Heat transfer and thermoelectric design considerations for a ground-source thermo generator

An energy harvesting device designed to produce small (sensor-scale) amounts of electric power is being developed at Mississippi State University, USA. The device will use the daily temperature difference between the air and the ground as input to a thermoelectric generator. The advantages of such a passive device include high reliability, long life-span, low visibility, night-time power production and ruggedness. In this paper, previous results which demonstrated optimum thermoelectric design parameters for this small /spl Delta/T case are extended to include effects of linearly and sinusoidally varying thermal resistance in the heat exchangers. Such variation would occur in an operating device from changes in the air-side convective heat transfer coefficient, for example. It is shown that for the linear case an optimum is reached at the geometric mean of the two extremes in thermal resistance. A closed form function of the mean value and fluctuation magnitude provides the optimum for the sinusoidal case.