No matter how efficient, a cooling tower can never chill the recirculating water to the WB temperature, and, at some point, costs and space requirements limit cooling tower size. Modern psychrometers are mechanically aspirated (fans move the air across the wetted wick) and are much more accurate. 2 This latter reading is the WB temperature, and it is the lowest temperature that can be achieved by evaporative cooling. Picture of a vintage sling psychrometer.Īfter a short time, the DB thermometer will still read 90☏ however, the other thermometer will read 71.2☏ (21.8☌). Cooling towers remove a very large amount of heat, primarily from the evaporation of a small amount of the recirculating water ( FIG. This is known as the latent heat of vaporization, which, at sea level, is typically around 1,000 Btu/lb.
For water to evaporate, it must consume a large amount of energy to change from a liquid to a gas. In the words of an excellent reference manual on cooling, “Evaporation is utilized to its fullest extent in cooling towers, which are designed to expose the maximum transient water surface to the maximum flow of air-for the longest period of time.” 1 Evaporation is the key to maximizing efficiency. This article outlines the fundamentals of heat transfer in a cooling tower and illustrates why the chemistry principles outlined in Parts 1 and 2-published in the June and July issues of Hydrocarbon Processing-are critical for maintaining cooling tower efficiency and structural integrity.
With the turnover that is occurring in nearly all industries due to the retirement of Baby Boomers, many new personnel are being introduced to cooling tower technology. Refineries, chemical plants and numerous other industrial facilities utilize open recirculating cooling systems equipped with cooling towers for cooling in scores of heat exchangers.
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