design of spiral plate heat exchanger is based on such an idea: by changing the arrangement of baffle on the shell side, the fluid on the shell side can flow in a continuous spiral shape. Therefore, the ideal baffle arrangement should be a continuous spiral surface. However, it is difficult to process the spiral surface, and the matching of heat exchange tube and baffle is also difficult to realize. Considering the convenience of machining, a series of fan-shaped plane plates (called spiral baffles) are used to replace the connection of curved surfaces to form an approximate spiral surface on the shell side, so that the fluid on the shell side has an approximate continuous spiral flow. Generally speaking, for the consideration of machining, a pitch of 2-4 baffles can be selected, and there are two ways of continuous lapping and staggered lapping between adjacent baffles. According to the flow channel, it can be divided into single helix and double helix structures.