The ACX program will design or analyze API type air cooled (or air heated) heat exchangers. These exchangers consist of rectangular tube bundles with air flowing once across the outside of the tubes. The tubes may be high fin, low fin or plain (no fins). The primary equipment type considered is that of an aerial cooler (heater) where axial flow fans force the air across the tubes. Other exchanger types considered by ACX are preheaters, recuperators and regenerators. The fluid outside the tubes may be air or other gases or gas mixtures. Applications include coolers, heaters, condensers and evaporators.