Heat exchange equipment classification 3. Inter wall heat exchanger (also known as surface heat exchanger or indirect heat exchanger) (1) principle: it is the use of inter wall (solid wall) to separate the cold and hot fluids for heat exchange, the cold and hot fluids for heat exchange are separated, and they are not in contact with each other, the heat is transferred from the hot fluid to the cold fluid through the inter wall. It is the most widely used heat exchanger in industry. Non contact section II Classification of heat exchange equipment (2) classification: Section II Classification of heat exchange equipment (3) features: various forms, wide application, etc（ 4) It is suitable for the situation where cold and hot fluids are not allowed to mix（ 2） Heater: used to heat the fluid to the required temperature, the heated fluid does not have phase change during heating. 2. Preheater: it is used to preheat the fluid to improve the efficiency of the whole process unit. Efficiency. 3. Superheater: used to heat saturated steam to superheat state. 4. Evaporator: it is used to heat the liquid and make it evaporate. 5. Reboiler: it is used to heat the condensed liquid and make it vaporize again. It is a special equipment for distillation process. 6. Cooler: used to cool the fluid to the required temperature. 7. Condenser: it is used to cool condensable saturated steam to release latent heat for condensation and liquefaction. Section 2 classification of heat exchange equipment (3) according to the materials used 1. Heat exchanger made of metal materials. Commonly used materials are carbon steel, alloy steel, copper and copper alloy, aluminum and aluminum alloy, titanium and titanium alloy. Because of the high thermal conductivity of metal materials.