Internal Sherwood numbers for diffusion in sorption operations

An approximate mathematical description of diffusion in sorption operations, based on the assumption of a linear driving force (LDF) for the diffusion process, is investigated. A method is presented to employ the LDF model as a useful tool for data analysis and process design for various sorption process types, by which elaborate numerical solution methods can be omitted or simplified considerably. The principal variable of the LDF model is an internal Sherwood number for the sorbent phase. It is shown that the internal Sherwood number is time dependent and a function of the second order time-derivative of the sorbate concentration in the sorbent particle at the surface. Correlative expressions for the internal Sherwood number are derived and their application to sorption process calculations is examined.