Numerical analysis of the flow behavior of a Nitrogen-Hydrocarbon mixture through an expansion capillary used in Joule–Thomson refrigerator

Joule–Thomson refrigerators signify a notable progression in refrigeration technology. These refrigerators are designed to reach cryogenic temperatures, specifically those under 123[Formula: see text]K. Capillary tubes play a crucial role as an expansion device in the throttling process of Joule–Thomson refrigerators. This study investigates the flashing behavior of a nitrogen-hydrocarbon refrigerant mixture within a J–T refrigerator, focusing on an expansion capillary of varying lengths and diameters. The simulation employs a homogeneous equilibrium approach. The numerical model developed in this study has been validated with the experimental results available in literature. Simulations were conducted using tubes with lengths ranging from 0.5–2[Formula: see text]m and diameters from 0.508[Formula: see text]mm to 1.52[Formula: see text]mm. The findings of this study indicate that an increase in capillary inlet pressure resulted in a mass flow rate increase of 20–40%, with all other variables held constant. Estimates also indicate a 40% reduction in mass flow rate for each 1–2[Formula: see text]m increase in capillary length. This study’s findings will improve the understanding of flow characteristics of mixed refrigerant in small closed cycle J–T refrigerators.