Properties of evaporating liquid 1. Concentration: As the concentration increases, the solution becomes more and more individualistic. The viscosity and density increase with solid content. The boiling point of the solution also increases with solid content. 2. Foaming: Some of the materials have tendency to foam that causes heavy entrainment. 3. Scale: Some solutions deposit scale on the heat transfer surface that results in reduction of heat transfer rate. 4. Temperature sensitivity: Some materials especially pharmaceuticals and food products are damaged when heated to moderate temperatures even for short time. For concentrating such materials, special techniques are to be used that reduce temperature and time of heating. 5. Material of construction: Generally evaporators are made of mild steel. Whenever contamination and corrosion is a problem, special materials such as copper, nickel, stainless steel may be used.