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Flow behavior and entropy production in microcapillary-based joule–thomson refrigeration under various inlet-to-outlet pressure ratios.

Author(s) : ZHANG X., YANG L., GONG H., BAO W., WANG B., ZHENG C., SHAO C., CUI Z.

Type of article: IJR article

Summary

The throttling flow characteristics in microchannels are crucial for cryogenic applications, yet the flow dynamics induced by abrupt cross-sectional changes at the microcapillary entrance and exit remain underexplored. In this study, the Joule–Thomson (J–T) throttling process in microcapillary tubes is investigated using computational fluid dynamics (CFD) simulations, with a particular focus on flow behavior and entropy production under varying inlet-to-outlet pressure ratios. The results demonstrate that the axial distributions of pressure, temperature,
density, and Mach number exhibit nonlinear behavior within the capillary, with the sharpest gradients occurring near the exit. The “vena contracta” at the tube entrance and the free jet at the exit are identified as the primary contributors to pressure drops, especially under choked flow conditions where shock waves form. The entropy production rate (EPR), which serves as a metric of energy loss, is used to quantify the energy conversion process. Substantial entropy production is observed at the “vena contracta”, within the mixing layer, and across the downstream shock structures. Viscous dissipation is found to be the dominant source of entropy production, accounting for over 92% of the total, while thermal diffusion has a negligible effect. These findings provide fundamental insights into energy conversion mechanisms in microscale throttling and offer practical guidance for improving the efficiency of J–T refrigeration systems.

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Pages: 12 p.

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Details

  • Original title: Flow behavior and entropy production in microcapillary-based joule–thomson refrigeration under various inlet-to-outlet pressure ratios.
  • Record ID : 30034776
  • Languages: English
  • Subject: Technology
  • Source: International Journal of Refrigeration - Revue Internationale du Froid - vol. 185
  • Publication date: 2026/05
  • DOI: http://dx.doi.org/10.1016/j.ijrefrig.2026.02.008

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