This paper presents the design criteria, methodology and results of the basic and detail engineering for a descending film ammonia absorber using air cooled finned tubes, that is part of an advanced absorption cooling system (Solar-GAX cycle). The design consists in determining all the construction parameters for the air cooled ammonia absorption unit, starting with the operating conditions defined by a thermodynamical simulation of the process considering both physical and operational design restrictions. In order to find the geometric parameters, first a geometry is proposed (tentative design) and its behavior evaluated; if it does not meet the service or requirements, it will be modified and evaluated again. This process is repeated as much as necessary until an array (geometry) is found that meets the process conditions. The chosen option was based on a comparison between advantages and disadvantages of each possible array, type and geometry. After performing the operational simulation, thermal and mechanical design and the consistency analysis, it was found that an absorption unit using 29 5/8″ NPT 14 (BWG) steel carbon ASTM A-179 tubes, with pure SB-234 aluminum fins was the best option. The tubes are arranged in an equilateral triangle fashion, with crossed air flow cooling.

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