3. A plate evaporator is concentrating milk from 10% solids to 30% solids at a feed rate of 1500 kg h-. Heating is by steam at 200 kPa absolute and the evaporating temperature is 75C. (a) Calculate the number of plates needed if the area of heating surface on each plate is 0.44 m2 and the overall heat-transfer coefficient 650 J m 2 s1.c(b) If the plates, after several hours running become fouled by a film of thickness 0.1 mm, and of thermal conductivity 0.1 Jm15-1c-1, by how much would you expect the capacity of the evaporator to be reduced? [(a) 50 (b) 13% of its former value]