Non-adiabatic Under-expanded Jet Theory for Blowdown and Fire Resistance Rating of Hydrogen Tank

The European Regulations on type-approval of hydrogen vehicles require thermally-activated pressure relief device (TPRD) to be installed on hydrogen onboard storage tanks to release its content in a fire event to prevent its catastrophic rupture. The aim of this study is to develop a model for design of an inherently safer system TPRD-storage tank. Parameters of tank materials and hydrogen, external heat flux from the fire to the tank wall, TPRD diameter, time to initiate TPRD are input parameters of the model. The energy conservation equation and real gas equation of state are employed to describe the dynamic behaviour of the system. The under-expanded jet theory developed previously for adiabatic release from a storage tank is applied here to non-adiabatic blowdown of a tank in a fire. Unsteady heat transfer equation is used to calculate heat conduction through the tank wall. It includes the decomposition of the wall material due to high heat flux. The convective heat transfer between tank wall and hydrogen is modelled through the dimensionless Nusselt number correlations. The model is validated against two types of experiments, i.e. realistic (non-adiabatic) blowdown of high-pressure storage tank and failure of a tank without TPRD in a fire. The model is confirmed to be time efficient for computations and accurately predicts the dynamic pressure and temperature of the gas inside the tank, temperature profile within the tank wall, time to tank rupture in a fire and the blowdown time.