Variable property effects on flow and thermal non-uniformity of a printed circuit heat exchanger

Printed circuit heat exchangers (PCHEs) are considered as promising candidates in supercritical Brayton cycle owing to their compactness, high-efficiency performance, and resistance to high temperature and pressure. Inevitable pressure gradient along the manifold of PCHEs causes flow maldistribution, which can lead to non-uniform distribution of temperature and thermal stress. Existing studies on flow maldistribution in PCHEs typically conducted using fluids with constant or mildly varying thermophysical properties, neglecting the influence of significant property changes on flow and thermal non-uniformities. Therefore, this study explored the influence of thermophysical properties variations on flow and thermal non-uniformity in PCHEs, focusing on supercritical CO2 near the pseudo-critical region under varying degrees of property changes. Comparison results between flow maldistribution under adiabatic and heated conditions show that variations of thermophysical properties exacerbate flow maldistribution by 4 %–7.2 %, which is primarily caused by the acceleration pressure drop. Variations in thermophysical properties alleviate temperature non-uniformity by 2 %–37 %, and further enhances the overall thermal effectiveness by 3.8 %–25 %. Despite its strong impact on temperature uniformity, flow maldistribution lowers overall thermal effectiveness by only 6.7 %, a consequence of just a 2.1 % deviation in mismatching numbers. Thus, by tailoring the matching between cold and hot sides, it is possible to attain the ideal effectiveness under uniform flow. The positive effects of variable fluid properties can be fully realized by harnessing the benefits of local heat transfer and improving maldistribution matching degree in the PCHEs design.