What is a Cooling Tower?
A Cooling Tower is a heat rejection device that extracts waste heat to the atmosphere by cooling a stream of hot water in the tower. This type of heat rejection is termed "evaporative" because it allows a small portion of the water being cooled to evaporate into a moving air stream and thereby provides significant cooling to the rest of that water stream. The heat that is transferred from the water stream to the air stream raises the air's temperature and its relative humidity to 100%, and this air is discharged to the atmosphere.
For more in-depth cooling tower information, visit the official website of the Cooling Technology Institute: http://www.cti.org/whatis/coolingtowerdetail.shtml
Film Fill Media
To improve the efficiency of the air/water mix, cooling towers can utilize several different types of “fill” media. (Brentwood designs and manufactures Cross Fluted, Offset Vertical, Vertical Flow, Herringbone, and Splash Fill types of fill media).
Many modern cooling towers now utilize efficient plastic film fills. These products are packs of thin, closely-spaced sheets (usually thermoformed PVC) which create a large surface area for the water to film over. These fills yield greatly-increased exposure to the air stream for significant improvements in evaporation and cooling.
The splash bars of Splash Fill systems break the water droplets into smaller droplets to increase water/air exposure.
Types of Cooling Towers
Cooling towers can be classified into two types: Counterflow and Crossflow. Each has the same fundamental components, but the configuration of these components differs to accommodate the difference in the air stream direction. (See diagrams at left).
These are the more common tower type and have the advantage of lower pumping costs (because the water is generally pumped to a lower elevation than in crossflow towers of similar size).
Crossflow towers have a smaller footprint than counterflow towers of the same capacity. This can be an advantage for sites where space is limited.
Natural Draft Towers
There are various styles of cooling towers (See Brentwood Gallery of Installations), but the most recognized are the large Natural Draft Towers. These towers can be either counterflow or crossflow types and operate using those same principles. What makes them unique is how they move air. They are basically large chimneys. The heat removed from the water and transferred to the air causes the air to rise naturally (induces a draft), creating a continual air stream upward through the tower. Natural draft towers have extremely high constuction costs but low operating cost, as there is no mechanical equipment needed to move the air. This high initial cost makes them practical only for applications having very large water volumes, such as large power plants.