Effects of aspect ratio, convection, and viscous dissipation on heat transfer in a moon-shaped microchannel

Microchannels offer enhanced heat transfer and are preferred in compact thermal management systems. The principal novelty of this work lies in the first numerical investigation of viscous dissipation and convective heat transfer in moon-shaped microchannels over a range of aspect ratios, Reynolds and Brinkman numbers (0.001 ≤ Br ≤ 0.1), compared with an equivalent circular channel. Results show that large aspect ratios generate sharp local velocity gradients in confined corners, causing localized heat generation that impairs performance. Higher Reynolds numbers (25 ≤ Re ≤ 125) enhance convective transport while extending the thermal entrance region, mitigating this degradation. Decreasing Br by increasing the imposed wall heat flux reduces the relative contribution of viscous dissipation, resulting in a higher Nusselt number. Conversely, decreasing Br via lower velocity reduces Nu due to weaker advection and a shorter thermal entrance region. Finally, performance evaluation criteria indicate that moon-shaped profiles outperform circular profiles for shorter microchannel lengths.