The tesla turbine

CHAPTER 1

INTRODUCTION

Tesla Turbine, though proposed by the famous Croatian engineer Nikola Tesla years ago, is still to find its foot among the modern power turbines. Analysts are divided as to what exactly is the main reason behind the Tesla Turbine not taking off as well as it should have, given its unique factors. There are many reasons for this, but the general agreement is that the low torque produced by its rotor is probably its biggest drawback. After a thorough investigation about the various factors plaguing the working of the Tesla Turbine, the need to change the working fluid from the current air / water at room temperature became very evident. Since all the fluids used till now have yielded a very low torque, it became very clear that a new fluid, which facilitates high momentum transfer from the fluid to the rotor, was the need of the hour.

Thus, this study investigates the use of a new working fluid and also analyzes its effects, structural and thermal, on the rotor. The structural and thermal effects analysis indicates that the current Tesla Turbine rotor materials will fail to prevent the rotor from excessive stress concentration and corrosion. Thus, with the proposal of a new working fluid came the imperative of proposing a new material for Tesla Turbine rotors, which will complement the new working fluid. As a result, this study proposes two new aspects for a Tesla Turbine: a new working fluid and a new rotor material. It is expected that once these proposals are implemented, the improved torque generation by the Tesla Turbine will improve its acceptance levels and lead to its increased popularity.

CHAPTER 2

LITERATURE REVIEW

Structural analysis of the rotor components (turbine blades) have so far been mostly confined to conventional turbines like steam turbines [1], gas turbines [2] and wind turbines [3]. These studies dealt with the structural and dynamic stresses, the crack propagation etc experienced in actual working conditions by the turbine blades. Though analyses of more specialized turbines like aero-engine turbines [4] have been done, Tesla Turbine analysis papers remain highly elusive.

Very few papers have been written researching Tesla Turbine because of its low level of commercial adoption. Engin et. al. designed, tested and analyzed a multiple-disk Tesla type fan two-dimensionally using the conservation of angular momentum principle. Their study showed that Tesla Turbines exhibited exceptionally low performance characteristics, due to the low viscosity, tangential nature of the flow, and large mechanical energy losses at both suction and discharge sections that are comparable to the total input power. Their research determined the local and shearing stresses developed within the rotor as also the power transmitted from the air to the rotor [5]. From this study, the main reason for low torque, low viscosity of the working fluid, was identified and this principle played a significant role in the proposal of the new working fluid later on in this study.

Couto et. al. reviews the physical principles behind the Tesla Turbine. After discussing the relative motion of rotating surfaces, the transport equations describing the flow between parallel rotating disks are derived, estimating the boundary layer thickness under laminar and turbulent regimes, leading to expressions yielding the width between consecutive disks. They have also described the device behavior acting as an air compressor or water pump. Even they have stated in their paper that a comprehensive discussion of the fluid mechanics involved in the design of Tesla Turbine components has never taken place [6]. From their analysis, it became clear that virtually no consideration was ever given for exploring new materials for the construction of Tesla Turbine rotors. This huge void had to be filled, but by doing so, the close relation between the working fluid and the rotor material had to be taken into account.

Armstrong made a modified Tesla Turbine and analyzed it way back in 1952 [7]. But in those days, the science of composite materials was not advanced enough for him to explore the use of laminated composite materials as rotor materials. But this study does exactly that i.e. proposing the new rotor material but within the framework of the laminar fluid characteristics of the new working fluid proposed.

CHAPTER 3

TESLA TURBINE CONSTRUCTION AND WORKING

3.1 Introduction

TheTesla turbine, invented by Nikola Tesla in the year 1913, is primarily a bladeless centripetal flowturbine. It is called a bladeless turbinebecause it utilizes theboundary layer effectinstead of fluid striking the blades as is the case in a conventional turbine.

3.2 Description

A Tesla turbine consists of a group of smooth disks held together with spacers in between them, with nozzles applying a moving fluid tangentially to the disk. The fluid rotates the disk due toviscosityof the fluid and theadhesionof the surface layer of the fluid to the disc. Since there are no projections in the rotor, it is very sturdy. All the plates and washers are interference-fitted on to a shaft provided with bearings at both ends. This construction allows free expansion and contraction of each plate under the constantly changing combined effect of heat and centrifugal force. The other advantages of such an arrangement are higher resultant active plate area and thus more power, higher efficiency, reduced warping, diminished leakage and reduced friction losses. The rotor is better suited for dynamic balancing and since surface friction resists disturbing forces, a quiet running is ensured. Because of this and also because of the flexibility of the discs, the turbine is insulated from damages which are usually caused by vibration or turbulence.

