Multiphase-Thermal Simulation on BOG/BOR Estimation Due to Phase Change in Cryogenic Liquid Storage Tanks

Abstract The purpose of the study is the high-precision, numerical calculation of the Boil-off-Gas (BOG) and Boil-off-Rate (BOR) of cryogenic liquid for the design of containment cargo system (CCS) by using high-fidelity multi-physics CFD simulation of heat transfer of insulation system and phase change of multiphase-thermal flow in the cryogenic liquid tank. The results are compared with those predicted by the conventional low-fidelity methods which are based only on the total heat transfer and does not consider detailed physics related to the phase change of the cryogenic liquid in the storage tank. The unsteady Reynolds-averaged Navier-Stokes (URaNS) equations with the realizable k- e turbulence model and the Rohsenow boiling model for phase change calculation are solved by commercial software of STAR-CCM+. First, for the validation of the phase change model, the cryogenic liquid stored in an independent tank of type C is calculated to study thermal fluid behaviors inside the tank and the corresponding values of BOG and BOR are compared with the experiments as well as the results from numerical simulations by other researchers. The estimated BOR value showed an excellent agreement with discrepancy less than 1%, resolving precisely the thermal convection caused by the vaporization of the cryogenic liquid. Subsequently, the multiphase-thermal flow in a membrane-type LNG (liquefied natural gas) storage tank was calculated for the BOR estimation, coupled with thermal conduction through the insulation system. It is concluded from those simulations that the high-fidelity CFD calculation with the phase change model was able to precisely predict the vaporization of the cryogenic liquid and to calculate the correct BOR values based on the actual BOG amount.