Three-dimensional Transient "Heavy Gas" Dispersion Model And Numerical Study

Accidental release of toxic, flammable or explosive materials produced and/or used in modern industries into the atmosphere often forms heavy gas clouds, drops down on the ground and disperses along the wind which may damage to the people living in the area. Especially heavy decease may be caused if it happens in a large population area.Therefore, it is necessary to take a quantitative assessment to the risk of the consequences of the accidental release of hazardous material into the atmosphere. It is unfortunately that there are still not enough effective data of field experiments to be used for risk assessment and precaution measures. The three-dimensional transport phenomena models based on the CFD can describe the physical phenomenon in the atmospheric turbulent flow at a more fundamental level and have been used extensively in many areas.In this paper, a transient heavy gas dispersion model is presented in which a k-e two-equation turbulence model modified with buoyancy effect, a control volume method and the SIMPLE procedure are adopted. Based on it, a self-compiled three-dimensional program is developed for the numerical simulation.Especially, the test data from the Thorney Island Phase I Trial No. 8, which is specially a instantaneous release of large quantity of heavy gas, are adopted here to verify the accuracy of the model and the correctness of the computation program. The numerical simulation based on this trial can visually show the phenomena appeared in the normal experiments, such as gravity driven slumping, entrainment of air, formation and development of vortex etc., and given the concentration and velocity figures at different times after the release. Especially, the results of the calculations are in good agreement with experimental data at several measuring stations.Based on the above models and algorithm, two continuous releases from ground-level tank have been simulated and analyzed in detail.The influence of the wind speed, release gas density and release rate to the process of heavy gas dispersion is numerically simulated and studied. A lot of useful results are achieved .