Numerical study on thermal and hydraulic performance of supercritical CO2 flowing in a microchannel heat sink with porous substrates

Supercritical carbon dioxide (sCO2) is widely acknowledged for its potential applications in various energy utilization systems, particularly in addressing the critical challenge of heat transfer. This study utilizes numerical simulation to model sCO2 flow within a microchannel heat sink (MCHS) equipped with porous substrates, aiming to evaluate both its thermal and hydraulic performance. The analysis investigates the influence of significant parameters such as shape, inlet temperature, Reynolds number, porous layer thickness, and operating pressure on key variables like pressure drop, Nusselt (Nu) number, thermal resistance, and Figure of Merit (FOM) within the microchannel. Findings reveal a progressive improvement in heat transfer efficiency, as demonstrated by Nu/Nu0, with rising inlet temperature. However, extending the inlet temperature beyond the critical threshold results in diminished Nu numbers across all models. Near the critical point (Tin = 305 K), the FOM reaches 3.59 for M1 (Model1) and 3.61 for M3, highlighting their effectiveness in balancing heat transfer enhancement and energy consumption. At each operating pressure, Nu undergoes a significant rise near the critical point, with the peak Nu notably observed at an operating pressure of 8 MPa, surpassing those at 9 MPa and 10 MPa due to the significantly higher heat capacity of the fluid at 8 MPa. Furthermore, the findings reveal a decreasing trend in FOM as porous thickness increases for the models, suggesting that utilizing porous inserts with smaller thickness values is more efficient when considering both heat transfer enhancement and required pumping power. All examined models successfully reduce thermal resistance, consistently maintaining values below those of non-porous MCHS across all Reynolds numbers. Additionally, increasing Reynolds number enhances heat transfer and reduces thermal resistance for all configurations.