Shell and tube air separation heat exchanger is the most representative wall heat exchanger. It has a long history of application and is still dominant in all heat exchangers.
Shell and tube heat exchanger is mainly composed of shell, tube bundle, tube sheet and head. Most of the shell is round, and there are parallel tube bundles inside. Both ends of the tube bundle are fixed on the tube plate. In shell and tube heat exchanger, there are two kinds of fluids for heat exchange. One kind of fluid flows in the tube, and its stroke is called tube side. The other flows outside the tube and its stroke is called shell side. The wall of tube bundle is the heat transfer surface. In order to improve the heat transfer coefficient of the fluid outside the tube, a certain number of transverse baffles are usually installed in the shell. The baffle can not only prevent the short circuit of the fluid and increase the velocity of the fluid, but also force the fluid to flow through the tube bundle many times according to the predetermined path, thus greatly increasing the turbulence degree. The commonly used baffle plate is circular and disc-shaped, and the former is more widely used. Each time the fluid passes through the tube bundle is called a tube pass, and each time it passes through the shell is called a shell pass. In order to improve the velocity of the fluid in the pipe, the appropriate baffles can be set at both ends of the head to divide all the pipes into several groups. In this way, the fluid can only pass through a part of the pipe bundle several times at a time, which is called multi tube pass. Similarly, in order to increase the flow rate outside the tube, a longitudinal baffle can be installed in the shell to make the fluid pass through the shell space many times, which is called multi shell pass. In shell and tube heat exchanger, the temperature of shell and tube bundle is different due to the different fluid temperature inside and outside the tube. If there is a large temperature difference between the two, there will be large thermal stress inside the heat exchanger, which may cause the tube to bend, break or loosen from the tubesheet. Therefore, when the temperature difference between tube bundle and shell exceeds 50°C, appropriate temperature difference compensation measures should be taken to eliminate or reduce the thermal stress.
