| 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 For condensers, an A-frame configuration (as shown in Figure) is often used, with the condensing vapor flowing downward through the tubes, which are oriented at an angle of 60◦ with the horizontal In units employing horizontal tubes, the fan may be located either below (forced draft) or above (induced draft) the tube bank. In either case, the air flows upward across the tubes. The fan drive assembly in an induced-draft unit may be mounted below the tube bundle or it may be mounted above the fan. With the former arrangement, the drive assembly is easily accessible for inspection and maintenance, and it is not exposed to the heated air leaving the unit. However, the drive shaft passes through the tube bundle, requiring omission of some tubes, and the relatively long shaft is more susceptible to vibration problems. |
