The processes occurring in the absorber, an essential component of absorption air-conditioning/heat-pumping systems, are not well understood, and absorption rate equations are not well founded (developed) as they are for the other heat and mass transfer processes that are present in absorption systems. As a result, a study was undertaken to experimentally investigate falling-film absorption for smooth horizontal tubular surfaces. Experimental data were obtained for absorption of water vapour into an aqueous lithium bromide (LiBr) solution flowing over internally cooled horizontal tubes. From the data, the absorption heat transfer has been correlated in terms of the film Nusselt number as a function of the film Reynolds number. Absorption rate is linearly related to heat transfer through the heat of absorption. The experimental data are also compared with the results of a numerical model for the falling-film absorption process. Additionally, the effects of tube diameter and surfactant additive concentration on the absorption process have been assessed.

KEYWORDS: absorption air conditioning, air conditioning, water, lithium bromide, tubes, absorption, Nusselt number.