Briefly describe the heat transfer form of closed cooling tower

As we all know, closed cooling towers play an important role in water cooling systems. After hot water is discharged through the heat exchanger, water droplets or water films are sprayed from the top of the tower, and the air flows from bottom to top in the opposite direction of the water droplets or water films, or flows horizontally. In the process of air-water contact, heat exchange is carried out to reduce the water temperature and achieve a cooling effect.

There are two main types of heat transfer: evaporative heat transfer and contact heat transfer. Evaporative heat transfer refers to when the saturated steam of water at its surface temperature is greater than the partial pressure of water vapor in the air, the water molecules on the surface of the water droplets overcome the attraction between the liquid water molecules, evaporate into the air, and take away the latent heat of evaporation, thereby reducing the temperature of the liquid water. For every 1kg of water evaporated, about 2.43*106J of heat should be taken away. The heat taken away by evaporative heat transfer accounts for about 75%~80% of the heat transfer of the closed cooling tower. Contact heat transfer refers to when the air wet bulb temperature is lower than the water temperature, the heat is transferred from water to air, raising the air temperature and lowering the water temperature. The heat taken away is sensible heat, accounting for about 20%~25% of the heat transfer.

The closed cooling tower is equipped with splashers or fillers, which are made up of rows of plates arranged in a staggered manner. The water falls along the plates in rows and splashes into water droplets. Film fillers can also be used, so that the water contacts the air in the form of a thin film on the surface of the filler. The filler must be well moistened, otherwise the water will form a stream on the filler instead of water droplets or a water film.