Cryogenic and Ambient Gaseous Hydrogen Blowdown with Discharge Line Effects

The present work performed within the PRESLHY EC-project, presents a simplified 1-d transient modelling methodology to account for discharge line effects during blowdown. The current formulation includes friction, extra resistance, area change, and heat transfer through the discharge line walls, and is able to calculate the mass flow rate and distribution of all physical variables along the discharge line. Choked flow at any time during the transient is calculated using the Possible Impossible Flow (PIF) algorithm. Hydrogen single phase physical properties and vapour-liquid equilibrium are calculated using the Helmholtz Free Energy (HFE) formulation. Homogeneous Equilibrium Mixture (HEM) model is used for two-phase physical properties. Validation is performed against the new experiments with compressed gaseous hydrogen performed at the DISCHA facility in the framework of PRESLHY (200 bar, ambient and cryogenic initial tank temperature 77 K and 4 nozzle diameters 0.5, 1, 2 and 4 mm) and an older experiment at 900 bar, ambient temperature and 2 mm nozzle. Predictions are compared against measured data from the experiments and the relative importance of line heat transfer compared to flow resistance is analysed.