Tesla Turbine Mythbusting … Part 1
A look into the common myths, misinformation, and misconceptions about the tesla turbine.
Let’s watch this youTube video by Lesics:
One of the most common myths said about the Tesla turbine is that it needs to be spun to incredibly high RPMs to generate power efficiently, or in the case of the Lesics video, it says that the 3 Meter diameter turbine Tesla was using would need to be spun to 50,000 RPM. Saying that the discs have to be spun to Mach 13 to be efficient is a fallacy. There are three things that can be done to increase the power and efficiency of the turbine:
1) One can increase the velocity gradient between the fluid and disc speed
2) One can increase the surface area of the discs
3) One can decrease the disc spacing to approximately twice the width of the laminar boundary layer
If the disc spacing is decreased, then one must increase the number of disc spaces (this means increasing the amount of discs - an important distinction). Doing so means that you can move the same amount of air despite the thinner spaces - so one is not choking the flow and can allow the same amount of fluid to subsequently flow through and be dragged across a larger surface area. The reason it becomes limiting to add too many discs is because the nozzle has to get wider, which increases friction in the nozzle due to the increased volume of space interacting with the boundary layer.
Tapered discs are stronger than flat discs of the same thickness because they have more material in the center to hold in a decreased amount of peripheral mass. Because of this, a tapered disc doesn’t have as much force working against it to hold it’s shape. It may help to think of it as “not needing to be as strong” rather than simply just being stronger. However, materials that are cold or hot rolled when manufactured see a drastic increase in their tensile strength (the kind of strength exhibited by a material when it resists being pulled apart). This is because of the crystalline structure within the metal that forms during repeating roll forming. This means that rolled metal discs may have higher tensile strength than a non-rolled metal tapered disc of any similar thickness.
The turbine is most efficient when not pulling power off of it (applying a load). As it goes into higher RPMs, it reduces the mass flow rate being pulled into the turbine because of the centrifugal head, so much that it only draws the exact amount of fluid/heat it needs to in order to keep the same RPM. The highest power is achieved when the discs are spinning at half the speed of the fluid - this can be regulated by the nozzle. A decrease in efficiency occurs due to using a load. This is overcome, not by chasing higher RPMs (which gets harder and harder to do), but by increasing torque in the other two ways described above. One can build the turbine oversized so it achieves the most efficiency for the given operational load desired.
Let’s look at a torque and efficiency graph for the Tesla turbine, as shown here by Ken Rieli. the y-axis is the percentage of total torque available to be provided by a given Tesla turbine system. One can achieve high power inefficiently or one can achieve efficient energy production with lower power:
Ken Rieli's Tesla Turbine Measurements
When one puts a load on the Tesla turbine, there will be slip that occurs which decreases efficiency. However, all slip generates heat, but what is known as the re-heat factor occurs, which is where the heat from slip is used to further spin the system. In order to utilize the re-heat factor one must increase the residency time of the fluid in the turbine. Unless you have a large turbine (specifically meaning in terms of disc surface area) that’s larger than 4 feet in radius, one will not get to utilize the re-heat factor without a second drive stage, because there’s not enough residency time for the fluid in the turbine to continue to be expanded. This is why Tesla recommends multiple drive stages in his patents.
In summary, increasing the velocity of the discs is not the only way to get power and efficiency increases. Efficiency increases when slip is reduced or when it’s recovered by the re-heat factor. For this reason, the turbine has the ability to operate very efficiently within specific operating parameters - granting the ability to super cruise if applied in a vehicle.
