Simulation On Thermal Response Of Liquefied Petroleum Gas Tanks Based On Non-equilibrium Thermodynamics

As a clean fuel, Liquefied Petroleum Gas is widely used in industrial production and daily life. However LPG tanks rupture and explosion accidents occurred frequently. It is important to study the thermal response of LPG tanks exposed to heat and suggest the prevention and control strategies for LPG tanks accident. A large number of experiments and numerical simulations have been carried out on thermal response of tanks under the fire environment for many years, but the experiment and theoretical analysis are greatly difficult due to the complexity and risk of process, the research on thermal response of tanks is still hot.The LPG tanks explosion is the heat source, tank walls, the heat transfer in the internal of media lead to the layer, rolling, boiling causing pressure rising sharply from thermodynamics. The explosion is the material strength declined sharply after tank wall heated from mechanical. There is coupling relationship. The thermal response of tanks is a non-equilibrium system from non-equilibrium thermodynamics. The internal temperature distribution of tank is nonuniform caused by tank heated. Heat conduction and liquid-vapor phase transition are the non-equilibrium irreversible process. Liquid-vapor phase transition process is achieved by thermodynamic flows driven by thermodynamic forces. According to the non-equilibrium thermodynamics theory, phenomenological relation between flows and forces reflects the degree of phase transition. The key scientific problem is that the process of LPG boiling based on non-equilibrium thermodynamic model and the coupling model between LPG boiling and tank wall temperature distribution. The main work and conclusions as follows:1,The physical and numerical models for storage tank under heat impingement are set up. RNG k-e model and mixture model are used to describe turbulent flow and two-phase flow, respectively. Phase transition in gas and liquid phases is handled by compiling user-defined functions based on non-equilibrium thermodynamics.2,The numerical simulation on pressure and temperature thermal responses of LPG tanks under heat impingement is made by means of FLUENT. The influences of heat fluxes, heating positions, filling rate, and tanks materials on pressure field, temperature field, density field and wall temperature distribution in the tank are analyzed. Compared with the experimental results, the deviation of calculated results is less than 10%. The numerical simulation results indicate that:The rising rate of tank pressure increases with filling rate but the rising rate of internal temperature decreases with filling rate. The maintain time of the temperature gradient in radial shorter and the temperature stratification in axial longer with fill rate. The rates of the pressure and internal temperature rise increase with heat flux. The higher heat flux is, the faster rising rate of wall temperature is. The maintain time of the temperature gradient in radial shorter and the temperature stratification in axial longer with heat flux. The rate of pressure rise increases with thermal conductivity, but the wall temperature decreases. When the partial area of tank is subjected to heat, compared with the bottom wall heated, the tank is prone to fail under side wall heated. Tank failure time increases with heat flux and fill rate.The innovation points are that the non-equilibrium thermodynamics theory is used to realize the heat exchange process of liquid-vapor phase transition after the tank heated and the thermal response of tank is analyzed by Phenomenological Coefficient.