Unconfined Hydrogen Detonations: Experiments, Modelling, Scaling

A series of unconfined hydrogen detonation bench-mark experiments are analyzed with respect to CFD code validation and safety measures development. 1-Dimensional in-house code COM1D was applied for validation against experimental data for unconfined detonation of a hemispherical envelope of about 3- and 5-m radius with hydrogen-air mixtures from 20 to 30% hydrogen in air. The code demonstrates a very good agreement with experimental data and allows an adequate simulation of the unconfined hydrogen detonation. All calculated data were scaled in Sachs coordinates to compare with experimental data and to approximate the data for practical evaluation of safety distances. Numerical experiments with different hydrogen inventories from 50 g to 50 kg and different sizes of the cloud from 1 to 2 m radius of the same amount of hydrogen 50g were carried out to clarify the problem of energy of gaseous explosion responsible for the strength of blast wave. Additionally, a comparison of hydrogen-air explosion pressure with blast wave properties from the hypothetical cloud of hot compressed combustion products (P=Picc; T=Ticc) and simply a hot air of the same initial pressure and temperature as combustion products showed very good agreement of shock wave strength at far distances, beyond the cloud. This confirms the governing role of energy of combustion on blast wave propagation and its ability to scale the strength of blast waves. The dynamics of the explosion process and combustion product expansion were also analyzed experimentally and numerically to evaluate the dimension of the heat radiation zone and heat flux from combustion products. To demonstrate the capability of tested COM1D code, the modeling and analysis of high-pressure hydrogen tanks rupture at 350 and 700 bar were conducted to investigate blast wave strength and evaluate the safety distances.