Shell-and-tube heat exchangers use wall of the tube bundle enclosed in the shell as the heat transfer surface. This kind of heat exchanger has simple structure, reliable operation, can be made of various structural materials, can be used under high temperature and high pressure, and is currently a widely used type. For the selection of shell and tube heat exchangers, the structural parameters are considered as follows:
1. Number of tube passes and shell pass type
There are several kinds of tube passes from 1 to 12. As the number of tube passes increases, the flow rate in the tube increases, and the heat transfer coefficient also increases. However, it will be affected by the pressure drop, and the flow rate in the pipe has a certain limit. The flow rate of water and similar water solutions is generally 1~2.5m/s. The flow rate of gas and steam can be selected between 8~30m/s.
2. The structural parameters of the tube
In order to meet the allowable pressure drop, it is generally recommended to use a 19mm pipe. For materials with easy structure, a tube with an outer diameter of 25mm is used to facilitate cleaning. Considering the tube manufacturing difficulty, heat transfer coefficient and pressure drop, the tube length is generally 4~6m. For large area or non-phase change heat exchangers, the tube length can be 8~9m. The distribution of pipes on the tube plate is mainly in two forms: square distribution and triangle distribution. The triangular distribution is conducive to the turbulence of the shell side. The square distribution is conducive to the cleaning of the shell side.
3. Shell side baffle
Baffle plate can change the direction of shell side fluid, make it flow perpendicular to the tube bundle, and obtain better heat transfer effect. The baffle mode can be divided into round baffle, ring-disc baffle and hole baffle.