Enhancing heat transfer and pressure drop characteristics in straight minichannel heat exchangers through cross-sectional variations

In order to improve the overall hydrothermal performance of minichannel heat exchangers (MCHEs), variations in the width and height of minichannels are investigated. A range of 3D numerical simulations are systematically conducted by varying the mass flux of water as the working fluid. The obtained results are comprehensively compared with the traditional design of MCHE, and new conclusions are drawn. The results indicate that different configurations of minichannel cause completely different effects on the thermal and hydraulic attributes of MCHE. It is found that by increasing the mass flux from 125 to 1000 kg m−2 s−1, the thermal enhancement index reaches 1.79 for the model that is converged on both sides of the cross section. Although converging the minichannels can ameliorate the thermal performance of MCHE, the hydraulic performance is unsatisfactory. However, when the cross section of minichannels diverges, MCHE exhibits better overall hydrothermal performance. Furthermore, the simultaneous divergence of both the width and height of the cross section leads to even better performance compared to diverging only one side. By comparing all minichannels, it seems that the minichannel model with complete divergence has the best performance in the studied ranges and achieved the maximum heat transfer rate to pumping power ratio of 25.4 × 10–5 at a mass flux of 125 kg m−2 s−1.