High-efficiency heat exchange and anti-corrosion equipment – PTFE heat exchangers

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High-efficiency heat exchange and anti-corrosion equipment – PTFE heat exchangers. I. Characteristics of PTFE heat exchangers: PTFE is a special engineering plastic, commonly known as the \"king of plastics\". When used in heat exchangers, it is referred to as a PTFE heat exchanger, and it constitutes a commonly used type of anti-corrosion equipment. There are many types of polytetrafluoroethylene heat exchangers, each with its own distinctive properties. Generally, they can be divided into the following two categories: shell-and-tube heat exchangers (the most widely used and in the largest quantities), and submerged heat exchangers (which are further divided into U-type submerged and coiled tubular submerged types). It has the following characteristics: 1) Excellent corrosion resistance: It remains unaffected by strong acids, strong bases, and strong oxidizing agents, even at extreme temperatures; its operating temperature range is from -180°C to 250°C℃ ； 2) Non-stick, anti-fouling properties: Due to the extremely smooth surface of PTFE tubes, which have a very low coefficient of friction, scaling is difficult to occur. For example, in saltwater, the heat transfer capacity of nickel tubes decreases by 80% after 76 hours, whereas that of PTFE tubes decreases by only 10% ； 3) Small size and compact structure: Thus, a larger heat transfer area can be achieved within a smaller volume. This type of heat exchanger has advantages such as light weight, long service life, easy installation, and low floor space requirement. Considering factors such as heat transfer area and thermal efficiency, PTFE heat exchangers generally use capillaries with small diameters and thin wall thicknesses. This not only helps to reduce the thermal resistance of the tube walls but also enables a larger heat transfer area per unit volume compared to metal heat exchangers. II. Regarding the composite modification of polytetrafluoroethylene: Heat exchangers made from PTFE possess advantages such as high resistance to corrosion, no scaling, a wide operating temperature range, light weight, and a long service life. However, using it to manufacture heat exchangers comes with disadvantages including poor mechanical strength, poor thermal conductivity, poor processability, and surface stickiness. If that is the case, then how is polytetrafluoroethylene widely used in anti-corrosion equipment? To address these issues, scientists have added various fillers to polytetrafluoroethylene, such as glass fibers, graphite, and asbestos, and conducted research on modifying it, thereby significantly improving its various properties. Currently, the modification of PTFE mainly relies on composite methods, including surface modification, filler modification, and blending modification. Through the application of surface modification and filling modification techniques, the key properties of PTFE materials that are relevant to heat exchange equipment, such as surface adhesion, thermal conductivity, mechanical strength, and processability, have been significantly improved. Polytetrafluoroethylene can be used to manufacture various types of heat exchangers. III. Applications of PTFE heat exchangers In recent years, PTFE heat exchangers have been widely used in areas such as industrial waste heat recovery, seawater desalination, lithium bromide absorption chillers, wastewater-source heat pumps, and the coating industry, owing to their excellent properties; they offer significant advantages in environments with high corrosion and contamination levels. 3.1 Application in lithium bromide absorption chillers: The use of polytetrafluoroethylene heat exchangers to replace metal heat exchangers in lithium bromide refrigeration units has been proven feasible. Based on the work requirements and the characteristics of plastic pipes, a measurement scheme was proposed in which the heat transfer tube adopts an Archimedes spiral coiled structure. Its application can effectively address the issue of cooling capacity reduction caused by corrosion, extend the service life of refrigerators, and reduce operating and maintenance costs. In lithium bromide absorption chillers, through the analysis of the heat transfer performance of plastic heat exchanger units, it is found that using polytetrafluoroethylene heat exchangers in the absorber offers the greatest advantages over traditional metal heat exchangers. 3.2 Application in wastewater-source heat pumps: It has been experimentally proven that fluoroplastic heat exchangers are resistant to the accumulation of fouling caused by physical and chemical processes, making them suitable for use in wastewater-source heat pump systems. By using polytetrafluoroethylene heat exchangers with fluoroplastic capillaries in place of metal heat exchangers, it has been shown that the heat exchange area per unit volume of such exchangers is greater than that of metal and non-metal heat exchangers. Heat exchangers made of polytetrafluoroethylene have a significantly lower mass for the same heat exchange area as metal and non-metal heat exchangers, and they can be used over a long period of time in the temperature range of -150°C to 260°C. Polytetrafluoroethylene heat exchangers have significant advantages in the field of wastewater-source heat pumps. 3.3 Applications in waste heat recovery: Utilizing the corrosion resistance, anti-scaling properties, and low cost of polytetrafluoroethylene, PTFE heat exchangers are applied in seawater desalination. Polytetrafluoroethylene heat exchangers have also opened up a new approach for the recovery of waste heat from the flue gases of coal-fired power plant boilers. Heat transfer and pressure drop formulas suitable for such operating conditions have been derived, providing reference data for optimizing the waste heat recovery process in coal-fired power plant boilers. 3.4 Applications in sodium acetate production In the production of sodium acetate, distillation is a key process, and the condenser is the most important equipment in this process; its efficiency directly affects the product’s absorption rate, energy consumption, and costs. Through continuous improvement and utilization of polytetrafluoroethylene, its production volume has increased significantly, energy consumption levels have dropped markedly, and good economic benefits have been achieved. This has eliminated the bottlenecks that constrained production, allowing for an expansion of production scales and the realization of favorable economies of scale. For the distillation of dilute acetic acid, polytetrafluoroethylene heat exchangers are an extremely ideal type of equipment. 3.5 Applications in the coating industry: In the production process of the coating industry, heating the solutions used for pickling and phosphating during pre-treatment poses a significant challenge; the pickling solutions in pickling tanks are extremely corrosive. Phosphating belongs to electroless plating; the zinc and phosphating solution used have strong self-plating properties, allowing them to bond well with the metal surface. A layer of phosphide is quickly formed on the surface of the heat exchange tubes, which leads to impaired heat transfer. To improve the corrosion resistance and anti-scaling ability of heat exchangers, the use of polytetrafluoroethylene heat exchangers has been successful. 3.6 Applications in metal composites: The use of fluoroplastics in combination with metals not only provides corrosion protection but also significantly improves the performance of heat exchangers. Experiments have shown that when PTFE is used as the lining plastic to induce droplet condensation, the condensation heat transfer coefficient of copper tubes coated with PTFE is 4.6 times that of ordinary copper tubes, and droplet condensation can persist for 22,000 hours. In the steam compression seawater desalination experiment, heat transfer was carried out by applying a hydrophobic Ni-P-PTFE coating to the surface of the brass heat exchanger, and it was found that the heat transfer coefficient increased by 4.3 times. Such heat exchangers can also be used as heaters, preheaters, evaporators, reboilers, condensers, fractional condensers, crystallizers, and coolers, offering very good application prospects.