Modeling on cryogenic heat exchangers considering variable properties, axial heat conduction and viscous heating

Abstract

Cryogenic heat exchangers are key components of low temperature refrigerators and determine the ultimate refrigeration performance. Accurate modeling on the cryogenic heat exchangers in sub-Kelvin regime has important theoretical and applied values, yet is still short of study. This study proposes local thermal nonequilibrium models of the heat exchangers in sub-Kelvin regime, including continuous and discrete ones. The effects of the variable properties, axial heat conduction, and viscous heating were investigated. The finite volume method was employed to solve the models numerically; in addition, the temperature and pressure distributions were obtained and analyzed. The proposed models were validated using a comparison of the obtained simulation results with experimental results in the literature. The analysis of the obtained results revealed that: (1) for continuous heat exchangers, the variable Kapitza thermal conductance leads to a large temperature gradient at the entrance. The outlet temperature was negligibly affected by applying different inlet temperature. (2) The axial heat conduction significantly degrades the performance of discrete heat exchangers. The performance was found to be limited by the axial heat conduction when the axial heat conduction parameter was larger than 0.02. (3) For the sintered heat exchanger, both the dimensionless temperature and pressure drop are obviously affected by the geometric impedance when it is greater than 4 × 1014 m−4. Consequently, the proposed mathematical models are useful for the accurate prediction and optimization of cryogenic heat exchangers.