Tesla Turbine – How Do they Work, Interesting Physics
In this post, we’ll look at how the Tesla Turbine works. To begin, we’ll look at how the maverick engineer Nikola Tesla contributed to the field of mechanical engineering by looking at one of his favorite creations.
- A Bladeless turbine or Tesla Turbine
The Tesla turbine featured a basic, one-of-a-kind design that allowed it to outperform steam turbines in terms of efficiency at a period when most turbines are complex, with blades with sophisticated geometry and stator elements. Nikola Tesla once stated that the Tesla turbine is his favorite creation, claiming that it has a 97 percent efficiency rate.
Let’s embark on a design journey to better comprehend this fascinating piece of technology, with the goal of verifying Tesla’s efficiency claim at the conclusion.
The fluid gushing over the airfoil cross-section generates lift force on it and causes the blade to turn in modern turbines, but to make this turbine spin, it uses the airfoil concept. Nikola Tesla used a completely distinct phenomenon called the viscous effect of fluid on solid surfaces, which you may have observed before when water flows over a rounded stone.
The stone moves due to the viscous force between the water and the stone surface, and Nikola Tesla used this force to power his turbine. Who knows, maybe tesla was inspired by this example when he designed his turbine.
If you apply a tangential force to a disc, it will begin to spin, which is the simplest form of a tesla turbine. However, this is a very inefficient turbine. Here, the majority of the jet’s energy is wasted.
Let’s make this design more functional and efficient. Assume that an intake fluid with somewhat greater pressure than atmospheric pressure is approaching the inlet nozzle at low speed and that the fluid enters through the outer casing tangential to it and that a provision for the fluid to depart is at the center of the turbine.
What do you think about the path this fluid takes?
The disc will not rotate because the fluid has a low velocity and the viscous force between the disc and the fluid is minimal. The exit hole is at atmospheric pressure, which means the fluid has a slightly higher pressure than the atmosphere and naturally flows towards the center almost in a straight line.
Let’s try increasing the fluid speed and see what happens. Because the fluid is moving faster, the interaction between the fluid and the disc surface produces enough viscous force to turn the disc.
When fluid particles rotate, they require a certain amount of centripetal force to maintain that motion. A fluid particle moving at the same velocity requires more centripetal force towards the center than it does away from it, therefore rotating fluid particles tend to migrate away from the center.
However, because the turbine exit is in the center, the fluid particles must ultimately reach there due to these conflicting effects. In the rotating instance, the particle velocity will curve out as demonstrated if you compare the radii of particle an in these two examples.
Now let’s progressively raise the fluid speed. As you can see, the curvature of the fluid particles increases and forms a spiral. This notion is clearer when you monitor the same fluid particle for different disc speeds. The higher the disc speed, the more the particle drifts away from the center.
The spiral structure of the fluid flow is actually a blessing in disguise since it improves the contact area between the fluid particles and the disc surface, enhancing the disc’s viscous force output. This phenomenon also implies that the quicker the turbine turns, the more energy it extracts from the fluid; in other words, the Tesla turbine is extremely efficient when operating at high speeds.
Boundary layer thickness
We need to comprehend a critical concept called boundary layer thickness to improve this design even more. The fluid particles that come into close contact with the disc attached to it and create a stationary layer in this system.
The following layer of molecules tries to pull the stationary layer into the flow direction, but loses energy in the process; the same thing happens with succeeding layers. This tendency of fluid particles to oppose the flow of other particles is known as viscosity.
The region up to which this velocity variation exists is known as the boundary layer region. Inside the boundary layer, one fluid layer produces a drag force on the neighboring layer because relative motion occurs between the layers, but outside the boundary layer, no relative motion occurs between the layers or the force between the layers does not exist.
To make use of this boundary layer phenomenon, Nikola Tesla came up with a novel idea: he added two more parallel discs. Now, let’s look at the flow. A boundary layer is produced on every surface, and the particles in the boundary layer region will try to drag or spin, as we observed earlier.
the corresponding disc Outside both boundary layers, however, you can see a zone where fluid particles are flowing freely without any velocity gradient. This free flow does not transmit any energy to the disc and contributes nothing to torque generation, making his turbine less efficient. Nikola Tesla drew the discs closer together, preserving the distance about twice the boundary layer. There is no free flow here.
The two boundary layer regions are touching, and we can observe that shear effects have taken over in the gap between the discs for steam. This optimal distance was determined to be 0.4 millimeters. Tesla enhanced the torque output of his turbine by employing this strategy. Tesla discovered that expanding the effective area between the disc and the fluid can increase the torque produced by the turbine, therefore he added more discs.
This device had a diameter of six inches, but it failed miserably because the turbine would spin at an extremely high speed of 35,000 rpm. The disc strength was insufficient to withstand the huge centrifugal force produced in the material, resulting in material expansion and disc failure by warping. Nikola Tesla never imagined that this turbine would produce such a high rpm, and the disc strength was insufficient to withstand the huge centrifugal force produced in the material, resulting in material expansion and disc failure by warping.
Nikola Tesla did not find any material that could resist such a high rpm at the time, so he had to limit the rpm to less than ten thousand to keep the discs from failing mechanically. Now for the main question, despite the fact that tesla turbines are so simple to build, do they work?
Why aren’t they used in the power generation industries?
The reason for this is that modern steam turbines are more than 90% efficient. We know that the tesla turbine becomes more efficient as the rotor speed increases, but the rotor must spin at a very high rpm, perhaps fifty thousand, for the tesla turbine to achieve such a high-efficiency level. The biggest challenge is that we require a disc size of two or three meters for industrial usage. Consider these hypothetical tesla turbine discs with a diameter of three meters. Operating such enormous diameter discs at a speed of 50,000 rpm is an engineering impossibility.
The key issue is blade tip velocity; contemporary steam turbine blades can achieve a Mach number of 1.8 at their tips, which is 1.8 times the speed of sound; a rough calculation suggests that these hypothetical discs will have a Mach number of 13, which is an engineering impossibility.
The only alternative left is to cut the rpm, which we know will result in a significant reduction in the turbine’s efficiency, thus Nikola Tesla’s claim of 97 efficiencies for his 6-inch model appears implausible; remember, he could only run this turbine at less than 10,000 rpm.
Despite these disadvantages, the tesla turbine has found some interesting niche applications. For example, because the tesla turbine is reversible, it can work as a pump if energy is supplied to the rotor. Also, because tesla turbines work based on fluid viscous effects.
these types of pumps are used in high viscosity applications such as wastewater plants, the petroleum industry, and ventricular assistance. Please remember to share this content with your friends before you depart.