Falling film evaporators are vertical shell and tube heat exchangers that widely used in industry for the concentration of solutions. It must be mentioned falling film evaporator is a device that is suitable for products with low viscosity and low tendency for fouling. Inside evaporator tube, a fluid layer is distributed as a thin film that absorbs heat from the wall and evaporation begins. In fact, the transfer of heat is carried out by available vapors outside the tubes which they get colder during the heat transfer process. High heat transfer coefficient, low energy loss, rather a low holdup time and ability to handle high capacities are some advantages of this types of evaporator.