Analysis of thermodynamic processes involving hydrogen

There is a need to explore potential hazard scenarios associated with several specific thermodynamic processes involving the storage and use of hydrogen subjected to thermal exposures. A potential real-life scenario is the heating of a hydrogen storage vessel abroad a hydrogen-powered vehicle in an automobile fire or in an accident at a refueling station. The effect of thermal exposures on these thermodynamic processes has been examined using the National Institute of Standards and Technology (NIST) REFPROP, Reference Fluid Thermodynamic and Transport Properties, database. The thermodynamic processes considered are isochoric (constant density) heating, isenthalpic expansion, and isentropic expansion. In addition, isochoric heating followed by either an isenthalpic or isentropic expansion process is also discussed. The initial fill density of a hydrogen system has a significant effect on the subsequent thermodynamic processes. From a standpoint of fire safety, a hydrogen system subjected to thermal exposure or preheating before an isenthalpic expansion would potentially increase the risk of fire, especially when the exposure temperature is very close to the hydrogen autoignition temperature.