Study Of Explosion Characteristics And Flow Coupling Of Unconfined Gas Cloud Explosion

Unconfined gas cloud explosion is one of the main forms of explosion disasters in the field of industrial production and life. The built-in obstacles and gas flow make the gas cloud explosion more complex. It is a key issue to understand scientifically the combustible gas cloud explosion process and its flow coupling law for the prevention and control of combustible gas explosion accidents. Methane-air, propane-air and hydrogen-air premixed gases were taken as the research objects. The unconfined gas cloud explosion and its flow coupling law were studied, and the influences of built-in obstacles, concentrations, volumes and gas activity on the explosion physical characteristics were explored.The results and main innovative contributions of the thesis are briefly described as the following:1. Influences of built-in obstacles on the characteristics of gas cloud explosionThis thesis revealed the dual influences of built-in obstacles on the characteristics of gas cloud explosion. It is equally important for the influences of volume blockage ratios and space distribution of the built-in obstacles on the gas cloud explosion parameters. Under a given space distribution, the explosion parameters reached the peaks at a certain volume blockage ratio. For a given volume blockage ratio, the explosion parameters rose as the built-in obstacles became denser. In this paper, when the built-in obstacles were arranged in 8 x 8 x 4, the methane-air explosion parameters reached the peaks at the volume blockage ratio of 0.74. When the volume blockage ratio was 3.07, the methane-air explosion parameters rose with the built-in obstacles being denser and denser. In this study, the dynamic pressure could reach 104 Par, and it also possessed a strong destructive effect. In addition, the combustion zone was larger than the initial premixed zone. The volume blockage ratio has a key influence on the size of combustion zone. The larger the volume blockage ratio was, the smaller the combustion zone was.2. The coupling law between shock wave and high temperature flow of gas cloud explosionThere was a coupling law between shock wave and high temperature flow of gas cloud explosion in time and space. When a space distribution of built-in obstacles was given, the time interval between overpressure peak of shock wave and temperature peak of gas flow decreased firstly and then rose with the volume blockage ratio increasing, and the minimum value was obtained in a certain volume blockage ratio. When a volume blockage ratio was given, the time interval reduced with the built-in obstacles being denser and denser. In this study, under the built-in obstacles arranged in 8 x 8 x 4, the minimum time interval was obtained in the volume blockage ratio of 0.74. The time interval reduced with the built-in obstacles became denser at the volume blockage ratio of 0.74.3. The physical characteristics of gas cloud explosion at different concentrationsThis thesis studied the methane-air cloud explosions under methane-lean and methane-rich conditions through the method of numerical simulation and revealed that the attenuation trends of different concentrations of methane-air cloud explosion were not exactly the same. A sudden rise of explosion overpressure would appear under certain conditions for methane-rich gas cloud. When the built-in obstacles were dense enough, a rise of explosion overpressure would occur at the boundary of the obstacles region for methane-lean gas cloud. The attenuation trends of combustion rate had a similar characteristic. The combustion rate decreased monotonically with the change of distance for the stoichiometric concentration and the methane-lean concentration of 7%. However, A rise of combustion rate appeared in the decay stage for methane-rich concentration of 12%.4. The volume effect and rules of gas cloud explosionThe volume effect of gas cloud explosion was revealed in this thesis. The temperature field had a significant volume effect. The non-dimensional stable high temperature zones became larger for bigger gas cloud under the stoichiometric and methane-lean concentration, and, for the methane-rich concentration, the non-dimensional stable high temperature zones narrowed as the gas cloud became larger. The volume effect of the flame region was also remarkable. For the stoichiometric concentration, the non-dimensional flame regions expanded with the volume of gas cloud increasing. The non-dimensional flame regions were similar for various volumes of gas cloud at a concentration of 7%. For the concentration of 12%, the larger the gas cloud was, the smaller the non-dimensional flame region was. This study found that the gas cloud explosion effect was not consistent with the geometric similarity any more. The relationship between explosion parameters and non-dimensional distance was related to the volume of gas cloud. The explosion overpressure, dynamic pressure and combustion rate at the same non-dimensional distance increased as the gas cloud became larger. But the distribution characteristic of temperature field was slightly different. The explosion temperature rose for the stoichiometric and methane-lean concentration but fell for the methane-rich concentration with the increase of volume of gas cloud.