Evaluation of LN2 Dewar Health Using a Weight-based Monitoring System
Cryogenic dewars are insulated, vacuum-sealed pressure vessels widely used for storing biological specimens including human reproductive cells and embryos. These samples are invaluable and irreplaceable, so it is important that dewars are kept at low temperatures (< -135°C). Liquid nitrogen is the most popular cryogenic fluid used to keep dewars cold; however, sample-handling, imperfect vacuum seals, and liquid dewar venting are all factors that lead to liquid nitrogen depletion. It is important that cryogenic dewars are refilled periodically to replenish liquid nitrogen levels to prevent dewar failure. Failure occurs when temperature gets too high and is a consequence of poor monitoring and management. There is no industry standard for liquid nitrogen alarms of monitors. Temperature probes are widely used but fail to send alarms until after liquid nitrogen levels are nearly depleted. Liquid level monitoring systems also exist but are primarily used for threshold monitoring. There is an unmet need in the cryogenic storage market for a system that warns of failures in advance rather than simply reporting when they occur or when dewars should be refilled. This article evaluates a weight-based system to monitor changes in liquid nitrogen evaporation rates over time as a method to continuously monitor the overall health of cryogenic dewars. The ability to continuously monitor the health of cryogenic dewars via evaporation rates may provide an early detection system for impending cryogenic dewar failure and therefore potentially prevent a catastrophic event.