Heat exchanger units often appear problems and deal with the treatment method, some common problems may often be ignored. It is very common and easy to be ignored in the operation of plate heat exchanger units, and the treatment methods are summarized, which has certain reference significance for the designers and users of plate heat exchanger units. Shell and tube heat exchanger shell and tube heat exchanger is also called tube heat exchanger. Is enclosed in the shell tube bundle wall as the heat transfer surface of the recuperator heat exchanger. This kind of heat exchanger is simple in structure, reliable in operation, can be made of various structural materials, can be used under high temperature and high pressure, and is a widely used type at present. The structure is composed of shell, heat transfer tube bundle, tube sheet, baffle plate and tube box. The shell is mostly cylindrical, with a tube bundle inside, and the two ends of the tube bundle are fixed on the tube plate. Heat exchange of two kinds of fluid, a flow in the tube, called the tube side fluid; another kind of flow in the tube, called the shell side fluid. In order to improve the heat transfer coefficient of the fluid outside the tube, several baffles are usually installed in the shell. The baffle can increase the fluid velocity on the shell side, forcing the fluid to pass through the tube bundle several times laterally according to the specified distance, and enhancing the degree of fluid turbulence. The heat exchange tubes may be arranged in an equilateral triangle or square on the tube sheet. The equilateral triangle arrangement is compact, the turbulence degree of the fluid 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 the fluid passes through the tube bundle is called a tube pass; each time it passes through the shell is called a shell pass. The diagram shows a very simple single shell pass single tube pass heat exchanger, referred to as 1-1 heat exchanger. In order to increase the velocity of the fluid in the tube, partitions can be set in the tube box at both ends, and all the tubes can be divided into several groups. In this way, the fluid only passes through part of the tubes at a time, so it goes back and forth many times in the tube bundle, which is called multi-tube pass. Similarly, in order to increase the flow rate outside the tube, longitudinal baffles can also be installed in the shell to force the fluid to pass through the shell space multiple times, which is called multi-shell pass. Multi-tube side and multi-shell side can be used together. Type 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 two temperatures are very different, a large thermal stress will be generated in the heat exchanger, causing the tube to bend, break, or pull off the tube sheet. Therefore, when the temperature difference between the tube bundle and the shell exceeds 50 ℃, appropriate compensation measures should be taken to eliminate or reduce the thermal stress.
According to the compensation measures adopted, shell and tube heat exchangers can be divided into the following main types: ① The tube plates at both ends of the tube bundle of the fixed tube plate heat exchanger unit are integrated with the shell, with simple structure, but only suitable for heat exchange operation when the temperature difference between cold and hot fluids is not large and the shell side does not need 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 the thermal stress. The tube sheet at one end of the floating head heat exchanger tube bundle can float freely, completely eliminating thermal stress; and the entire tube bundle can be extracted from the shell, which is convenient for mechanical cleaning and maintenance. The floating head heat exchanger is widely used, but the structure is more complex and the cost is higher. ③ U-tube heat exchanger Each heat exchange tube is bent into a U-shape, both ends are fixed on the same tube plate up and down two areas, with the help of the tube box partition is divided into inlet and outlet two chambers. This heat exchanger completely eliminates the thermal stress, the structure is simpler than the floating head, but the tube is not easy to clean. Non-metallic material heat exchanger in the chemical production of strong corrosive fluid heat transfer, need to use ceramic, glass, PTFE, graphite and other non-metallic materials to make shell and tube heat exchanger. This type of heat exchanger has poor heat transfer performance and is only used for occasions with low pressure, low vibration and low temperature. Selection of flow channels The hot and cold fluids for heat exchange shall be selected according to the following principles: ① unclean and scaling fluid should go through the tube path, because cleaning in the tube is more convenient; ② Corrosive fluid should go through the tube path to avoid corrosion of tube bundle and shell at the same time; ③ Fluid with high pressure should go through the tube path to prevent the shell from bearing pressure. ④ Saturated steam should go through the shell path, because the steam condensation heat transfer coefficient has nothing to avoid, and the condensate is easy to discharge; ⑤ If the temperature difference between the two fluids is large, when selecting a fixed tube plate heat exchanger unit, it is advisable to make the fluid with large heat transfer coefficient go through the shell to reduce the thermal stress. When the heat transfer coefficient on both sides of the tube wall is very different (such as the heat exchange between liquid and gas with small viscosity), the thermal resistance on the side with low heat transfer coefficient should be reduced. If the heat transfer coefficient outside the tube is small, an externally threaded tube (low finned tube) can be used to increase the heat transfer area and fluid turbulence on the outer side of the tube and reduce the thermal resistance. If the heat transfer coefficient in the tube is small, twist iron, spiral ring and other additives can be set in the tube to enhance the disturbance in the tube and enhance the heat transfer. Of course, the flow resistance of the fluid will also increase at this time. The content of the article comes from the internet, please contact me to delete it if you have any questions!