Phase equilibrium calculations for fluids confined inside capillary tubes or porous media are formulated using the isofugacity equations. In this situation, the phase pressures are not equal and it is assumed that they are related by the Laplace equation. With this formulation, existing procedures for phase equilibrium calculations can be readily modified to include capillary effects. In this paper, we review some of the main authors who have studied the behavior of fluids inside porous media and perform bubble- and dew-point calculations for pure components and mixtures, using the Peng-Robinson equation of state to model the coexisting phases and several planar surface tension models. Comparisons with results from the literature indicate that the proposed formulation is adequate for representing phase equilibrium inside capillary tubes.
Phase equilibrium; Porous media; Surface tension; Confined fluids; Laplace equation
