Heat exchanger type and average temperature difference heat exchanger: it is used to transfer heat from hot fluid to cold fluid to meet the specified process requirements. 9.2.1 classification of heat exchanger????? Casing type? Shell and tube filter????? Tube bundle??????? Plate fin????? Spiral plate cross flow heat exchanger shell and tube type???????? Regenerative hybrid wall type tube bundle type tube fin type tube belt type according to the operation process? Inter wall heat exchanger: refers to the heat exchanger in which the cold and hot fluid is separated by the wall for heat exchange. Such as air heater, gas heater, condenser and evaporator;? There are many kinds of wall heat receiver, which can be divided into shell and tube type, shell and tube type? There are many kinds of wall heat receiver, which can be divided into shell and tube type, fin tube type, plate type, plate fin type, spiral plate type and so on. The former two types are most widely used. In addition, according to the direction of fluid flow, there are downstream, countercurrent and cross flow. Regenerative heat exchanger: the heat exchanger is composed of heat storage materials and is divided into two parts. The cold and hot fluid alternately passes through half of its channel, so as to alternately absorb and release heat, that is, when the hot fluid flows through the heat exchanger.