Fundamentals and applications of environmental and geophysical multiphase flows

This thesis is concerned with fundamentals and applications of environmental multiphase flows. The study contains four parts covering gas hydrate dissociation in porous media and rock fracture, gas-liquid flows in rock fractures, and transport of pollutants in outdoor air.; Dissociation of gas hydrate in a porous sandstone core as well as a fracture rock was studied using a computer modeling approach. Using Fluent(TM) code, an axisymmetric model of the core and a two dimensional model of the fracture were developed and solved for multiphase flows during the hydrate dissociation. The developed models account for the presence of three separate phases, namely, methane hydrate, methane gas, and liquid water. At the start of simulation, one end of the core/fracture was opened, exposing the hydrate to pressure below the hydrate equilibrium pressure; hydrate began to dissociate and methane gas and water began to flow. The depressurization was controlled by adjusting the pressure at the outlet valve of the core and/or fracture exit pressure. A comprehensive User Defined Function (UDF) for analysis of hydrate dissociation process was developed and implemented into the FLUENT code.{09}The kinetic model introduced by Kim et al. (1986) was used in the new UDF, and could model multiple zones dissociation and multiphase flows. Variations of relative permeability of each phase were accounted for using Corey's model. The new computational model allowed for variations of the porosity with hydrate saturation. For different temperatures and various outlet pressures, the spatial and temporal variations of temperature, pressure and flow fields in the core/fracture were simulated. The time evolutions of methane gas and water flow rate were also evaluated. It was shown that the rate of hydrate dissociation was a function of surrounding environment temperature, outlet pressure condition, and sample permeability.; Single-phase fluid flows through a rock fracture were simulated. The fracture geometry was obtained from the CAT (Computerized Axial Tomography) scans of a rock fracture produced by the Brazilian method in a sandstone sample. (Abstract shortened by UMI.)...