Good morning everyone! I’ve been spending the last few days doing very in-depth research on the design of an efficient tesla turbine, and I’ve come to share my results thus far! To be honest, I never knew a tesla turbine could be so complicated and advanced even though there are few moving parts and construction seems so simple. However, do not be fooled! For this turbine to have descent torque, high horsepower, and obtain efficiency up to Tesla’s claimed 95%, this turbine requires an engineer’s intellect to be properly calibrated to the most fine detail and precision. Anyway, I hope I don’t blow your mind and I provide enough sources to appease the wiki readers! 🙂
Three Main Factors
The most important thing to keep in mind on building a tesla turbine is the fact that we know something is important on it, but what? Well, I went out seeking an answer to this trivial question and it seems that there are three main factors in obtaining the best torque and horsepower ratio: inlet nozzle size and configuration, disk spacing and geometry, and outlet nozzle sizing. With these three factors in mind, we can build a tesla turbine that is not only extremely efficient, but we can also fine-tune for the need of more torque or higher horsepower, similar to an automobile engine. Some experts say to work backwards from the outlet nozzle size to the disk configuration and then the inlet nozzle, but others say the reverse while some don’t care which comes first, the chicken or the egg! With that in mind, I will list what I have learned in respective order to how the system flows and let you decide from there.
Inlet Nozzle Configuration
The most important part about the inlet nozzle or hose is that it can deliver a high-powered jet stream directly to the gaps in the turbine. This part is tricky because to get proper distribution to the plates’ spacing inside the casing, there much be quite a few little holes to jet the pressurized whatever in between the plates. The key here is the more precise, the higher the efficiency. One thing to focus on with this then is to make sure the plates do not move side to side once positioned in the casing. If they move even 1mm from the lining on the preset holes, the overall efficiency will decrease since gas has to bounce off the top of the plate (even though it’s thin) and then flow back through the gaps, causing that loss in efficiency. Just how much of a loss is this? Well, that part is still unsure but I aim to test the theory and punch numbers for everyone to know once this project is finished! It may be astronomical, it may be miniscule to bother precision tuning.
Another key factor to consider with the inlet nozzle is the form of the nozzle to provide both a high-pressure boost. For example, if you try to smash 40psi coming from a one inch diameter hose into a 0.1 inch diameter hole, the 40psi will be amplified up to, if not faster than, the speed of sound! This is the theory of compression at work, costing you virtually nothing. But to get such high compression from such a small inlet, you have to consider durability over time. What will handle the 400psi at the tip of the nozzle? The first thing that comes to my mind is a copper fitting, mainly because copper can withstand hundreds of psi just on the tubing itself!
And now for the actual design of the nozzle. Fortunately, for us there are a variety of input nozzle configurations that we can choose, but one stands out from the rest. It is similar to an old calligraphy pen shape, which is also called a traditional convergent-divergent nozzle. The convergent (compressing) part in the figure below is “A” where the pressurized gas gets squeezed through point “d” (diameter) and then goes to the divergent (expanding) part to get un-scrambled. After that, it forces itself back into the parallel section of the nozzle to straighten the flow of the gas for direct injection into the turbine.
This nozzle seems difficult to manufacture for some, so a simpler model was designed which achieves the same effect. Below is an example of what it looks like. NOTE: The same calculations from above must be followed!
Disk Geometry and Spacing
The next thing we need to consider is the size of our disks or platters and their construction, mainly focusing on spacing. Before we choose a material for our excited platters, we have to ask ourselves a few questions. First, how fast do we want the turbine spinning and which materials will handle that consistently? Second, what disk spacing would be optimal for our specific use and psi rating (believe it or not, there’s an equation for that)? Then finally (from my research so far), what design should I cut onto the disks for the exhaust holes? The last part I have yet to research in depth as there is much speculation on various groove designs.
