoming fluid. I believe they call this "gating". There is literature on this avaiable on the web. I feel you and I approaching the same reasoning from opposite sides.

 

I think you will find the patent that Tesla filed will give you the best information of what can be expected for the turbine.

Not sure how well i remember, but two things he made reference to, was a thermodynamic conversion, and that best efficiency was achieved at about 50% turbine speed/ inlet velocity.

 

I definitely think we're on the same page, and think you might be right; we're talking about the same thing... But there is a lot of imprecision out there when it comes to explaining the mechanism of agreed-upon phenomena, so I always find it interesting to try to come to understanding of the actual effect at work. I will definitely have to learn more about the centrifugal force in this situation; thanks for the steer on the word "gating". But leaving that aside for a moment (let's say we come up with a method that will negate that effect entirely), wouldn't you think there will still be an efficiency drop as the linear speed of the turbine approaches the speed of the stream driving it? So, assume there is no disruption of the corkscrew at all--- won't we still have efficiency drop as an expected result of the speed differential approaching zero?

I actually found out about Tesla turbines because of work I've been doing on vortex phenomena of all types; it seems like vorticies are one of those (I think of them as 'magic') areas of science where you get a synergistic payoff from what goes in... Of course, there's no such thing as a free lunch, but some things (like latent heat, for example) really seem to have potential benefits that in some way 'go beyond' what you might expect.

I wouldn't be suprised if the 'corkscrew' or vortex effect in the Tesla turbine is an important (if not indeed critical) component of how it functions in the first place.

 

Yes, RonL, that's what I was thinking; there must be some optimum relationship between the incoming charge speed and the turbine's speed.

Leave it to you to go to the source and make light of all our serious musings... LOL... just kidding, of course.

I should have thought to read the patent...

Have you guys noticed how often a post, which must've taken ten minutes to write, would be obviated by as little as 3-5 minutes of reading on the subject? I find myself thinking "Wikipedia, silly!" all the time on here when reading some of the less-well-informed posts...

 

I think you are on spot with the vortex and turbine working together.
In the past I have used a vortex tube cooler, and much later found a detailed description of how it works, in a refrigeration Manuel, the air in is broken into three values
1. cold air out
2. hot air out
3. internal friction of the air against the tube wall

In my opinion this turbine is a segmented flywheel, that can transfer thermal energy from the atmosphere, a key issue, is to enhance the separation of the delta T, and pressure differences within the blades. This is the area that caused Tesla much grief (in my opinion) too much thermal difference in a small area led to blade distortion.

There might not be a free lunch here, but if not i think a good snack might be in store (as long as we have sunshine everyday)

 

Hehehe... I like that.

I really wonder about the thermodynamic component myself... I'd really love to see tests done (or do them myself) to establish some of these things we're wondering about.

 

In my mind an area of focus that most researchers miss, is how little can they get by with. The general approach is to build for high pressures, and output from the least size, which equates to higher cost in almost all respects.

I'll share a few of my thoughts and efforts to devise a plan for slower speed and more volume, no real details, but rather what and why.
First as i see it, the vortex tube puts out air at two (in general) temperatures, which is a compromise of volume at each end, the temperature varies from extreme cold at the center to very hot at the wall of the tube, air friction put an effort toward twisting the tube, and if the tube is allowed to rotate some of this energy could be recovered.

The refrigeration Manuel gave the values as follows,
air in 25 CFM,
100 PSI(794 kPa), and
temperature 100 F (38 C),
75% of the air spirals inward, expands and cools to 40 F (4 C), the other 25% of air churns in the tube, heats up to 270 F (132 C).

Air enters a spin chamber at a tangent and forms a cyclone effect, spinning at 500,000 RPM, air tries to speed up to 5,000,000 RPM while spiraling inward, is retarded by the air column in the tube, forcibly turns column with an effort equal to 1/2 horsepower.

The size of the tube is less than 1" Dia. and the spin chamber is 2" Dia. or less, an overall length of around 8".


This should give a good idea of thermal change in a vortex and this is with no moving parts.
Inserting a turbine and increasing the diameter will have a great effect on the speed of things, but a thermal change will still take place.

My plan is to use 4 canister vacuum units working in series, 1 unit on each side of the turbine pulling a vacuum at the center discharge ports, and plumed to push air toward the other two that are in series and blowing air at an increased velocity into the turbine at a tangent.
The heat from the motors will continually be cycled thru the air flow, and the insertion of jet ejector principles will allow for a replenishing of warmer air from the atmosphere.

