Method of evaluating the actual number of stages in interphase-contacting, multistage, mass transfer devices based on the transfer-unit concept, without using the number of ideal stages or the overall efficiency

The proposed method which developed out of a comparison of the methods for design of a heat exchanger and a mass transfer device relates the mass transfer characteristics of the stages directly to the required number of stages, without considering the number of ideal stages. The number of transfer units as calculated for a countercurrent device is considered to be the sum of the number of transfer units for each equivalent countercurrent stage. The proportion of the resistance to mass transfer in each phase is determined by a dashed-line approximation of the equilibrium curve using tie lines. The method does not have to deal with plate efficiencies greater than 100%.