Cool-down characteristics of liquid nitrogen transfer line

Abstract

In a large scale cryogenic liquid transfer system with long lines, the considerable effort should be devoted to minimize the loss of cryogenic liquid. To understand that cool-down characteristics in a transfer system is one of the important considerations. For that purpose, numerical and experimental studies were performed to estimate the cool-down time in a vacuum insulated transfer line for liquid nitrogen. Single and two-phase heat transfer coefficients were estimated by Dittus-Bolter and Kandlikar correlations. The temperature-time history in a transfer line was calculated based on the first law of thermodynamics. Vapor quality was also calculated along the transfer line as time progressed. The calculation results showed good agreements with the experimental data. The glass tube was installed at the middle of the transfer line to observe the flow patterns of liquid nitrogen in a cooldown process. Annular flow pattern was observed mostly at the initial stage of cool-down process and changed to stratified flow pattern after cool-down process.