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This study presents a direct numerical simulation of the geometry effect on fluid flow and heat transfer characteristics in the transitional flow over backward and forward facing steps. A computer program of FORTRAN code is used to solve the governing equations according to finite volume method. The effects of the bottom wall length and the step height are investigated. With the increase of bottom wall length, a fundamental frequency of flow fluctuation appears at L b = 10 h and then disappears at L b = 14 h. This fundamental fluctuating frequency decreases with the increase of step height. The fact that the heat transfer performance is better in the reattachment region at L b = 12 h and S = h indicates that the periodic flow fluctuation with a larger fluctuating velocity has positive effects on heat transfer enhancement. The results of the relationship between flow fluctuation and heat transfer enhancement are significant for certain practical applications of energy conversion. [ABSTRACT FROM AUTHOR]

Abstract: Thermoelectric generators (TEG) convert heat energy to electrical power by means of semiconductor charge carriers serving as working fluid. In this work, a TEG is applied to a parallel microchannel heat sink. The effect of the inlet plenum arrangement on the laminar flow distribution in the channels is considered at a wide range of the pressure drop along the heat sink. The particular focus of this study is geometrical effect of the TEG on the heat transfer characteristics in the micro-heat sink. The hydraulic diameter of the microchannels is 270 μm, and three heat fluxes are applied on the hot surface of the TEG. By considering the maximum temperature limitation for Bi2Te3 material and using the microchannel heat sink for cooling down the TEG system, an optimum pumping power is achieved. The results are in a good agreement with the previous experimental and theoretical studies. [Copyright &y& Elsevier]