Abstract
A modelling approach is presented that couples a detailed model of the heat flow through the insulation and walls of a cryogenic storage tank to a description of the fluid that accounts isobaric boil-off and for thermal stratification of the gas phase. We apply this approach to simulate the boil-off of both liquefied nitrogen (LN2) and liquefied hydrogen (LH2) at different fill ratios in an example case. The simulation results show that experimentally measured boil-off rates are captured well by the model. Thermal stratification in the gas phase resulted in heat flow from the gas side of the tank to the liquid side through the inner tank wall. This heat flow was most important for the LN2 case, but was also of some significance for the LH2 case, and lumped-phase tank models may therefore benefit from accounting for it. An equation for this heat flow was fitted and found to describe the variation with fill level accurately.