EVAPORATOR

Frequently in the food industry a raw material or a potential foodstuff contains more water than is required in the final product. When the foodstuff is a liquid, the easiest method of removing the water, in general, is to apply heat to evaporate it. Evaporation is thus a process that is often used by the food technologist.
The basic factors that affect the rate of evaporation are the:
rate at which heat can be transferred to the liquid,
quantity of heat required to evaporate each kg of water,
maximum allowable temperature of the liquid,
pressure at which the evaporation takes place,
changes that may occur in the foodstuff during the course of the      evaporation process.

Considered as a piece of process plant, the evaporator has two principal functions, to exchange heat and to separate the vapour that is formed from the liquid.
Important practical considerations in evaporators are the:
maximum allowable temperature, which may be substantially below 100°C.
promotion of circulation of the liquid across the heat transfer surfaces, to attain reasonably high      heat transfer coefficients and to prevent any local overheating,
viscosity of the fluid which will often increase substantially as the concentration of the dissolved materials      increases,
tendency to foam which makes separation of liquid and vapour difficult.