The Tesla Turbine: Overhyped or Feasible?

[maikeru]

I'm not an engineer, but I have always been somewhat interested in mechanical and electronic things, as an aside from microbiology. However, my math abilities are limited, and maybe that's why I never became an engineer like my dad. ;) I've spent a lot of time recently looking at alternative energy and new emerging technologies, and something I encountered every now and then among blogs and websites was the Tesla turbine. So I looked it up on Wikipedia a while back:

 

Tesla turbine - Wikipedia, the free encyclopedia

 

And watched YouTube videos of the Tesla turbine made by gadgeteers and amateur scientists or experimenters. I must admit this is a fun little invention, and it's remarkably simple and elegant.

 

It seems that Tesla invented this in response to problems with bladed turbines and also with the intent to use it to help generate electricity from steam from geothermal sources. (Yeah, I have to admit geothermal energy and how to harvest it has also been on my mind a lot, since people have been claiming we're in an "energy crisis." I've also noticed that among the "Green Energy Revolution" that geothermal energy is being ignored or criticized...but that's a separate subject.)

 

As I understand it, this turbine offers some of the following advantages over conventional bladed turbine designs:

 

- Simple to build, maintain, and modify the design. Fluid/air injectors, valves, discs, size, materials, etc. can all be modified. Hard to get simpler than discs with holes punched in them for exhaust, attached to a rotor in a case. :Alien:

 

- Safer in the case of disc/blade failure or other parts failure, since the housing compartment or casing can be made strong enough to contain broken or cracked discs, and often the failure of one or more discs will not necessarily lead to the failure of the entire turbine. This design is often described as very sturdy, because the discs and rotor are bolted solidly together and there's minimal wear except on bearings.

 

- Does not suffer from cavitation or particulate problems that many turbines and fans must deal with.

 

- Can work with a wide variety of working fluids and over a wide range of temperatures. Water, steam, conventional air, corrosive working fluids, high-temperature working fluids, or complex mixtures which may have particulates or contaminants in them. This adds a great deal of flexibility to it, and may make it able to be powered by several types of fuels such as charcoal or biodiesel when incorporated into an engine, vehicle, or power generator.

 

- Allows the ability to work in both "forward" and "reverse," since the discs can be made to rotate in either direction.

 

- Supposedly has a good power-to-weight ratio, because the discs are thin, compact, and there are few other moving parts in it and not a lot of pistons, casing, gears, etc. I remember reading criticism of Stirling heat engines as often being cumbersome because of their pistons, flywheels, and gears. (Although I've seen some really cool-looking Stirling engines!)

 

- Directly converts kinetic motion of the fluid into rotary motion via the boundary layer effect and adhesion.

 

- Now is poised to take advantage of new materials, construction, and high-tech stuff that was not available in Tesla's day. For example, I've read suggestions that the turbine's discs can be manufactured from high-strength carbon fiber, plastics like Kevlar, high-performance ceramics, steel alloys, titanium alloys, or aluminum. Given that new cars and parts are increasingly being manufactured from high-tech materials, it makes me wonder how this "old technology" can perform when it's upgraded.

 

- It has been touted as being one of the most efficient turbine designs, with theoretical efficiency approaching 90% or slightly more of Carnot cycle efficiency in a single stage or few stages, I think. If I make a mistake, though, please correct me. :eek2: I've read that only a few engine and some turbine designs can approach this level of efficiency. For example, the internal combustion engine is often cited as having about 20-30% efficiency, with most of the energy being lost as heat.

 

These, however, are the disadvantages and criticisms I've seen leveled at Tesla's design and the Tesla turbine in general:

 

- It attains high rpm but cannot translate the rpm into useful or high torque. Is this true? I spent a lot of time reading about steam engines and steam-powered vehicles like locomotives and steam-powered cars, and one of the advantages of the steam engine, from what I read, was that it provided high torque and power at relatively low rpm.

 

It might be pointed out that Tesla did envision this primarily used for geothermal energy from steam, but most studies, tests, and experiments I've seen have not been conducted with steam or any other working fluid than regular air.

 

- Testing of experimental Tesla turbines have yielded efficiency measurements of around 35-40ish%. In other words, better than most internal combustion engines, but really nothing to write home about. Many bladed turbine designs can can exceed this.

 

- It suffers from too much friction and energy losses when heat is produced as the fluid flows over the discs. These are parasitic losses that cripple the turbine.

 

- It currently uses ball bearings, which cause further efficiency losses due to friction, heat, sound, etc. Most engines and turbines use oil and bearings for lubrication, and the newer designs have foil bearings, such as the Capstone microturbine, which significantly reduce friction and increase efficiency.

