Heat transfer in microchannels: substrate effects and cooling efficiency for rectangular and circular ducts

Recent advances in electronics lead to smaller sizes and higher heat generation rates. Heat removal at a very tight thermal envelope is only possible with liquid cooling technologies such as the microchannel heat sink cooling. While a large number of studies have focused on experimental analysis, there is a limited number of computational data to understand the interaction between flow, material properties and geometric variables. Therefore, a computational study is performed to examine the hydraulic and thermal characteristics of microchannel heat sinks operating in laminar flow regime. Square and circular cross-sectional shapes are studied where the hydraulic diameter varies from 60 to 240 microns for water as the working fluid. The relationships and strengths for both conductive and convective thermal resistances, wall heat transfer coefficient and the maximum source temperature are presented through Pareto charts. It is found that the convection thermal resistance values comparably higher than the conduction resistance values due to high conductivity of the heat sink materials. Copper and Aluminum heat sinks demonstrate comparable performance as convective thermal resistance dominates over conduction thermal resistance. Finally, it is shown that the wall heat transfer coefficient values are more dependent on the geometrical features than the flow rate values. However, the maximum source temperature values show dependency on the geometry and flow rates as well as the thermal conductivity of the substrate.