Abstract:

The currently used methods for determining the thermodynamic equilibrium of the mixed two phases substances is to judge the equality of the coefficient of each component in two phases，and with this analysis，each component mole fraction can be got at the equilibrium state.But this method can not be used in analyzing the process from the initial two phases nonequilibrium state to the final equilibrium state.To address this issue，diffusion equation to describe various gas and liquid components from exposure to the stabilization process is introduced in this paper，a mathematical model to describe the two phases nonequilibrium diffusion process established.By using the method，a gasliquid two phases system that changes from contact to steady status in the PVTcanister is analyzed.The whole process pressure change rule of the system is obtained.The methane concentration distributing rule that changes with altitude in the balance state got，too.The results compared with the experimental data proved the feasibility of the method，thus the nonequilibrium phase transition analysis of the issue gives a new train of thought.

Key words: two phases, nonequilibrium process, numerical simulation, PVT cell, separation of variables 