What are the differences between various heat exchangers?

3.6.1 Classification of heat exchangers According to their uses, they can be divided into heaters, coolers, condensers, evaporators and reboilers. According to the principles and methods of heat exchange between cold and hot fluids, they can be divided into three categories:: Hybrid type, thermal storage type, partition type. Main content: (1) Performance and characteristics of various heat exchangers in order to select the appropriate type according to industrial requirements. (2) Determine the basic size of the heat exchanger, calculate the heat transfer area, and calculate the fluid resistance, etc., so as to select the appropriate specifications among the heat exchangers with serialized standards. Partitioning wall heat exchangers are most widely used. The following focuses on the types, calculations, etc. of this type of heat exchanger. Types of dividing wall heat exchangers 1. Jacketed heat exchanger structure: The jacket is placed outside the container, forming a closed space between the jacket and the container wall, which becomes a fluid channel. advantage: It has simple structure and convenient processing. shortcoming: The heat transfer area A is small and the heat transfer efficiency is low. use: Widely used for heating and cooling of reactors. In order to improve the heat transfer effect, a stirrer or coiled tube and external circulation can be added to the kettle. 2. Structure of immersed coiled tube heat exchanger: Snake tubes are generally made of bent metal tubes, adapted to the shape required by the container, and immersed in the container, allowing hot and cold fluids to exchange heat inside and outside the tube. advantage: The structure is simple, easy to prevent corrosion, and can withstand high pressure. shortcoming: The heat transfer area is not large, and the convection heat transfer coefficient outside the coiled tube is small. In order to enhance heat transfer, stirring is added inside the container. 3. Spray heat exchanger structure: The cooling water pours down from the spray device of the uppermost pipe and flows down the pipe surface. The cooled fluid flows in from the uppermost pipe and flows out from the lowermost pipe to exchange heat with the cooling water outside. During the downstream process, cooling water can be collected and redistributed. advantage: It has a simple structure, low cost, high pressure resistance, easy maintenance and cleaning, and good heat transfer effect. shortcoming: The cooling water spray is not easy to be uniform and affects the heat transfer effect, so it can only be installed outdoors. use: Used to cool or condense liquids in pipes. 4. Structure of sleeve-and-tube heat exchanger: Concentric casings composed of different diameters can be connected with U-shaped tubes according to heat exchange requirements to increase the heat transfer area. ； Hot and cold fluids can flow countercurrently or concurrently. advantage: It has a simple structure, is easy to process, can withstand high pressure, has a large heat transfer coefficient, can maintain complete counterflow to maximize the average logarithmic temperature difference, and can increase or decrease the number of pipe sections for easy application. shortcoming: The structure is not compact, the metal consumption is large, the joints are many and easy to leak, and it occupies a large area. use: It is widely used in ultra-high pressure production processes and can be used in situations where the flow rate is small and the required heat transfer area is small. 5. Tube heat exchanger (shell and tube heat exchanger) Tube heat exchanger, also known as shell and tube heat exchanger, is the most typical dividing wall heat exchanger. It has a long history and plays a leading role. It is mainly composed of shell, tube bundle, tube plate, baffle and head. A fluid flows in a tube, and its journey is called the tube path ； Another fluid flows outside the tube, and its journey is called the shell side. The wall surface of the tube bundle is the heat transfer surface. advantage: The heat transfer area per unit volume provided by the equipment is large, the heat transfer effect is good, the structure is solid, a wide range of structural materials can be selected, and the operation flexibility is large, and it is commonly used in large-scale installations. In order to increase the flow rate of the shell-side fluid, a certain number of baffles that are perpendicular to the tube bundle are often installed in the shell. The baffles not only prevent the fluid from short-circuiting and increase the fluid flow rate, but also force the fluid to cross-flow through the tube bundle multiple times according to the prescribed path, greatly increasing the degree of turbulence. Commonly used baffles include round and disc shapes, with the former being more commonly used. A tube bundle is installed in the shell, and both ends of the tube bundle are fixed on the tube plate. Due to the different temperatures of hot and cold fluids, the shell and the tube bundle are heated differently and expand to different degrees. If the temperature difference between the two is large, the tubes will twist, fall off the tube sheet, and even damage the heat exchanger. Therefore, the tube-and-tube heat exchanger must consider the influence of thermal expansion from the structure and adopt various compensation methods to eliminate or reduce thermal stress. According to the temperature difference compensation measures taken, tube and tube heat exchangers can be divided into the following types. (1) If the temperature difference between the fixed tube plate shell and the heat transfer tube wall is greater than 50C, a compensation ring, also called an expansion joint, is added. When there is a temperature difference between the shell and the tube bundle, the elastic deformation of the compensation ring is used to adapt to the different thermal expansion between them. Features: The structure is simple, the cost is low, and the maintenance and cleaning of the shell side are difficult. The shell side must be a clean medium that is not prone to scale and corrosion. (2) The tube sheets at both ends of the floating head type are not connected to the shell at one end and can float freely along the length of the tube. When the temperature difference between the shell and the tube bundle causes thermal expansion, the tube bundle together with the floating head can freely expand and contract in the axial direction within the shell, completely eliminating thermal stress. Features: The structure is relatively complex, the cost is high, and the temperature difference stress is eliminated. It is a structural form that is widely used. (3) The U-shaped tube type bends each tube into a U shape, and fixes both ends on the same tube plate. Each tube can be freely expanded and contracted to solve the thermal compensation problem. Features: The structure is relatively simple, and the tube side is not easy to clean. It is often a clean fluid and is suitable for heat exchange of high-pressure gas. The above is the structure, advantages and disadvantages of commonly used heat exchangers. The information is good, please try it out. Thank you for your support! ! !

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