Spatial-temporal Pattern And Influencing Factors Of Heavy Gas Leakage And Diffusion:Model Simulation And Experimental Study

With the rapid development of modern industry,the demand for toxic and harmful gases in industry and related industries is increasing year by year.Leakage is often caused by accidental damage or improper maintenance during transportation and use,and toxic and harmful heavy gases have heavy gas effects,which will cause serious harm to people ’s health and asset safety accidents.Therefore,studying the spatial and temporal pattern and influencing factors of diffusion after toxic and harmful heavy gas leakage can reduce the injury of personnel after the accident to a certain extent and provide some reference for the safety design of reducing the accident.Based on this background,this paper uses the combination of experimental simulation and Fluent computer numerical simulation to study the leakage and diffusion of toxic and harmful heavy gas.The experimental platform is built to carry out the gas release experiment and the corresponding physical model is established for simulation.The influence of different influencing factors of atmospheric environment on gas diffusion under the background of valley-type narrow street under no wind and low wind speed can be simulated by the experimental platform.The spatial and temporal distribution of gas concentration is analyzed.The main contents and conclusions are as follows :(1)The related theories of toxic heavy gas leakage are studied,and the gas hazards and characteristics are classified and summarized,and the general leakage source types of dangerous gas leakage and the leakage and diffusion process of highpressure liquefied heavy gas are analyzed.Analyze the main influencing factors of gas leakage and diffusion,such as gas nature,leakage source,meteorological conditions,surface topography and other conditions;this paper retrieves the domestic research status in recent years,and uses the bibliometric method to analyze the number of publications,journals and keyword co-occurrence in this field in recent years,summarizes the current research methods at home and abroad,and draws the research methods of this paper.(2)Based on the similarity theorem and combined with the influencing factors,a small toxic and harmful gas diffusion experimental system was designed and built.In order to ensure the safety of the experiment,carbon dioxide gas was selected as a typical representative of heavy gas,and several small-scale leakage experiments were carried out.The effects of different leakage hole heights and different leakage flow rates on the initial concentration and overall trend in the non-closed finite space without wind conditions were explored.The results show that the height of the leakage hole affects the concentration change in the space to a certain extent.Different dangerous areas are generated in a short time,and the gas accumulates near the wall for a long time.In general,the leakage ratio below the monitoring plane is higher than that at the monitoring plane,and the concentration rises faster and more dangerous under the same monitoring plane.The leakage flow greatly affects the concentration rising trend in the space,and the concentration of each measuring point increases exponentially in the same leakage period.(3)Based on the experimental system,a CFD Fluent computer fluid simulation physical model is established.Compared with the experimental system,the error is about 20 %,which shows that the system and physical model can meet the simulation of gas leakage process and leakage phenomenon.In the low wind speed valley-type narrow street scene,three low wind speed conditions are set,and the CFD Fluent simulation results are mainly used for analysis.Firstly,the land subsidence in the-X direction and the Z direction are explored respectively.The results show that for every0.2 m/s increase in the-X direction wind speed,the maximum concentration settlement distance near the ground is extended by 0.3 m,and the dilution effect is faster.Due to the blocking effect of the near wall and the increase of the wind speed,the normal distribution of the concentration in the Z direction in the space will be gradually affected,and the gas will accumulate near the wall,and the risk of leakage accident will be greater.Secondly,when exploring the influence of different wind speeds on the vertical jet,it is concluded that at t = 20 s,0.2 m/s and 0.4 m/s have almost no horizontal skewness on the jet,but 0.6 m/s has a more obvious horizontal skewness,indicating that when the wind speed reaches 0.6 m/s,it can greatly affect the initial concentration diffusion path.Finally,according to the lethal concentration of toxic chlorine 1000 ppm,the diffusion range on the horizontal plane of Y=0.9 m was explored.The results showed that the length of the dangerous zone increased by 0.2 m for every 0.2 m/s increase in wind speed,and the larger the wind speed,the narrower the concentration distribution,and the shorter the horizontal and longer the vertical.In the longitudinal section of Z=0.96 m,the influence of heavy gas effect and wind speed blessing effect is mainly explored.As a whole,it can be seen that the gas cloud in the longitudinal section is lifted as a whole when the wind speed is 0.6 m/s,which has little effect on the near surface.