| Air cooled heat exchangers use ambient air for cooling and condensing. They are typically used in locations where there is a shortage of cooling water. Air-cooled heat exchangers are usually used when the heat exchanger outlet temperature is at least 20°F above the maximum expected ambient air temperature. They can be designed for closer approach temperatures, but often become expensive compared to a combination of a cooling tower and a water-cooled exchanger. Air cooled heat exchangers use electrically driven fans to move air across a bank of tubes. There are two basic arrangements: Induced draft Fans draw air through the tube banks. Forced draft Fans blow air through the tube banks. Air cooled exchangers are expensive compared to water cooled exchangers due to their large size, low heat transfer coefficients on the air size, and structural and electrical requirements. In addition, air cooler exchangers require large plot areas and must be designed to handle diurnal and seasonal changes in air temperature. The very low heat transfer coefficient associated with air on the outside of the tubes is partially overcome through extensive use of finned tubes to increase the outside surface area Advantages Do not use water for cooling Typical Applications Cooling and condensing where cooling water is unavailable or is uneconomical to use. |
