Thermal radiation from cryogenic hydrogen jet fires

Abstract

The thermal hazards from ignited under-expanded cryogenic releases are not yet fully understood and reliable predictive tools are missing. This study aims at validation of a CFD model to simulate flame length and radiative heat flux for cryogenic hydrogen jet fires. The simulation results are compared against the experimental data by Sandia National Laboratories on cryogenic hydrogen fires from storage with pressure up to 5 bar abs and temperature in the range 48-82 K. The release source is modelled using the Ulster's notional nozzle theory. The problem is considered as steady-state. Three turbulence models were applied, and their performance was compared. The realizable k-ε model showed the best agreement with experimental flame length and radiative heat flux. Therefore, it has been employed in the CFD model along with Eddy Dissipation Concept for combustion and Discrete Ordinates (DO) model for radiation. A parametric study has been conducted to assess the effect of selected numerical and physical parameters on the simulations capability to reproduce experimental data. DO model discretization is shown to strongly affect simulations, indicating 10x10 as minimum number of angular divisions to provide a convergence. The simulations have shown sensitivity to experimental parameters such as humidity and exhaust system volumetric flow rate, highlighting the importance of accurate and extended publication of experimental data to conduct precise numerical studies. The simulations correctly reproduced the radiative heat flux from cryogenic hydrogen jet fire at different locations.

Simulation of thermal hazards from hydrogen under-expanded jet fire

“…It was found that the change of turbulence intensity (TI) and turbulent length scale (TLS) from TI=30% and TLS=0.33Deff to TI=4% and TLS=0.07Deff has a considerable effect (up to 30% decrease) on the monitored radiative heat flux in the closest sensors at distances 1.0-1.5 m. The set of turbulence characteristics were defined according to a parametric study conducted at HySAFER on hydrogen concentration jet decay (TI=30%, TLS=0.33Deff) and experimental data on air under-expanded jets (TI=4% and TLS=0.07Deff) [26]. Minor effect of turbulent characteristics on radiative heat flux was found by the authors for steady state cryogenic jet fires where maximum variation was 15% [27]. This difference is presumed to be due to the different source modelling technique, as the volumetric source is more sensitive to the applied turbulence characteristics whereas they have minor effect for the constant diameter notional nozzle implementation with specified velocity at inflow boundary condition.…”

Numerical validation of pressure peaking from an ignited hydrogen release in a laboratory-scale enclosure and application to a garage scenario

“…Since the product of hydrogen combustion is water vapour, the Exponential wide band (EWB) model, suggested by Yan et al [26] is used in this study. The model has been tested and validated against experimental results in previous work at Ulster [27]. The radiative transfer equation (RTE) was discretised by using 3 x 3 pixels and 5 x 5 angular divisions.…”

“…It is recommended that 5 x 5 divisions are a strong candidate to be used for the variation of temperature in space [28]. However, a previous study [27] investigated the effect of radiation model angular discretisation, and 12 x 12, 10 x 10, 7 x 7 and 5 x 5 angular discretisation were compared. For their geometry and simulation, 10 x 10 or above provided better results on the sensors to receive the radiation emitted by the flame along all its length.…”

“…With this in mind, a value of 50% has been investigated, for comparison with dry air, to understand the effect of humidity in the air on pressure peaking prediction. Cirrone et al [27] studied the effect of air humidity on radiative heat flux for hydrogen jet fires, and it was shown that relative humidity might have an impact on reproducing experimental data. Two simulations were conducted, and the effect of wet air (50% RH) has been compared to dry air for both Yan et al (2015) [26] and Hubbard and Tien (1978) [32] absorption coefficients as can be seen in figure 10.…”

A comparative study of radiation models on propane jet fires based on experimental and computational studies

“…(2019) Thermal imaging Propane Horizontal Correlated heat release rate based on jet flame Froude number experimentally. Cirrone et al. (2019a) CFD code.…”