What is a cooling tower and how does it work?

A cooling tower is a specialized heat exchanger developed for cooling down big amount of water by directed airflow

Water, which has been heated by an industrial process, is pumped to the cooling tower through pipes. The water flows through nozzles, spraying water into the material called “fill,” which slows the flow of water through the cooling tower, and maximize water surface for air-water contact. As the water falls down through the cooling tower, it is exposed to air, which is being pulled through the cooling tower by the electric motor-driven fan.

When the water and air meet, a small amount of water is evaporated, creating a cooling action. The cooled water is then pumped back to the process equipment where it becomes reheated. It will then be pumped back to the cooling tower to be cooled once again.

TYPES OF COOLING TOWERS

Cooling towers are designed and manufactured in several types. Understanding the various types, along with their advantages and limitations, is important when determining the right cooling tower for a project. Below there is a brief description of available type of cooling towers.

Factory-assembled cooling towers (FAP)

Factory-assembled cooling towers undergo virtually complete assembly at their point of manufacture, whereupon they are shipped to the site in as few sections. A relatively small cooling tower would ship essentially intact. A larger, multi-cell cooling tower is assembled as modules at the factory, and are shipped with appropriate hardware for assembly by the user. Factory-assembled cooling towers are also known as “packaged” or “FAP” towers. Factory-assembled cooling towers can be crossflow or counterflow, induced draft or forced draft, depending on the application.

Field-erected cooling towers (FEP)

Field-erected cooling towers are primarily constructed at the site of ultimate use. All large cooling towers, and many of the smaller cooling towers, are prefabricated, piece-marked, and shipped to the site for final assembly. The cooling tower manufacturer usually provides supervision for final assembly. Field-erected cooling towers can be crossflow or counterflow, depending on the application.

Crossflow cooling towers

In crossflow cooling towers the water flows vertically through the fill while the air flows horizontally, across the flow of the falling water. Because of this, air does not have to pass through the distribution system, permitting the use of gravity flow hot water distribution basins mounted at the top of the cooling tower above the fill. These basins are universally applied on all crossflow cooling towers.

Counterflow cooling towers

Counterflow cooling towers are designed so that air flows vertically upward, counter to the flow of falling water in the fill. Because of this vertical airflow, it is not possible to use the open, gravity-flow basins typical in crossflow designs. Instead, counterflow cooling towers use pressurized, pipe-type spray systems to spray water onto the top of the fill. Since air must be able to pass through the spray system, the pipes and nozzles must be much farther apart so as not to restrict airflow.

Induced draft vs. forced draft cooling towers

Induced draft cooling towers have fans that are typically mounted on top of the cooling tower and pull air through the fill media. Conversely, air is pushed by blowers located at the base of the air inlet face on forced draft cooling towers.