CHARACTERISTICS OF TWO-PHASE FLOW DURING CHILLDOWN PROCESS IN A CRYOGENIC TRANSFER LINE
A numerical investigation on the chilldown process in cryogenic transfer line has been made. Attempt has been made to study and capture the time variation of different hydrodynamic properties like velocity, pressure and two-phase flow-structure at different cross-sectional planes situated at different axial location of the transfer line. The variations of temperature with time have also been investigated at those cross-sectional plane. Unlike the previous works, the present investigation exclusively focuses on the transient dynamics of chilldown process where the transfer line has been considered nearly at the saturation temperature. Transient numerical simulation has been made using Finite Volume-based Volume of Fluid (VOF) Method. k–ω model has been used to capture the turbulence. Initially, the transfer line has been considered as completely filled with saturated liquid cryogen. The mass interaction between the liquid and vapor phases (through evaporation-condensation) has been captured by using Lee model coupled with VOF. Here, the working fluid has been chosen as liquid nitrogen, and it has been entered as saturated liquid into the transfer line. The simulations have been carried out for two different Reynolds number (Re = 5000 and 1500) with a common wall heat flux of 500 W/m2. The time variation of temperature and different hydrodynamic properties (pressure, velocity, volume fraction of secondary phase, etc.) for both the cases have been plotted at different cross-sectional planes along the length of the transfer line. Contours of these properties at those planes have also been extracted at different instants of time. Comparison between the said transient dynamics of the two cases have also been made.