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Classification and characteristics of air cooler
- Aug 14, 2018 -

Air cooler According to the use of different occasions, can be divided into power plant air cooler and petrochemical air cooler.

According to the cooling mode, can be divided into dry-type, wet, and dry-wet combined type air cooler.

Wet type air cooler: The wet air cooler can be divided into 3 kinds of surface evaporation type, humidification type and spraying type according to the water spraying mode, which is mainly in the later two kinds of petrochemical industry. The surface evaporative air cooler is a kind of air cooling device, which is made up of heat transfer by evaporation of the tube external membrane and the light tube. Humidification type of wet air cooler is only applicable to the relative humidity of less than 50% dry, hot areas, because the lower relative humidity of dry air, humidification after the more cooling, the more significant cooling effect.

The spray type wet air cooler is a spray-like water directly on the finned tube bundle, and the heat transfer is enhanced by using the latent heat exchange of water evaporation and the air being humidification and cooling. At the same time, the presence of water mist can make the inlet air temperature of the air cooler close to the ambient wet bulb temperature, improve the average temperature difference of heat transfer, under 3% spray quantity, the heat transfer coefficient can be increased 2 ~ 4 times times than that of dry air cooler. In short, compared with the Yu Gan-type air cooler, in the hot summer, when the ambient temperature is high, the use of wet air cooler more favorable. However, the wet air cooler in the pipe fluid temperature of more than 70 ℃, it is very easy to scale, and the air resistance outside the larger loss, about 1 of dry-type air cooling. 4 times times.

The area of tube bundle can not be too big, so the relative area of unit device is small and the price is relatively high.

Dry type Air Cooler: Dry air cooler only depends on the air temperature rise of the hot way to exchange heat, by the fin tube and fan forced circulation to enhance heat transfer.

Simple operation, easy to use, but because its cooling temperature depends on the dry ball temperature of the air, it is generally only the heat flow in the tube cooling to the ambient temperature of 15 ~ 20 ℃. Therefore, for the hot and humid areas of southern China, the evaporative effect of the wet air cooler is not good, and the dry type air cooler is generally used. From the heat transfer point of view, the specific heat of the air is only 1/4 of the specific heat of water, air density is far less than the density of water, so if the same heat transfer, cooling medium temperature rise the same, the required air volume will be 4 times times the water, compared to the water cooler, dry air cooler volume is very large. The key is that the air side of the heat transfer coefficient is very low, about a ~ 60w/(M2 ℃), the total heat transfer coefficient of the optical tube air cooler is very low, the heat transfer coefficient of the water cooler is about 10 ~30 times, in order to counteract the influence of the lower heat exchange coefficient of the air, the air cooler generally adopts the fin tube extending the surface, its fin ratio is roughly 10. ~ 24 times times. Plate air cooler with plate heat transfer element is also used, because the shape of the cross section formed by the plate is changing along the direction of flow. Enhanced disturbance, low Reynolds number with high heat transfer efficiency and low pressure drop, especially for the petrochemical industry large devices (such as large ethylene equipment, etc.) of the air cooler, but due to the plate air cooler flow channel narrow , in the cold winter in the north of China, it is easy to cause the flow channel cooling medium condensation and plug the flow path, and easily scaling to plug the flow, and because of the processing technology for the whole welding structure, local damage or blockage, it is necessary to replace the whole air cooler, resulting in a great waste. Therefore, the finned tube is still the mainstream heat transfer element of air cooler, the essence of air cooler can be seen as air-heat pipe-fin heat exchanger, the key to strengthen the heat transfer performance of air cooler is to develop the fin tube with low contact resistance, high heat transfer efficiency and small flow resistance.

When the heat exchanger internal pressure of a higher fluid, pipe plus ribs, is equivalent to the use of low-cost ribs without pressure to replace the pressure of high-quality pipe, the economic effect is significant.

Dry-wet Combined type air cooler: Dry-Wet Combined air cooler is the combination of dry air cooler and wet air cooler. The general principle of the combination is that the dry air cooler is used in the process fluid high temperature zone to act as a gas condensation, and a wet air cooler is used in the cryogenic zone to play the role of condensing liquid cooling. In short, choose which form of air cooler, according to the local atmosphere temperature, wind speed and relative humidity and other environmental climatic conditions, combined with the final cooling temperature and other heat transfer technology requirements, and take into account the economic, comprehensive consideration to determine.