Analysis and Comparison of the Fluid Flow Characteristics of Nitrogen‐Hydrocarbon Zeotropic Mixtures in an Adiabatic Expansion Capillary Utilized in a Joule‐Thomson Refrigerator

ABSTRACT This research investigates J‐T refrigerators that employ nitrogen hydrocarbon zeotropic refrigerant mixtures and expansion capillary for producing low temperatures. Capillary tubes are frequently utilized as expansion devices within J‐T refrigerant systems. The refrigerant undergoes a phase transition subsequent to the flashing process within an expansion capillary. This study examines two mixtures capable of producing temperatures both below and above 123 K (at the capillary exit) to evaluate their flow characteristics within an expansion capillary. The simulation employs a homogeneous equilibrium approach. The numerical model developed in this study has been validated with the experimental results documented in existing literature. This study employs capillary tubes featuring diameters of 0.965 and 1.52 mm, with lengths varying from 1 to 2 m. It is estimated that the expected reduction in mass flow rate is between 20% and 30% as the capillary length increases from 1 to 2 m. Increasing the diameter from 0.965 to 1.52 mm is expected to yield a flow rate increase by a factor of 3.25. It is also calculated that the rise in temperature varies from 1 to 5 K as the capillary inlet pressure increases from 15 to 19 bar. It is calculated that gradient boosting regressor (GBR) and random forest (RF) exhibit a significant correlation between the actual and predicted mass flow rate values.