3.2.1 The Rotor and the Stator

Compared to a reciprocatory engine, the Tesla turbine is simplicity incarnate. The two most important parts of the turbine, the rotor and the stator, are explained ahead in more detail.

The Rotor

Unlike the conventional turbine, the Tesla turbine does not have blades and uses a combination of disks and spacers instead. The diameter and number of the disks can change depending upon factors concerned with a particular application. Each disk is provided with openings surrounding the shaft. Between every two dics, there are metal spacers provided to ensure a gap is maintained between discs, so as to ensure free flow of fluid. Once a free flow is ensured, space should be provided for the fluid to exit, and for that, the above mentioned openings are provided. All the discs and spacers are interference-fitted on the shaft and thus their rotation is transferred to the shaft.

The Stator

The rotor assembly is enclosed within a square stator, which is the stationary part of the Tesla turbine. The square shape should be just slightly bigger than the rotor in order to allow efficient flow of fluid. The stator also has an inlet in the form of a hole. This is the fundamental design. To rotate the turbine, a high-pressure fluid is passed through the hole provided at the top. The fluid makes its way through the rotor disks and causes the rotor to rotate. Finally, the fluid exits from the exhaust ports at the center of the turbine.

3.2.2 The Principles behind the Operation

Fluid path of the Tesla turbine

The reason why the Tesla turbine rotates with such high rpm can be found in two very basic properties of fluids: adhesion and viscosity. Adhesion is defined as the propensity of dissimilar molecules to get attracted. Viscosity is defined as the resistance developed within a fluid when subjected to flow. These two properties produce a combined effect in the turbine for transferring the energy from the air/water to the rotor or the other way round in the following manner:

  • As the fluid moves over each disk, the force of adhesion slows down the fluid molecules just above the disc and thus, they stick on to the surface.
  • The molecules just above the ones which are glued to the surface slow down when they strike them.
  • This process continues level by level and thus a chain reaction is initiated.
  • The farther the distance from the surface, the smaller the effect of adhesion.
  • But the viscous forces prevent the molecules from separation.
  • This results in a torque being transmitted to the disk, which imparts rotation to the disk in the direction in which the fluid interacts with it.

Thus, this thin layer of fluid which imparts torque to the discs by acting on the boundaries of the fluid-disc contact surface is called boundary layer and the net effect is called boundary layer effect. The net results of this whole process in that fluid takes a spiral path from the boundary to the centre of the disc, from it exists through the exhaust holes provided, thereby rotating the discs rapidly.

CHAPTER 4

QUALITATIVE ANALYSIS

4.1 Definition of Important Terms

  • Specific gravity of a fluid is a ratio of the weight of the fluid to an equal volume of water at a standard temperature and pressure. It is dimensionless.
  • Fluid flow can be laminar as long as the particles move in parallel layers. As the velocity increases above some critical value the fluid becomes turbulent where the particle motion is no longer steady but varies in magnitude and direction. For fluids with relatively low viscosity (water, air) the behavior is dominated by inertia forces described by pressure. There will be a thin layer near the surface of a body where the velocity change is very large as a result of the adhesion and viscosity of the fluid. This is called the boundary layer.
  • Dynamic viscosity () is defined as the resistance to flow of a fluid. It is expressed as the ratio of the shearing stress (t) or force between adjacent layers of the fluid to the rate of change of velocity (V) of the fluid perpendicular to the direction of motion. It has units of kg/m-sec

    An equally important characteristic of fluid for turbo-machine design is the kinematic viscosity (?) defined as the absolute viscosity divided by the mass density.

    The viscosity of a fluid is affected by its temperature. Because of the molecular interactions, the viscosity of most liquids decreases with temperature, while the viscosity of a gas increases with temperature.

  • The Reynolds Number (R) is a dimensionless number that is a useful descriptor of flow resistance.
  • where V is the fluid velocity, d is some characteristic dimension of the passage through which the fluid flows, ? is the fluid density and is the dynamic viscosity. A large Reynolds Number (> 2500) indicates turbulent flow.

