Accidental release from a hydrogen car tank in a confined space like a tunnel poses safety concerns. This Computational Fluid Dynamics (CFD) study focuses on the first seconds of such a release, which are the most critical. Hydrogen leaks through a Thermal Pressure Relief Device (TPRD), forms a high-speed jet that impinges on the street, spreads horizontally, recirculates under the chassis and fills the area below it in about one second. The “fresh-air entrainment effect” at the back of the car changes the concentrations under the chassis and results in the creation of two “tongues” of hydrogen at the rear corners of the car. Two other tongues are formed near the front sides of the vehicle. In general, after a few seconds, hydrogen starts moving upwards around the car mainly in the form of buoyant blister-like structures. The average hydrogen volume concentrations below the car have a maximum of 71%, which occurs at 2 s. The largest “equivalent stoichiometric flammable gas cloud size Q9” is 20.2 m³ at 2.7 s. Smaller TPRDs result in smaller hydrogen flow rates and smaller buoyant structures that are closer to the car. The investigation of the hydrogen dispersion during the initial stages of the leak and the identification of the physical phenomena that occur can be useful for the design of experiments, for the determination of the TPRD characteristics, for potential safety measures and for understanding the further distribution of the hydrogen cloud in the tunnel.

The DISCHA engineering tool has been extended to perform liquid hydrogen (LH2) tank-to-tank transfer operations. The tool uses Helmholtz free energy-based equations of state for hydrogen’s physical properties. The tanks can be modelled either with single-zone or multizone models, including heat transfer through the tank walls. The flow through the transfer lines is modelled using a method that accounts for phase change, friction, area change and heat transfer through the pipe walls. The maximum (choked) flow is calculated using the Possible Impossible Flow algorithm. Pumps can also be added to the transfer line. The present work presents the DISCHA tool’s recent validation as well as an investigation of the parameters that affect the tank-to-tank transfer most.