According to different occasions,air cooler can be divided into power plant air cooler and petrochemical air cooler.
According to the cooling mode, can be divided into dry type, wet type.
Wet air cooler
According to the water spraying method,the wet air cooler can be divided into three types: surface evaporation, humidifying type and spray type, and the latter two are mainly in the petrochemical industry.
The surface evaporative air cooler is an air cooling device which USES the evaporation of the outer water film to strengthen the heat transfer and the composition of the optical tube.
Humidity-humidified air cooler can only be used in dry and hot areas where relative humidity is less than 50%, because the drier air relative humidity is, the more cool it is after humidification, the more significant the cooling effect is.
Spray type wet air cooler is spray water directly on the fin tube.Using evaporation latent heat exchange, and the air is cooling humidifying to strengthen heat transfer, at the same time, the existence of water mist can make the air cooler inlet air wet-bulb temperature close to the environment, increasing the average temperature difference heat transfer, heat transfer coefficient under 3% spray 2 ~ 4 times higher than dry air cooler.
In short, compared with dry air cooler, it is more advantageous to apply the wet air cooler in the hot summer when the ambient temperature is higher.
However, wet air cooler fluid temperature exceeds 70 ℃, the tube is extremely easy scaling, and tube outside air resistance loss is bigger, about 1 of dry type air cooling. 4 times. The area of the tube bundle should not be too large, so the relative area of the unit device is relatively small and the price is relatively high.
Dry air cooler
Dry air cooler only depends on the sensible heat of the air temperature rise to exchange heat, by the finned tube and the fan forced circulation to strengthen the heat transfer. The operation is simple, easy to use, but as a result of its cooling temperature depends on the air dry bulb temperature, so normally only cooling tube heat transfer fluid to higher than the environment temperature 15 ~ 20 ℃.
Therefore, for the wet and hot area of south China, the evaporation of the wet air cooler is not good, and the dry air cooler is generally used.
From the perspective of heat transfer, the specific heat of air is only 1/4 of the specific heat of water, air density is far less than the density of water, therefore, if the same heat transfer, cooling medium temperature is the same, the required amount of air will be four times that of water, compared to the water cooler, the volume of dry type air cooler is very large.
The key point is that the air side has a very low heat transfer coefficient of about 50-60 W / (m2·℃), resulting in a very low total heat transfer coefficient of the air cooler and a heat transfer coefficient of about 10 less than that of the water cooler ~ 30 times, in order to offset the lower impact of air-side heat transfer coefficient, air-cooled finned tubes are generally used to expand the surface of the fin ratio is roughly 10 to 24 times.
Plate-type air coolers using plate-type heat transfer elements are also used because the cross-sectional shape of the flow channel formed by the plate is constantly changing along the flow direction to enhance the perturbation and to have 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 China, Thus blocking the flow path, but also due to the processing of all-welded structure, partial damage or blockage, you must replace the whole air cooler, causing a lot of waste
Therefore, the finned tube is still the mainstream heat transfer element of the air cooler. The essence of air cooler can be seen as the air-heat exchanger tube-fin heat exchanger. The key to strengthen the heat transfer performance of air cooler is to develop low contact resistance , High heat transfer performance and flow resistance of 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 remarkable.
Dry - wet air cooler.
Dry - wet air cooler is the combination of dry air cooler and wet air cooler.
The general principle of the combination is to use dry air cooler in the high-temperature zone of process fluid playing the role of condensing gas. Wet air cooler is used in low temperature area, playing the role of condensing condensate.
In short, the choice of which type of air cooler depends on the local atmospheric temperature, wind speed and relative humidity and other environmental climatic conditions, combined with the final cooling temperature of the media such as heat transfer process requirements, taking into account the economy, a comprehensive consideration to determine.