Numerical Investigation of Multiphase Helium Flow and Entropy Generation in a Joule-Thomson Valve

Abstract

Background: Joule–Thomson (JT) cryocoolers are widely employed in compact and spaceborne cryogenic systems due to their structural simplicity, high reliability, and the absence of moving parts in the cold region. In such systems, the throttle valve is a key component that produces a large pressure drop and induces partial liquefaction of helium, leading to inherently multiphase flow during expansion. A detailed understanding of the associated flow structure and thermodynamic irreversibilities is crucial for enhancing cooling performance and improving overall system efficiency. Methods: In this work, a comprehensive numerical investigation of multiphase helium flow through a micro–JT throttle valve is conducted. A compressible multiphase mixture model coupled with real-gas thermophysical properties is employed to simulate the expansion and phase change process under cryogenic conditions. Moreover, a conventional flow-field analysis and a second law-based entropy generation framework are implemented to quantify irreversible losses due to both viscous dissipation and thermal conduction. Further, the effects of orifice length on the flow structure, phase distribution, and entropy production are systematically examined. Findings: The results reveal that rapid expansion through the micro-orifice leads to strong flow acceleration and the formation of a distinct liquid–vapor mixture region immediately downstream of the throttling section. The size and strength of the two-phase region are observed to vary significantly with the orifice length. Longer orifices promote stronger viscous dissipation and enhanced entropy generation within the restriction, whereas shorter orifices shift the dominant irreversibility to the downstream expansion region. However, the quantitative comparisons show that an optimal orifice length exists at which the total entropy generation is minimized while maintaining the desired pressure drop and cooling effect. Therefore, the present study provides detailed physical insight into the complex multiphase throttling process of helium, offering useful guidelines for the optimal design of miniature JT valves for high-performance cryogenic cooling applications.