Operating principle: Cooled process product moves inside bimetallic finned pipes and transfers its heat to a cooling agent through the walls. The ambient air is employed as a cooling agent. An ACHE is mainly used where the use of other heat transfer systems is not feasible or not expedient economically. The obvious advantage of an ACHE is that it does not require water, which means that industrial consumers requiring large cooling capacities for their process fluids, vapors, and gasses need not be located near a supply of cooling water. For these purposes, specifically designed air-cooled heat exchangers are used instead. Depending on the application, ACHE can be subdivided into condensers, gas coolers, liquid coolers, and lube oil coolers.
An ACHE consists of the following components: one or more bundles of heat transfer surface, an air-moving device, such as a fan, blower, or stack, unless it is natural draft, a driver and power transmission to mechanically rotate the fan or blower, a plenum between the bundle or bundles and the air-moving device, a support structure high enough to allow air to enter beneath the ACHE at a reasonable rate, optional louvers for process outlet temperature control, optional recirculation ducts and chambers for protection against freezing or solidification of high pour point fluids in cold weather.
ACHE sections are tube bundles assembled of finned tubes, headers, side frames, and tube supports and fastened by means of flaring with or without welding. The tube sheet is connected to the header, to which cooling medium feed and discharge piping is connected. ACHE sections consist of finned tubes, and fins are attached to the tubes in a number of ways: they can be extruded, embedded, or wrapped-on. Such tubes have an increased heat transfer ratio compared to bare tubes, thus enabling to compensate a low heat reject of air.
