Transient three-dimensional simulations are done for a phase-change material (PCM)-based heat sink subjected to constant heat flux of 1.59 kW/m(2) with commercially available FLUENT software. Numerically obtained temperature-time histories are matched up with experimental results obtained earlier by our group to determine the overall heat transfer coefficient from the geometry that reconciles the differences between simulations and experiments. For a constant power level and fixed volumes of heat sink material (aluminum) and PCM (n-eicosane), simulations were done for 30 different geometric configurations to determine the time to reach complete melting. A feed-forward back-propagation neural network was then used in conjunction with a genetic algorithm to perform an exhaustive search and estimate the dimensions of the heat sink cavity for which the melt time and hence the thermal performance of the heat sink is maximum.