Simulation of Desorption Process of Capillary Condensate from Pore Network

Abstract

During the desorption process from the interconnecting pore texture by the bottle-neck mechanism, the vapor/liquid interface is not formed for all pores in the texture. The pore which is not faced toward the vapore phase is described as being blocked. Evaporation from the pore is prohibited regardless of pore size or relative pressure, and then hysteresis behavior appears.
For quantitative evaluation of the blocking effect, the percolation process on a network model shown in Fig.1 has been simulated with the aid of a digital computer (Fig.2). For obtaining information on the porous substances with extensively different sizes of granules, the Monte-Carlo simulation method was applied to three types of the model with different ex ternal forms (Fig.3, 4). The surface obtained as solution of the percolation problem was smoothed by using spline functions (Fig.5), and thus, the ψ-π-σ relation could be reffered by interpolation of the spline parameters stored in a computer.
It become possible to get plausible explanation for such phenomena as scanning adsorption isotherms (Fig.6), light scattering in porous silica impregnated with liquid, and Hg-intrusion into pore texture. Moreover, it was shown that the established configurations of hysteresis loops could be expressed with only little modification of pore size distribution (i. e., shape of adsorption branch) and/or of σ (i. e., size of granules); cf. Fig.7-9.
As characteristics of the pore size distribution and the amount sorbed were normalized by using π and ψ (Eq. ( 3 ), ( 4 )), the blocking effect and therefore the hysteresis were found to be analyzed generally for any porous substance by a brief numerical calculation.