Simulation and Parametric Study of Cryogenic Liquid Transfer Line Chill-down Characteristics

Abstract

With the developing of various industries, the demand of cryogenic liquids, such as liquid oxygen, liquid hydrogen, liquid helium and liquefied natural gas, is widely increased. One of the most important applications for cryogenic liquids are used as the propellants for vehicles, ships and even space vehicles. In general, cryogenic systems require single-phase liquid transfer to the destination; however, cryogenic fluids easily evaporate due to the small latent heat. The “hot” transfer line of cryogenic liquids, therefore, must be thermally insulated and be precooled to cryogenic temperatures before transporting the cryogenic liquids to the destination. Generally, a part of transporting liquids are used as the coolant to chill down the transfer line. The physical phenomena are complex during the line chill-down process due to transient two-phase flow heat transfer characteristics, which resultantly make the line chill-down time and the amount of cryogenic fluids consumption are difficult to be predicted by calculation. This paper aims to precisely predict the line chill-down time and identify the sensitivity of some parameters which affect the cryogenic line chill-down time. SINDA/FLUINT, a thermal analysis and simulation tool, was used to simulate the line chill-down process of cryogenic liquids. The simulation results are compared with the previous experimental data. The line chill-down experiments for the 10.5 m long (9 m vertical, 1.5 m horizontal) vacuum insulated stainless steel tube were conducted with liquid nitrogen (LN2). The mass flow rate of LN2 was passively determined by the pressure drop inside the chill-down line. According to the simulation results, the mass flow rate is the primary parameter which significantly affects the line chill-down time.