Comparative analysis of microchannel heat sinks for different values of the Prandtl and Reynolds numbers

Purpose
This study aims to perform a comprehensive comparative analysis of the performance of microchannel heat sinks (MCHS) across a wide range of operating conditions. It investigates the interplay between heat transfer efficiency, frictional effects and flow dynamics in different channel configurations and fluid types.

Design/methodology/approach
The analysis is conducted through numerical simulations, solving the governing equations for mass, momentum and energy conservation. Multiple channel geometries are evaluated, each incorporating specific strategies to disrupt the thermal boundary layer along the heated channel surface. The study also considers the influence of transverse vorticity effects arising from abrupt or smooth geometric variations. The performance is assessed for three distinct fluids – mercury, helium and water – to examine the complex interplay between fluid properties (e.g. viscosity and thermal diffusivity), momentum losses and heat transfer gains. Key parameters, including the Reynolds number and Prandtl number, are systematically varied to uncover their impact on heat transfer coefficients, vorticity distribution and flow stability.

Findings
The study reveals that microchannels with wavy geometries and double internal bifurcations consistently deliver superior thermal performance compared to other configurations, regardless of the working fluid. The results highlight that variations in the Prandtl number significantly influence the dimensional convective heat transfer coefficient, vorticity patterns and the onset of fluid-dynamic instabilities for a fixed Reynolds number and geometry. The authors introduce a correlation for the Nusselt number with the exponents for the Reynolds and Prandtl numbers being ½ and ¼, respectively; the authors also show that, in agreement with existing literature, the friction factor is primarily affected by the Reynolds number and channel shape, demonstrating no dependence on the Prandtl number.

Originality/value
This research provides novel insights into the non-linear scaling of heat transfer and momentum loss with fluid properties in MCHS. The systematic exploration of fluid and geometric interactions enriches the current understanding of microchannel heat transfer mechanisms, presenting actionable recommendations for real-world applications.