Abstract
Objective To evaluate a weight-based system to monitor changes in liquid nitrogen (LN2) evaporation rate over time as a method to continuously monitor the overall health of cryogenic dewars. Design Prospective experimental study performed within an academic institution. Materials and Methods Two cryogenic dewars were used in this study - a new ( 20 yrs.) MVE – XC 47/11 (Dewar B). Dewars were placed atop CPWplus 75M (Adam Equipment®) scales and weight was continuously recorded under both Control and Experimental conditions using an interface in conjunction with a Network Telemetry Monitoring System (Networked Robotics). Under Control conditions (baseline), dewars were filled with LN2 and, except for measuring the LN2 level 3x/week, the dewars were otherwise left undisturbed during the monitoring period. Experimental conditions were identical to the Control, except the dewar's foam core access plug was removed and left off during the monitoring period. One run was performed for each dewar under each condition. Results Under both Control (baseline) and Experimental conditions the change in weight of both dewars exhibited a linear relationship with time (R2 ≥ 0.99), while the temperature within the dewars remained relatively constant throughout the monitoring period. Linear regression analysis of the Control condition data revealed an LN2 evaporation rate of 0.340 liters LN2/day and 0.414 liters LN2/day for Dewar A and Dewar B, respectively. Similarly, linear regression analysis of the Experimental condition data revealed an LN2 evaporation rate of 0.954 liters LN2/day and 1.38 liters LN2/day for Dewar A and Dewar B, respectively. Differences between the Control and Experiment LN2 evaporation rates for both dewars could be detected within a few hours. Conclusions This study suggests that a weight-based monitoring system could be used to detect relatively small changes in LN2 evaporation rates under these experimental conditions. The ability to continuously monitor the health of cryogenic dewars via evaporation rate may provide an early detection system for impending cryogenic dewar failure and therefore potentially prevent a catastrophic event. Additionally, the use of a continuously monitored weight-based system could reduce the time, energy, and financial resources involved when manually measuring LN2 levels 3x/week. Disclosures Nothing to disclose. Funding REI Division/ UW-Madison School of Medicine and Public Health/ Department of Obstetrics and Gynecology.
Published Version
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