9.1 Packing Efficiency 9.1.1 The transfer unit concept
Figure 9.1 analyzes a mass transfer element in a packed column. The number of moles per hour flowing into the section is and the number of moles per hour flowing out is Vy2. The number of pound moles per hour transferred, N', is given by
Since the volume of the element is AT dH (Fig. 9.1a), the number of moles transferred per unit volume over the section is given by (N is in pound-moles per hour per cubic foot)
Flgur« 9.1 Mass transfer in packed columns, (a) Differential section; (6) driving force diagram.
The number of moles transferred per unit volume can also be calculated from the mass transfer equation
N = hoc a, P(y* - y) (9.4) Combining Eqs. (9,3) and (9.4) and rearranging gives
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