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Air cooler classification and features

Air cooler according to different occasions, can be divided into power plant air cooler and petrochemical air cooler. By cooling, can be divided into dry, wet, and dry - wet combined air cooler.

Wet air cooler
Wet air coolers can be divided into three types: surface evaporation type, humidification type and shower type, according to the water spraying method. The latter two types are mainly used in the petrochemical industry. Surface-evaporative air cooler is a kind of air-cooled device which utilizes the evaporation of water outside the tube to enhance the heat transfer. Humidification type wet air cooler is only suitable for dry and hot areas with relative humidity lower than 50%. The smaller the relative humidity of dry air, the more cooling after humidification, the more remarkable the cooling effect. Spray type wet air cooler is directly sprayed water in the fin tube bundle, the use of latent heat exchange of water evaporation and air humidification cooling to enhance heat transfer, while the presence of water mist can make the air cooler inlet air temperature close to Environmental wet bulb temperature, raising the average heat transfer temperature, the 3% spray amount of heat transfer coefficient than the dry air cooler increased 2 to 4 times.
In summary, the use of a wet air cooler is more advantageous than dry air coolers in hot summer months and at warmer ambient temperatures. However, wet air coolers are extremely susceptible to fouling when the fluid temperature in the tube exceeds 70 ° C, and air loss outside the tube is greater, about 1.4 times that of dry air cooling. Tube bundle area can not be too large, so the relative small unit device area, the price is relatively high.

Dry air cooler
Dry air coolers rely solely on sensible heat of air temperature to exchange heat, forced circulation through finned tubes and fans to intensify heat transfer. Simple operation, easy to use, but because of its cooling temperature depends on the air dry bulb temperature, it is generally only the heat pipe cooling to higher than ambient temperature 15 ~ 20 ℃.
Therefore, for the hot and humid areas in southern China, wet air cooler evaporation is not good, generally mainly with dry air cooler. From the perspective of heat transfer, the specific heat of air is only 1/4 of the specific heat of water, and the density of air is much lower than the density of water. Therefore, if the same heat is transferred and the temperature rise of the cooling medium is the same, the required amount of air Will be 4 times that of water, compared to water coolers, the volume of dry air coolers is substantial. Most importantly, the air side has a very low heat transfer coefficient of about 50-60 W / (m2 · ° C), resulting in a very low total heat transfer coefficient of the air pipe cooler and a lower heat transfer coefficient than the water cooler 10 to 30 times, to offset the lower air side heat transfer coefficient of the air cooler are generally used to expand the surface of the finned tube, the wing ratio is roughly 10 to 24 times. Plate air coolers employing plate heat transfer elements are also particularly useful because the cross-sectional shape of the flow path formed by the plate varies constantly along the flow direction, increasing the perturbation, with high heat transfer efficiency and low pressure drop at low Reynolds numbers However, due to the narrow flow path of the plate air cooler, it is easy to cause the cooling medium in the flow path to condense and clog the flow path in the cold winter in the north of our country, and the air coolers in the large petrochemical industry (such as large ethylene plant) Easy to scale and thus block the runner, but also due to the processing of mostly welded structure, partial damage or blockage, you must replace the entire air cooler, resulting in a great waste. Therefore, the finned tube is still the mainstream heat transfer element of the air cooler. The essence of the air cooler can be seen as the air-heat exchanger tube-fin heat exchanger. The key to enhancing the heat transfer performance of the air cooler is to develop low contact Thermal resistance, high heat transfer performance and resistance to small finned tube. When the internal heat exchanger for the high pressure fluid, the tube plus ribs, the equivalent of non-pressure-bearing cost-effective alternative to low cost fins, the economic effect is significant.

Dry - wet combined air cooler
Dry - wet combined air cooler, is the combination of dry air cooler and wet air cooler. The general rule of combination is to use a dry air cooler in the high temperature zone of the process fluid to effect condensation of the gas and a wet air cooler in the low temperature zone to cool the condensate. In short, the choice of what kind of air cooler, according to the local atmospheric temperature, wind speed and relative humidity and other environmental climatic conditions, combined with the final cooling medium temperature and other heat transfer process requirements, taking into account the economy, a comprehensive consideration to determine.

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