Heat exchangers are classified according to different ways of heat transfer: 1. Hybrid heat exchanger. The main working principle of this kind of heat exchanger is that two kinds of media transfer heat each other through contact to realize heat transfer. The contact area directly affects the heat transfer. The medium of this kind of heat exchanger is usually one kind of gas and the other kind of liquid, which is mainly the heat transfer equipment with cooling tower equipment as the main body, But it usually involves mass transfer, so it is difficult to distinguish the relationship with the tower. It is usually classified as tower equipment, and the cooling tower used in chemical plant and power plant is the most typical hybrid heat exchanger. 2. The principle of this kind of heat exchanger is that the hot medium first reaches a certain temperature by heating the solid material, then the cold medium is heated by the solid material, and the cold and hot alternate to achieve the purpose of heat transfer. It is mainly used to recover and utilize the heat of high temperature waste gas. 3. The principle of this kind of heat exchanger is that the cold and hot media are separated by the solid partition, and heat exchange is carried out through the partition. The consumption of this kind of heat exchanger is very large, accounting for 99% of the total. According to the different structure, it can be divided into tube type, plate type and other types.