The mechanism of surface flow of adsorbing gas molecules through the porous adsorbent is interpreted, and a new hopping model is derived by separately taking into account the hopping behaviors of monolayer and multilayer molecules. The reported experimental results containing the data measured here are correlated well. Finally, some considerations are given to the two experimental constants appearing in the model.
Drying of coated film of polyvinylalcohol (PVA) aqueous solution is studied theoretically and experimentally, focusing on the diffusion process of water and the volumetric shrinkage of film occurring by evaporation of water. The diffusion coefficients were measured over the whole range of concentration by three methods, and drying experiments of coated films using hot air were performed. Numerical solutions were obtained from a set of transport equations for water using the observed diffusion coefficients and were compared with the experimental results.
The flow mechanism of adsorbable gas through the porous adsorbent in the presence of capillary condensation is interpreted, and a new transport model is derived by separately taking into account the hopping behavior of adsorbed molecules in the adsorbed phase and the viscous flow of capillary condensate. Surface flow coefficients including the contribution of capillary flow calculated with this model agree with published experimental data.
SCOPEBesides gaseous diffusion and flow in pores, surface flow of physically adsorbed gases is important in evaluating the apparent mass transfer rate through porous media. Capillary condensation begins to occur in the fine pores with increase of the gas-phase pressure of the adsorbable gas, and not only surface flow but also flow of capillary condensate should be taken into account. The static behavior of capillary condensate is comparatively well-understood (Gregg and Sing, 1967;El-Sabaawi and Pei, 1977; Okazaki et al., 1978). The dynamical behavior has, however, been studied only by a few investigators (Carman and Raal, 1952;Gilliland et al., 1958), despite the research that would benefit many practical fields such as drying and adsorption processes.For the case that capillarysondensation is not taking place, the authors have proposed a random hopping model for surface flow by introducing the average holding times of the molecules adsorbed in the monolayer and multilayer as the time taken to hop to a neighboring site (Okazaki et al., 1981). Surface flow coefficients can be explained well by this model in the range of monolayer to multilayer adsorption.On the other hand, for the case that capillary condensation coexists, Gilliland et al. (1958) attempted to explain their experimental results by proposing that the transport mechanism is multilayer surface flow alone even though they recognized the existence of capillary condensation. There are, however, some experimental results which cannot be expressed by their correlating equation.The purpose of this paper is to propose a transport model for the flow of adsorbable gas through porous media by taking into account the hopping behavior of molecules adsorbed in the adsorbed phase and the viscous flow of the capillary condensate. The calculated results by this model are compared with published data.
A new method is proposed to predict adsorption equilibria of mixtures of solvent and water vapor on activated carbon. It is based on evaluating the amounts of solvent and water in the capillary condensed phase in the fine pores and in the ordinary adsorbed phase in the coarse pores, respectively. Predicted results are comparedwith experimental ones on two kinds of activated carbons having different pore-size distributions for water-soluble solvents (methanol and acetone) and water-insoluble solvents (benzene and toluene), respectively. Both results agree fairly well.
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