Use of liquid nitrogen in CA storage: Theoretical analysis and experimental validation

Liquid nitrogen (LN2) is a colorless, odorless, low boiling cryogenic liquid. Due to its inertness and high expansion ratio (646 between liquid and gaseous N2 at 0 °C), it is an excellent material for rapid purging of the initial O2 gas from the space of the controlled atmosphere (CA) storage. The present study establishes a relationship for predicting the amount of LN2 required for reducing O2 concentration in the CA storage. Simulations were carried out for predicting the amount of LN2 required for flushing at different conditions such as purity level of LN2, O2 set point of the CA storage and flow rate of LN2. The simulation results were validated using the laboratory scale CA storage system having a storage capacity that could hold 10 kg of apples. It was found that higher the purity level lower was the consumption of LN2. At O2 set point of 3%, the consumption of LN2 was found to increase from 0.12 to 0.21 kg when the purity level decreased from 100% to 97.5%. Higher level of O2 set point was found to consume less amount of LN2 at a given purity level. Flushing of LN2 at flow rate of 1.51 × 10−6 m3/s reduced O2 concentration more efficiently and also avoided the freezing temperature inside the CA storage.