Evaporators are used for concentration or crystallization of liquids. In most of the cases evaporators are used to increase the solid contents of the liquid product prior to drying. This is a cost effective method of removal of moisture. Depending on the number of effects used in an evaporator the quantity of water evaporated per kilogram of steam increases. In case of multiple effect evaporators, steam jet ejectors or thermo-compressors are used to increase the thermal efficiency.

An evaporator consists of either plate type or shell and tube type heat exchanger. The liquid feed is passed through the heat exchanger and indirectly heated with the help of steam. This operation is either done at atmospheric pressure or under vacuum. Evaporation under vacuum is most energy efficient and also ensures that the product does not get
over heated. The different types of evaporators are: