A Numerical Study of Mixed Convective Heat Transfer From a Parallel Fin Heat Sink

*† The heat transfer rate from a simple parallel fin heat sink with air flowing over it has been numerically studied. The main intention of the study was to determine the conditions under which buoyancy force effects start to have a significant influence on the heat transfer rate, i.e., to determine the conditions under which mixed convective flow exists. In the flow situation being considered, the base of the heat sink is horizontal, the fins are vertical and there is a solid adiabatic plane surface above the heat sink, this surface being parallel to base of the heat sink. There is a forced air flow over the heat sink parallel to its base and to the fins. The flow has been assumed to be laminar and it is, of course, three-dimensional. The governing equations, written in dimensionless form, have been solved using a commercial finite element software package. Solutions have been obtained for a Prandtl number of 0.707. The heat sink fin height has been assumed to be equal to the length of the heat sink in the flow direction. The main parameters on which the solution depends are the Reynolds and Grashof numbers, the dimensionless fin spacing, the dimensionless fin thickness, and the dimensionless gap between the top of the fins and the upper adiabatic surface. The variations of the mean Nusselt number with the Reynolds and Grashof numbers have been determined for various values of the heat sink geometric parameters. These results have been used to determine the conditions under which the effects of the buoyancy forces start to have a significant influence on the heat transfer rate.

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