Tine Stevens

Micropower generation with microgasturbines: A challenge

Abstract This paper describes the development of a microgasturbine with a rotor diameter of 20 mm. The target electrical power output lies around 1 kW. The total system fits in a cylinder with a diameter of 95 mm and a length of 120 mm. The system contains the same components as a large gasturbine generator: compressor, recuperator, combustion chamber, turbine, and electrical generator. Major challenges are the high rotational speed (500 000 r/min), high turbine inlet temperature (1200 K), and the efficiency of the components. Because of the small dimensions, the flow through compressor and turbine is characterized by relatively low Reynolds numbers. The higher flow losses and inherently lower efficiency require a higher blade tip speed (524 m/s) than for large turbines (300-400 m/s). To minimize wear and frictional losses, the rotor is mounted on aerodynamic bearings. To withstand the high centrifugal stresses, a high-strength steel is used for compressor and shaft. The turbine is made of a Si3N4-TiN ceramic composite to withstand the combination of elevated stress and temperature.

Collector Pressure Losses in Micro Heat Exchangers

As collector losses are expected to play a crucial role in micro heat exchangers, an experimental method is developed to determine these losses. Experiments are performed on a micro heat exchanger consisting of 42 parallel microchannels positioned in a 6 by 7 matrix, with hydraulic diameters in the range of 260-280 mum. The proposed method is successfully applied. From the experimental results it can be concluded that the pressure drop of a small collector performs according to classical correlations. However, in a wider collector design the pressure drop clearly deviates from macro scale behaviour

Digital and Continuous Liquid Cooling for Electronic Systems

In this paper both digital and liquid cooling concepts are proposed. Microchannel cooling techniques either actuated by a separate feed pump or actuated by electrowetting are investigated and their cooling capabilities and pumping requirements are assessed. Though the continuous liquid microchannel cooling clearly outperforms the other systems with respect to global thermal resistances, the low energy consumption and the flexibility as a reconfigurable cooling system, make the electro-actuated cooling systems attractive.

Integrated solution for micro power generation

Battery systems have a much lower energy density than fuels. The use of fuel based micro power generation units instead of batteries can therefore become interesting in certain applications. This paper describes the problems that occur when designing such a power generation unit. It is shown that operational conditions and geometrical restrictions impose tough requirements on the design of different components. The solutions as found in traditional fuel based generation systems cannot simply be downscaled, but several concepts have to be fundamentally rethought