Open Cycle Joule-Thomson Cryocooling by Mixed Coolant
Mixed coolants are conventionally employed for the closed cycle Joule-Thomson mode of cryocooling. Here, the potential of mixed coolants is utilized for reducing the pressure of operation. Numerous experimental and theoretical studies of closed cycles have been reported. However, the preferred compositions for closed cycle mixtures at low pressure are not the same as for elevated pressure open cycle use. Elevating the charging pressure is essential for the open cycle mode of cryocooling since it enables one to store more coolant in the vessel and prolong the mission. However, the reported experience with open cycle mixed coolants is quite rare. Traditionally, open cycle J-T cryocoolers employ pure coolants: nitrogen and argon for the 80 K and 90 K range, respectively. The present study is an experimental demonstration of a mixed-coolant open cycle system for the same temperature range, performing at elevated pressures. This mixture combines the advantages of nitrogen and argon: it reaches the lower temperature of nitrogen but still cools down as fast as argon. The examined mixture includes more than 80% of nitrogen (by volume) and hydrocarbons.