SINOPSIS

This paper presents a numerical study of the effect of the substrate material and liquid cooling medium on the heat transfer characteristics for three-dimensional conjugate heat transfer problem of laminar flow through a circular minichannel. A uniform heat flux of 100 kW/m² is applied at the bottom-side of the substrate while the topside surface is considered adiabatic. Three different materials of the substrate have been adopted: copper (k_s = 398 W/m·K), silicon (k_s = 189 W/m·K), and stainless steel (k_s = 15.9 W/m·K). Two different coolant liquids have also been proposed − water and mercury. The thermal characteristics of the conjugate heat transfer problem are represented by the local Nusselt (Nu) number, local bottom-side surface temperature of the channel, local heat flux, and local temperature difference between the solid and fluid domains. The effect of inlet coolant velocity is investigated with two different inlet velocities of 0.1 m/s and 0.05 m/s. The study shows that the thermal characteristics of the minichannel using water as a coolant medium with the three different substrate materials are in contradiction with those of the minichannel using mercury. The contradiction is generated as a result of the competitive effects of axial fluid conduction, and axial wall conduction as well as the competitive effects of the radial and circumferential heat diffusion in the fluid domain. The theoretical model has been verified by comparing the predicated results with those obtained from the available analytical and experimental data with maximum deviation of 6.7%. The study is considered as the benchmark and helpful guidelines in the design of small-scale circular channels which are used for electronic cooling systems.