Simulation and classification optimization design of ultra-low temperature heat exchangers in dilution refrigerator using local thermal nonequilibrium model.

Dilution refrigeration is widely used in a variety of cutting-edge scientific fields such as quantum computations. The ultra-low temperature heat exchangers play a crucial role for the ultimate performance of dilution refrigerator. To study the classification optimization design of ultra-low temperature heat exchangers, an integrated local thermal nonequilibrium model have used. By considering the ultra-low temperature heat exchangers as an integrated unit consisting of a number of interconnected sub-modules, an optimized design study of the
geometrical parameter configurations of continuous heat exchanger, three-stage step heat exchanger, and connecting tubes has been carried out. Using the optimized configuration for continuous heat exchanger with a length of 19 m, an inner tube diameter of 10 mm, and an outer tube diameter of 15 mm at a molar flow rate of 1.5 mmol/s, the classification optimization of step heat exchanger is carried out. By adjusting the ratio of the sintered volume to the whole sintered volume (g1 = 0.15, g2 = 0.3 and g3 = 0.55) and the ratio of concentrated heat transfer area to the total heat transfer area of this stage (f1 = 0.35, f2 = 0.4 and f3 = 0.45), the heat transfer efficiency of the three-stage step heat exchanger can be further improved without additional resources. And the impact of length and diameter of connecting tubes has also been discussed in this paper. This study provides quantitative guidance for the design of ultra-low temperature heat exchangers, which is important for improving the overall performance of dilution refrigerators.