A three stage co-current evaporator is used to concentrate a NaCl solution from 3% (m/m) to 20%(m/m). The first effect operates at 1 atmospheric pressure with the second effect operating at 0.6 atmospheres. Steam at the rate of 1.9kg/s is fed to the first at a pressure of 200kPa. Assume that the overall heat transfer coefficients are 2.7, 2.1 and 1.9 kW/m2K, for the three effects, respectively and that the physical properties of the solution are that of pure water. Make rough estimates of the pressure in the last effect and the surfaces areas for heat transfer if the surfaces areas are at the same in all three effects.