TABLE OF CONTENTS The performance of all air-cooled heat exchangers and cooling towers are affected by changes in ambient conditions. Changes in temperature, humidity, winds, inversions, rain, snow, hail, and solar radiation all influence the performance of air-cooled heat exchangers and cooling towers to a greater or lesser extent. The influences of winds and inversions are described in detail in the following sections. Rain tends to reduce the drybulb temperature nearly to wetbulb values. Some wetting of finned surfaces may occur in dry systems, and this has a beneficial influence on performance. In natural-draft cooling towers, cooling of the air in the tower and a reduction of the draft due to the falling droplets will have a detrimental effect on performance according to Heberholz and Schulz. Generally, the effects on performance due to rain and snow are small.
During periods of very low ambient temperatures, frozen cooling water can lead to serious structural and performance problems. Different devices and procedures are employed to avoid freezing according to Fabre, Michell, and Drew. In areas where hailstorms occur, protective screens are installed above finned surfaces. A maximum solar radiation of about 1 kW/m 2 may strike the heat transfer surface for a short period during the day. This will reduce the rate of heat rejection in some installations. According to Nouri-Borujerdi, the draft and corresponding heat rejection rate of an aluminum-clad, natural-draft, dry-cooling tower is not affected to any degree when the tower shell is exposed to solar radiation.
According to Barbaud,...
