Modeling comparison and structural optimization of stepped sintered heat exchangers in dilution refrigerator

As a key device for achieving sub-Kelvin temperatures, the performance of dilution refrigerator heat exchangers at low temperatures directly determines the overall cooling efficiency of the system. This work develops a coupled numerical model combining a continuous counterflow heat exchanger (CCHE) with stepped sintered heat exchangers (SSHE), and compares two mainstream stepped exchanger configurations available in the market. The two types are analyzed using the local thermal nonequilibrium (LTN) model and the efficiency-number of heat transfer units method (ε-NTU), respectively. The control equations are discretized using the finite volume method, with comprehensive consideration of Kapitza resistance, axial heat conduction, viscous heating, and pressure drop. The model systematically analyzes the resulting temperature, pressure, and concentration distributions. The study investigates the influence of heat transfer area distribution in three-stage SSHE, compares the contributions of different heat transfer mechanisms, and evaluates the effect of channel factor on exchanger performance. Finally, the differences between the two heat exchanger configurations and the impact of ³He flow rate on thermal efficiency are examined.