TABLE OF CONTENTS Air-cooled heat exchangers are second only to shell-and-tube exchangers in frequency of occurrence in chemical and petroleum processing operations. These units are used to cool and/or condense process streams with ambient air as the cooling medium rather than water. Cooling with air is often economically advantageous, e.g., in arid or semi-arid locations, in areas where the available water requires extensive treatment to reduce fouling, or when additional investment would otherwise be required to expand a plant's existing cooling-water supply. Regulations governing water use and discharge of effluent streams to the environment also tend to favor air cooling. Although the capital cost of an air-cooled exchanger is generally higher, the operating cost is usually significantly lower compared with a water-cooled exchanger. Hence, high energy cost relative to capital cost favors air cooling. Air cooling also eliminates the fouling and corrosion problems associated with cooling water, and there is no possibility of leakage and mixing of water with the process fluid. Thus, maintenance costs are generally lower for air-cooled exchangers.
In an air-cooled heat exchanger, the hot process fluid flows through a bank of finned tubes, and ambient air is blown across the tubes by one or more axial-flow fans. For applications involving only sensible heat transfer, the tubes are oriented horizontally as shown in Figures 12.1 and 12.2. For condensers, an A-frame configuration (Figure 12.3) is often used, with the condensing vapor flowing downward through the tubes, which are oriented at an angle...
