Geometric optimization of porous structures for enhanced heat transfer in a dilution refrigerator mixing chamber

For dilution refrigerator, one of the most crucial parts is the mixing chamber. Currently, little research has been conducted on optimizing the heat exchange structure of the mixing chamber. In this study, a model that couples fluid flow, heat transfer and diffusion is constructed. A general conclusion that applies to a broader range of dilution refrigerator designs is proposed, improving heat exchange capacity by 14% when the load is 30 μW. Firstly, the heat exchanger structure should be as high as feasible when fully immersed in the diluted phase. Secondly, a larger porous medium volume provides better heat exchange. Moreover, the structure greatly influences the mixing chamber's heat exchange capacity. Designing a structure that has a large upper surface, a proportion of the upper part's height exceeding 36% of the total structure height, and a bottom area greater than 4% of the mixing chamber bottom area approaches optimality. The findings of this study are of importance to the advancement of dilution refrigerators.