Numerical Simulation Of Liquid Mist Explosion In A Closed Vessel

As a kind of fossil fuels,liquid fuels are widely used in petroleum,chemical,plastic and rubber industries.With the frequent occurrence of liquid-vapor explosions,the research on the mechanism of liquid-vapor explosions has a significant impact on the improvement of equipment and accident prevention.In this thesis,a model of liquid-vapor diffusion and explosion simulation in a 20L closed explosion vessel was set up with computational fluid dynamics software ANSYS-Fl UENT.The diffusion and explosion process of heptane,hexane and JP-10 liquid-vapor were numerically simulated,and was compared with experiment.Through the numerical simulation of liquid-vapor formation and explosion process in a 20L closed container,the following research results are obtained:（1）The space and time distribution of liquid-vapor in the vessel is a function of space and time,which is the prerequisite and foundation for the study of explosion parameters.The results show that when the spray pressure is among 0.3～0.7MPa,the number of droplets rapidly increases with time in the spraying period（0～20ms）,and the droplets are densely distributed in the vicinity of the nozzle and the wall.During the rest period（20～100ms）,the amount of drops gradually decreases with time,and the droplet distribution in the vessel is relatively uniform.（2）Turbulence is another important factor that affects the explosion parameters.This paper examines the distribution characteristics of turbulence with spray time and space under different spray pressures,which lays the foundation for the reasonable choice of liquid mist ignition delay time and ignition position.The results show that when the spray pressure is 0.3～0.7MPa,the distribution of turbulent flow in the container varies greatly during the spraying period.The maximum turbulent kinetic energy appears at around 15ms,which is 18800m²·s^-2,located near the nozzle with the minimum value of 100 m²·s^-2 or less,and the greater the spray pressure,the greater the turbulence difference.During the rest period,the turbulence gradually weakened from the geometric center to the wall.The maximum turbulent kinetic energy difference of liquid-vapor under different spray pressures at 100 ms was less than 3 m²·s^-2.（3）Uniformity of concentration in vessel interpret the basis of liquid-vapor explosion parameters.Different with dust and gas phase,the formation of liquid-vapor is more complex and is manifested in the mutual coupling of gas and liquid concentration in the vessle.It is found that when the concentration of heptane was 80g·m^-3,the liquid-phase concentrations of heptane under different spray pressure（0.3、0.5 and 0.7 MPa）were 56、51 and 46 g·m^-3 and the gas-phase concentrations were 21.46、25.33 and 30.85 g·m^-3 at 100ms respectively.（4）The influence of liquid mist particle size on the explosion parameters depends on the type of fuel.It is found that the peak(p_max)of liquid-vapor of heptane explosive overpressure increases with D₃₂（in the range of 6.81～18.1μm）from 0.951MPa to0.902MPa,and the maximal of increase rate（dp/dt）_max of explosion pressure suddenly jumps at D₃₂=10.1μm.The maximum flame velocity jumps sharply at D₃₂=10.1μm,indicating that there is a surge in the intensity of liquid-vapor explosion when the particle size within the range of 6.81～12.9μm,this result is consistent with the existing experiments.（5）The variation law of liquid-vapor explosion overpressure peak value and maximum explosion pressure rate of heptane,hexane and JP-10 within the concentration range64～214g·m^-3 was simulated,the peak value of explosion overpressure and the maximum value of the maximum explosion pressure rise rate all appear at the concentration corresponding to the fuel air equivalence ratioΦ=1.25.Under the same concentration,the maximum explosion pressure of hexane liquid-vapor is the highest（1.114MPa）,and the maximum explosion pressure of JP-10 liquid-vapor is the lowest（0.1837MPa·ms-1）.