Modeling and Experimental Analysis of Two-Phase Recuperation Heat Transfer in Systems Using Mixed-Refrigerant

Efficient heat recuperation is one of the most critical factors influencing the performance of mixed-refrigerant Joule–Thomson (MR JT) cryocoolers. This becomes even more significant in precooled systems, which enhance overall performance but simultaneously intensify the challenges associated with recuperation effectiveness. Modeling the recuperation process is inherently complex because it involves gaseous, liquid, and two-phase flow regimes. Furthermore, the use of mixed refrigerants introduces additional complexity in predicting thermo-hydraulic properties. Experimental validation of modeling results is also highly demanding, particularly with respect to determining the mixed-refrigerant composition, which may differ substantially from the initially charged proportions during operation. This paper presents a comprehensive modeling approach for the complete two-phase recuperative heat transfer process. In total, 96 combinations of heat transfer correlations were evaluated. The modeling results were compared with experimental data obtained using a novel, validated, noninvasive, continuous method for determining refrigerant composition. Such an approach, including analysis of the impact of MR composition uncertainty on the results, has not been performed in previous, similar studies. The optimal set of correlations was identified, yielding a mean average error of 20.16K without composition correction (when applying a composition correction of 13.67K). The validated modeling approach provides valuable insight into heat transfer phenomena occurring in the recuperation section of MR JT cryocoolers and other mixed-refrigerant-based systems.