ANALYSIS AND CONSTRUCTION OF A TESLA TURBINE

 JESSICA GISSELLA MARADEY LÁZARO

Escuela de Ingeniería Mecánica

Universidad Industrial de Santander

jessicamaradey_AT_yahoo_DOT_com

ORLANDO PARDO URIBE

Escuela de Ingeniería Mecánica

Universidad Industrial de Santader

orlandopardo_AT_hotmail_DOT_com

 The main objective of this project was to foster the assessment of modern and recent alternatives such as the Tesla turbine which are considered more efficient and definitely lead to improvements concerning the energy utilization and its forward transformation. Likewise; by developing our project, we expect to contribute to the Mechanical engineering School’s mission in the Universidad Industrial de Santander and to implement and develop technologies to support the productive and energetic processes made in our country. 

One of the proposed objectives when this project was initially submitted was making a Tesla turbine sample model, through which we could assess and analyse the performance and operation of a Tesla turbine and measure its outcoming power as well. 

We decided to start then, the initial design stage of the turbine by researching geometrical known data that might have resulted of previous experiments and attempts of construction in this direction so far. The available capacity for the Tesla turbine to be tested and mounted in the current thermal machines laboratory of our university as well as the design recommendations advised by Ken Rieli (President of PNGinc and founder of Phoenix Turbine Builders  Club in Michigan, USA) whose knowledge regarding this topic is quite wide due to their experience in making several turbine models and alternative machines in general, were determined from this consulted documentation.

The original design of the Turbine consists of a set of parallel smooth-texture discs mounted on a shaft and separated from each other by washes distributed along the outer area of such discs. Additionally, it has star-shaped washes strategically located in the narrow spaces between discs, all of them in the inner area of the set of discs.  See figure 1.

 The stator is composed of a set of discs (2 externals and 8 internals), which were made of stainless steel sheets type AISI 304 with a 2B superficial finish since they will be in direct contact with the working fluid (saturated steam). Besides, avoiding any possible corrosion and obstruction sign in the discs that might end up causing turbulence, is highly required. Likewise, this condition is necessary due to the narrow space existing between discs (separating washers are 0.912 mm wide), which might considerably affect the turbine operation. We have to bear in mind that one of the main operating principles of the turbine is the viscous dragging between discs and in order to keep this effect it is very important to make sure having a good superficial finish on the discs. 

To make discs and star-shaped separating washes, laser-cutting technology was used (CNC).  The advantages showed by this process were:

• Precision, it achieved ± 0.01mm tolerances in the part’s dimensions, an important factor for the assembly process and the whole system’s balance.
• The laser basically works without touching the surface to be processed; consequently, it does not exert any force on it, avoiding possible deformations and scratches on the material. The above-mentioned feature makes this process advantageous over the other conventional manufacturing processes (Plasma cutters, Cross section cutters).
• Better quality finish in the cutting area (No debris left along the edges).
• The laser is a multifunctional tool, if the part’s geometry is either simple or complicated; the laser solves both situations with considerable easiness.

 The rounded washers were made of aluminium sheets size 20 (Width: 0.0912mm), with an external diameter of 17mm and an internal diameter of 5.1mm, through a mintting process.

Screws with bristol-shaped heads (M5 *35mm) were used as pins for the stator assembly. The assembled stator’s total width was 32.5mm.

For the turbine´s stator and shaft assembly, a special bushing made from a steel tube (Steel type 1020) was made.

The turbine model proposed by Phoenix Turbine Builders Club differs from the original Tesla model since the former uses blades along the external area of the discs and separating flange-shaped washers in the central area of the discs, which are fixed in place with pins. This modified model has been tested and proved to show about 30% more efficiency over the conventional Tesla turbine.

The stator of the modified turbine is composed of discs in a similar way of the conventional Tesla stator. See figure 2.

For the steel discs, blades and ring-shaped separating parts fabrication, laser cutting technology was used (CNC). 

The blades were made of stainless steel sheets, size 20 (Width: 0.0912mm), with an inclination angle of 37º.

Screws with bristol-shaped heads (M5 *35mm) were used as pins for the stator assembly. The assembled stator’s total width was 32.5mm.

A convergent-divergent action nozzle to allow the working fluid´s expansion and increase of velocity at the entrance of the system was built. The throat internal diameter of the nozzle is 12,1mm and the external diameter is 27,27mm.

The housing is mainly composed of three parts: A frontal cover, a back cover, and a ring. These three parts were made of steel type HR 1020 and then treated on their corresponding surfaces with a galvanization process, which was intended to protect such surfaces from any early corrosion sign due to their exposure to the surrounding environment and saturated steam.