 

- The high rpm can cause disc warping or cracking, and this was a serious problem with it in Tesla's day. Apparently metallurgical knowledge in the early 1900s wasn't quite good enough to provide Tesla with strong enough materials to make his turbine function as he wanted. The iron/steel discs he used would warp and stretch, raising concerns about the viability of the turbine. No one is quite sure about long-term functionality of this turbine, since it has not been used widely commercially or rigorously tested and validated.

 

- If it worked well, it would've been adopted by industry and for a wide variety of applications. Most of the Tesla turbine builders are "eccentric academics" or "backyard tinkerers." That's what I've read on some blogs. However, I have found some papers and experiments done by mechanical engineering students and professors, who seem rather intrigued by it. Most of these academics are connected to "green technologies" or research into alternative energies/fuels.

 

Sorry for the long post. I find this little machine to be really fascinating, much like the Stirling engine, and I wonder if it has any use or practicality...or if it's another "footnote" in the history of science and technology. Any answers, explanations, or musings would be much appreciated. I'd like to try to improve my understanding on this. Wiki and net surfing only go so far. ;)

[lawcat]

 

- It attains high rpm but cannot translate the rpm into useful or high torque. Is this true?

 

Not sure if it's true in all applications, but it certainly has been a complaint on some sites. Of course, torque is function of design. Any desired torque may be achieved, but at what price. Remember Archimedes pushing the moon with a long stick.

Here, notice that the power comes from the forces of adhesion of the fluid to the edges of disks. This is the laminar part. If you needed to produce higher torque, which is : Force x radious; you would need to up either. To create movement, you need to introduce fluid velocity. The velocity of the fluid between the disks is what produces the forward force. This force is translated to the disk by laminar adhesion--laminar means right next to the disk. But as you increase the fluid velocity to create more force, your laminar force of adhesion decreases because the flow of the fluid between the disks becomes turbulent. So, in this turbine, it seems to me the fluid velocity, and force, have optimal operating range, beyond which the turbine will stall due to flow. http://en.wikipedia.org/wiki/Laminar_flow; Turbulence - Wikipedia, the free encyclopedia

 

So the only way to increase torque, to account for higher loads on the turbine's shaft, would be to increasae the radius of the disks. And this presents physical challenges. That maybe the reason that this invention has not been widely used.

[alexander]

So what if we consider using electro-magnetic bearings? Also, you would have to define the operating range pretty clearly to get a consistent 60 hertz, and have to set that in gearing from the start, or else you have to go with a DC generator, to convert this to useable energy (talking green household, ofcourse). Actually perhaps DC motor would be the best for this motor's operation, as you can adjust the water flow to maximize on the efficiency of the engine/generator a little more easily then you can do with AC, but then you have to consider the inefficiencies of inverters (which will inevitably give you the cleanest power, unless you figure out a constant pressure source)

 

But consider a solar collector, that heats up water (well some sort of a heat-absorbant surface) , that drives a turbine with a heat recovery system to warm up incoming water... Something that takes relatively little space, and i am wondering if the efficiency of the system would be higher then that of piston driving ones used today...

[maikeru]

Not sure if it's true in all applications, but it certainly has been a complaint on some sites. Of course, torque is function of design. Any desired torque may be achieved, but at what price. Remember Archimedes pushing the moon with a long stick.

Here, notice that the power comes from the forces of adhesion of the fluid to the edges of disks. This is the laminar part. If you needed to produce higher torque, which is : Force x radious; you would need to up either. To create movement, you need to introduce fluid velocity. The velocity of the fluid between the disks is what produces the forward force. This force is translated to the disk by laminar adhesion--laminar means right next to the disk. But as you increase the fluid velocity to create more force, your laminar force of adhesion decreases because the flow of the fluid between the disks becomes turbulent. So, in this turbine, it seems to me the fluid velocity, and force, have optimal operating range, beyond which the turbine will stall due to flow. http://en.wikipedia.org/wiki/Laminar_flow; Turbulence - Wikipedia, the free encyclopedia

 

Good points.

 

So the only way to increase torque, to account for higher loads on the turbine's shaft, would be to increasae the radius of the disks. And this presents physical challenges. That maybe the reason that this invention has not been widely used.

 

I believe Tesla noted that he was able to increase torque by adding washers and settled on a star-shaped design (as opposed to his earlier circular washer choice, but I'm not sure how a star-shaped washer influences and enhances the torque exactly), increasing the size of the rotor shaft, and of course increasing radius of the discs.

