Evaluation Method for Actual Number of Stages in Interphase Contacting Multistage Mass Transfer Devices Based on the Transfer Unit Concept — Without using the number of theoretical stages or overall efficiency —

A reasonable method entitled is proposed. It has been obtained through comparing between the desigh methods of the heat exchanger and of the mass transfer device and is superior to the current method in the following points. 1) It is easy to understand because of its concise operation, in which the required number of transfer units calculated as a countercurrent device is considered to be the sum of the number of transfer units of each stage evaluated as a countercurrently equivalent one. 2) In approximating the equilibrium curve with straight sections, the effect of the mass transfer resistance in two phases is reasonably taken into account through use of tie lines. 3) Efficiencies capable of becoming greater than 100% are not needed.