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Shell and tube heat exchanger's knowledge

Release time:

2025-01-07

Basic knowledge of shell and tube heat exchangers

Shell and tube heat exchanger is also called tube heat exchanger. It is a wall heat exchanger with the wall surface of the tube bundle enclosed in the shell as the heat transfer surface. This heat exchanger is simple in structure, reliable in operation, can be made of various structural materials (mainly metal materials), can be used at high temperature and high pressure, and is the most widely used type at present.

Structure and type of shell and tube heat exchanger

The shell and tube heat exchanger is composed of a shell, a heat transfer tube bundle, a tube plate, a baffle plate and a tube box. The shell is mostly cylindrical, and the tube bundle is arranged inside, and the two ends of the tube bundle are fixed on the tube plate.

The cold and hot fluids for heat transfer, one of which flows in the tube, are called tube flow; The other flows outside the tube, called shell flow. In order to improve the heat transfer coefficient of the fluid outside the tube, a number of baffles are usually installed in the shell.

The baffle can increase the velocity of the shell fluid, force the fluid to pass through the tube bundle several times according to the specified path, and enhance the degree of fluid turbulence.

The heat exchange tubes can be arranged in equilateral triangles or squares on the tube plate. The equilateral triangle arrangement is compact, the fluid turbulence outside the tube is high, and the heat transfer coefficient is large. The square arrangement is convenient for cleaning outside the tube and is suitable for fluids that are easy to scale.

Each time a fluid passes through a tube bundle is called a tube pass; Each pass through the shell is called a shell pass. The diagram shows the simplest single-shell single-tube heat exchanger, referred to as type 1-1 heat exchanger. In order to increase the fluid velocity in the pipe, partitions can be arranged in the pipe boxes at both ends to divide all the pipes into several groups.

In this way, the fluid only passes through part of the pipe at a time, and therefore goes back and forth many times in the tube bundle, which is called multi-pipe. Similarly, in order to increase the flow rate outside the tube, a longitudinal baffle can also be installed in the housing to force the fluid through the housing space several times, known as multiple shell passes. Multi-pass and multi-shell pass can be used together.

Because the temperature of the fluid inside and outside the tube is different, the temperature of the shell and tube bundle of the heat exchanger is also different. If the temperature difference between the two is very large, the heat exchanger will produce a large thermal stress, causing the tube to bend, break, or pull away from the tube plate.