Flow regime transformation in cryogenic micro flow heat transfer

The research on cryogenic micro flow heat transfer (MFHT) is critically important in the fields of superconductive technology, space cryocoolers, quantum engineering, and other advanced domains. To elucidate the transformation of flow regimes in cryogenic MFHT, this paper introduces the microscale effect as a novel criterion for distinguishing slip flow from continuum flow, moving beyond the traditional Knudsen number approach. The microscale effects related to velocity slip and temperature jump are analyzed using a Lattice Boltzmann Model (LBM). It is observed that significant microscale effects occur within a channel length range of 0< l <100 μm; specifically, the ratios V slip /V 0 and T jump /T w decrease by approximately 95% within this interval. During cooling process, the gaseous flow enters into continuum regime from slip regime at 35.380< L <229.740 μm and 77<T<500 K. This transformation includes two modes: speed priority and temperature priority and the alternation of the two modes occurs at the points of V 0 =16 m/s, T w =355 K and b=78 μm. The transition node temperatures can establish a maximum temperature range of 64 K for flow regime transformation—this represents a notable distinction from the traditional Knudsen number which relies on a single constant transition temperature. This study aims to enhance understanding of cryogenic micro flow heat transfer while providing valuable insights for optimizing microchannels and improving heat transfer efficiency.