EXPERIMENTAL INVESTIGATION OF MARANGONI CONVECTION AND SURFACE TENSION OF AQUEOUS LITHIUM BROMIDE SOLUTIONS WITH ADDITIVES AT LOW PRESSURE

摘要

Optimization of absorption chillers is a fundamental task to pursue in the refrigeration industry, sincernthese chillers are still characterized by large sizes and low efficiency. An efficient way to achieve thisrnaim is by the mean of alcoholic surfactants. Indeed, when added to the working fluid pair (waterlithiumrnbromide) in small quantities, they lower the surface tension and induce a local Marangonirnconvection at the liquid/vapor interface. As a consequence of the better wetting of the tubes, the heatrnand mass transfer in the absorber is increased. Nevertheless, values of surface tension measured inrnliterature tend to scatter and the influence of many factors on the enhancement mechanism is not yetrnfully understood.rnSurface tension of water and aqueous lithium-bromide solution with different surfactants isrnexperimentally investigated. 1-octanol and 2-ethylhexanol are used as additives. Their concentration inrnthe solution is varied in a wide range. Surface tension is measured by the pendant drop method. Amongrnthe two additives investigated, 1-octanol leads to the smallest values of surface tension. Highestrnreduction of surface tension is observed when the additive is delivered to the surface through vaporrnphase. Based on results obtained, a new experimental setup for measurements at low pressure isrndeveloped and first surface tension measurements at low pressure are presented.