Preparation of subcooled liquid argon and test of its cooling ability

Subcooled liquid nitrogen and nitrogen slush are often considered for high-speed cooling, but their preparation and maintenance are not easy. To address this issue, a unique device was designed to prepare subcooled liquid argon (SLA) using liquid nitrogen (LN). The cooling process was mathematically modeled to predict the preparation time. If the interlayer space between LN and liquid argon is filled with nitrogen gas, liquid argon could be cooled to 3.5 K subcooling within 1 h. If the interlayer is filled with air, 2 h are required to achieve the same subcooled state. An additional 1000 mL of LN was required for the preparation of 600 mL of 3.5 K SLA. The cooling tests of 3 μL microdroplets in 3 mm–6 mm capillary quartz tubes were duplicated to evaluate the potential of SLA. It was found that the cooling rate of microdroplet in the 3.5 K subcooled SLA is very close to that in the 3 K subcooled LN, higher than that in the saturated LN. The convenience of preparation and maintenance of SLA can make it good choice of cryogen for cryopreservation of biomaterials.