Nicola Tesla was a genius when he invented the tesla turbine. Whether he intended for it or not, he allows for as much customization on his turbine as iPhone has apps for, maybe even more! If you want more torque, you just have to squeeze the disks closer together. If it’s horsepower you want, make the disks a smidgin’ larger. Every little thing you do to the platters used in your turbine will affect efficiency, torque, and horsepower. As far as disc materials go, you could use almost anything as long as it holds up to some air pressure (you would have to use appropriate liquid-resistant materials for liquid pressure, of course). Common household items such as CDs, hard drive platters (now my original post makes sense, huh?), and even cardboard could be used to fabricate the sophisticated device! These options only require that your material hold up to the elements of durability and longevity that you desire it run with. For example, cardboard is not a smart option for a steam-powered turbine because cardboard swells in water. However, aluminum or CDs would work well for testing purposes, but stainless steel would probably be best for the final product once all calculations and revisions are made.
Torque is the rate or force at which something can increase its speed at an instant. To put it simply, if a young child tries to twist your arm (aka. Indian rug burn) there isn’t much heat generated because they can’t apply as much “twist” in one instant. However, if a grown weight lifter were to twist your same arm, he has so much instantaneous force that it might snap your limb in two! This is a very simple demonstration of torque and how it applies to the real world. So how does that affect a tesla turbine? If we don’t have enough torque to turn the turbine when it’s connected to a generating motor, the system won’t spin and we generate a whopping 0 watts! However, if we have enough torque to start the system from a stop then our generator will be able to accelerate as the day goes. So how do we adjust torque? There are a variety of ways for the tesla turbine, but the key focus is gapping between the plates. There is a dispute over how much space you really need in a tesla turbine, but one user came up with a calculation to provide the most efficient spacing for a turbine. Remember, the shorter the gap, the more torque we generate!
Formula for disk spacing: 1376 x (Kinematic viscosity / RPM), Kinematic viscosity being in square feet per second (sq. ft./sec.)
From what I know, you just kind of wing it for the RPM you are aiming for. For example, my DC motors spin at about 2700RPM and 3250RPM if I remember right, meaning if I did a direct connect to the turbine for one I would be shooting for about that much. The tesla turbine is meant to spin at crazy high RPMs (over 20,000RPM) so I will probably need to gear and belt the setup to run both motors at once. As you can tell, the higher the RPM the closer you can put the disks. For the author of the article I found, he had his disks around .017″ apart, meaning 1/5 the thickness of a CD (super thin!). Anything more than your ideal range is just lost efficiency because air just exits without being used. The viscosity for the liquid you want to use can be found through researching it. Here is an example of the formula in action:
Water in steam form has a kinematic viscosity of 0.317sq. ft./sec. and I will be using steam to power my turbine. I want it to spin at around 25,000RPM so I would plug it in like this: 1376 x (0.317 / 25,000) = 0.01745″, so I need a really thin washer between each plate for maximum efficiency.
Exhaust Valve Construction
Finally, the third element we need to consider with our tesla turbine! After all that crazy math and science above, now we are somewhere short and sweet. From what I know now, the exhaust port size will vary three variables: torque, horsepower, and efficiency. Sounds familiar, right? Well it’s much like the inlet nozzle except for the fact that it’s not so complicated…yet. The rule of thumb is that the larger the turbine exhaust port, the more torque and horsepower is achieved, but the lower the efficiency. The goal here is to keep the exhaust port in proportion to work effectively and help boost efficiency to the system. That’s it! 🙂
Congratulations, you passed the boring math of the technical aspects involved in making a tesla turbine! I didn’t think there would be so much math involved until I dove into research, but I’m glad I did because now my solar thermal tesla turbine will be much more efficient than it originally would have been! Now we get to the fun part, looking at pictures! Here are a few different designs and materials that people use to create their ferocious turbines.
AOL CD Tesla Turbine – wouldn’t you like your internet to be that fast?
Hard Drive Platter Tesla Turbine – overclock your hard drives!
Hard Core Tesla Turbine – so beefy it will blow your socks off!