Mass Transport of Multiple Fluid Phases Under Isothermal Conditions

In Chap. 4, we assumed that a single fluid occupies the entire void space. In the present chapter we treat the simultaneous mass transport of a number of fluid phases that together occupy the void space. The fluids may be a liquid and a gas (e.g., water and air), two liquids (e.g., oil and water), or two liquids and a gas (e.g., water, oil and some gaseous hydrocarbon). At the microscopic level, i.e., within the void-space, each fluid occupies a distinct portion of the void-space, and is separated from other fluids (and from the solid) by boundary surfaces.