Efficacy of divergent minichannels on cooling performance of heat sinks with water-based MEPCM suspensions

Abstract

This work aims to investigate the influence of diverging minichannels on the contribution of microencapsulated phase change material (MEPCM) suspensions in heat sinks. The cross-section divergence angle is varied from 0° (parallel) to 1.38° and 2.06° and the behaviors of wall temperature distribution and thermal resistance are evaluated at different flow rates and heat fluxes. Furthermore, in order to clarify the effectiveness of the MEPCM suspensions, the measurements of the coefficient of performance (COP) and the figure of merit (FOM) are conducted and compared in the parallel and divergent MCHSs. It was found that increasing MEPCM particle concentration up to 10% can effectively suppress the wall temperature distributions by up to 20%, thereby reducing the difference between the bulk fluid and wall temperatures leading to the reduction of thermal resistance and the improvement of heat transfer. Diverging cross-section of channels increased the suppression of wall temperature profile by up to 33%. It also led to the enhancement of COP values (more than 2 times), especially at high Reynolds numbers (Re = 1375). It was due to the significant reduction in the required pumping power in the divergent MCHSs in comparison with that in the parallel one. However, the measurements of FOM revealed that the increase of pumping power outweighs the enhancement of heat transfer by adding MEPCMs in most of the experiments (0.7 ≤ FOM ≤ 1.1), especially at lower Reynolds numbers (Re = 238). Therefore, diverging minichannels is only effective to improve the contribution of MEPCM suspensions in heat sinks in a certain range of parameter combinations.