Operating principle of a cooling tower

The cooling tower is a piece of equipment designed to disperse a heat flux in atmospheric air. A heat flux is provided by cooling water. In a cooling tower, cooled water comes into direct contact with atmospheric air.

Hot water flows to the main sewer of the water distribution system. Then, the water is distributed through a pipe system to spray nozzles. Nozzles cause the dispersion of the water onto the wet deck surface, thus creating water film of large contact surface. The water coming off the lower edges of the wet deck surface falls down in the form of droplets to the cooled water tank, from where it is pumped back to the cooled equipment.

The process of water cooling occurs mainly as the result of the evaporation of a small amount of cooled water to the air stream (transport of mass), making the use of the heat of phase transition (heat of vaporisation), which is collected from the water stream and to a lesser extent as the result of convective heat transfer form water to air (heat transfer)

Counter-current air flow in the cooling tower is inducted by the suction produced by the axial fan with a capacity adapted to the required cooling parameters. The fan is mounted inside the enclosure on the roof of the cooling cell. The air is sucked into the cell through inlet ports equipped with shutters, which protect the system from sucking things such as foliage and from splashing cooled water outside the cooling tower. Then, the sucked air flows through the rain zone under the wet deck surface, through the fill, splash zone above the wet deck surface and then it undergoes the process of mist elimination, which minimizes water loss resulting from dissipation of droplets. The heated and moisten air flows through the fan, and then it is blown away outside through the upper section of the fan casing to the environment.

Water cooling level in the wet cooling tower depends on the wet bulb temperature of ambient air, air volume (fan efficiency) and technical solutions used in a given model of a cooling tower. Wet cooling towers are designed in such a way to obtain desired cooling effect in the most unfavourable conditions (high temperature, humidity along with the need to remove as much heat from the water as possible.) The power of the fan is selected appropriately to these conditions. When ambient temperature or amount of heat is reduced some of the power installed becomes redundant. In order to reduce operating costs and to improve operating safety, the fan can be equipped with two-speed motors (optionally). Fans' RPM and consequently their power consumption are determined based on the temperature of the cooled water.

In order to ensure stable and safe operation of the cooling system, it is necessary to maintain adequate parameters of the cooling water, because of the fact that constant evaporation results in chemical and mechanical pollution concentration in the cooling cycle. The desalination, desludging and maintenance of the cooling system are one of the most important parameters affecting the durability of components and other related equipment.