Circulating Composition Shift Characteristic Of A Mixed-gases Joule-Thomson Refrigerator Driven By An Oil-free Compressor

In the last few decades, great progress has been achieved for mixed-gases Joule-Thomson refrigerators, which is widely used not only in the cryogenic field but in the refrigeration engineering. But the problem still exist, that is circulating composition shift of multi-component mixtures because of the phase holdup caused by the velocity differences in the two-phase flow in the multic-omponent mixed-gases refrigeratorsThe circulating composition shift is one of the most important reasons for the discrepancy between the real thermodynamic performance and the designed performance. The phase holdup caused by the velocity difference in the two-phase flow is one of the key factor which induce the composition shift of multi-component mixtures. Therefore, the composition shift characteristic caused by the phase holdup has been investigated in this paper.At first, a model for calculating the composition shift was proposed. The Beggs-Brill-Moody correlation modified by Palmer was employed to calculate the phase holdup. With this model, influences of the pipe angle and fluid temperature on the composition shift were discussed. Results of calculation show the concentration variation of different compositions changes with the temperature, and fits well to the result of measurement.An experimental system driven by an oil-free compressor was developed to investigate the dynamic characteristics of the mixture composition variations in the closed throttling refrigeration cycle. The composition shift characteristic has been systematically studied. Experimental results show the variation of mixture composition and distribution characteristics at different quantity of mixture charged in the cryocooler system. The mixture composition variations at different temperatures were also measured. The mixture composition shift features were finally obtained. The results obtained in this study will be helpful for further study of the dynamic characteristics and optimal design for multi-component mixed-refrigerant Joule-Thomson cryocoolers.