Efficient hybrid microjet liquid cooled heat sinks made of photopolymer resin: thermo-fluid characteristics and entropy generation analysis

In this contribution, an investigation on the performance of a hybrid design of active liquid cooled heat sinks is presented. A numerical analysis was performed via 3-D CFD simulations of a set of hybrid microjet heat sinks formed by a pair of fractal channel manifolds, used as liquid inlet and outlet conduits (manufactured in stereolithographic resin), an array of impinging microjets for uniform cooling, and a metallic heat spreader attached to a heat source. The pressure losses generated by the small channels in the manifolds were targeted for minimization using various structural modifications, while the metallic heat spreader in contact with the heat source was optimized for improving the cooling capabilities of the heat sink. A parametric analysis was conducted to determine the improvements in the overall performance; additionally, a local entropy generation analysis was conducted to obtain a heat sink design with the lowest intrinsic irreversibility. The entropy generation rates were obtained by coupling a local entropy generation model with the governing equations in the CFD simulations. The results obtained from the entropy generation analysis indicated that the major irreversibility source is the heat transfer in the metallic heat spreader. The addition of area-enhancement features, such as microchannels and pin fins to the original heat spreader led to increasing the cooling capabilities of the hybrid heat sinks. The implementation of the entropy generation analysis allowed to identify the local sources of irreversibility and the impact of the hydrodynamic and thermal deficiencies in the operation of the heat sink. Lastly, an overall performance indicator (PPTR) enabled a proper assessment of the thermo-fluid response of the heat sinks and the results drawn from this parameter matched the fundamental observations obtained from the entropy generation analysis.