Evaluation of an existing helium liquefier in refrigerator and mixed-mode operation through exergy analysis

Abstract

Present day, all small scale helium liquefiers operate in Claude cycle with two turbines in series arrangement. In this paper, an effort has been made to investigate the exergy characteristics of a small scale liquefier and its components at design and various off-design refrigeration and mixed mode operation under steady state condition. The variation of exergy efficiency, exergy destruction, exergy output-destruction interrelations, refrigeration- liquefaction capacity correlation, etc. have been evaluated by increasing refrigeration load in steps starting at pure liquefaction till pure refrigeration mode in the experiment. As the experimental data were not sufficient for complete analysis, Aspen Hysys software has been used to determine the remaining process parameters required to understand the thermodynamic cycle. The significance of the variation of exergy parameters at different modes of operation have been reported to establish the importance of the present study. Though the results are specific for the existing helium liquefier (model HELIAL 50 of Air Liquide DTA, France) with some associated constraints, the results may be useful to the designers of helium systems where flexibility of operation is a desirable feature.