M

where >>,. is the molar fraction of /'-component in the vapor phase.

Thus, the molar rates J with respect to the molar average mixture velocity in matrix equation form is:

where the superscript "7" denotes the phase interface.

The flux of the last c component, Jvc and J'c:, isn't independent, but is obtained by

The molar rates N with respect to a laboratory-fixed coordinate reference frame in matrix equation form is:

where yi and x, are the average mole fraction, in general, yl = (yi + j>/) / 2 and x, = (x, +x')/2. Nlr and N'r are the total mass transfer rates, and are written as:

For the assumption of constant molar flow in a distillation column, N\. = 0 and

N'r = 0, which, however, at most cases isn't valid. A schematic diagram of the flow of liquid and vapor phases in tray n is shown in Fig. 2, which consists of three trays or a segment of a packing column possibly converted according to the concept of HETP (height equivalent of theoretical plate).

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