Simulation of the thermal behaviour of hydrogen tanks

Compressed gaseous hydrogen (CGH 2 ) with a nominal working pressure (NWP) of 70 MPa is currently the fuel of choice for weight sensitive fuel cell electric vehicle applications (e.g. light-commercial vehicles and long-haul trucks), where higher cargo capacity compared to battery electric vehicles due to its high gravimetric energy density. The refuelling time of fuel cell vehicles should ideally be within a few minutes, comparable to conventional vehicles using liquid fossil fuels. Due to the rapid and high pressure increase during filling, usually starting from 2 MPa, high temperatures over 80 °C are generated inside the tank owing to enthalpy input and compression heat, while during the emptying low temperatures down to −40 °C can be reached because of the gas expansion enthalpy decrease. The fuelling protocol for light duty gaseous hydrogen vehicles according to the standard SAE J2601 (SAE-J2601, 2014) establishes that a safe filling or emptying up to the design capacity can only be guaranteed if the internal gas and temperature are evenly distributed during the process and does not exceed the design temperature range between − 40 ° C ≤ T g a s ≤ 85 ° C . This paper presents a simulation methodology, which allows to predict the gas temperature rise and fall inside a high-compression hydrogen tank and its heat losses through the multi-layer shell during and after a refuelling or emptying process. It is a zero dimension (0D)-thermodynamic-transient-model developed in MATLAB/Simulink and established to investigate the detailed temperature history of heat transfer from gas through tank wall due to thermal conduction and convection. The thermodynamic model includes two different methodologies obtained from the literature to calculate the convective heat transfer coefficient that occurs between the fluid and the solid domain during the refuelling and emptying process. To assess the accuracy of the thermodynamic model, the results are compared and validated with experimental data obtained from measurements performed by the European -HyTransfer- project (European Commission, 2013) in a 37-litre type IV cylindrical high-pressure hydrogen tank on-board. The temperature profiles of the gas inside tank, at the surface between the plastic liner and carbon fibre composite as well as on the outer surface itself predicted by the simulation model show good accordance against the available experimental data. Result of this work is a fast-calculating simple model allowing to obtain rapid estimations of the averaged temperature of the inner fluid. This can be used to optimize fast filling of compressed hydrogen tanks and to design/develop new filling protocols, e.g. reduce the need for pre-cooling, while guaranteeing safety. • Loading and unloading of compressed gaseous hydrogen tanks. • 0D-thermodynamic-transient model to simulate thermal behaviour. • Modelling convective heat transfer between hydrogen, tank wall and the atmosphere.