  • Velocity head or kinetic head is the energy in the fluid due to its motion. The energy is the common expression for kinetic energy
  • Pressure head (P) is the energy contained in a fluid due to its height.
  • Bernoullis Theorem says that the total energy in a fluid is a constant, neglecting any losses in transmission.

As a fluid enters a narrow passage in a pipe, for example, the velocity increases (continuity equation) and the pressure therefore drops. This is a good approximation for liquids at low velocities but the error gets larger for high velocities because of the losses due to friction and turbulence. These losses increase approximately with the square of velocity and depend on factors such as passage roughness, abrupt changes in dimension, length, etc.

If a fluid flows radially between two disks, the continuity equation says that where R is the radius, b is the distance between the plates, and Vr is the radial velocity at R. For any stream tube Q/2 is constant so that RbVr = constant, and if the disks are parallel RVr = constant.

We can also look at the case where the fluid flowing between disks is purely rotary, that is it has no radial component but flows tangent to a given circumference. It can be shown that in this case RVu = constant where R is the radius and Vu is the tangential velocity. The velocity distribution is hyperbolic, the velocity being lower at larger radius.

In a Tesla turbine the flow has both radial and tangential components. By superimposing the two cases we get the resultant velocity Vr/Vu = constant.

This describes a logarithmic spiral; the path of the fluid within the disks and also after it leaves the disks. If the disks are not parallel, but diverge with radius, the radial component decreases more rapidly and the spiral is tighter than the log spiral.

4.2 Operation Principles

The fluid adherence to a wall (i.e. the no-slip condition) is the basic phenomenon behind the Tesla turbine. As the fluid acquires the velocity of the wall over which it flows, therefore a disk has the tendency to acquire the velocity of the fluid imparted over it. If this fluid is injected tangentially to a disk surface then the tangential component of the velocity vector is zero for a reference system attached to the disk surface, moving with it, then the only velocity component seen in this system which influences the fluid flow is the velocity component towards the center of the disk which pushes it to that region where it is discharged through the existing exhaust ports around it (so that, for an external observer, the fluid describes a spiral circuit around the disk face). As the disk tends to acquire the velocity of the fluid flowing over it, then, for a more effective momentum transfer to take place, the flow should be laminar. Then knowing the flow mean velocity at the turbine inlet and also that in theory its rotor will start rotating, speeding up until reaching that tangential velocity when the relative velocity between the disks and the flow will be zero. From this moment and on, the only non zero velocity relative to the disks will be that of the fluid penetration velocity between consecutive disks and this is the velocity to be taken into account to calculate the design Reynolds Number. Well established theory [5] yields the laminar Darcy friction factor, flam, for laminar flows in ducts.

Theory offers reasonable precision when one makes use of the hydraulic diameter, being quite precise if the effective diameter is used. Using the consecutive disks separation distance, a, (i.e., the gap between them), one may write Dh = 4pDext a / 2(pDext + a) where Dext is the disk external (outer) diameter.

4.3 Calculating the Ideal Number of Discs

To estimate the total number of disks for the turbine, assume that at a given internal circumference of the disk, the flow Reynolds number is less than 2300 (i.e., at that region the flow is laminar).

4.4 Determining the Ideal Temperature of the Fluid

For maximum moment transfer, the fluid flow should be laminar and so the Reynolds Number as expressed by equation (19) should be around 1700, in order to retain both the conditions. Certain assumptions are made:

  1. The relative velocity between the discs and the fluid = 3 m/sec
  2. The disc separation distance = 3 mm
  3. Pressure of the fluid = 30 psi

It is clear that the higher the temperature, the better the ability of air to transfer the momentum to the disc due to the higher viscosity. So at 80C, it is observed that for a disc separation of 3mm, the Reynolds Number is too high and as a result the laminar nature of the fluid flow is very difficult to be maintained. But at the disc separation of 2 mm, the Reynolds Number is well within the limits of laminarity. A disc separation of less than 2 mm would be too less for the smooth flow of fluid in between them and a disc separation of more than 3 mm would make the fluid flow turbulent. Also, a temperature of 80C is not high enough to cause scaling or corrosion problems in the turbine disc. So a temperature of 80C, at a disc separation of 2mm, is chosen for further analysis on this topic. It is to be noted that this temperature is the ideal temperature only for those values of the certain assumptions made. Since the principle aim of this paper is to find the effects of hot air on the disc, the magnitude of the temperature is not as significant as its effects.

