Rural electrification is needed to improve the livelihoods of individuals that are located where centralized power grids do not reach. Pico hydro, hydro systems of 5 kW capacity or less, can address this need at relatively low cost and with virtually no negative environmental or social impacts. An alternative and less complex design for a pico hydro generator rotor, proposed by Nikola Tesla, uses the viscosity of fluids to efficiently transfer the fluid energy to the rotor, resulting in useable work. Numerous analytical and experimental investigations have been performed to characterize the flow within the Tesla turbine design. It has been found that efficiencies reported by Tesla have not been reproduced by others. Inefficiencies are often attributed to the losses due to flows through the nozzle and outlet. Tesla turbines will not be considered competitive in the general market until efficiencies surpass that of conventional designs and power densities can be improved. That said, the relatively simple design of the Tesla turbine lends itself well to small scale power projects since it can be easily manufactured and maintained locally. Debris in water sources is a significant concern in small scale hydro systems. The disk rotors are not sensitive to abrasion and can continue to perform under these types of flows. A preliminary design of a Tesla turbine for pico hydro applications has been undertaken employing Rice’s analytical method. The investigation yielded a design capable of generating 300 W under conditions of 20 m head and 2.5 L/s flow. The efficiency of the preliminary turbine design was near 80% but it is believed that the bulk of efficiency losses will be found in inlet and exhaust flows, which are not considered in this analysis. Challenges remain for the application of Tesla turbines to pico hydro generation.

Tesla Turbine for Pico Hydro Applications

In this article, the fluid dynamics of work transfer within the narrow spacing (usually of the order of 100 μm) of multiple concentric discs of a Tesla disc turbomachine (turbine or compressor) has been analysed theoretically and computationally. Both the overall work transfer and its spatial development have been considered. It has been established that the work transfer mechanism in a Tesla disc turbomachine is very different from that in a conventional turbomachine, and the formulation of the Euler's work equation for the disc turbomachine contains several conceptual subtleties because of the existence of complex, three dimensional, non-uniform, viscous flow features. A work equivalence principle has been enunciated, which establishes the equality between the magnitudes of work transfer determined rigorously from two different approaches—one based on the shear stress acting on the disc surfaces and the other based on the change in angular momentum of the fluid. Care is needed in identifying the shear s...

The fluid dynamics of work transfer in the non-uniform viscous rotating flow within a Tesla disc turbomachine

Loss Mechanisms in Shear-Force Pump With Multiple Corotating Disks

This paper presents an experimental study of the heat transfer and pressure drop characteristics of a single phase high heat flux microchannel cooling system with spiraling radial inflow. The heat sink provides enhanced heat transfer with a simple inlet and outlet design while providing uniform flow distribution. The system is heated from one conducting wall made of copper and uses water as a working fluid. The microchannel has a 1 cm radius and a 300 μm gap height. Experimental results show, on average, a 76% larger pressure drop compared to an analytic model for laminar flow in a parallel disk system with spiral radial inflow. The mean heat transfer coefficients measured are up to four times the heat transfer coefficient for unidirectional laminar fully developed flow between parallel plates with the same gap height. Flow visualization studies indicate the presence of secondary flows and the onset of turbulence at higher flow rates. Combined with the thermally developing nature of the flow, these characteristics lead to enhanced heat transfer coefficients relative to the laminar parallel plate values. Another beneficial feature of this device, for high heat flux cooling applications, is that the thermal gradients on the surface are small. The average variation in surface temperature is 18% of the total bulk fluid temperature gain across the device. The system showed promising cooling characteristics for electronics and concentrated photovoltaics applications with a heat flux of 113 W/cm2 at a surface temperature of 77 °C and a ratio of pumping power to heat rate of 0.03%.

Experimental Study of Single Phase Heat Transfer and Pressure Loss in a Spiraling Radial Inflow Microchannel Heat Sink

Steady flow of incompressible fluid between two co-rotating disks

superimposed on the vortex flow field. This superimposed jet is directed outward and is just sufficient to counterbalance the inward radial jet caused by the rotating flow over the stationary plate. The result is zero net radial flow in the interaction zone. Apparently such a solution can only exist at low Reynolds numbers. Of course, at low Reynolds numbers the boundarylayer equations cannot be used. At high Reynolds numbers it makes no difference whether the boundary-layer equations or the complete Navier-Stokes equations are used; the similarit3 transformation considered by Kidd and Fan-is will not yield a solution to the problem posed.

Laminar Inward Flow of an Incompressible Fluid Between Rotating Disks, With Full Peripheral Admission

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Laminar Inward Flow of an Incompressible Fluid Between Rotating Disks, With Full Peripheral Admission