Semicontinuous Pseudo Steady State

The equations look largely the same, except that the solution phase balance on the salt has a convective flow term for the mass of salt leaving the unit by this process  

The interfacial area in this case will be taken to be a constant well approximated by the surface area of the unit. In the diagram this would be the cross-sectional area of the tank ttt. This means then that the salt is removed by a process that removes layers, making the change in salt volume a one-dimensional problem of computing the salt thickness at any time. 

The equations work out as follows for the pseudo-steady state  

This very simple solution comes about as a result of the fact that at the steady state the concentration of salt is a constant and the exit mass flow has to be equal to the rate of salt mass transfer into the solvent. 

---