First, the concept of heat exchanger \ x0d \ x0d \ A heat exchanger is a device that transfers part of the heat of a hot fluid to a cold fluid, also known as a heat exchanger. Heat exchanger is a common equipment in chemical industry, petroleum, electric power, food and many other industrial sectors, and plays an important role in production. In chemical production, heat exchangers can be used as heaters, coolers, condensers, evaporators and reboilers. , and more widely used. Due to different purposes, types and performances, heat exchange equipment can be divided into shell-and-tube structure and plate structure. \x0d\\x0d\ II。 Working principle of heat exchanger \ x0d \ x0d \ A heat exchanger is a device that transfers part of the heat of a hot fluid to a cold fluid, that is, water or other media is filled in a large closed container, and a pipeline passes through the container. Let hot water flow through the pipe. Because of the temperature difference between the hot water in the pipeline and the cold and hot water in the container, heat exchange will be formed, which is the thermal balance of junior high school physics. The heat of a high-temperature object is always transferred to a low-temperature object, so that the heat of water in the pipeline is exchanged to the cold water in the container. A heat exchanger is also called a heat exchanger. \x0d\\x0d\ III。 \ x0d \ x0d \ heat exchangers with mechanical structure can be classified in many ways, which can be classified according to heat transfer principle, structure and use. According to its structure, there are two main types: shell-and-tube type and plate type. \ x0d \ x0d \ According to the principle and mode of heat exchange between cold and hot fluids, it can be basically divided into three categories, namely, zonal type, mixed type and heat storage type. \x0d\\x0d\ 1, type of baffle heat exchanger \x0d\\x0d\ Jacket heat exchanger This kind of heat exchanger is formed by installing a jacket on the outer wall of the container and has a simple structure; However, the heating surface is limited by the wall of the container, and the heat transfer coefficient is not high. In order to improve the heat transfer coefficient and make the liquid in the kettle heated evenly, a stirrer can be installed in the kettle. When cooling water or heating agent without phase change is introduced into the jacket, spiral baffles or other measures to increase turbulence can be installed in the jacket to improve the heat transfer coefficient at one side. In order to supplement the heat transfer surface, a serpentine tube can also be installed in the pot. Jacket heat exchanger is widely used for heating and cooling in the reaction process. \x0d\\x0d\ Immersed snake tube heat exchanger This kind of heat exchanger bends the metal tube into various shapes suitable for the container and immerses it in the liquid in the container. The advantages of serpentine heat exchanger are simple structure, high pressure resistance and corrosion resistance. Its disadvantages are low turbulence of liquid in the container and low heat transfer coefficient outside the tube. In order to improve the heat transfer coefficient, a stirrer can be installed in the container. \ x0d \ x0d \ spray heat exchanger This kind of heat exchanger is called spray cooler because rows of heat exchange tubes are fixed on a steel frame, hot fluid flows in the tubes, and cooling water drips evenly from the upper spray device. The outside of spray heat exchanger is a liquid film with high turbulence, and the heat transfer coefficient outside the tube is much higher than that of immersion heat exchanger. In addition, most of these heat exchangers are placed in the air circulation area, and the evaporation of cooling water also takes away some heat. \x0d\\x0d\ Double-tube heat exchanger A double-tube heat exchanger is a concentric tube composed of straight tubes with different diameters, which are connected by U-shaped elbows. In this heat exchanger, one fluid passes through the tube and the other fluid passes through the annular gap, both of which can obtain higher flow rate, so the heat transfer coefficient is larger. In addition, in the double-tube heat exchanger, the two fluids can be pure countercurrent, and the logarithmic average driving force is large. The invention has simple structure, high pressure resistance and convenient use (the number of pipe sections can be increased or decreased as required). In particular, because of the advantages of large heat transfer coefficient, large heat transfer driving force and high pressure resistance, the heat exchangers used in ultra-high pressure production processes (such as high-pressure polyethylene production process with operating pressure of 3000 atmospheres) are almost always sleeve-type. \x0d\\x0d\ Shell-and-tube heat exchanger Shell-and-tube heat exchanger is the most typical baffle heat exchanger, which has a long history of industrial application and still occupies a dominant position in all heat exchangers. \ x0d \ x0d \ Shell-and-tube heat exchanger is mainly composed of shell, tube bundle, tube sheet and head. The shell is mostly round, with parallel tube bundles inside, and both ends of the tube bundle are fixed on the tube sheet. Two fluids that exchange heat in a shell-and-tube heat exchanger, one flows in the tube, and its stroke is called tube side; A kind of flow outside the tube, its stroke is called shell