Numerical study of the boil-off rate in a storage tank for liquid hydrogen

A widespread rollout of alternative fuels is desirable to mitigate the issue of global warming. Hydrogen is widely considered one of the most promising solutions to reduce the environmental impact of the transport sector. This thesis work, performed in collaboration with the Norwegian University of Science and Technology NTNU, is based on the numerical study of the boil-off rate (BOR) of liquid hydrogen. The BOF represents the amount of liquid hydrogen that evaporates and that must be vented, through a pressure relief valve, in order to avoid the overpressurization of the tank. The case study considered is a cryogenic tank with a maximum capacity of 900 kg used as storage system in a liquid hydrogen refueling station. Two different insulation systems were considered: the high-vacuum multilayer (MLI) and the polyurethane foam insulation. The numerical computation was performed with OpenFoam , a computational fluid dynamics (CFD) open-source software. In order to accurately simulate the evaporation process that takes place inside the tank the Lee evaporation model and the kinetic gas evaporation model were used and critically compared. The results obtained show a great difference in terms of BOR between these two insulation systems. A layer of 15 mm of MLI makes it possible to obtain a BOR value an order of magnitude lower than that obtained with 1 meter of polyurethane foam.