Sorption of water vapor by capillary-porous substances in relation to temperature

Dushchenko, V. P.; Panchenko, M. S.; D'yachenko, S. F.

doi:10.1007/bf00835358

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“…In order to describe the thermodynamic state of such moisture in a colloidal dispersion under these conditions, one needs the entire set of thermodynamic differential functions, namely: the internal energy AU, the free energy AF, and the bound energy TAS of the bond at any given moisture content u and temperature T in model specimens of different porosity structures.Four grades of silica gel of the same chemical composition SiO 2 .nH20 were chosen as model specimens rather adequately representing the structural types of such sorbents: KSK-2 (uniformly coarse porosity), KSS-4 (uniformly medium porosity), KSM-5 (uniformly fine porosity), and 5-A (uniformly ultrafine porosity) according to the classification given in [2,3,4]. Their structural-sorptive characteristics and their structure geometry have been described in [5].The said problem was solved using a sorption apparatus with thermostatic control and vacuum [6] along with an isothermal electrocalorimeter for measuring the specific heat of evaporation of the moisture and of the colloidal dispersions [7].The free energy AF of the bond between moisture and silica gel was determined from the desorption branches of isotherms for various temperatures and moisture content levels, on the basis of conventional physicochemical thermodynamic relations. The result of calculations is shown in Fig.…”

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“…The said problem was solved using a sorption apparatus with thermostatic control and vacuum [6] along with an isothermal electrocalorimeter for measuring the specific heat of evaporation of the moisture and of the colloidal dispersions [7].…”

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“…2. Ratio of bound energy to internal energy differentials (TAS/AU) of a moisture bond as a function of the moisture content in silica gel: 1) 293~ 2) 301.5~ and 3) 308~ an intensive breakup of the moisture polylayers, which makes it possible that no capillary condensation will occur during the adsorption of water vapor [6].…”

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On the thermodynamics of moisture retained in models of capillary-porous models

Panchenko¹,

Panasyuk²,

Mosievich³

1971

Journal of Engineering Physics

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The thermodynamic differential functions of moisture retained in silica gel models of capillary-porous bodies are shown here as function of moisture content, temperature, and porosity structure.The general laws governing the mechanism of moisture absorption in colloidal dispersions can be established and the state of the retained moisture can be determined by the methods of thermodynamic analysis in conjunction with a set of physicochemical research techniques.Moisture absorbed by a colloidal dispersion is retained in it by forces of various origins and magnitudes [1], the effect of these forces possibly varying with the moisture content level, with temperature, and with the porosity structure of the medium. In order to describe the thermodynamic state of such moisture in a colloidal dispersion under these conditions, one needs the entire set of thermodynamic differential functions, namely: the internal energy AU, the free energy AF, and the bound energy TAS of the bond at any given moisture content u and temperature T in model specimens of different porosity structures.Four grades of silica gel of the same chemical composition SiO 2 .nH20 were chosen as model specimens rather adequately representing the structural types of such sorbents: KSK-2 (uniformly coarse porosity), KSS-4 (uniformly medium porosity), KSM-5 (uniformly fine porosity), and 5-A (uniformly ultrafine porosity) according to the classification given in [2,3,4]. Their structural-sorptive characteristics and their structure geometry have been described in [5].The said problem was solved using a sorption apparatus with thermostatic control and vacuum [6] along with an isothermal electrocalorimeter for measuring the specific heat of evaporation of the moisture and of the colloidal dispersions [7].The free energy AF of the bond between moisture and silica gel was determined from the desorption branches of isotherms for various temperatures and moisture content levels, on the basis of conventional physicochemical thermodynamic relations. The result of calculations is shown in Fig. 1A.The internal energy AU of the bond between moisture and a specimen was determined as the difference between the specific heat of isothermal evaporation of moisture and that of free water at the same temperature. These quantities are shown in Fig. 1B as functions of moisture content and temperature.

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