The effect of the environment conditions on the prediction of flammable cloud dispersion

Abstract

In order to quantify the damage caused by undesired events involving leakages of flammable materials, specific models are used to analyze the spills or jets of gas and liquid, gas dispersion, explosions and fires. The main step of this analysis is to estimate the concentration, in space and time, of the vapor cloud of hazardous substances released into the atmosphere; the purpose is to determine the area where a fire or explosion might occur and the quantity of flammable material in that area. Recently with the computational advances, CFD tools are used to short and medium range gas dispersion scenarios, especially in scenarios where there is a complex geometry. However, the accuracy of the simulating strongly depends on the boundary conditions. Therefore, this study investigates the sensitivity degree of the prediction of cloud dispersion to changes in values of wind speed, ambient temperature, atmospheric pressure and ground roughness. This paper con-tributes to an appropriate assessment of the effects of these environment conditions to perform an accurate dispersion simulation using CFD tools and therefore contributes to a more effective analysis of the consequences. REFERENCES INTRODUCTIONSpecific models are used to evaluate the release and dispersion of flammable substances when an undesired event occurs; the determination of the dispersion features is essential to model the consequences such as fires and explosions. The consequence analysis is used to define the extent and nature of effects caused by such events and thus is of great help when quantifying the damage caused. Dispersion models estimate the evolution and the features of the cloud, such as concentration, temperature, velocity and dimensions as a function of time and position. In the case of flammable substances, these models facilitate the prediction of an area where a fire or explosion might occur and the quantity of flammable material in that area.Nowadays, the use of numerical methods associated with different algorithms of computational fluid dynamics (CFD) to determine the concentration of the vapor cloud of hazardous substances released into the atmosphere, in space and time, has grown considerably (Comier 2008, Middha 2009, Dharmavaram, 2005. CFD is found in some commercial software tools such as CFX, FLACS and FLUENT. The CFD tools transform the governing equations of the fundamental physical principles of fluid flow in discretized algebraic forms, which are solved to find the flow field values in time and space (Anderson, 1995).CFD tools have proven promising to perform analyzes of consequences in environments with complex geometry, as in the comparative study about the use of integral and CFD tools to evaluate cloud dispersion reported by . Nevertheless, as reported by Plasmans et al. (2012), previous studies have shown that consequences analysis using CFD are frequently not easily reproduced and, in many occasions, large differences can arise between the simulation results when working with different tools and/or different C...