In absorption heat pumps that employ water as the refrigerant and, for example, lithium bromide as the absorbent, falling-film absorbers employing internally cooled, horizontal tubes are widely used. The literature contains a significant amount of data from experimental investigations into such systems; however, there is still much to be understood. This paper presents a review of the literature containing experimental results from falling-film absorption of water vapor on horizontal tubes. The effects of surfactant, absorber geometry including advanced tube surfaces, tube diameter and spacing, and operating conditions such as liquid film flow rate and inlet conditions are systematically considered and the results of different investigations compared. Attempting to utilize the results found in the literature for design optimization reveals that the effects of many of these important parameters are not fully quantified and so areas and methods for further research are suggested.
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