Numerical Simulation Of Heavy Gas Dispersion

As it is well-known, many industrial and domestic gases are toxic and flammable and are stored in highly-pressurized vessels at liquefied state with ambient temperature. If there is by chance a sudden release, it often forms heavy-than-air vapour clouds called heavy gases. The accident release and dispersion of toxic and flammable heavy gas can present a serious risk to the public's safety and to the environment. Disease may be caused when people breathe the toxic heavy gas. Fire or vapour cloud explosion may take place when the flammable heavy gases are lit. Although great attention has been paid to the hazard of heavy gas dispersion, effective data of field experiments are still insufficient to make risk assessment and precaution. Therefor, it is necessary to investigate the numerical simulation of heavy gas dispersion. The fluid dynamic models based on Computational Fluid Dynamics (CFD) can not only be applied to reflect the physical phenomenon in the air turbulent flow with heavy gases, but also is possible to be used to simulate the heavy gas dispersion where topography change or obstacles exists. In this paper, the CFD models are employed to investigate the regular pattern of heavy gas dispersion. All the works are described in eight chapters.Chapter 1 is the outline, in which the objective and significance of heavy gas dispersion investigation are described and a brief introduction about the process of heavy gas dispersion is given.Chapter 2 contents the reference review in the field of heavy gas dispersion. A brief review is given for the current status of the modeling of heavy gas dispersion, and the problems associated with using dispersion models beyond their range of validation or stated application are discussed. Based on the analysis, the contents and objectives of this paper are presented.Chapter 3 discusses the numerical models of heavy gas dispersion. A set of three-dimensional, time-dependent conservation equations is developed. Three kinds of turbulence models are introduced in this chapter. By comparison, the two-equation turbulence model with the modification of buoyancy effect is used in the simulation.Chapter 4 describes the numerical simulation method of heavy gas dispersion. The conservation equations are discretized in terms of the finite volume method in space and are fully implicit in time. They are solved by means of a method, based on the SIMPLE algorithm. The resulting linear equations are solved iteratively by the TDMA method. And some source releasemodels are adopted in this paper.In Chapter 5, the three-dimension models are validated by simulations of Thorney Island Trial 008 field experiment. From this validation it can be concluded that the models and algorithm used in this paper are acceptable.Chapter 8 contributes to the numerical analysis by applying the numerical models mentioned above. In this chapter, the influence of released gas density and the wind speed on the process of heavy gas dispersion is analyzed and various of useful results are achieved.In Chapter 9, two kinds of heavy gas dispersion processes (continuous point source release and dispersion, pool evaporation and dispersion) are simulated and investigated. The influence of release rate and obstacles to the dispersion process is also analyzed.Chapter 8 is the conclusions and remarks of the dissertation.