English name: Air cooler Heat Exchangers Air coolers are one of the devices used in most refinery and petrochemical units to reduce the temperature of fluids. In air coolers, the air hits the pipes containing hot fluid with the ambient temperature and reduces the temperature of the pipe wall, thus reducing the temperature of the fluid inside the pipe. The standard length of pipes used in air cooling converters is usually 20, 30 and 40 feet. One of the most important issues with air coolers is the ratio of fan area to bay area. This ratio is called converge fan and its value in air cooling converters should not be less than 0.4. Air cooling converters are commonly used in the following two configurations: – Forced Draft – Induced Draft These transducers use ambient air to reduce the temperature of the fluid inside the pipes. The main components of these converters include one or more pipes that are exposed to the air flow of the fans, its fan and motor equipment, the fan speed controller and the necessary equipment to conduct the currents. In these exchangers, the flow of hot fluid after passing through a nozzle enters the pipes that are adjacent to the fan. These tubes transfer heat faster due to the blades located on the outer wall of the tube. In the passage of fluid through the vicinity of the fan, each set of tubes containing hot fluid is called a bundle, which itself consists of several tubes. Usually several bundles pass through the fan in parallel with each other. This set is called a Bay. In some cases, two fans operate in series on parallel streams of bundles in a bay. This mode consists of two bundles of tubes containing hot fluid that pass adjacent to two series of fans. Typically, several bays that are placed in parallel are used to cool hot fluid by an air-cooled converter in industry. The collection of these bays is called Unit. The diameter of the fans used in air-cooled converters is in the range of 3 to 28 feet. However, fans with a diameter of 14 to 16 feet are usually the largest fans used in the petrochemical industry. Figure 2 Two Bays with 4 Bundles As mentioned, the air at ambient temperature hits the pipes containing hot fluid and reduces the temperature of the pipe wall, thus reducing the temperature of the fluid inside the pipe. Blade tubes are used to increase heat transfer. Blade tubes are used in a variety of ways in air-cooled converters. One of the most important types of blades is the extruded fin, which is usually made of aluminum. The method of making these blades is to place a layer of the relevant metal on the pipe and then install this layer on the pipe by applying pressure by another device. The mold of this device works in such a way that the outer surface of the pipe eventually becomes in the form of spiral blades or other shapes, and thus the outer surface of the pipe increases. These blades are usually used at temperatures below 200 ° C. Figure 3 A unit consisting of two bays and six bundles. Another type of blades used in air cooling converters are embedded fins. These blades are also usually made of steel or aluminum. These blades are in the form of thin rods with a circular or square cross section that are embedded inside the wall of the tube containing hot fluid. In Figure 6, four types of these blades are shown schematically. According to this shape, we find that these blades have a lot of variety. These blades are used in converters that operate at high temperatures and discontinuous processes. Operation and adjustment of the device with changes in air temperature Air coolers are designed for hot summer weather, and temperature changes as a result of seasonal changes can cause them to change their cooling, which may not be desirable. One way is to reduce the amount of air flow to reduce the amount of fluid heat transfer inside the tube. Multi-speed motors are used for this purpose. Most motors can operate at two different speeds. The second way to control is to place Louvers as a cover or roof on the pipes and the other is to use fans with variable pitch (fan blades can change the slope) Louver has a lot of control. This control can be done manually or automatically by electric motors or air systems that are commanded by system temperature and pressure controllers. Louvers are commonly used for constant speed fans. In fans with variable inclination, the inclination of the fan blades to supply the required air flow varies according to the system temperature and pressure. The blade angle decreases when the temperature drops, which causes the fan to lower. Hydraulic motors can also reduce fan speed. When low airflow is required, fan power is also reduced. Another solution to control heat transfer in the system is to control the fluid flow in two directions. In this case, instead of controlling the air flow (as the cooling fluid inside the pipes), the flow of hot fluid inside the pipes is controlled. Two-stream systems are such that there is an input nozzle at the bottom of the header. This nozzle reflects the natural flow of fluid. In some high viscosity fluids, this is sometimes the only way to prevent the fluid from freezing. The last change that can be made in the air temperature, especially in cold weather, is the use of hot air circulation.