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ABSTRACT:
Treatment of a bladeless turbine designed by Nikola Tesla is given. First this invention, which can also be used as a pump, is generally described. Conventional turbines are mostly reaction and impulse type or both. Often technical challenge faced by conventional turbines in Himalaya is erosion by sediment. Financial feasibility of power plants is depended upon innovations to prevent erosion of mechanical equipments or alternatives which better handle these conditions. Tesla turbine is an unconventional turbine that uses fluids properties such as boundary layer and adhesion of fluid on series of smooth disks keyed to a shaft. It has been garnering interest as Pico turbine where local communities could manage such stations in low capital. It provides a simple design which can be produced locally and maintained at low cost. It can be useful in plants for pumping of water and other viscous fluids. Tesla Turbine pump has been used as a blood pump. Due to its uniqueness it has its own cliché uses giving importance to identify the scope of use of Tesla Turbine in Nepal also.
BASIC OPERATION
In the modern age – with the advent of mobile, residential, and remote renewable power applications – demand for low-power generators is growing, and it is a well-known problem that inertial turbines suffer heavy losses as they scale down. When turbine power and size are reduced, surface area-to-volume ratio increases: surface tension, adhesion, and 3 cohesion forces begin to dominate inertial forces, lowering the efficiency of such turbines. In contrast, Tesla rotors use kinematic viscosity and surface effects (rather than inertia) to convert flow energy into rotational motion.
As such, Tesla turbines are excellent candidates for micro-scale power generation machinery. In Tesla turbines, the adhesion and viscosity of a moving medium are used to propel closely-spaced disks into rotation (Figure 1-2). The fluid enters the inner space between the disks from the periphery and exits through central holes near the axle (as indicated by the dotted lines). There are no constraints or obstacles to couple inertial forces (i.e., vanes) as in traditional turbines. The fluid enters tangentially at the periphery and makes several revolutions while spiraling toward the central exhaust (again, the dotted lines). During this process, the fluid transfers momentum to the disks.
APPLICATIONS
Applications Prior to 2006, Tesla turbine was not commercially used. On the other hand, Tesla pump has been commercially available since 1982. It is used to pump fluids that are abrasive, viscous, contain solids or are difficult to handle with other pumps. The concept of Tesla turbine is used as a blood pump and gave good results. Research in this field still continues. In 2010, a patent was issued for a wind turbine based on Tesla design. In Tesla’s time efficiency of classic turbines was low, because aerodynamic theory needed to construct effective blades did not exist and quality of materials for blades was low. That limited operating speeds and temperatures. Its other drawbacks are shear losses and flow restrictions. But that can be an advantage when flow rates are low. Tesla’s design can also be used, when small turbine is needed. Efficiency is maximized, when boundary layer thickness is approximately equal to inter-disc spacing. So at higher flow rates, we need more discs, which means larger turbine. Because thickness of boundary layer depends on viscosity and pressure, various fluids cannot be used as motive agents in the same turbine design. Discs have to be as thin as possible, to prevent turbulence at disc edges.
Specific applications
After two original designs patented by Tesla, inventors tried to improve them. In U.S. patent 4655679 from 1987, planar carbonized composite discs were proposed instead of metal ones. These discs can sustain considerable mechanical and thermal stress and are more resistant than multi-bladed rotors made from the same material. At higher temperatures of incoming gases, higher efficiencies are obtainable. Turbines of this design can operate at temperatures above 1000◦ C. Disks are separated by rings 32, and have circular exhaust openings 33 (figure 11) . Electronically controled guidewall 55 is used to direct gas to the entire rotor or only a part of it, when gas flow varies. This maintains flow between two discs within desired range, so efficiency is not compromised. Vanes 50 divide inflowing gasses into channels 51 with as little turbulence as possible. Turbulence is minimized because gasses are not permitted to expand significantly prior to their entry into the rotor and because inlet channels 51 act to smoothly divide gasses into individual flow paths in agreement with spaces between discs. This design can also be used as a pump, for example in cars to deliver compressed air to carburation system.
In U.S. patent 0053909 from 2003, there are airfoils between discs. Airfoils are placed in such manner, that they guide fluid flow toward central opening 5 that acts as exhaust (figure 12). Fluid flows through nozzles, that direct fluid between discs and on leading edges of airfoils, as arrow 3 shows . Momentum is exchanged through 3 mechanisms: fluid flow strikes the leading surface of airfoils, fluid flow around airfoils produces lift on them and viscous interaction between disc surface and fluid. They all contribute to rotational output, for lift on an airfoil is perpendicular to freestream velocity [8]. Only some airfoils extend from outer edge of the disc to the outer edge of exhaust outlet, because we have to have enough opening area for exhaust gasses. Shaft can be connected to one of the outer discs, that does not have a central opening, and exhaust gasses leave the turbine from space between this and adjacent disc. Such turbines can be made of composite materials. It has only few moving parts (cheaper manufacture) and lubrication is required only for shaft bearings (environmentaly friedly). Because discs are connected through airfoil shaped parts, they are more resistant to deformations at higher angular speeds. It is intended for use in turbine engines.
Low-Head or Low-Flow River Turbines
River turbines operate at low head with a medium to high flow that contains microorganisms and dust particles. The components of a standard river turbine are shown in Figure 1-3. Small dams (weir) are installed along the river to collect water and the water is supplied to the turbine through a penstock after filtering river particulates. The water at turbine exhaust is rerouted to the river downstream
CONCLUSION
Tesla turbine is a versatile turbine. It can be used in Pico hydropower which can be locally produced and managed by village communities. It can be used as pumped storage systems. It can be used as radial ventricular devices which are ‘gentle’ on blood pumps and doesn’t causes loss of platelets because of its energy transfer mechanism. Tesla pump has been reported to handle different kinds of industrial and agricultural and waste fluids . It can also be alternative to Improved Water Mill (IWM). It can be concluded that the study on Tesla turbine has yielded important understanding of the turbine. There are still many rooms for improvement which makes it interesting topic for further research.
ACKNOWLEDGMENT
This project is a result of team work of project members and people who directly and directly helped for its completion. We are thankful to Department of Electrical Engineering, MumbaiUniversity. We are thankful to our project supervisor Mrs. Neha Bansa for her guidance. We thank Dr. Anupama Deshpande, for her unconditional help and support, for her guidance and experience which helped us to sort our problems and set definite goals of project. We would also like to acknowledge Mrs. Pragya Jain(HOD Of Electrical Engineering) and all staff members for their support in carrying out the project.