A physical process and mechanism of liquefied petroleum gas (LPG) flow dispersion in porous media for the releases at vapor and liquid region of Underground Storage Tank (UST) was analyzed. On the basis of the mixture model principle, a mathematical model was developed to simulate LPG flow dispersion in porous media. The gravity, capillary force, viscous force, interior resistance of porous media and gas-liquid interaction were incorporated into this model. And the non-Darcy coefficient of multiphase flow which is variable with Reynolds number was taken into account in the model, which was according with actual flow state. For LPG is insoluble in water, the formulation of LPG volumetric concentration was deduced, which simplifies computation process. The model was carried out to simulate a propane gas migration process in sand pond for UST release. From the simulation results, a detailed analysis was performed to investigate the effect of various influencing factors on infiltration flow: the direction of gas infiltration diffusion is influenced distinctly by gravity, release direction and the position of outlet in tank pond; the flow about release site and outlet is more active where the non-Darcy effect is obvious; the pressure drive is crucial for LPG infiltration; the gravity is a main factor to water infiltration; the saturation and viscous force of water can restrain the infiltration speed of propane. The model can lead to a good understanding of flow development and field effects of LPG in unsaturated porous media and can offer boundary conditions for modeling the subsequent fire explosion accidents.

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