Cooling tower is a kind of equipment which uses the contact of water and air to dissipate the waste heat produced in industry or refrigeration and air conditioning by evaporation. The basic principles of its work are:

Dry (low enthalpy) air passes through the fan and enters the cooling tower from the intake network; high temperature water molecules with high saturated vapor partial pressure flow to low pressure air, and hot (high enthalpy) water self-seeding system sprays into the tower. When water droplets are in contact with air, on the one hand, because of the direct heat transfer between air and non-air, on the other hand, because of the pressure difference between the surface of water vapor and air, evaporation occurs under the action of pressure, which brings the latent heat of evaporation to the present time and takes the heat of water away, namely evaporation heat transfer, so as to achieve the purpose of cooling.

The working process of the cooling tower is illustrated by the working process of the circular countercurrent cooling tower.

Hot water self-contained engine room presses circulating water to the seeding system of cooling tower through water pump through pipeline, cross throat, curved throat and central throat, sprinkles water evenly on the packing through the small holes in the seeding pipe, and dried low-gradient air enters the tower through the air network at the bottom under the action of the fan, and forms water film and air for heat exchange when hot water flows through the surface of the packing. The hot air with high humidity and high heat value is drawn out from the top, the cooling water drips into the bottom basin, and flows into the main engine through the outlet pipe. Generally, the air entering the tower is the dry air with low wet bulb temperature. There are obvious differences in the concentration and kinetic energy pressure of water molecules between water and air. When the fan runs, under the action of static pressure in the tower, water molecules evaporate into the air continuously and become vapor molecules. The average kinetic energy of the remaining water molecules will be reduced, so that the temperature of circulating water will drop. 。 From the above analysis, it can be seen that the evaporative cooling has nothing to do with the air temperature (usually the dry bulb temperature) lower or higher than the water temperature. As long as the water molecules can continuously evaporate into the air, the water temperature will decrease. However, the evaporation of water into the air will not go on indefinitely. When the air in contact with water is unsaturated, the water molecules evaporate into the air continuously, but when the air on the water-air interface reaches saturation, the water molecules can not evaporate, but are in a dynamic equilibrium state. The number of water molecules evaporated is equal to the number of water molecules returned from the air to the water, and the water temperature remains unchanged. It can be seen from this that the dryer the air in contact with water is, the easier evaporation is and the lower the water temperature is.