This is Separation Principles. Multistage evaporation.

BACKWARD feed with DOUBLE EFFECT EVAPORATOR  and mass of feed is 3kg/s.  I need to compare my answer with yours. I am posting this question for the second time because an expert answered it wrongly, he took an example of a triple effect evaporator with 1.25 kg/s which is totally different from the question I had posted.

3 kg/s of a salt solution is concentrated from 10% to 55% solid in a backward feed double effect evaporator using steam at 393 K. the effects are operated under vacuum such that the bubble point in the second effect is 325 K. The feed is initially at 297 K and each effect is identical. Additional information: a. C, is taken to be 4.18 kJ/kg K b. Boiling point rise can be neglected c. The overall heat transfer coefficients are as follows: First effect= 2.5 kW/m? K Second effect= 2.0 kW/m2 K d. Since the feed enters as a cold stream, the first effect requires more heat than the second effect. AT1 must be increased and AT2 must be decreased proportionately. In this case, assume AT, is increased by 2 degrees K and AT, is decreased by 2 degrees K. 2.1. Draw the flowsheet for this process and define the applicable operating conditions for each effect. (2) 2.2. Calculate the steam consumption required? (19)