Impact of Release Temperature on Hydrogen Jet Mixing with Ambient Air

Liquid hydrogen leaks produce large volumes of cryogenic, flammable mixtures, posing major safety risks to personnel and equipment. This work studies the impact of hydrogen release temperature on jet mixing and dispersion in ambient air. Controlled release experiments are conducted with dry air in an open-ended chamber, with the hydrogen storage temperature varying from 35 to 290 K while the release pressure or mass flow rate is kept constant. The hydrogen mass fraction and mixture temperature are measured using a sampling probe at 20–255 mm axially and 0–50 mm radially from the release nozzle. For release temperatures between 35 and 129 K, the centreline decay of the hydrogen mass fraction and the mixture enthalpy both become slower as the release temperature decreases. This decay rate, determined using Kleinstein’s classic method (Kleinstein, 1964), is between 0.2 and 0.3 for the hydrogen mass fraction, comparable to previous experiments analysed using Chen and Rodi’s (1980) method. On the other hand, the radial decay rate of both scalars, characterized by Gaussian functions, increases as the release temperature decreases. While some scattering exists in these trends, the relative decay of the hydrogen mass fraction and the mixture enthalpy, representing the turbulent Lewis number (Le_t), shows a consistent variation with the release temperature. At room temperature Le_t approaches 1, as commonly assumed in CFD simulations of turbulent jet mixing. As the release temperature decreases, Le_t drops approximately linearly and reaches approximately 0.8 at 70 K and even lower at colder release temperatures where Kleinstein’s analysis becomes more challenging. These results provide the first experimental data evidencing this slower decay with colder jets, which leads to longer and larger flammable envelopes. The experiments are also simulated using the open-source HyRAM software. While the low-order model reproduces the axial and radial measurements reasonably well at deep cryogenic conditions, the performance deteriorates with increasing release temperature, particularly at room temperatures, likely due to the identical, temperature-invariant decay rates assumed for the hydrogen concentration and the mixture temperature in the model.