Modeling Impregnation of Porous Materials in a Force Field with Account of the Diffusion of Trapped Gases
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 4, July, 2020
MODELING IMPREGNATION OF POROUS MATERIALS IN A FORCE FIELD WITH ACCOUNT OF THE DIFFUSION OF TRAPPED GASES I. N. Karpovich
UDC 004.942.532.685:537.228
It has been shown that a nonuniform electric field can have a significant effect on the kinetics of diffusion capillary imbibition of liquids into thin dead-end capillaries that are a model of pore strictures. The results of calculations are in satisfactory agreement with experimental data. Keywords: cylindrical dead-end capillary, liquid column, gas diffusion, nonuniform electric field, mass transfer, porous body. The displacement of liquids and gases under the action of capillary forces inside many dispersed natural and artificial materials occurs in the space of communicating pores. Optimization of capillary impregnation is an important technological problem. Control over this process makes it possible to substantially change the properties of building and fiber materials, timber, elements of heat pipes, sorbents, catalysts, porous electrodes, pharmaceutical preparations, and other materials. Mass transfer in porous materials is accompanied by the phenomena of wetting, spreading, sorption, and transfer of the phase boundary due to the action of surface forces [1]. The main factors affecting the conduct of internal mass transfer are forces of surface tension, gravity, inertia, and friction, which turn out to be substantial at different stages of capillary impregnation. In actual practice, the capillary impregnation of a porous medium is accompanied by the entrapment of a significant part of the gas by dead-end and quasi-dead-end pores which, according to [2, 3], occupy the predominant part of the pore space. There are two stages of impregnation of dead-end capillaries: an intense one, whose velocity is determined by the viscous displacement of the wetting liquid, and a slow one having a velocity several times lower than the velocity of impregnation at the first stage. At the slow stage of impregnation, the liquid borders the trapped gas (or a mixture of gases) and exerts an excess capillary pressure on it. The solubility of the trapped gas in the pores is higher than its solubility in the liquid outside the porous material. This concentration difference causes a diffusion gas flow from the specimen. Since the gas pressure in the pores always exceeds the atmospheric pressure, the impregnation continues until the gas is completely dissolved, i.e., until the pore space is filled with the liquid. In a number of cases, the problem of controlling the velocity of the liquid′s motion becomes important, especially at the final stage of the process of capillary saturation. As was shown by theoretical and experimental investigations [4–6], an electromagnetic field, in particular, a nonuniform electric field (NEF), is an efficient method to control heat and mass transfer processes in interaction of different surfaces with liquids and gases. In [7], the influence of a nonuniform electric field on the
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