Steady state heat transfer characterization of a liquid metal thermal switch

by Travis Sloan Wiser, M.S. Washington State University August 2005 Chair: Robert Richards Steady state heat transfer characteristics have been quantified for a liquid metal thermal switch. The application motivating this research is the P micro heat engine which converts heat energy into electrical power using the charge generating property of PZT. Stacks of engines are necessary to produce a useable charge and cyclic heating must be realized to make these stacks efficient. The thermal switch consists of a silicon substrate with mercury micro-droplets deposited in a 1600 droplet array. Droplets are deposited using a vapor deposition process where mercury vapor preferentially condenses on 30 μm gold pads sputtered on the silicon substrate. When the droplet arrays make contact with a second silicon substrate heat is transferred and the switch is “on”. When the droplet arrays do not make contact, heat transfer across the resulting gas gap is sharply reduced and the switch is “off”. Three gas gaps are compared for the thermal switch. The reference condition is a gap filled with air at ambient pressure. The second condition is Xenon at ambient pressure. The third condition is air at a pressure of 0.5 torr.

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