Experimental And Numerical Study Of Leakage And Dispersion From Multi-source Gas

With the rapid development of modern petrochemical industry, there are a lot of inflammable, explosive, toxic and hazardous gases in the production, use, transportation and storage process. And significant accidental leakages from these gases occur frequently, causing enormous casualties, economic losses and environmental pollution. Thus, both of the domestic and foreign scholars focus on the gas leakage and dispersion, which have practical significance.However, previous studies were mostly related to the gas leakage from single source, and there was a serious lack for the research of multi-source gas leakage. In reality, the multi-source gas leakage occurred occasionally, such as when suffered from accidents or natural disaster. Therefore, the research about gas leakage and dispersion from multi-source was conducted in this paper, aiming to reveal its flow characteristics and evolution rules over time, and to predict the temporal and spatial concentration distribution, so as to provide strong theoretical guidance for emergency rescue and evacuation decision-making.In this article, both of the near-field and far-field regions of multi-source gas leakage were studied systematically. For the near-field region, a small-scale experiment system was established based on the similarity theory. Helium and carbon were selected to be the typical representative of light and heavy gas, respectively, The experimental studies on the flow of these two gases released from single and multi-source in stagnant free space were conducted. And the basic characteristics of flow field was revealed, through the Schlieren and high-speed imaging system. Meanwhile, the corresponding physical model were founded with the combination of small-scale experiments. Both of the k-s turbulence unsteady simulation and large eddy simulation have been made to study the dynamics process of light gas and heavy gas, the internal mechanism of multi-source interaction with the theoretical analysis. In addition, according to the results of experiments, numerical simulations and theoretical analysis, the influence mechanism of the factors of leakage rate, leakage angle, distance between multi-source and source number were revealed.For the far-field region, the established gas dispersion models were modified and developed to be that of multi-source. Then, the temporal and spatial concentration distribution characteristics as well as the accident consequences of multi-source gas leaskage could be predicted by numerical simulation.In the dispersion model of light gas, although Gaussian model was most widely used, there were still some deficiency in it. So the Briggs plume rise model and the definition of ground roughness were chested in the Gaussian model. Based on the this modified Gaussian model, the dispersion of single continuous and instantaneous leakage from light gas were both simulated to predict the concentration distribution in the space over time. Combining the toxicity criteria, the influenced area, the maximum downwind and crosswind distance as well as the concentration evolution at a fixed position were all calculated. Furthermore, a multi-source dispersion model of light gas on the basis of this modified Gaussian model was founded. The influencing analysis and significance analysis of involved factors were made to reveal the rules and importance.In various dispersion models of heavy gas, an appropriate one was selected by the methods of validity verification and statistical analysis. It was founded that the SLAB model was quite reliable and accurate by comparing its prediction results with that of field tests, other heavy gas model and real accident case. Therefore, an intensive study of SLAB model was conducted and the impact factors and regularity in the dispersion of heavy gas were revealed. Meanwhile, a multi-source dispersion model of heavy gas based on the SLAB model was developed.