Combining CFD and experimental approaches to optimize a spray release in a 20 L sphere

Abstract

European regulations require that the risk of an explosive atmosphere (ATEX) associated with the production of a flammable mist be assessed. In order to properly investigate mist flammability, a dedicated experimental tool was developed based on the standardized 20L explosion sphere and an additional Venturi injection system. As part of its design, the conditions of mist generation must be fully controlled. To complement the experimental approach, a computational fluid dynamic modeling (CFD) has been developed with an Euler-Lagrange method. It aimed at determining the homogeneity of the mist and the influence of the turbulence on the droplet size distribution (coalescence / fragmentation dynamics) as it greatly influences the mechanism of combustion. Based on previous studies and on industrial considerations, ethanol and kerosene were chosen. Modeling results were compared to the droplet size distribution determined by laser in-situ measurements and to the flow characteristics measured by particle image velocimetry. The CFD modeling confirmed the significant effect of the turbulence on the droplets coalescence and enabled to improve the understanding of the phenomenology related to the dispersion of a flammable mist into a 20L sphere. These results are consistent with the droplet particle distributions measured experimentally and show that CFD modeling can support further experimental developments so that it can constitute the basis for a new standard 20L explosion sphere for mists testing.