The structure of the shell-and-tube heat exchanger (column heat exchanger) is relatively simple, compact, and inexpensive, but it cannot be mechanically cleaned outside the tube. The heat exchanger tube bundle is connected to the tube sheet, and the tube sheets are respectively welded to the two ends of the shell, and a top cover is connected thereto, and the top cover and the shell are provided with fluid inlet and outlet joints. A series of baffles perpendicular to the bundle of tubes are typically placed outside the tube. At the same time, the connection between the tube and the tube sheet and the outer casing is rigid, and the outside of the tube is a fluid of two different temperatures. Therefore, when the temperature difference between the tube wall and the shell wall is large, due to the difference in thermal expansion between the two, a large temperature difference stress is generated, so that the tube is twisted or the tube is loosened from the tube sheet, and even the heat exchanger is destroyed.
In order to overcome the temperature difference stress, there must be a temperature difference compensation device. Generally, when the temperature difference between the pipe wall and the casing wall is 50 ° C or more, the heat exchanger should have a temperature difference compensation device for safety. However, the compensating device (expansion joint) can only be used when the temperature difference between the shell wall and the tube wall is lower than 60-70 ° C and the shell-side fluid pressure is not high. Generally, when the shell-side pressure exceeds 0.6Mpa, the compensation ring is too thick, it is difficult to expand and contract, and the function of temperature difference compensation is lost. Other structures should be considered.