Gas Mixing Process And Flammability In Confined Space

The gas explosion is one of the most destructive disasters in our life and industry manufacture.The gas flammability limit is a key parameter to judge the explosion risk of mixed inflammable gases.The propagation law of gas explosion are foundation of the explosion evolution and accident analysis.Both of them are the base of accident emergency rescue plan and safety technical measure.It was found that there was different in the results of measured lower flammability limit(LFL)or upper flammability limit(UFL).There was not any research reports about whether concentration distribution was related to that difference.In order to prevent gas explosion from occurring and make production safety,this thesis presents the gas mixing process,concentration distribution law,turbulence distribution law and their effects on gas flammability and propagation law of gas explosion by using the methods of numerical simulation and experiment.This thesis reveals the physical essence of difference of measured flammability limit results.The main contents and innovative works in this thesis are as follows:In the experiment of measuring the gas flammability limit,the premixed gas was ignited after stirring or standing.The thesis studies the gas mixing process,researches the concentration distribution law,presents the correlation between the ignition position and measured flammability limit.The quantitative influences of inlet pressure,geometric features features of vessel,gas species on concentration distribution are achieved.The physical essence of difference of measured flammability limit results is non-homogeneous concentration distribution.The ignition position is the key to control the deviation of measured flammability limit values.Hydrogen is used or produced in high temperature and pressure conditions.This thesis researches the hydrogen-air mixing process in the high temperature and pressure conditions,presents the law of concentration distribution.It is found that the initial high temperature has influence on concentration distribution,however the initial high pressure has no influence on concentration distribution.After the hydrogen-air(hydrogen macroscopic volume fraction: 4%)standing 5 min in vessel of 5 L(?0.14 m×0.33 m),at the initial temperature of 294 K and 348 K,the relative deviations of hydrogen concentration in center are 6.75% and 3.75%,in bottom 52.5% and 57.5%,and in top 51.75% and 57%.At the initial pressure of 0.1 MPa and 0.4 MPa,the relative deviation of hydrogen concentration in center are 6.75% and 6.6%,in bottom 52.5% and 52.125%,and in top 51.75% and 51.1%.It is a commonly used method to study the gas explosion in the experimental pipe.The influence of concentration distribution on gas explosion is one of basic issues of gas explosion.Such influence needs systemically to be studied.The thesis states the gas mixing process,researches the concentration distribution law in pipe.The quantitative influences of inlet pressure,geometric features of vessel,gas species on concentration distribution are achieved.The influence of concentration distribution on the propagation law of gas explosion is explained.It is difficult to measure the concentration of gas mixture in roadway.Whether the concentration distribution is homogeneous is lack of attention.Taking gas mixing process in roadway for research object,the thesis presents the concentration distribution.The quantitative influences of standing time,height of roadway,premixed gas dimension on concentration distribution are achieved.After methane-air mixture standing 9 h in tunnel(2.7 m×2.7 m×50 m),the relative deviation of methane concentration in center is 0.01%,in both ends are 4.42% and 4.52%,as the macroscopic volume fraction of methane is 9.5%.Turbulence increases overpressure values,and then it can have an influence on measured flammability limit values.The thesis researches the turbulence distribution in premixed gas and its influence on measured flammability limit values.In spherical vessel of 20 L,as the macroscopic volume fraction of methane is 5% and 15%,the turbulence intensity is 13% and 17% after standing 1 s,and 0.58% and 0.56% after standing 1 min.