Extensive experiments were performed aimed at obtaining physical insight into the behavior of in-line pin fin heat sinks with pins of square cross-section. Detailed pressure measurements were made inside an array of square pins in order to isolate the inlet, developing, fully developed, and exit static pressure distributions as a function of row number. With this as background data, overall pressure drop was measured for a self-consistent set of aluminum heat sinks in side inlet side exit flow, with top clearance only. Pin heights of 12.5 mm, 17.5 mm, and 22.5 mm, pin pitch of 3.4 mm to 6.33 mm, and pin thickness of 1.5 mm, 2 mm and 2.5mm were evaluated. Base dimensions were kept fixed at 25 × 25 mm. In total, 20 aluminum heat sinks were evaluated. A “two-branch by-pass model” was developed, by allowing inviscid acceleration of the flow in the bypass section, and using pressure loss coefficients obtained under no bypass conditions in the heat sink section. The experimental data compared well to the proposed hydraulic models. Measurements in the array of pins showed that full development of the flow occurs after nine rows, thus indicating that none of the heat sinks tested could be characterized as fully-developed.

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