Optimization of Rectangular Microchannel Heat Sinks for Non‐Uniform Heat Flux Removal

High heat flux dissipation in compact electronics requires optimized thermal management solutions. This study applies the constructal method to optimize the geometric configuration of rectangular microchannel heat sinks subjected to a non‐uniform (step‐function) heat flux. Analytical relations, derived via the intersection of asymptotes method, determined optimal internal dimensions under fixed length and volume constraints. Three‐dimensional numerical simulations validated these predictions, identifying geometries that maximize the dimensionless global conductance. Results reveal that non‐uniform heat flux significantly shifts the optimal aspect ratio. Specifically, as the base heat flux was varied from 100 to 91 W/cm², the optimal external aspect ratio ( H / G ) opt , decreased while the maximum temperature rose. Comparative analysis demonstrates that parallel flow configurations achieve lower maximum temperatures and superior thermal uniformity compared to series arrangements, which exhibit a steeper decline in mass flow and higher peak temperatures due to cumulative heating. These findings establish that accounting for spatial variations in heat flux is essential for accurate micro‐scale heat sink optimization.