This paper details the numerical analysis of combined microchannels with solid and perforated rectangular fins. The goal of the numerical process is to maximise global thermal conductance in the geometric configurations studied. Three scenarios are investigated: a microchannel with solid rectangular fins, a microheat sink with single square perforation on the fins and a combined microchannel with two square perforations. The volume and axial length of the combined microchannel are fixed, while the width varies. An imposed high-density heat flux \({q}^{{\prime\prime}}\) of 250 W/cm2 is applied at the bottom surface of the combined microchannels with fins. Water is used as a coolant to remove the heat deposited at the channel walls and the entire microchannel heat sink. The finite volume method in Ansys Fluent is employed to discretise the computational domain and the thermal and fluid fields solved. The results showed that hydraulic diameter, external aspect ratio and Reynolds number of water \(({\mathrm{Re}}_{{w}})\) have an effect on minimised temperature and global thermal conductance. When the Reynolds number of fluid increases by 20%, the minimised temperature diminishes by 2.6, 2.5 and 2.1%, in the three configurations investigated. The numerical optimisation shows that the combined microchannel with two square perforations on fins is the best. The design technique and innovation employed to reduce the volume, weight, cost of production and solid substrate used in the heat sink manufacturing enhanced the performance and increased heat transfer. The numerical code validation is carried out using analytical results.
