Gas explosion is a process involving complex hydrodynamics and chemical reactions.In order to investigate the interaction between the flame behavior and the dynamic overpressure resulting from the explosion of a premi...Gas explosion is a process involving complex hydrodynamics and chemical reactions.In order to investigate the interaction between the flame behavior and the dynamic overpressure resulting from the explosion of a premixed gasoline-air mixture in a confined space,a large eddy simulation(LES)strategy coupled with sub-grid combustion model has been implemented.The considered confined space consists of a long duct and four branches symmetrically distributed on both sides of the long duct.Comparisons between the simulated and experimental results have been considered with regard to the flame structure,flame speed and overpressure characteristics.It is shown that the explosion process can qualitatively be reproduced by the numerical simulation.Due to the branch structure,vortices are generated near the joint of the branch and long duct.Vortices rotate in opposite directions in the different branches.When the flame propagates into the branch,the flame front is influenced by the flow field structure and becomes more and more distorted.The overpressure displays a similar behavior in the two branches which have a different distance from the ignition point.It is finally shown that the overpressure change law can directly be put in relation with the shape of flame front.展开更多
The study on the special phenomenon,occurrence process and control mechanism of gasoline-air mixture thermal ignition in underground oil depots is of important academic and applied value for enriching scientific theor...The study on the special phenomenon,occurrence process and control mechanism of gasoline-air mixture thermal ignition in underground oil depots is of important academic and applied value for enriching scientific theories of explosion safety,developing protective technology against fire and decreasing the number of fire accidents.In this paper,the research on thermal ignition process of gasoline-air mixture in model underground oil depots tunnel has been carried out by using experiment and numerical simulation methods.The calculation result has been demonstrated by the experiment data.The five stages of thermal ignition course,which are slow oxidation stage,rapid oxidation stage,fire stage,flameout stage and quench stage,have been firstly defined and accurately descried.According to the magnitude order of concentration,the species have been divided into six categories,which lay the foundation for explosion-proof design based on the role of different species.The influence of space scale on thermal ignition in small-scale space has been found,and the mechanism for not easy to fire is that the wall reflection causes the reflux of fluids and changes the distribution of heat and mass,so that the progress of chemical reactions in the whole space are also changed.The novel mathematical model on the basis of unification chemical kinetics and thermodynamics established in this paper provides supplementary means for the analysis of process and mechanism of thermal ignition.展开更多
Alternative refrigerants have been used in refrigerating and air-conditioning systemsdue to the phase out of CFC-12, HCFC-22 and R502 etc. Most of them are mixtures.The composition fractionation and thermal performanc...Alternative refrigerants have been used in refrigerating and air-conditioning systemsdue to the phase out of CFC-12, HCFC-22 and R502 etc. Most of them are mixtures.The composition fractionation and thermal performance change during refrigerant leakedout from system must be paid attention. The compositions of mixture THR02 were mea-sured by gas chromatographic analysis. Then we developed a general model to calculate thecomposition fractionation of zeotropic, near-azeotropic and azeotropic mixtures. The max-imum deviations between the calculated compositions and experimental results are within5% for the mixture THR02, R4O7C, R404A and R507. THR02 is a near-azeotropic mixture,it is remain unflammable under the worst case, and the change of system performance onlyresulted from composition fractionation during refrigerant leakage can be neglected.展开更多
基金supported by the National Outstanding Youth Science Fund Project of National Natural Science Foundation of China[grant numbers 51704301]Foundation Strengthening Project of China[grant numbers 2019-JCJQ-JJ-024].
文摘Gas explosion is a process involving complex hydrodynamics and chemical reactions.In order to investigate the interaction between the flame behavior and the dynamic overpressure resulting from the explosion of a premixed gasoline-air mixture in a confined space,a large eddy simulation(LES)strategy coupled with sub-grid combustion model has been implemented.The considered confined space consists of a long duct and four branches symmetrically distributed on both sides of the long duct.Comparisons between the simulated and experimental results have been considered with regard to the flame structure,flame speed and overpressure characteristics.It is shown that the explosion process can qualitatively be reproduced by the numerical simulation.Due to the branch structure,vortices are generated near the joint of the branch and long duct.Vortices rotate in opposite directions in the different branches.When the flame propagates into the branch,the flame front is influenced by the flow field structure and becomes more and more distorted.The overpressure displays a similar behavior in the two branches which have a different distance from the ignition point.It is finally shown that the overpressure change law can directly be put in relation with the shape of flame front.
文摘The study on the special phenomenon,occurrence process and control mechanism of gasoline-air mixture thermal ignition in underground oil depots is of important academic and applied value for enriching scientific theories of explosion safety,developing protective technology against fire and decreasing the number of fire accidents.In this paper,the research on thermal ignition process of gasoline-air mixture in model underground oil depots tunnel has been carried out by using experiment and numerical simulation methods.The calculation result has been demonstrated by the experiment data.The five stages of thermal ignition course,which are slow oxidation stage,rapid oxidation stage,fire stage,flameout stage and quench stage,have been firstly defined and accurately descried.According to the magnitude order of concentration,the species have been divided into six categories,which lay the foundation for explosion-proof design based on the role of different species.The influence of space scale on thermal ignition in small-scale space has been found,and the mechanism for not easy to fire is that the wall reflection causes the reflux of fluids and changes the distribution of heat and mass,so that the progress of chemical reactions in the whole space are also changed.The novel mathematical model on the basis of unification chemical kinetics and thermodynamics established in this paper provides supplementary means for the analysis of process and mechanism of thermal ignition.
文摘Alternative refrigerants have been used in refrigerating and air-conditioning systemsdue to the phase out of CFC-12, HCFC-22 and R502 etc. Most of them are mixtures.The composition fractionation and thermal performance change during refrigerant leakedout from system must be paid attention. The compositions of mixture THR02 were mea-sured by gas chromatographic analysis. Then we developed a general model to calculate thecomposition fractionation of zeotropic, near-azeotropic and azeotropic mixtures. The max-imum deviations between the calculated compositions and experimental results are within5% for the mixture THR02, R4O7C, R404A and R507. THR02 is a near-azeotropic mixture,it is remain unflammable under the worst case, and the change of system performance onlyresulted from composition fractionation during refrigerant leakage can be neglected.