The bearings´ selection process was carried out based on the calculated loads exerted on the parts they were mounted, which are mainly radial loads, and the working rotational velocity (18.000 RPM max). Thus, the selected bearings have the designation 6005 in FAG brand and are special bearings for high-speed applications.

A lubrication system similar to oil circulating systems was designed. Based on the value of rotational speed, maximum value 18.000 RPM, the type of oil had to be selected. The process took into account the type of bearing (Deep grovee ball bearing DGBB) along with the type of oil, to determine the cinematic viscosity which in this case had a value of 8.5cst (53.7 SSU). The type of oil was finally determined based on the ISO classification, from which we took the oil ISO 68, that basically shows fluency during the lubrication process.

A shaft with a diameter of 25 mm was designed and made, with a security factor of 2.

Shaft and Bearings Box Assembly.

A Prony brake device to allow the measure of the turbine’s torque and performance was designed.  

The Prony brake device is composed of three parts: A brake section, the system’s support and the brake-arm, on which a dynamometer was installed in order to read the torque measure at several RPM values.

For the brake section’s construction, a complete Renault 4´s braking system device was used including the its housing and breaking shoes. The selected material to make the whole system’s support and braking-arm was steel type 1020. 

Afterwards, The complete assembly of all the above-mentioned parts was finally made.  See figure 5 y 6.

The mathematical model to analyse the turbine was done based on the previously consulted documentation and the general turbomachinery-applied concepts learned in our Fluid Mechanics subject. This information facilitates the proper understanding of the operating parameters (Torque, power and efficiency) and certainly explains their relationship with the geometrical characteristics of all the previously described parts. Basically, two different alternatives were proposed: The simplified model and the free vortex model, which easily make us understand the existing relationship between the outcoming power of the turbine, the space between discs and the disc’s diameter.

The turbine was assembled in the school of Chemical Engineering laboratory, taking advantage of an existing boiler, in order to assess and measure its performance. We initially proposed to do this process in our own lab, Mechanical Engineering laboratory, but due to a restructuring work in it, this was literally impossible. 

The Chemical Engineering laboratory owns a pirotubular boiler of 30 HP, which is able to work in a steam pressure range of 75-100 psi, by mean of an on-off control system.  This boiler produces saturated steam.

Due to the physical lay out and conditions of the laboratory that is being used, the turbine steam’s intake or connection for operation is set approximately 50 mts away from the boiler steam’s outlet whose pipes have 1.1/2" of diameter. The boiler plumbing is properly isolated with fibreglass. The shunt that takes the steam into the turbine is approximately 6 mts long using pipe of 1" of diameter properly isolated with fibreglass and reduced, near the turbine, to a pipe of 3/4" of diameter and finally to section of 1/2" of diameter. These two last sections, right before reaching the turbine, are not isolated.

After we put the turbine to the several tests to assess its results, the final condition of the stator was carefully checked, but no considerable changes were found in neither geometrical measures nor surface conditions of the discs.

According to the obtained RPM data from the performed tests, the fact that the Tesla Turbine is a machine that considerably develops the highest rotational velocity range but the lowest outcoming torque result was proved to be true. This premise becomes a disadvantage when the turbine is applied in several industrial applications, due to the extra-costs generated by the lubrication and sophisticated cooling systems that should be implemented when dealing with extremely high rotational velocities. These costs are associated to the equipment handling and control as well.

The calculated outcoming power of the turbine, based on the above-mentioned theoretical methods, (The simplified model and the free vortex model) is lower than the real power obtained from the performed tests. This phenomenon is understandable if we bear in mind that the theoretical mathematical models do not take the spacing washers of the stator into account in the calculations, which have a direct influence in the outcoming power performed by the turbine.

Comparing the performance of the Tesla Turbine with other steam turbine models (action and reaction principle), we can state that due to the operating principle of the Tesla Turbine (Dragging of the discs due to friction and presure), the conversion of energy of the working fluid results mainly in the development of high rotational velocities (RPM), whereas other turbines, due to the steam´s change of direction and value of the velocity, the energy tends to convert mainly in torque rather than RPM. 

The result is a turbine that owns a high versatility, long longevity (due to the fabrication methods and the materials that were properly used), facility for its mounting and overhouling processes, and high rotational velocities, which might become an important alternative to improve the existing energetic systems and definitely starts new investigation areas aiming at the commercial and  technical development of this type of turbine.

