AIR COOLED HEAT EXCHANGERS
Air cooler uses the refrigerant to boil in the tube to absorb heat, changing from liquid to gas, so that the forced air outside the tube is cooled. That is, the high-pressure refrigerant liquid from the condenser is separated by the liquid distributor, and then enters the serpentine heat transfer tube after throttling, depressurizing, and cooling through the respective capillary tube, boils in the tube and absorbs the heat of the air outside the tube, and finally passes The air pipe is sucked away by the compressor
The air cooler is mainly composed of tube bundles, brackets, and fans. The hot fluid of the air cooler flows inside the tubes, and the air blows through the outside of the tube bundle. Due to the large amount of ventilation required for heat exchange and the low wind pressure, axial fans are often used (see fluid conveying machinery). The type and material of the tube bundle have a great influence on the performance of the air cooler. Because the heat transfer coefficient of the airside is very small, fins are often added outside the tube to increase the heat transfer area and fluid turbulence and reduce thermal resistance.
Most air coolers use radial fins. Air coolers usually use light tubes with an outer diameter of 25mm, low-fin tubes with a fin height of 12.5mm, and high-fin tubes with a fin height of 16mm. Fins are generally made of materials with high thermal conductivity (the most commonly used is aluminum), wound, or inlaid on the light pipe. In order to strengthen the heat transfer effect of the air cooler, water can be sprayed in the inlet air for humidification. This not only reduces the air temperature but also increases the heat transfer coefficient. The use of air coolers can save a lot of industrial water, reduce environmental pollution, and reduce infrastructure costs. Especially in water-scarce areas, replacing water-cooling with air-cooling can alleviate the contradiction of water shortage.
The outlet temperature of the hot fluid is mainly controlled by adjusting the air volume through the tube bundle, that is, adjusting the inclination angle of the blades, the fan speed, and the opening degree of the shutters. For the fluid that is easy to condense and freeze in winter, hot air circulation or steam heating can be used The way to adjust the fluid outlet temperature.
①Blowing type: The air first flows through the fan and then into the tube bundle. The blast operation cost is more economical, the turbulence generated is beneficial to heat transfer, and it is used more.
②Induced wind type: The air flows through the tube bundle first and then flows into the ventilator. The induced airflow is evenly distributed, which is conducive to precise temperature control and has low noise, which is the direction of development.
Treatment method of tube bundle leakage:
1. Heat exchange tube plugging:
After running for a period of time, the air-cooler tube bundle may cause leakage due to corrosion and other reasons. It can be treated by repairing methods such as chemical sticking, punching glue injection, and pipe plugging. When the leakage of the heat exchange tube is small, the fins outside the tube can be removed without shutting down, and then chemically repaired and bandaged or stamped and glued to stop the leakage; if the above methods cannot be used to eliminate the leakage, the tube bundle should be shut down Purge clean, remove the wire plug on the tube box, and block the two ends of the heat exchange tube with a metal circular table with an angle of 3°～5° to eliminate leakage.
2. Change the tube:
When the air cooler tube bundle leaks due to non-uniform corrosion or manufacturing defects, the tube can be replaced to eliminate the leakage. First remove the pipe to be replaced and clean the pipe hole of the pipe box. When replacing a new tube, pull and bend the middle of the tube slightly to penetrate through the tube plate holes at both ends, and expand or weld after penetration.
Because most of the cooling water contains calcium, magnesium ions, and acid carbonate. When cooling water flows over the metal surface, carbonates are formed. In addition, the oxygen dissolved in the cooling water can cause metal corrosion and form rust. Due to the generation of rust, the heat exchange effect of the condenser is reduced. In severe cases, cooling water has to be sprayed outside the shell. In severe cases, the tube will be blocked and the heat exchange effect will be lost. Research data shows that scale deposits have a huge impact on the loss of heat transfer, and the increase in deposits will increase energy costs. Even a thin layer of scale will increase the operating cost of the scaled part of the equipment by more than 40%. Keeping the cooling channel free of mineral deposits can improve efficiency, save energy, extend the service life of the equipment, and save production time and costs.
For a long time, traditional cleaning methods such as mechanical methods (scraping, brushing), high-pressure water, chemical cleaning (pickling), etc. have encountered many problems when cleaning equipment: they cannot completely remove deposits such as scale, and acid causes corrosion to equipment and forms loopholes. , The residual acid causes secondary corrosion or under-scaling corrosion to the material, which will eventually lead to the replacement of equipment. In addition, the cleaning waste liquid is toxic and requires a lot of money for wastewater treatment.
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