Question

3-17. A double effect evaporator is fed with a solution that enters the first effect at 40 ° C and must be concentrated from 10% to 50% by weight. For the heating of the first effect, it has saturated steam at 1 at, and in the second effect a pressure is maintained that allows the solution to boil at 50 ° C. The integral coefficients of heat transmission for direct current feeding they are worth 2,500 and 1,500 Kcal / m2.h. ° C for the first and second effects, respectively. The solution does not present an appreciable increase in the boiling point and we can assume that the heat lost to the outside is null. The specific heat of the solution can be assumed equal to its weight fraction of water. Calculate: a) The output concentration of the first effect. b) The boiling temperature in the first effect. c) The economy of the system. d) The heating surface area depending on the supply.

Answer 1

as basis Solution Considie 100kg/he of feed Heal Benefee cocffiunt in first effect f=8500 Kcal/mthoc. Heat teen coeffiunt in second effut ų - 1500 Kcal/mihoc To limparture of steam T tempontice of fiect effect Boiling tempanture in 2nd effut = 50°c boiling TS-T Ts-50 100-T ISDO

B 100-T = 18-75 S125°C Thi biting tempontice in fiest effut 81.25°C