Experimental hydraulic characterization of pin fin heat sinks with top and side bypass

Extensive tests were conducted to obtain hydraulic characteristics of pin fin heat sinks with pins of square cross-section under different top and side bypass conditions. A consistent set of aluminum heat sinks with constant platform area and variable pitch were utilized. The heat sinks were tested in a second-generation adjustable cross-section wind tunnel which provides 0 to 1 top and 0 to 10 side clearance ratios. Detailed pressure distributions around the heat sinks were measured, and the influence of top and side bypass was explored. It was found that side clearance only results in higher overall pressure drop compared to top clearance only, at the same clearance ratio. But overall pressure drop surprisingly scales very well on overall clearance ratio CL when both top and side clearance are present. A novel, non-iterative two-branch semi-inviscid bypass model was developed to calculate the pressure drop across the heat sinks. The analytical results compared well with experimental data.