Leveraging the entropy generation minimization and designed porous media for the optimization of heat sinks employed in low-grade waste heat harvesting

Abstract

• A porous media model and optimization procedure to design heat sinks is presented • Different geometries of the heat sinks are treated within the same framework • Which geometry should be employed depends on operational conditions and size • Entropy generation is a reliable metric for low-grade waste heat recovery systems A comprehensive optimization procedure for the design of heat sinks used to harvest low-grade waste heat for secondary processes is proposed. A designed porous medium approach is used, providing modelling versatility and allowing for the treatment of several internal geometries within the same framework. Two applications, taken from the cooling of high concentration photovoltaic cells and membrane distillation, are used to illustrate the proposed procedure. Three internal heat sink geometries, namely plate fins, pin fins, and metal foams, are analyzed, and the selection as to which one is the more advantageous is shown to be dependent on size and operational conditions. Possible pitfalls of a traditional design procedure are pointed out, for heat transfer capability, under high heat load condition, should be emphasized over fluid friction avoidance. The entropy generation rate is then shown to be a reliable metric when designing for low-grade waste heat recovery, automatically focusing on either viscous dissipation or thermal resistance minimization without introducing any artificial figure of merit for that purpose.