Local equilibrium sorption model

The first transport model (local equilibrium sorption) is formulated by assuming that local equilibrium exists along the column. No immobile-water phase is present. The water velocity is... 

Most field-scale modeling studies of contaminant plumes make the local equilibrium assumption (LEA) [18,19]. The LEA is based on the premise that the interactions between the contaminant and the aquifer material are so rapid compared to advective residence times that it can be assumed that the interactions are instantaneous [3]. Linear equilibrium sorption assumes that the binding of contaminants to aquifer solids is instantaneous and that the concentration of sorbed contaminant is directly proportional to the concentration of the dissolved contaminant. This can be modeled by a linear sorption isotherm [2] ... 

Analytical mathematical models describing (a) the propagation of constant pattern MTZ and (b) the desorption profiles under local equilibrium conditions in packed columns for ad(de)sorption of bulk binary liquid mixtures having an U shaped surface excess isotherm and obeying SELDF kinetic mechanism are available [27]. 

The third and fourth models are based on the assumption of an immobile-water phase. This phase can be caused by the existence of crevices or pits on the grain surfaces and by dead-end pores created by tight packing of the grains. In this article, we did not consider an immobile-water film that could cover entire grain surfaces. Diffusion of Mo(VI) into the immobile-water phase retards transport because of the capacitance of this phase and also provides a rate-limiting step for sorption on the solid matrix adjacent to the immobile-water phase. For these models, transport of Mo(VI) from the flowing phase can occur by sorption to the solid phase or by diffusion to the immobile-water phase which then is followed by sorption to the solid phase. The sorption from either phase is assumed to be at local equilibrium with the adjacent fluid phase. An additional balance equation for the solid phase adjacent to the immobile-water phase is as follows ... 

The dual-mode sorption model considers the glassy solid to consist primarily of an equilibrium-densified matrix with a small volume fraction of uniformly distributed molecular-scale gaps, or holes, throughout the matrix. Gaps that are smaller in size than a penetrant molecule may be locally redistributed during the... 

When modeling dynamic water sorption phenomena, information about evaporation and condensation is contained in the boundary conditions that account for water exchange across membrane-gas interfaces. The rate of interfacial water exchange is determined by values of the instantaneous water content on the PEM side of the interface, Xm, and by the vapor pressure, of the adjacent gas. The deviation of these local variables from their chemical equilibrium establishes the driving force of interfacial vaporization exchange. 

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