Validity of pseudo-gas-side-controlled models to predict the behaviour of desiccant matrices

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In the present work, a detailed model of simultaneous heat and mass transfer through a desiccant micro-porous media of an element of a channel wall of compact desiccant matrix was used to numerically evaluate the overall transfer coefficients of pseudo-gas-side-controlled models (PGSCMs). In the detailed modelling, the relevant phenomena considered within the porous medium are the surface diffusion of adsorbed water, Knudsen diffusion of water vapour, heat conduction and the sorption process. The convective mass and heat fluxes predicted by the detailed model are used to estimate the evolution of the pseudo-global resistances to heat and mass transfer during a sorption process, which are required by the PGSCM. The simplified formulation of the PGSCM is presented for an element of the channel wall of the desiccant matrix. Results of the evolutions of these pseudo-global resistances are presented for a wide range of values of the layer thickness of the porous medium, which is supposed to be silica gel RD. It is concluded that the pseudo-gas-side-controlled model with constant transfer coefficients is valid only for layer thicknesses lower than 0.1 mm, approximately.