REFERENCES

 [1] BARLIS, Glenn A. Turbomachine Termodynamics. Milwaukee, USA: TEBA, Tesla Engine Association News. Issue #21. 2002. 20p. www.execpc.com/~teba

 [2] BARLIS, Glenn A. Basic Theory for Turbomachines. Milwaukee, USA: TEBA, Tesla Engine Association News. Issue #20. 2001. 20p. www.execpc.com/~teba

 [3] BREITHER, Mark C y Pholhausen Karl. Laminar Flow Between Two Parallel Rotating Disks. Ohio, USA: Aeronautical Research Laboratory. 1962. 49p.

 [4] BUCKINGHAM, E. "Model Experiments and the Form of Empirical Equations." Trans. ASME 37, 263, 1915.

 [5] CAIRNS, W.M.J. The Tesla Disk Turbine. Gran Bretaña: Salisbury Printing Co. Ltd. 2001.  34 p. www.camdenmin.co.uk

 [6] DENTON, J.H.: “Loss Mechanism in Turbomachines”. ASME Journal of Turbomachinery, Vol. 115, 621-656, October, 1993.

 [7] DISKFLO - Manufacturer of Pumps. 10850 Hartley Rd, Santee, CA 92071 [online] Available in internet: <URL:http://www.diskflo.com>.

 [8] ENTRINCAN, Sonny. How to build a Real Tesla Turbine. Milwaukee, USA: TEBA, Tesla Engine Association News. Issue #15. 1998.  20p. www.execpc.com/~teba

 [9] ENTRINCAN, Sonny. Physics of the Tesla Turbine. Milwaukee, USA: TEBA, Tesla Engine Association News. Issue #16. 1999. 20p. www.execpc.com/~teba

 [10] FAY, James A. Mecánica de Fluidos. México DF: Compañía Editorial Continental, S.A de C.V.1996.

 [11] GINGERY, Vincent R. Building the Tesla Turbine. Rogersville, MO, USA: David J. Gingery Publishing LLC. 2004. 48p.

HAYES, Jeffrey. Tesla's Engine A New Dimension for Power. Milwaukee: TEBA, Tesla Engine Association News. 1994. 224p. www.execpc.com/~teba

 [12] HINGLE, Mike. The Eleven inch Tesla Turbine Revisited. Milwaukee, USA: TEBA, Tesla Engine Association News. Issue #15. 1998. 20p. www.execpc.com/~teba

 [13] REY, Andrés F. Numerical Simulation of the Flow Field in a Friccion-Type Turbine (Tesla Turbine). Diploma Thesis. Viena: UNAL-Viena University of Technology. 2004. 108p.

 [14] RICE, W.: “An Analytical and Experimental Investigation of Multiple-Disk Turbines”, Journal of Engineering for Power, Trans. ASME, series A, Vol. 87, No. 1  1965, pp. 29-36

 [15] SPANGLER, S.M. Boundary Layer Vortex Generation. Milwaukee, USA: TEBA, Tesla Engine Association News. Issue #21. 2002. 20p. www.execpc.com/~teba

 [16] SCHMIDT, Darren D.: “Biomass Boundary Layer Turbine Power System”, California Energy Commission (CEC), EISG PROGRAM [online] Available from Internet: <URL: http://eisg.sdsu.edu/Fullsums/00-06.htm ><URL:http://eisg.sdsu.edu/shortsums/shortsum0006.htm>, 1991, California, USA. <URL: http://eisg.sdsu.edu/Far/00-06%20FAR.pdf>

 [17] SINGLETON, Craig. Investigation and Analysis of Tesla's Bladeless Turbine. Milwaukee, USA: TEBA, Tesla Engine Association News. Issue #21.  2002. 20p. www.execpc.com/~teba

 [18] STEIFER, Marc. Tesla's Turbine R&D. Milwaukee, USA: TEBA, Tesla Engine Association News. Issue #20.  2001. 20p. www.execpc.com/~teba

 [19]STRICKLAND, Kneass L. Practice and Theory of the Injector. Bradley IL, USA: Lindsay Publications Inc. 2004. 182p. www.lindsaybks.com

 [20] TAHIL, William. Theoretical Analysis of a Disk Turbine. Milwaukee, USA: TEBA, Tesla Engine Association News. Issue #15. 1999. 20p. www.execpc.com/~teba

 [21] TEBA, Tesla Engine Association News. Tesla Turbine Operational Characteristics. Milwaukee, USA: Issue #15. 2001. 20p. www.execpc.com/~teba

TESLA, N.: “Turbine” United States Patent No. 1061206, May 6, 1913.

Phoenix Turbine Builders Club

www.phoenixnavigation.com/ptbc