What is a Tesla Turbine : Working & Its Applications

Tesla turbine was invented by Nikola Tesla, in the year 1909. It’s a special category of turbines which don’t have any blades. Unlike other turbines like Kaplan etc, this turbine has limited and specific applications. But due to its design considerations, it is one of the versatile turbines. Its invention has led to many major engineering applications. It works on the principle of boundary layer effect, where due to airflow, the turbine rotates. The best part of this turbine is it can achieve an efficiency of up to 80%. Its speed range can be reached up to the level of 80,000 rpm for small rated machines. Specifically, this turbine cant is used in power plant operations but can be used for general applications like pumps, etc.

Tesla Turbine Diagram

The basic structure of the Tesla turbine is shown in the figure. It consists of a bladeless turbine that has an input through an air pipe nozzle. The body of the turbine has two outlets, one is for the incoming of the air and the other for the outgoing of the air. Apart from that, the rotating disc consists of 3 to 4 layers, which are joined together. There is a thin air gap between the layers where the air is passed at a very high speed.

The rotating disc has two faces, outface and rear face. In both aspects, there is no scope for the air to flow outside the turbine body. The air can only enter through the inlet pipe and release through the outlet pipe. The turbine body consists of multiple disk rotor which is joined together. All the rotor discs are joined together on a common shaft where the disc can rotate.

There is outer housing for the disks to be placed. The discs are usually connected through bolts. The front-end and rear-end have exhaust output ports through which the air can exit the turbine body. The placement of the holes is done such that, a vortex of inlet air is created.

Tesla Turbine Theory

The input to the rotor blades is air at high pressure. Using an air hose, which is connected to the inlet of the turbine, the air is made entry into the body which consists of rotor disks that are placed on the shaft and can be easily rotated. As the air enters the turbine housing it is forced to create a vortex due to the shape of the turbine.

Vortex means a whirling mass of air like in a whirlpool or whirlwind. Due to the creation of a vortex, the air is able to rotate at very high speeds. The formation of a vortex is fundamental because of the design of the turbine. The font and rear cover body of the turbine is placed such that, the air has to exit through the holes present in the front and rear covers.

The exit of air in this nature creates a vortex of air. And makes the turbine rotate. When the air molecules pass the disk, they create a drag on the disk. This drag pulls the turbine down and makes it rotate. It may be noted that the turbine can rotate in both directions. It just depends on which inlet pipe is used for input of air.

Tesla Turbine Design

The design consists of two inlet pipe, out which one is connected to the air hose pipe. Out of the two inlets, anyone can be used as input. Inside the body, the rotor disks are placed which are joined together with the help of bolts. All the discs are placed on one common shaft which is connected to the outer body.

For example, if it is used as a pump, then the shaft is connected to the motor. There is a thin air gap between the discs, where the air flows and makes the discs rotate. Due to the air gap, the air molecules are able to create a drag on the disc. The front and rear cover have 4-5 holes through which the inlet air is able to be passed to the atmosphere. The holes are placed such that, a vortex is created and the air can rotate at a very high speed.

Due to this high-speed air, it exerts a high-speed drag on the disc and makes the disc rotate at very high speeds. The disc gap is one of the critical parameters for the design and efficiency of the turbine. The optimum gap size required to maintain the gap layer depends on the peripheral velocity of the disc.

Turbine Design Calculations

Many design aspects are important to achieve high efficiency. Some of the major design calculations are
The working fluid or the inlet air has to have minimum pressure. If it is water, then the pressure is expected to be at least 1000 kg per meter cube. The peripheral velocity must be 10e-6 meter square per second.

The gap between the disc is calculated based on the angular velocity and peripheral velocity of the disc. It depends on the pollhausen parameter which is constantly based on velocities. The flow rate for each disk is calculated as a product of the cross-sectional area of each disc and velocity. Based on the data, the number of discs is estimated. Again, the diameter of the disc is also important to have good efficiency.

Tesla Turbine Efficiency

The efficiency is given by the ratio of output shaft power to the input shaft power Its is expressed as

The efficiency depends on many factors such as the diameter of the shaft, speed of the blades, the number of blades, the load connected to the shaft, etc. In general, the turbine efficiency is high as compared to other conventional turbines. For small applications, efficiency can even reach up to 97%.

How does Turbine Work?

Tesla turbine works on the concept of the boundary layer. It consists of two inlets. In general, the water of air is used as the inlet to the turbine. The turbine body consists of rotor disks that are joined together with the help of bolts. All the disks are placed on a common shaft. The turbine body consists of two cases, the front casing, and the rear casing. In each casing, there are 4 to 4 holes. All these factors like the number of disks, disk diameter, etc., play an important role in evaluating the efficiency of the turbine.

When the air is allowed to flow through the hose pipe, it enters the turbine body. Inside the turbine body, discs are placed which are connected to each other. There is a thin air gap between the discs. When the air molecules enter the turbine body they exert a drag on the discs. Due to this drag, the discs start rotating.

The front and rear casings consist of holes such that when air enters it gets exit through these holes. The holes are placed such that, a vortex of air or water is established within the disc body. Which causes the air to exert more drag on the discs. This causes the discs to rotate at a very high speed.

The area of contact between the vortex and discs is low at low speeds. But as the air gains speed, this contact increases, which allows the discs to rotate at a very high speed. The centrifugal force of the discs tries to push the air outwards. But the air has no path except the holes on the front and rear casings. This makes the air exit, and the vortex becomes more strong. The speed of the discs is almost equal to the speed of the airflow.

Advantages and Disadvantages of the Tesla Turbine

The advantages are

• Very high efficiency
•  Production cost is less
•  Simple design
• Can be rotated in both direction

The disadvantages are

• Not feasible for high power applications
• For high efficiency, the flow rate must be small
• Efficiency depends on in and outflow of the working fluids.

Applications

Tesla’s turbine due to its output power and specifications has limited applications. Some of them are mentioned below.

•  Compression of liquids
• Pumps
• Vane type turbine applications
• Blood pumps

Hence we have seen, the constructional aspects, working principle, design, and applications of Tesla turbines. Its major drawback is since it is compact and small in size, it has limited applications over conventional turbines like the Kaplan turbine. Since its efficiency is very high, it must be thought that how Tesla turbines can be made to have major applications like in power plants. That would be a great boost to the low efficient plants.