Detailed static pressure and temperature measurements were made in fine pitch parallel plate copper heat sinks with and without top bypass flow. A set of heat sinks with differing fin pitch and with and without anodized finish were tested in a 3rd generation cross-flow wind tunnel that provides zero to one top clearance ratio. Static pressure measurements were made in the vicinity of the heat sink in order to study the influence of the top bypass for approach velocities from 1 to 10 m/s. A comparison was made with existing ad hoc models that model the core flow with laminar theory and the inlet and exit losses with empirical correlations from the compact heat exchanger literature. In general, excellent agreement was found in the laminar regime. However, significant deviation was found for approach velocities exceeding 5 m/s, probably because the flow transitions to turbulent beyond this approach Reynolds number. In the case of flow bypass a non-iterative two-leg bypass model yielded excellent agreement for pressure drop, indicating that an ad-hoc approach such as this has value. Precise temperature measurements were taken at different stream-wise locations at the centerline of the heat sinks, under conditions where the heat sink base was heated uniformly and when the base area was heated with a smaller heat source with a 1-to-11 heater-to-base area ratio. The combined data allow the direct evaluation of base heat spreading effects. The experimental results were compared to well-known models that solve the conduction problem by assuming either an isothermal boundary condition on the top of the base of the heat sink or a specified uniform effective heat transfer coefficient. Excellent agreement was found with the latter model.

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