Influence of unsuitable operational conditions on the transient performance of a small hydrogen liquefier

Joule-Thomson cooling systems are used in refrigeration processes such as cryogenic gas liquefaction. Although extensive studies have been carried out by researchers, most of them include cryogenic heat exchangers and their associated fields. In the current study, an attempt was made to indicate the effect of using inappropriate operational conditions in a cryogenic Joule-Thomson cooling system including recuperative heat exchanger, expansion valve and collector. Mass flow rate and operational pressure were selected as design parameters while cool-down time and final temperature of high-pressure gas at heat exchanger outlet were considered as responses. The results showed that using mass flow rate smaller than the design value led to considerable decrease in performance. Operational pressure had lesser effect on cool-down time. Increasing the pressure had no significant effect on the gas temperature at expansion valve inlet for high mass flow rates. Using unsuitable values for mass flow rate and operational pressure might lead to fail liquefaction despite using heat exchanger with high effectiveness.