 

Wouldn't adding more discs to the turbine also increase torque? Most of the turbines I've seen used or designed so far are running perhaps 5-10 discs. I was wondering if adding more similarly sized discs might help to increase torque so long as they are supplied by additional and sufficient amounts of air. Let's say instead of 10, you could increase this to 20 or 30. Or do you think performance would suffer in comparison to simply making the radius of fewer discs larger?

[maikeru]

So what if we consider using electro-magnetic bearings? Also, you would have to define the operating range pretty clearly to get a consistent 60 hertz, and have to set that in gearing from the start, or else you have to go with a DC generator, to convert this to useable energy (talking green household, ofcourse). Actually perhaps DC motor would be the best for this motor's operation, as you can adjust the water flow to maximize on the efficiency of the engine/generator a little more easily then you can do with AC, but then you have to consider the inefficiencies of inverters (which will inevitably give you the cleanest power, unless you figure out a constant pressure source)

 

But consider a solar collector, that heats up water (well some sort of a heat-absorbant surface) , that drives a turbine with a heat recovery system to warm up incoming water... Something that takes relatively little space, and i am wondering if the efficiency of the system would be higher then that of piston driving ones used today...

 

You know, that's a really good suggestion. One that I hadn't considered. As far as I know and have researched, I've never seen anyone design this particular turbine with electromagnetic or any kind of magnetic bearings. That might help reduce the friction losses from ball bearings a lot. In a similar application, I believe NASA pioneered the use of magnetic bearings for use in flywheel energy storage and it makes a huge difference in performance.

 

Flywheel energy storage - Wikipedia, the free encyclopedia

 

Perhaps some type of constant pressure source could be provided by water reservoirs, streams, etc. or steam created by a solar apparatus as you mentioned.

 

I really wish I had the proper machines and materials to give these suggestions a go. Perhaps I can build a model Tesla turbine out of plastic or wood and tinker a bit. I've thought about it.

[alexander]

yeah, i'm on the same page with you, i wish i just had a machine shop to build all the ideas i have... and a billionare to sponsor my random thought building projects :)

[ManicalEngineer]

- Safer in the case of disc/blade failure or other parts failure, since the housing compartment or casing can be made strong enough to contain broken or cracked discs, and often the failure of one or more discs will not necessarily lead to the failure of the entire turbine. This design is often described as very sturdy, because the discs and rotor are bolted solidly together and there's minimal wear except on bearings.

 

.....

 

- The high rpm can cause disc warping or cracking, and this was a serious problem with it in Tesla's day. Apparently metallurgical knowledge in the early 1900s wasn't quite good enough to provide Tesla with strong enough materials to make his turbine function as he wanted. The iron/steel discs he used would warp and stretch, raising concerns about the viability of the turbine. No one is quite sure about long-term functionality of this turbine, since it has not been used widely commercially or rigorously tested and validated.

 

I'd like to address the two points above:

 

The first one is not really true - Steam Turbines are designed to with stand loss of blade events (in other words if a blade breaks off its not exiting the turbine), the driving factor in most of the turbine shell/casing design is temperature/pressure not containment concerns (except in the low pressure sections where blades are as much as 60" long). Steam turbines also typically run at 3600 RPM (for 60 Hz applications) or 3000 RPM (50 Hz) applications, much slower (hence less danger) than the tesla turbines.

 

The second point still rings true today, with new "modern" material the cost issue typically stems from the labor intensive process to include the materials (particularly composites). While materials have gotten better the high rotational speeds of the tesla turbine create chanenges for most materials due to high centrifugal forces.

 

Those two points aside, I feel if there were as much focus on the development of Tesla turbines as there has been on the traditional bladed turbine it might see improvements, but without a clear & realistic estimation of that improvement companies won't invest in pursuing that.

 

PS I'm a mechanical engineer that designs steam turbine shells

Edited June 1, 2016 by ManicalEngineer

[GAHD]

Holey necro-post batman!

That aside, Noted torque inefficiency should be addressed via increased viscosity of the driving/driven fluid.
AS for mechanical sheer stresses developed in high RPM, I'd think a suitable composite could be manufactured with PVD lamination of a few choice materials. Beryllium, boron carbide ceramic, and certain carbon structures(hard to control those though) come to mind.

Funniest part is if you're motivated, you could do the CVD in your garage with some old microwave transformers(wired backwards), a reinforced pressure-cooker(DIY vacuum chamber) and appropriate rods (chem/refinery supply 99.9 fine)Edit: And a salvaged Braking Pump off a semi, again, backwards)

Edited June 3, 2016 by GAHD