The shell-and-tube heat exchanger consists of components such as the shell, heat transfer tube bundle, tube sheet, baffle (partition), and tube box. The shell is usually cylindrical, with the tube bundle installed inside, and the ends of the tube bundle are fixed to the tube sheet. There are two types of fluids involved in heat exchange: one flows inside the tubes, known as the tube-side fluid; the other flows outside the tubes, known as the shell-side fluid. To improve the heat transfer coefficient of the shell-side fluid, several baffles are typically installed inside the shell. The baffles can increase the velocity of the shell-side fluid, forcing it to pass transversely through the tube bundle multiple times along a specified path, enhancing the turbulence of the fluid.

Structure of shell-and-tube heat exchangers

       Shell-and-tubeHeat exchangerIt consists of components such as the shell, heat transfer tube bundle, tube sheets, baffles, and tube boxes. The shell is mostly cylindrical, with the tube bundle installed inside, and the ends of the tube bundle fixed to the tube sheets. The two fluids involved in heat exchange, one flows inside the tubes, called the tube-side fluid; the other flows outside the tubes, called the shell-side fluid. To enhance the heat transfer coefficient of the shell-side fluid, several baffles are usually installed inside the shell. The baffles can increase the velocity of the shell-side fluid, forcing it to pass transversely through the tube bundle multiple times, thereby enhancing the turbulence of the fluid.

       The heat transfer tubes can be arranged in an equilateral triangle or square pattern on the tube sheets. The equilateral triangle arrangement is more compact, resulting in a higher turbulence level of the shell-side fluid and a larger heat transfer coefficient; the square arrangement, however, allows for easier cleaning of the outer tubes, making it suitable for fluids prone to scaling. Each time the fluid passes through the tube bundle is called one tube pass; each time it passes through the shell is called one shell pass. To increase the velocity of the tube-side fluid, partitions can be set up in the tube boxes at both ends, dividing all the tubes into several groups. This way, the fluid only passes through part of the tubes each time, thus traveling back and forth multiple times in the tube bundle, which is called multiple tube passes. Similarly, to increase the shell-side fluid velocity, longitudinal baffles can also be installed inside the shell, forcing the fluid to pass through the shell space multiple times, known as multiple shell passes. Multiple tube passes and multiple shell passes can be used in combination.

       The tube-type heat exchanger (also known as the tube-type condenser) is classified by material into carbon steel tube-type heat exchangers, stainless steel tube-type heat exchangers, and mixed tube-type heat exchangers of carbon steel and stainless steel. It is classified by form into fixed tube sheet type, floating head type, and U-tube type heat exchangers, and by structure into single tube pass, double tube pass, and multiple tube passes, with a heat transfer area of 1 to 500 m², customizable according to user needs.

Classification of shell-and-tube heat exchangers

       Due to the different temperatures of the fluids inside and outside the tubes, the temperatures of the shell and the tube bundle in the heat exchanger are also different. If the temperature difference is significant, large thermal stress will be generated inside the heat exchanger, leading to bending, breaking of the tubes, or detachment from the tube sheets. Therefore, when the temperature difference between the tube bundle and the shell exceeds 50°C, appropriate compensation measures must be taken to eliminate or reduce thermal stress.

       According to the compensation measures adopted, shell-and-tube heat exchangers can be divided into the following main types:

       ① Fixed tube sheet heat exchangers have the tube sheets at both ends of the tube bundle integrated with the shell, making the structure simple, but they are only suitable for heat exchange operations where the temperature difference between the hot and cold fluids is not large, and the shell side does not require mechanical cleaning. When the temperature difference is slightly larger and the shell side pressure is not too high, an elastic compensation ring can be installed on the shell to reduce thermal stress.

       ② Floating head heat exchangers have one end of the tube bundle with a tube sheet that can float freely, completely eliminating thermal stress; the entire tube bundle can be withdrawn from the shell, facilitating mechanical cleaning and maintenance. Floating head heat exchangers are widely used, but their structure is relatively complex and costlier.

       ③ U-tube heat exchangers have each heat transfer tube bent into a U shape, with both ends fixed to the upper and lower sections of the same tube sheet, divided into inlet and outlet chambers by partitions inside the tube box. This type of heat exchanger completely eliminates thermal stress, has a simpler structure than floating head types, but the tube passes are not easy to clean.

       ④ Vortex heat film heat exchangers use the latest vortex heat film heat transfer technology to enhance heat transfer efficiency by changing the fluid's motion state. When the medium passes over the surface of the vortex tubes, it strongly scours the tube surfaces, thereby improving heat exchange efficiency, reaching up to 10000 W/m²°C. At the same time, this structure achieves corrosion resistance, high-temperature resistance, high-pressure resistance, and anti-scaling functions.

       Other types of heat exchangers have fixed directional flow channels, forming a flow around the surface of the heat transfer tubes, which reduces the convective heat transfer coefficient. Data shows that the most significant feature of vortex heat film heat exchangers is the unity of economy and safety. By considering the flow relationships between the heat transfer tubes and between the heat transfer tubes and the shell, it no longer uses baffles to forcibly block and induce turbulence but relies on the natural induction of alternating vortex flows between the heat transfer tubes while ensuring that the tubes do not rub against each other, maintaining the necessary vibrational intensity. The rigidity and flexibility of the heat transfer tubes are well configured, preventing collisions, thus overcoming the damage caused by collisions between floating coil heat exchangers and avoiding the scaling issues common in ordinary shell-and-tube heat exchangers.

       Shell-and-tube heat exchangers are general-purpose process equipment for heat exchange operations. They are widely used in industrial sectors such as chemical engineering, petroleum, petrochemical, electric power, light industry, metallurgy, atomic energy, shipbuilding, aviation, and heating. They hold an extremely important position, especially in petroleum refining and chemical processing facilities.