Evaporation enthalpy-concentration diagram

Above the enthalpy-concentration diagram in Fig. 2.5-1 the dew-point temperature and the bubble-point temperature are shown as a function of the mole fraction and valid for the pressnre of 14 bar. According to this diagram, a mixture with the mole fraction = 0.26, the temperature T = 290 K, and the pressnre 14 bar starts boiling and is in eqnihbrinm with a vapor which has the mole fraction = 0.54. Next, the enthalpy of the vapor (14 bar, 290 K) is caleulated. This enthalpy is composed of three contribntions the enthalpy of the liquid phase, the heat of evaporation, and the heat of superheating. 

After the decision of the number of effects, the concentration spread x -x ) has to be fixed to determine the flow masses of the liquid (Z ) and the vapor (i j - L ) under the condition that the energy released in one effect is the same necessary for evaporation in the next. Such calculations are extensive and can be carried out in an easy way when an enthalpy-concentration diagram is available for the system under discussion. 

Fig. 7.2-5 Representation of a two-effect feed forward evaporation unit in an enthalpy-concentration diagram...

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