Equations of change for species concentration in a mixture

In Section 3.2.1, a rectangular separator vessel Wcis considered in which there was no bulk velocity of the solvent/fluid in any direction further, the solute species i was subjected to a force in one coordinate direction (z-coordinate). The balance equation for molar 

We will now consider each of the above terms in some detail using molar rates  

Additional terms for the molar rate at which species i enters the volume element and leaves the volume element through the faces perpendicular to the y-axis and the z-axis can be easily developed following (6.2.2b) and (6.2.2c). When all such terms are introduced into the balance equation (6.2.1), we get 

Dividing by (AxAyAz) and allowing each of Ax, Ay and Az to go to zero, we obtain in the limit 

Here i = 1, 2,. .., n, if the total number of species in the system is n. This is the general differential equation of balance for species i in molar units in a system in the presence of any chemical reactions involving species i. An alternative form in vector notation is 

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Separation is most often implemented in open systems/devices with bulk flow(s) in and out The treatment of separation achieved in such separators is carried out in Chapters 6, 7 and 8. Chapter 6 begins with the sources and the nature of bulk flow in separation systems in a multiscale context as well as the feed introduction mode vis-a-vis time (Section 6.1). The various equations of change for species concentration in a mixture, the equation of motion of a particle in a fluid and the general... 

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