CHAPTER 5

MODEL FORMULATION AND ANALYSIS

5.1 Modeling the disc with exhaust holes

Figure 5.1 shows the side view of the disc, i.e. the rotor, with its various exhaust holes. The disc has a diameter of 15 cm and 8 exhaust holes of 5 mm diameter each were made on the disc. For the analysis purpose, a finite element on the circumference of this disc is selected.

5.2 Structural analysis of a finite element of the disc

For the structural analysis, a finite element from the circumference of the disc was chosen. Following are the various assumptions, values and dimensions:

  • Dimension: 200mm X 100mm X 20mm
  • Pressure: 30 psi, in the positive x direction
  • Youngs modulus: 5 X 105 N/m2
  • Poissons Ratio: 0.33
  • Boundary Conditions: All the 3 sides except the upper side have zero degrees of freedom

Figure 5.2 shows the finite element model after the pressure has been applied, figure 5.3 shows the deformed + un-deformed finite element, figure 5.4 shows the Contour Plot for displacement, figure 5.5 shows the Contour Plot for stress and figure 5.6 shows the Vector Plot for displacement.

Discussion: When all the above plots are read and analyzed together, it is clear that the upper half of the finite element is the area which is subjected to maximum displacement and stress. To be very accurate, the middle part of the upper half of the finite element is what merits serious attention i.e. since the height of the finite element is 20mm, the area from 3-7mm is the priority area identified through the structural analysis of the finite element. Although the maximum displacement (red area in Figure 5.4) occurs at the very top, the area of displacement is small. But in the yellow and green areas, both the displacement and the area over which it is spread are high.

5.3 Thermal analysis of a finite element of the disc

For the thermal analysis, a finite element from the circumference of the disc was chosen. The purpose of this analysis is to understand the convection heat transfer from the hot fluid to the disc. Following are the various assumptions, values and dimensions:

  • Dimension: 200mm X 100mm X 20mm
  • Convective heat transfer co-eff. of air: 50 W/m2C
  • Thermal Conductivity: 15 W/my
  • Type of Heat Transfer: Steady-state
  • Temperatures: 80C for the upper side (temperature of the air), 20C for the lateral sides and 10C for the bottom side (to consider the effects of conduction through the solid)

Discussion: As in the structural analysis, it has been established that the priority area is the middle part of the upper half. This is the area where the maximum distribution of relatively high temperature takes place. Although, the maximum temperature (the red area) is at the very top (Figure 5.7), since it is distributed only at a small area, it is not that significant. The yellow and green areas deserve the maximum priority since they are widely distributed and the temperature magnitude is also high.

CHAPTER 6

ANALYSIS OF LAMINATED COMPOSITES

6.1 A brief introduction of laminated composites

The word composite means made up of distinct particles or substances. Naturally a composite material is a material that consists of two or more distinct constituent materials that are joined together to form an integral unit. An obvious advantage laminated composites have over conventional engineering materials such as copper, steel, aluminum, titanium etc. is its high specific strength and modulus. The definition of specific strength is the ratio of the material strength to the material density and the specific modulus is defined as the materials Youngs modulus per unit material density.

High specific strength and specific modulus have important applications on the engineering applications of composite materials. It means that the composite materials are stiff and strong yet light in weight. Such characteristics are very desirable in the aeronautical and aerospace industry. The weight savings realized by fabricating structural components out of composite materials is directly translated into fuel savings which in turn makes the operation of an aero plane or a space vehicle more economical.

Laminated composites also afford the flexibility of placing strength and stiffness in critical areas without the penalty of weight increment as would be with macroscopically isotropic engineering materials. In many applications, a structure is required to retain its strength and stiffness at an ultra high temperature. The leading edges of the wings and the nose-cone of a space vehicle are examples of such structures which may encounter temperatures as high as 3000 degree F during re-entry. Laminated composites are capable of withstanding such temperatures.

6.2 Mechanics of laminated composites

6.2.1 Plane stress equations for composite lamina

Many structural applications of fiber-reinforced composite materials are in the form of thin laminates, and a state of plane stress parallel to the laminate can be assumed with reasonable accuracy. For this reason, formulations in plane stress are of particular interest for composite structures.

