Absorption chillers represent a promising alternative to traditional vapor compression chillers, especially for the air conditioning systems. Indeed, they provide the same cooling supply without such a high electrical consumption, being driven by a low-temperature heat source. On the other side, they are not yet competitive with compression chillers because of their large size and high costs of investment. Their optimization becomes then a fundamental task to perform. Among the several components of these chillers, the absorber has been identified as the limiting one. The main obstacle is the low wetting on its tube bundle, which limits the absorption process. One way to overcome this problem is by the mean of additives. Indeed, small quantities of alcoholic surfactants in the working fluid lower the surface tension, promoting local turbulence at the vapor-liquid interface (Marangoni convection), which in turns leads to higher heat and mass transfer coefficients in the absorber. Nevertheless, only two kinds of additives are mostly used in these chillers, and the anhancement mechanism is not yet fully understood.

Surface tension of aqueous lithium-bromide solution with different surfactants is experimentally investigated in this work. 1-octanol, 2-ethylhexanol, 3,5,5-trymethyl-1-hexanol and 3-phenyl-1-propanol are used as additive. Their concentration in the solutions is varied in a wide range. Surface tension is measured according to pendant drop method. Investigations are carried out with different surrounding atmosphere. It is observed how surface tension is mainly affected by additive delivered at liquid interface through vapor phase. Among the four additives investigated, 1-octanol shows the highest surface tension reduction. Based on results obtained, a new experimental setup for measurements at low pressure is developed and first surface tension measurements at process condition are presented.