side. The wall surface of the tube bundle is the heat transfer surface. In order to improve the heat transfer coefficient of the fluid outside the tube, a certain number of transverse baffles are usually installed in the shell. Baffles can not only prevent the fluid from short circuit and improve the fluid velocity, but also force the fluid to pass through the tube bundle many times according to the specified path, which greatly increases the turbulence. There are two kinds of baffles commonly used: circular notch and disk, and the former is more widely used. Every time the fluid passes through the tube bundle in the tube, it is called tube side, and every time it passes through the shell, it is called shell side. In order to improve the flow velocity of the fluid in the pipe, appropriate baffles can be set in the heads at both ends to divide all the pipes into several groups equally. In this way, the fluid can only pass through some tubes and return to the tube bundle many times at a time, which is called multi-tube pass. Similarly, in order to improve the flow velocity outside the tube, longitudinal baffles can be installed in the shell to make the fluid pass through the shell space many times, which is called multi-shell pass. In the shell-and-tube heat exchanger, the temperature of shell side and tube bundle is different because of the different fluid temperatures inside and outside the tube. If the temperature difference between them is large, great thermal stress will be generated inside the heat exchanger, which may make the tube bend, break or loosen from the tubesheet. Therefore, when the temperature difference between tube bundle and shell exceeds 50℃, appropriate temperature difference compensation measures should be taken to eliminate or reduce thermal stress. \ x0d \ x0d \ 2。 Hybrid heat exchanger \ x0d \ x0d \ Hybrid heat exchanger relies on direct contact between hot and cold fluids for heat transfer. This heat transfer method avoids the fouling thermal resistance of the heat transfer partition and its two sides. As long as there is good contact between fluids, there will be a great heat transfer rate. Therefore, where fluids are allowed to mix with each other, hybrid heat exchangers can be used, such as gas washing cooling, circulating water cooling, mixed heating of steam and water, steam condensation and so on. Widely used in chemical metallurgical enterprises, power engineering, air conditioning engineering and many other production departments. \x0d\\x0d\ According to different uses, the hybrid heat exchanger can be divided into the following different types: \ x0d \ (1) cooling tower \x0d\\x0d\ In this equipment, natural ventilation or mechanical ventilation is adopted to improve the output. For example, circulating water in thermal power plants or nuclear power plants, cooling water in synthetic ammonia production, etc. After being cooled by water cooling tower, it can be recycled. This method has been widely used in practical engineering. \x0d\ \x0d\(2) Gas scrubber (or scrubber) \x0d\ \x0d\ There are many uses for washing gas in industry, such as absorbing some components in gas mixture with liquid, removing dust from clean gas, humidifying or drying gas, etc. But its most extensive use is cooling gas, and the liquid used for cooling is mostly water. Spray chamber, which is widely used in air conditioning engineering, can be considered as a special form of it. The shower room can not only cool the air like a gas scrubber, but also heat the air. However, it also has some shortcomings, such as high requirements for water quality, large area and high energy consumption of pumps. Therefore, at present, the spray room is not often used in general buildings or only used as humidification equipment. But it is still widely used in textile mills and cigarette factories whose main purpose is to regulate humidity! \x0d\ \x0d\(3) Jet heat exchanger \x0d\ \x0d\ In this equipment, high-pressure fluid is ejected from the nozzle to form a high speed, and low-pressure fluid is introduced into the mixing chamber to directly contact with the jet for heat transfer, and then enters the diffusion tube together, and is delivered to the user after the outlet of the diffusion tube reaches the same pressure and temperature. \x0d\\x0d\(4) Hybrid condenser \x0d\\x0d\ This equipment usually condenses steam by direct contact between water and steam. \x0d\\x0d\3。 Regenerative heat exchanger \ x0d \ x0d \ Regenerative heat exchanger is used for regenerative heat exchange. Built-in solid filler is used to store heat. Firebricks are generally used to build fire grids (sometimes corrugated metal strips are used). The heat exchange is carried out in two stages. In the first stage, hot gas passes through the fire grate and transfers heat to the fire grate for storage. In the second stage, the cold gas passes through the fire grate and receives the heat stored in the fire grate to be heated. These two stages alternate. Usually, two heat accumulators are used alternately, that is, hot air enters one and cold air enters the other. It is often used in metallurgical industry, such as regenerator of steelmaking open hearth. It is also used in chemical industry, such as air preheater or combustion chamber of gas furnace and regenerative cracking furnace of artificial stone oil plant. \ x0d \ x0d \ Regenerative heat exchanger is generally used in occasions with low requirements for medium mixing.