Some cold air discharge will take place between the two vacuum units and the two pressure units.

My turbine will consist of common 10" saw blades rated for 7,000 RPM, and the center hole between 1" and 2" there is a total of 8 holes to use for bolting the pack of blades together and i will use a slightly larger spacing between the blades. The carbide tips will be left in place and hopefully act as impact blades, they are at angles that should prove useful against the air flow. The blades are about 1 pound each and i plan to use around 30 in the stack.

Another idea that i started a patent for in 1996 (but did not follow thru) is to allow the blades to move crosswise, this will produce a slide action and give the turbine a variable volume, creating the possible cycle for building and depleting pressure of the air flow.

As for taking power off the turbine, i'll leave that alone for now because the post is getting too long, hope some of this will help anyone that has an interest in Tesla's Turbine.

A good book for reference is " The Tesla Disc Turbine" by W.M.J. Cairns, I.Eng., M.I.E.D.

 

I think that the end of this discucion is to build a series of different sizes of turbines and variables. Compress air and get how much energy it takes to do it, then expand it on the diferent turbines, at diferents presures and speed to see how much energy you recover. If nobody wants to modeling the system by computer to get the best values of the turbine, disc, gap dimensions and speed of the fluid in motion. The practice will be the only way out. Im trying to find someone who do the modeling because i have to make a thesis to end my career of mechanical engineering.

 

I agree, Argentina... I have reviewed all of Tesla's patents on the turbine, to better understand his own thinking on the advantages of the design; based on those I have some comments I will post a bit later. I think we can come up with a 'standard' design that features easily-changed major variables that should allow us to establish the numbers we seek.

 

Hi Argentina, and Isarmann

It would be great if you find a thermal modeling program to evaluate the turbine action, and share with the forum, your findings.

It is my thinking that, the compression of air you mention above, has to be a part of the turbine's energy cycle or you have too much loss outside the system.
A closed loop system should look exactly like a heat pump, with the turbine acting as the expansion valve, and giving it the ability to expand and contract the space between the blades, while turning, is important to the pressure/vacuum buildups.

So many things can be done with the basic design, it is good to see experimenters looking at Tesla's idea.

RonL

 

Im trying to get FLOWORKS ( a tool for solidworks ) and see if i can get some data if i build a small 2 o 3 disc tesla´s turbine. First i have to know how the program works and if is usefull for this kind of things.

I will tell you if a know something else.

See ya

 

Yeah, I agree that modelling software is the way to go... I'm using pro/ENGINEER from PTC, and it does include a module to do mechanical stress modelling--- but I think the key would be something more like what Argentina mentioned; thermodynamic modelling. I know of a very capable product along those lines, but I'll have to look it up--- can't remember the name. I don't think floworks is the one I've seen before... I seem to remember a different name. Regardless, once we have some models completed in any of the programs, we should be able to move them to whichever analysis software.

I do believe they will show us exactly what we're hoping to see.

 

I think the first step is building the turbine with the best efficiency to transform the motion of the fluid to motion on the axle. With the less turbulence and loss of boundary layer between the disc. I dont know if the floworks works with diferent surfaces on the materials, i hope so because i think there is the key ( also on the disc speed ).

 

Yes! I could certainly see boundary-layer and surface effects being considered second-order in the minds of those who wrote the programs; but for our purposes, they're clearly first-order effects. I think Flotherm (or Flowtherm) may have been the program I was looking at before, and it's main focus is overall flow through a system, showing hotspots, eddies, and the like.

I'm sure, even if they consdiered it a secondary consideration, that these programs must take into account surface textures, especially when the walls are close--- so hopefully, at worst, changing some of the values to emphasize that portion of the modelling would still give us the general analysis we're looking for. Actual testing of a built model will firm it up... As long as the software can help us avoid major missteps, I believe it will work.

 

I need the EFD.LAB, thats the program we are looking for... If someone has it, please contact me. I cant find it.

 

There are a lot of efficiency for a turbine, thermodynamic efficiency(which one can get from tables), then there is a hydraulic efficiency(in case of water turbine) or blade efficiency(indicating how well blade is taking energy from the working fluid), then is mechanical efficiency.

The case of flow irregularities(non uniform flow, turbulence, boundary layer separation, fluid friction) all cause a dip in blade efficiency,

I am not sure which efficiency are we talking about here.

And output power is parabolic with speed, and assuming constant input power, efficiency(blade efficiency) ll take a dip with rpm