Tubular heat exchanger is one of the most widely used heat exchangers in chemical industry and alcohol production. It is mainly composed of shell, tubesheet, heat exchange tube, head and baffle. Figure (4) shows the schematic diagram of the most common type of tubular heat exchanger-fixed tubesheet. A plurality of parallel tubes are installed in the circular shell, and both ends of the tube bundle are welded or expanded on the tube plate (commonly known as the flower plate). The head with inlet and outlet pipes is connected with tube plates welded at both ends of the shell by screws, and the space between the head and the tube plate constitutes a fluid distribution chamber. Because the tubesheet, shell and tube are welded together and their positions are completely fixed, it is called fixed tubesheet. The required materials can be made of ordinary carbon steel, copper or stainless steel. During heat exchange, a fluid enters from the connecting pipe of the head, flows in the pipe and flows out from the outlet pipe at the other end of the head, which is called tube side; Another fluid enters from the nozzle of the shell and flows out from another nozzle on the shell, which is called shell side.

In tube heat exchanger, the surface area of tube bundle is the heat transfer area of heat exchanger. When the heat transfer area is large and the number of tubes is large, in order to improve the flow velocity of the fluid in the tubes and increase the heat transfer film coefficient of the fluid on one side of the tubes, all the tubes are often divided into several groups on average, and the fluid only flows through one group of tubes at a time, that is, the multi-tube pass structure is adopted. The method comprises the following steps: installing a partition plate in a head, and installing the partition plate in a head at one end to form two pipe passes; Install two baffles at the inlet end and one baffle at the other end to form a four-tube channel; In this way, other multi-tube passes can be set, but too many will increase the fluid resistance, the partition will occupy the area of the distribution tube, and the heat transfer area will decrease.

In the condenser used for alcohol distillation, in order to improve the fluid velocity in the shell, a certain number of baffles perpendicular to the tube bundle are usually installed in the shell. There are two common types of baffles: circular notch (also known as bow plate) and disc ring.