Experiments and modeling of the hydraulic resistance of in-line square pin fin heat sinks with top by-pass flow

In pin-fin heat sinks, the flow within the core exhibits separation and hence does not lend itself to simple analytical boundary layer or duct flow analysis of the wall friction. Indeed, form or bluff-body drag may be even more important than viscous wall friction in establishing the overall pressure drop. In this paper, we present some early findings from an experimental and analytical study aimed at obtaining physical insight into the behavior of square, in-line pin fin heat sinks. In the experimental study, various size aluminum heat sinks were utilized, where the pin heights were 12.5 mm, 17.5 mm, and 22.5 mm, and the base dimensions were kept fixed at 25 x 25 nun. A "two-branch by-pass model" was developed, in which a one-dimensional differential approach was used to model the fluid flow through the heat sink and its top by-pass duct. Central to the analysis is the introduction of accurate correlations for inlets exit and core pressure drop within the heat sink. Pressure drop predictions correlated well with the experimental data when pressure drop coefficients measured for the heat sinks were used. Agreement was poorer when classical circular tube bundle pressure drop correlations were utilized, but the accuracy was high enough for design purposes. Inlet and exit pressure losses were as important as the core pressure drop in establishing the overall flow and pressure drop. Available literature models for inlet and exit effects were mostly adequate.