Tesla Turbine | The interesting engineering behind it

The maverick engineer Nikola Tesla also made his contribution in the field of mechanical

engineering

. He looked at one of his favorite inventions: a bladeless

turbine

or Tesla

turbine

. The Tesla turbine had a simple and unique design, but was capable of exceeding the efficiency levels of steam turbines at the time. Normal turbines have a complex design with complicated geometry blades and stator parts. Nikola Tesla once said that the Tesla turbine is his favorite invention and even claimed a 97 percent efficiency level for this turbine. Let's begin a design journey to understand this

interesting

piece of technology. and towards the end we will also check Tesla's efficiency, the claim that modern turbines operate on the principle of the aerodynamic profile.

You can see that the fluid gushing over the cross section of the airfoil will generate lift force on it and cause the blade to rotate, however, to make this turbine rotate, nikola. Tesla relied on a totally different phenomenon: the viscous effect of fluid on solid surfaces. You may have seen this effect before. When water flows over a rounded stone, it causes the stone to move due to the viscous force between the water and the surface of the stone. Nikola Tesla extrapolated this. a lot of force to run your turbine, who knows Tesla might have gotten inspiration for his turbine from this very example, if you produce the viscous force tangential to a disk, it will start to spin, hooray, you have produced the simplest form of

tesla

turbine, however this is quite an inefficient turbine most of the jet energy is lost here let's make this design more efficient and practical let's place this pair of shaft discs inside a casing now the fluid enters through the outer casing tangential to it a provision for the fluid to exit is at the center of the turbine assume that an inlet fluid with a pressure slightly higher than atmospheric pressure enters the inlet nozzle at low velocity.

What do you think about the path this fluid takes? Since the fluid has a low velocity, the viscous force between the disk and the fluid will increase. will be minimal and the disc will not rotate, the outlet hole is at atmospheric pressure, which means that the fluid will have a slightly higher pressure than the atmosphere and will naturally flow towards the center almost in a straight line. Now let's increase the velocity of the fluid and see what This happens here, since the fluid has a higher velocity, the interaction between the fluid and the surface of the disk will produce enough viscous force to rotate the disk.

Here comes an

interesting

twist when the fluid particles are rotating, they need a certain amount of centripetal force to maintain that motion. A fluid particle of the same speed requires more centripetal force near the center than away from it, for this reason rotating fluid particles tend to move away from the center, however, the turbine outlet is at the center, so that the fluid particles have to reach it eventually. due to these opposite effects in the case of rotation, the motion of the particles will be curved as shown if you compare the radii of the particle a in these two cases clearly the particles with curved path have more radius now let's gradually increase the speed of the fluid, You can see the curvature of the fluid particles will increase even more and form a kind of spiral.

This concept is clearer when tracking the same fluid particle for different disc speeds. The higher the speed of the disk, the further the particle moves from the center. The spiral shape of the fluid flow is in fact a blessing in disguise: the spiral shape increases the contact area between the fluid particles and the surface of the disk, thereby increasing the production of viscous force in the disk. This effect also means that the faster the turbine spins, the more energy it extracts from the fluid, in other words, the Tesla turbine exhibits high efficiency during high-speed operations. To further improve this design, we need to understand a key concept called boundary layer thickness.

We can observe in this system that the fluid particles that are in close contact with the disk adhere to it and form a stationary surface. The next layer of molecules tries to pull the stationary layer in the direction of flow, however, in this process they lose some energy to the molecules of the stationary layer. The same happens with the subsequent layers. This tendency of fluid particles to resist the flow of other particles is known as viscosity. In this way, a variation in velocity can be clearly observed. The region up to which this variation in velocity exists is known as the boundary layer region, clearly within the boundary layer a layer of fluid produces a drag force on the neighboring layer as relative motion occurs between However, layers outside the boundary layer either no relative motions occur between the layers or the force between the layers is zero to make use of of this boundary layer phenomenon.

Nikola Tesla came up with a unique idea: he added two more parallel disks. Now let's look at the flow. The boundary layer forms on each surface, as we saw above, the particles in the boundary layer region will try to drag or rotate the respective disk; However, you can see a region outside both boundary layers where fluid particles flow freely without any such free velocity gradient. The flow imparts no energy to the disc and contributes little to torque generation to make your turbine more efficient. Nikola Tesla brought the disks closer together keeping the separation about twice the boundary layer.

There is no free flow here. The two boundary layer regions touch each other. and we can see that shear effects are now dominant among the disk space for vapor. This ideal distance was found to be 0.4 millimeters. Using this method, Tesla improved the torque output of its turbine. Tesla discovered that by increasing the effective area between the disc and the fluid, the turbine could produce more torque, so he added more discs. This model had a diameter of six inches, however this design failed terribly. The problem was that this turbine would run at a very high speed, 35,000 rpm.

Nikola Tesla never thought that this turbine would produce such high rpm and the strength of the disc was not enough to withstand the enormous centrifugal force produced in the material, which caused expansion of the material and failure of the disc due to deformation. Nikola Tesla could not find any material that could withstand such high rpm at the time, eventually he had to reduce the rpm to less than ten thousand to prevent the discs from suffering mechanical failure. Now comes the big question, even though Tesla turbines are so easy to build, why are they not used in power generation industries?

The reason is that modern steam turbines are more than 90 percent efficient, we know that the Tesla turbine becomes more efficient as the rotor speed increases, but for the Tesla turbine to reach such a high level of efficiency, the rotor has to spin at a very high rpm, maybe fifty thousand, the biggest challenge is that for industrial applications we need a disk size of two or three meters consider these hypothetical

tesla

turbine disks with a diameter of three meters it is an impossibility

engineering

operate discs of such a large diameter at a speed of 50,000 rpm the main problem is that of the blade Tip speed The blades of the most modern steam turbines are capable of reaching a Mach number of 1.8 at their tips or 1.8 times the speed of sound.

A rough calculation shows that these hypothetical disks will have a Mach number of 13 at the tips, definitely an engineering impossibility. the only option left is to reduce the rpm and we know that this will lead to a huge drop in turbine efficiency, therefore Nikola Tesla's claim of 97 efficiency for his 6 inch model seems unrealistic. Remember that you were only able to run this turbine with less than 10,000 rpm despite these drawbacks, the Tesla turbine has found some interesting specific applications, for example, the Tesla turbine is reversible, it can work as a pump if power is supplied to the rotor .

We also know that Tesla turbines operate based on the viscous effects of the fluid, so these types of pumps are used in high viscosity applications such as wastewater plants, the oil industry, and ventricular assist pumps. Before you leave, don't forget to be a member of the lessex team, thank you.