Heat exchanger is a kind of heat exchange equipment which transfers part of the heat of hot fluid to cold fluid and makes the fluid temperature reach the index specified in the process flow, also known as heat exchanger. 2、 The classification of heat exchangers is applicable to heat exchangers with different media, different working conditions, different temperatures and different pressures, and their structural types are also different. The specific classification of heat exchangers is as follows: (1)_ Heat exchanger is classified according to the principle of heat transfer. 1. Surface heat exchanger: surface heat exchanger is the flow of two kinds of fluids with different temperatures in the space separated by the wall. Through the wall heat conduction and fluid convection on the wall surface, the heat transfer between the two fluids is carried out. Surface type heat exchanger has shell and tube type, sleeve type and other types of heat exchanger. 2. Regenerative heat exchanger: the regenerative heat exchanger transfers heat from high-temperature fluid to low-temperature fluid through the heat storage body composed of solid materials. The hot medium first reaches a certain temperature by heating solid materials, and then the cold medium is heated by solid materials to achieve the purpose of heat transfer. Regenerative heat exchanger has rotary type, valve switching type and so on. 3. Fluid connected indirect heat exchanger: fluid connected indirect heat exchanger is a heat exchanger that connects two surface heat exchangers by circulating heat carrier, which circulates between high temperature fluid heat exchanger and low temperature fluid.