Shell and tube heat exchanger, also known as tubular heat exchanger. It is a partition type heat exchanger with the wall of the tube bundle enclosed in the shell as the heat transfer surface. This type of heat exchanger has a relatively simple structure and can be made of different structural materials (mainly metal materials). It can be used at high temperatures and pressures and is currently a widely used type.

structure

A shell and tube heat exchanger consists of a shell, heat transfer tube bundle, tube plate, baffle (baffle), and tube box. The shell is mostly cylindrical and equipped with tube bundles, which are fixed at both ends on the tube plate. Two types of fluids, hot and cold, are used for heat exchange. One flows inside the tube and is called the tube side fluid; Another type of fluid that flows outside the tube is called shell side fluid. To increase the heat transfer coefficient of the fluid outside the tube, several baffles are usually installed on the shell. The baffle can increase the velocity of the shell side fluid, forcing the fluid to pass through the bundle laterally multiple times along the specified path, thereby increasing 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 relatively compact, resulting in high turbulence of the fluid outside the tube and a large heat transfer coefficient; Square arrangement makes cleaning outside the tube convenient and suitable for fluids that are prone to scaling.

FPR floating coil volumetric heat exchanger

FPR floating coil volumetric heat exchanger

Each passage of fluid through a tube bundle is called a tube pass; Each pass through the shell is called a shell pass. The illustrated single shell and single tube heat exchanger, abbreviated as 1-1 type heat exchanger. To increase the fluid velocity inside the tube, partitions can be installed inside both ends of the tube box to divide the tube into several groups. This way, the fluid only passes through a portion of the tubes at a time, so it travels back and forth multiple times in the bundle, which is called multi tube pass. Similarly, to increase the flow velocity outside the pipe, longitudinal baffles can also be installed in the shell to force the fluid to pass through the shell space multiple times, known as multi shell pass. Multi tube and multi shell can be used in conjunction.

type

Due to the different temperatures of the fluid inside and outside the tube, the shell and tube bundle of a shell and tube heat exchanger also have different temperatures. If there is a significant temperature difference between the two, a large thermal stress will be generated inside the heat exchanger, causing the tubes to bend, break, or detach from the tube sheet. Therefore, when the temperature difference between the tube bundle and the shell exceeds 50 ℃, appropriate compensation measures need to be taken to reduce thermal stress. According to compensation measures, shell and tube heat exchangers can be divided into the following main types:

① The tube plates at both ends of the fixed tube plate heat exchanger bundle are integrated with the shell, with a simple structure, but only suitable for heat exchange operations when the temperature difference between cold and hot fluids is not large and the shell side does not require mechanical cleaning. When the temperature difference is slightly large and the shell side pressure is not too high, an elastic compensation ring can be installed on the shell to reduce thermal stress.

② The tube plate at one end of the floating head heat exchanger bundle can float freely, reducing thermal stress; And the entire bundle can be extracted from the shell for easy mechanical cleaning and maintenance. Floating head heat exchangers have a wide range of applications, but their structures are relatively complex and their costs are high.

③ Each heat exchange tube of the U-shaped tube heat exchanger is bent into a U-shape, with both ends fixed in the upper and lower zones of the same tube plate, and divided into inlet and outlet chambers by partitions inside the tube box. This type of heat exchanger reduces thermal stress and has a simpler structure than the floating head type, but the tube side is difficult to clean.

④ The eddy current hot film heat exchanger adopts a new eddy current hot film heat transfer method, which increases heat transfer by changing the fluid motion state. When the medium passes through the surface of the eddy current tube, it flushes the tube surface, thereby improving heat transfer efficiency. Up to 10000W/m2 ℃. At the same time, this structure achieves the functions of corrosion resistance, temperature resistance, pressure resistance, and minimal scaling. The fluid channels of other types of heat exchangers are in the form of fixed directional flow, forming a swirling flow on the surface of the heat exchange tube and reducing the convective heat transfer coefficient.

According to the promotion of heat exchange equipment, the characteristic of vortex heat film heat exchangers is their unified economic efficiency. Due to the consideration of the flow relationship between the heat exchange tubes and between the heat exchange tubes and the shell, turbulence is not forced out by using baffles to forcefully block it. Instead, alternating vortex flows are naturally induced between the heat exchange tubes, and the appropriate vibration force is maintained without friction between the heat exchange tubes. The rigidity and flexibility of the heat exchange tubes are well configured and will not collide with each other, which not only overcomes the problems caused by collisions between floating coil heat exchangers, but also reduces the problem of scaling in ordinary shell and tube heat exchangers.