Effect of Reynolds Number on the Thermal Resistance and Pressure Drop of a Rectangular Microchannel Heat Sink

Increasing coolant flow in rectangular microchannel heat sinks can enhance cooling performance but also increase pressure drop and pumping requirements, creating a thermo-hydraulic trade-off. This study investigates the effect of Reynolds number on this trade-off for a fixed rectangular microchannel heat sink under steady single-phase water flow. Published numerical and experimental data are analyzed, with a rectangular configuration of aspect ratio AR = 5.180 selected for quantitative evaluation over Re = 200–2000. The thermal-resistance and pressure-drop data are then analyzed using curve fitting and normalization, and normalized thermal-benefit and hydraulic-penalty indicators are introduced to evaluate their combined behavior. The results show that thermal resistance decreases rapidly at relatively low Reynolds numbers but exhibits diminishing improvement as Reynolds number increases, whereas pressure drop continues to rise sharply. A normalized comparison identifies approximately Re = 600–800 as a favorable compromise range for the selected configuration, providing substantial cooling improvement with a relatively limited hydraulic penalty. Although this range is configuration-specific, the proposed normalized framework can be adapted to evaluate Reynolds-number selection in other microchannel thermal-management systems.