The thermal resistance of in-line square-pin fin heat sinks was experimentally investigated. In a companion paper [1], extensive results for the hydraulic behavior of such heat sinks with and without top-bypass were reported. It was shown that the top-bypass, as well as pin pitch, strongly influence the fin flow available for cooling. Systematic measurements of the overall thermal resistance with a uniformly heated base were performed for the same set of twenty aluminum heat sinks. Pin height was varied from 12.5 mm to 22.5 mm, pin pitch was varied from 3.4 mm to 6.33 mm, and base dimensions were kept fixed at 25 × 25 mm. The overall base to ambient thermal resistance was measured as a function of heat sink geometry, approach velocity and by-pass height. Experimental results were compared with predictions based on a simple one-dimensional "two-branch bypass model". It was found that the overall heat transfer is governed by the fin flow, hence, empirical data for the zero bypass case can be used to predict the decrease of heat sink performance with flow bypass.
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