Advantages and Disadvantages of Air Coolers

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Based on the comparison based on the heat transfer area of ​​the light tube, the investment cost of the air cooler is more than 2 to 3 times that of the water cooler (only the hardware cost). There are two main reasons for this. First, the thermal conductivity of air is much lower than that of water, which will inevitably cause the heat transfer coefficient to drop even lower. Second, since the ambient temperature taken during design is always higher than that of water, the logarithmic average temperature difference of the air cooler is always lower, especially when the outlet temperature of the process medium is very low. Due to these two reasons, the heat transfer area required for air coolers is much larger than that for water cooling under the same heat load. And the complex support system required for its large heat transfer area increases the cost even more. However, as engineers know, the investment (or fixed) cost of equipment is only a part of the overall cost, and it is important to consider the total cost, which is the sum of fixed investment costs and operating costs. The operating cost of a water cooler is much greater than that of an air cooler because it includes the cost of initial raw water, supplementary cooling water, water treatment chemicals, and factory cooling towers. When water is scarce, the operating cost of the water cooler will increase. Therefore, from economic considerations, it is more likely to use an air cooler. Advantages and Disadvantages of Air Coolers Air coolers have several important advantages compared with water coolers.: One of them is that water is not directly used as a cooling medium, so the cost of using water is high, such as the cost of raw water, supplementary water and water treatment chemicals. The cooler and the factory itself do not need to be located close to water sources (such as rivers or lakes), so heat loss and chemical contamination of the water sources can be prevented. Maintenance costs are also reduced because there is no need to frequently clean the water side of the cooler to remove scale, microbial scale and sediment. And the corresponding pipelines are removed, making the installation simpler. Another advantage is that the air cooler can be operated continuously, even when power fails, by using natural wind and operating at reduced heat exchange capacity. Finally, the control of the medium fluid outlet temperature (and in this regard the heat load) can be accomplished by various methods, such as starting or stopping the fan, using a second gear or variable speed motor, using a self-regulating fan (the blades are adjustable even when the fan is running), etc. Limit range: Of course, air coolers also have many limitations. As mentioned before, the thermal conductivity and specific heat of air are much lower than that of water, so the initial cost of an air cooler is much higher than that of a water cooler. In cold climates, additional cold protection facilities are necessary to ensure that the medium does not fall below freezing temperatures, which also increases the initial investment cost. A more economical method is to keep the temperature difference between the outlet temperature of the medium fluid and the ambient air within the range of 10 to 15°C. In a water cooler, this temperature difference can be as low as 3 to 5°C. This shortcoming can be compensated by adding an air cooler and a rear water cooler. Due to the large heat transfer area, the air cooler occupies a larger area than the water cooler. But this disadvantage can be overcome by placing the air cooler on a tube rack so that useful floor space is not wasted. The specific heat of air is very low, requiring a large amount of air to be forced through the tube bundle. This can be accomplished by using large diameter blades that rotate at high speed, but this will produce a lot of noise. Seasonal changes in air temperature can affect the performance of air coolers, so expensive control systems must be used to ensure the stability of their operation. Air coolers should not be placed near large obstacles, such as buildings, as this will recirculate air and reduce efficiency. The design of air coolers is quite complex, so there are far fewer manufacturers of air coolers than water-cooled shell and tube heat exchangers. For cooling high-viscosity liquids, air coolers are more expensive due to the low heat transfer coefficient in the tube side (such fluids will generate high heat transfer coefficients due to strong turbulence when flowing outside the tubes of shell-and-tube heat exchangers). However, this situation can be improved by using an intratubular insert * * Expand its heat transfer area to compensate. However, this technology has not yet been fully publicized. The best choice between air cooling and water cooling In many applications where the medium outlet temperature is very low, it is not feasible to use an air cooler alone. For example, when the ambient temperature is 42°C and the designed cooling water temperature is 33°C, it is impossible to cool a light hydrocarbon liquid to 40-45°C. In response to this situation, an air cooler plus post-water cooling can be used. For some other use cases, air coolers are not economically feasible. For example, when the ambient temperature is 42°C and the cooling water temperature is 33°C, for a naphtha stabilizer condenser with inlet and outlet temperatures of 50°C and 40°C respectively, it is not possible to use an air cooler because the temperature difference is too small. A separate water cooler can be considered here. Therefore, some occasions are suitable for the use of air coolers alone, others can use a combination of air coolers and water cooling, and others should use water coolers alone. The most suitable temperature turning point for air cooling and water cooling (referring to the temperature at which the medium fluid leaves the air cooler and enters the water cooler) is determined by the overall economic plan of the specific engineering project. It will depend on the equipment costs of air coolers and water coolers, the total cost of water usage and power costs. Generally speaking, the most suitable temperature is about 15℃~20℃ higher than the ambient temperature. The important point worth mentioning is that even with a combined cooler (air cooler plus water cooler), the air cooler will handle the main heat load, i.e. 80% or more of the total heat load, so that * * Reduced cooling water consumption. When using a combined cooler, if there is no aftercooler, the air cooler is usually best designed so that the ambient temperature is slightly lower. The medium fluid temperature considered when designing with an aftercooler should be when the air cooler is at the maximum (or close to the maximum -) ambient temperature. This is because aftercoolers are much less expensive than air coolers when handling media at higher ambient temperatures.