CFD modelling of the isobaric evaporation of cryogenic liquids in storage tanks

Abstract

A new CFD model relevant to isobaric cryogen evaporation and weathering in storage tanks has been developed. It treats the heat influx from the surroundings into the vapour and liquid phases separately and allows for heat transfer between the two phases. The model accurately predicts the dynamics of the vapour flow and the vapour to liquid heat transfer. It provides well-resolved velocity and temperature profiles in the vapour phase, as well as evaporation and boil-off gas rates. It demonstrates that the main flow pattern is that the vapour circulates upwards close to the tank wall, then radially along the roof towards the tank axis, where the flow is partitioned; between a fluid that leaves the tank, and a fluid that recirculates back towards the vapour bulk. The results of simulations, carried out in different sized tanks with different initial amounts of cryogen, were compared with the results of the Huerta and Vesovic non-equilibrium model. The results indicate that, for the purposes of modelling heat transfer between the phases, steady-state vapour temperature and boil-off gas rate, the complex flow established in the vapour phase can be adequately modelled by the effective advective, upward flow from the interface.