Numerical and thermal resistance analysis on the cryogenic porous medium heat exchanger with liquid channel

The porous medium heat exchanger has been increasingly utilized in cryogenic applications, especially in the milli-Kelvin region. This study focuses on the porous medium heat exchanger with liquid channel commonly used in the dilution refrigerator and proposes a numerical model, which applies the local thermal non-equilibrium (LTNE) model coupled with N-S equations and Brinkman-Forchheimer model. Comparing with literature results validates the numerical model. By analyzing the heat transfer characteristics of the heat exchanger, a thermal resistance network model is developed to capture the heat transfer mechanism. The results show that the total thermal resistance mainly depends on the fluid conductive thermal resistance and Kapitza thermal resistance inside the porous medium. The fluid conductive thermal resistance dominates at higher temperature while the Kapitza thermal resistance dominates at lower temperature. The expression of critical temperature is derived to determine the priority of reducing thermal resistance. At cryogenic temperatures, the porous medium serves to bypass the significant Kapitza thermal resistance by introducing much lower thermal resistances, while at normal temperatures, the porous medium reduces the overall thermal resistance by incorporating a parallel thermal resistance but without magnitude difference.