Note that in the plane stress-strain relations for orthotropic solids in a state of plane stress, there are four independent material constants. For fibrous composites, E1(Youngs modulus in the fiber direction), E2 (transverse Youngs modulus), G12 (longitudinal shear modulus), and 12 (transverse/longitudinal Poissons ratio) are often used to characterize the composite in a state of plane stress.

6.2.2 Nomenclature for the stacking sequence

There is more than one way to denote the stacking sequence of laminates. However, once one method is learned, any other is easy to interpret, even though it may not be in the form that the user is accustomed to.

Once the 0 fiber direction has been defined (and thus the x-axis), the plies that are not at 0must be assigned an angle. To do this, start from the x-axis and rotate to the fiber direction of the ply being defined. Clockwise rotations are positive angles, and counterclockwise rotations are negative angles, although the reverse can also be used since only plane-stress is being examined for plates and the material is the same whether viewed from one surface or the other surface. Now that all plies have an angle associated with them, a method of presenting the stacking sequence follows.

If the laminate is symmetric, then start with the angle of the outermost ply and denote the ply angles, separated by a slash, until the mid-plane is reached. Enclose this string of angles in brackets or parentheses and subscript the brackets or parentheses with an S to denote "symmetric." If the laminate is not symmetric, then proceed as above until the bottom ply is reached. Subscript the brackets or parentheses with a "T" to denote "total" laminate.

Further simplifications can be made when two or more plies of the same orientation are grouped together. The angle of these plies need only be written once with a subscripted number denoting the number of plies in the group. For example, [0/ 90/ 90/90/90/0] T can be written as [0/90 4 /0] T. Since this laminate is symmetric, further simplifications can result, and this laminate could be described by [0/ 90 2] S. If a symmetric laminate consists of an odd number of plies, then the geometrical mid-plane of the laminate will lie at the mid-plane of the center ply. In this case, a bar is placed over the angle of this ply to denote that half of it resides in the top half of the laminate and the other half resides in the bottom half of the laminate. For example, a laminate with stacking sequence [0/ 90/ 90/ 90/ 0] T can be written as [0/90/ 90] S. Any repeating units within the laminate can be placed in parentheses with a subscripted number representing the number of repeats. For example, a [0/ 90/ 0/ 90/ 0/ 90/ 0/ 90] S laminate can be written as [(0/ 90)4] S. If adjacent plies are of the same angle, but with different signs, then a plus-minus sign is usually placed in front of the angle of the plies. For example, a [0/ +45/ -45/ 90/ +30/ -30] T laminate can be written as [0/45/ 90/ 30] T.

6.3 Modelling and finite element analysis of structures

6.3.1 Finite Element Method

The basis of the FEM is the representation of an arbitrary shaped structural continuum in the form of an assemblage of a finite number of small pieces of well-defined (regular) shape. This process of dividing the geometry of the structure is called discretization or idealization or meshing of the structure. These well-shaped (line, triangle, quadrilateral, tetrahedral, hexahedral etc.) components are called elements. These elements are interconnected at the corner points called the nodes. By virtue of regular shapes, formulation of governing equations of solid mechanics and theory of elasticity is simpler for these elements. Assuming independent polynomial displacement fields within these elements and applying proper variational methods, element matrices viz. stiffness matrix, mass matrix or stress stiffness matrix are formulated, based on the analysis type, for individual elements and then assembled to form huge global matrices for the whole structure. Similarly, the loads acting on the individual elements are assembled to form global load vector.

6.3.2 Stress Analysis

Also known as static analysis, the stress analysis is carried out to determine the distribution of displacements, strains and stresses in the structure for the given loads and boundary conditions. Displacements are the primary output of the analysis. The strains are computed from the spatial derivative of the displacements. The stresses are computed using the srains and the material properties of the element. The basic equation solved here is [K] {u} = {f}, where [K] is the global stiffness matrix, {f} is the global load vector and {u} is the vector of nodal displacements.

