Local forced convective heat transfer from protruding and flush-mounted two-dimensional discrete heat sources

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Experiments are undertaken to measure the local forced convective heat transfer characteristics of an array of two-dimensional discrete heat sources. Air flow rates yielding effective channel Reynolds numbers in the range from 1000 to 10000 are employed. Flush-mounted and protruding heater configurations are investigated in the study. Two different channel wall spacings independent of the heat source protrusion are also studied. Local temperature measurements are made along the uniformly heated surface parallel to the flow direction. The results of the experiments show that protruding heat sources yield higher heat transfer than flush-mounted heat sources at the same channel Reynolds number. The interruption of the thermal boundary layer in the adiabatic sections between the heaters results in heat transfer enhancement. Heat source protrusion yields significantly higher heat transfer rates for the second and subsequent heater for channal Reynolds numbers above 2000. This is explained in terms of a separated flow and vena contracta effect, with eventual downstream transition to turbulent flow, and is borne out by flow visualization experiments. The local heat transfer measurements reveal significant variation in wall temperature across the heater faces, which is strongly affected by the flow structure. Average heat transfer coefficients calculated by spatially integrating the local measurements are correlated and presented in terms of Reynolds number and the dimensionless geometric parameters studied.