6.3.3 Buckling Analysis

Buckling is a mode of structural failure characterized by a sudden change in the intended shape/configuration of the structure when subjected to excessive compressive loads. The normal deformed shape (the equilibrium state) under the action of the applied loads spontaneously changes and the structure acquires a new equilibrium state. Under this condition, the structure is considered to be functionally failed. Buckling analysis makes use of the stress distribution obtained from the previous analysis to compute stress stiffness matrix [Ks], which is a measure of weakening of the structure due to induced stress. Then an eigen value problem is solved as ([K] + ?[Ks]) {u} = 0, where the eigenvalue ? is the critical load factor. The product of the applied loads with ? gives the critical load beyond which the structure will fail due to buckling. If ?>1, the structure is safe. ?<1 indicates that the applied load is already higher than the critical load and the structure cannot withstand it. The eigenvector {u} represents nodal displacements (normalized) which correspond to the buckled shape.

6.3.4 Free Vibration Analysis

Free vibration analysis computes the natural frequencies of free vibration and corresponding mode shapes. Design constraints on the frequencies are imposed to keep the natural frequencies of the structure well separated from the frequencies of external excitations. The FE procedures compute the stiffness matrix [M] for the structure and solves the eigenvalue problem ([K] + ?[M]) {u} =0. The first non-zero eigenvalue represents 4?2 f2, where f is the fundamental frequency of free vibration. The eigenvector {u} provides the vibration mode shape.

6.4 Analysis of finite element of a laminated composite rotor

Only the structural analysis will be done on the laminated composites for 2 main reasons:

  1. The temperature distribution inside the laminated composite materials is expected to show a similar pattern like the normal materials.
  2. Laminated composites are designed to withstand very high temperatures. A temperature of around 80C is way below its upper tolerance limit temperature.

6.4.1 Structural analysis of laminated composites

The structural analysis of the following laminated composites will be done:

  1. Unidirectional laminate [0/0/0]
  2. Angle ply laminate [45/45/45]
  3. Unsymmetrical angle ply laminate [0/45/30]
  4. Unsymmetrical cross-ply laminate [0/90/90]

For the analysis, the following dimensions, assumptions and values have been taken:

Finite element dimension = 200mm X 100mm X 15mm

Thickness of each layer = 5mm

Youngs Modulus in x direction = 2 X 107 N/m2

Youngs Modulus in y and z direction = 1 X 107 N/m2

Poissons ratio in XY and XZ planes = 0.3

Poissons ration in YZ plane = 0.25

Shear Modulus in XY and XZ planes = 45 X 105 N/m2

Shear Modulus in YZ plane = 40 X 105 N/m2

Boundary conditions and forces : Same as earlier structural analysis.

The following figures from Figure 6.2 6.13 show the Contour Plots for displacement and stresses and also the deformed + un-deformed image (i.e. before and after the application of the forces) for the four types of laminated composites under consideration.

6.4.2 Deduction

It is to be noted that the Contour Plots for displacement (Figure 6.3, Figure 6.6, Figure 6.9 and Figure 6.12) for all the four laminated composites are very similar in their pattern. But the Contour Plots for stress show contradicting patterns. The Contour Plot for Stress of the composites [0/0/0], [45/45/45] and [0/45/30] i.e. Figure 6.4, Figure 6.7 and Figure 6.10, make it clear that the stresses in these laminated composites are still concentrated in the priority area identified by the first analysis, i.e. the middle part of the upper half. But this is not the case for [0/90/90] (Figure 6.13). Thus it has been determined that the laminated composite [0/90/90] would be the best material to be used for constructing the disc.

Due to the unique structure of laminated composites, the thermal stresses and the pressure-induced stresses are concentrated in different areas. Nowhere is this concentration more different than in [0/90/90]. In [0/90/90], the middle part of the upper half has a very stable and low-magnitude stress distribution (Figure 6.13). In fact, red and orange, the two colors which indicate the maximum stresses dont appear in the contour plot at all. Furthermore, due to the extremely low weight of [0/90/90], the overall weight of the rotor comes down significantly, thereby allowing the fluid to convert more of its kinetic energy to torque, without compromising on the stiffness of the disc.

CHAPTER 7

COMMERCIAL VIABILITY OF THE NEW PROPOSALS

7.1 The Efficiency factor

Tesla Turbine is more efficient than most of the prime movers which are currently in use commercially [10]. The following chart shows the average efficiency of a bladed turbine (Pelton turbine, Kaplan turbine, Francis turbine etc.), a gas piston, a diesel engine, a fuel cell and a Tesla Turbine.

Thus, if the Tesla turbine is adopted on a commercial basis, the efficiency level of the process, be it generating current or pumping water, will see a marked improvement when compared to the current scenario. By adopting the newly proposed fluid and rotor design, this efficiency is expected to increase even further, thereby pushing the cause of the Tesla Turbine even further.

7.2 The Cost factor

The following is the comparison between the estimated cost of the new proposed Tesla turbine and the other machines mentioned earlier

Here, it can be seen that the expected cost of the proposed Tesla Turbine is not too high when compared to its peers. This expected cost has been calculated after taking into account the cost of the laminated composite rotors. The costs of the other machines are their average market costs.

Thus, the Tesla turbine provides an alternative solution to todays energy problems, at a cost which is much lower than the other commercially wide-spread machines.

7.3 The Sustainability factor

In todays world which emphasizes green technologies, the Tesla turbine is an ideal candidate for future power generation, water pumping etc. The fact that the properties of adhesion and viscosity combine together to generate much more power than the power consumed by the compressor which is used to provide the compressed air to the Tesla Turbine rotor is of much importance. Even the power consumed by the air heater to heat the air to 80C will be compensated in the former of a much higher torque generation by the proposed modified Tesla turbine. Especially in areas such as hydraulic power applications, such a high torque can play a very significant role.

CHAPTER 8

CONCLUSION AND SCOPE FOR FUTURE WORK

8.1 Conclusion

In this thesis, an effort has been made to push the case of the commercialization of the Tesla Turbine. The first step was to identify a suitable temperature of air (the fluid) so that the property of higher viscosity of air at higher temperatures can be made use of to generate more torque. This temperature had to be determined without compromising the laminar nature of the fluid flow over the disc. The effect of hot air fluid on the disc was analyzed and the priority areas were identified.

Then four different types of laminated composites were analyzed for their structural behavior under the same operational conditions. Based on this analysis, the most suitable type of laminated composite material which can be used for future rotor constructions was identified. Laminated composites, with their ultra light weight, and superior thermal and structural stress concentration absorbing capacity, will be a perfect candidate for future Tesla Turbine rotors.

Although Tesla himself described that the Tesla Turbine was his greatest invention, it has not found widespread acceptance. It is expected that by analyzing the reasons for that and suggesting improvements like a new working fluid and a new rotor material, a small step forward to commercialize this turbine has been made. The higher torque generation of such a modified Tesla Turbine is expected to revive its fortunes in the commercial market.

8.2 Scope for future work

For increasing the torque generation capacity of the Tesla Turbine even further, the shape of the rotor from a perfect disc can be altered. A disc with sharp edges, like that of a saw, can be considered. This will considerably increase the grip of air over the rotor and lead to increased momentum transfer.

In such a scenario, the ability of the laminated composite material, with which the rotor is proposed to be constructed, to absorb high stress concentration levels, both thermal and structural, will prove to be beneficial.

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[3] Otero, A.D. and Ponta, F.L. (2004) Finite element structural study of the VGOT wind turbine, International Journal of Global Energy Issues, Vol. 21, No.3, pp.221 - 235.

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[5] Engin, T., Ozdemir, M. and Cesmeci S. (2009) Design, testing and two-dimensional flow modeling of a multiple-disk fan, Experimental Thermal and Fluid Science, Vol. 33, Issue 8, pp. 1180-1187.

[6] Couto, H.S., Duarte, J.B.F. and Bastos-Netto, D. (2006) The Tesla Turbine Revisited. Paper Presented at the 8th Asia-Pacific International Symposium on Combustion and Energy Utilization. October 10-12, 2006. Sochi, Russian Federation.

[7] Armstrong, J.H., An investigation of the performance of a modified Tesla turbine, M.S. Thesis, Georgia Institute of Technology (1952).

[8] Lal, Sreeyuth, A Report on Design and Fabrication of Tesla Turbine, BITS, Pilani Dubai, 27 August 30 December 2009, pp. 9-12.

[9] Gurdal, Z., Haftka, R.T., and Hajela, P., Design and Optimization of laminated composite materials, 3rd Edition, Wiley Interscience, New York, 2007, pp. 271 295.

[10] Rieli, K. (2003) Rebirth of the Tesla Turbine, Extraordinary Technology, Vol. 1, No. 3.

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