The Experimental Study On Absorption Enhancement Mechanism Of Surfactant Additives

The importance of heat and mass transfer additives in absorption chillers has been recognized for over four decades. Investigation on the mechanisms responsible for enhanced absorption rates has made great progress. The Marangoni effect—an instability arising from gradients in surface tension at the liquid-vapor interface—is generally accepted as the cause of the convective flows that enhance transfer rates. However, a universally accepted model for the mechanisms how the surfactant additives induce Marangoni convection has yet to be proposed. The vapor surfactant theory holds that the enhancement additives are surfactants delivered to the film from the vapor together with the water vapor and produce enhancement by generating surface tension gradients which cause Marangoni convection.This study investigates the absorption rate of water vapour into the lithium bromide solution with surfactant additives to examine the mechanisms responsible for enhanced absorption rates. Absorption of water vapour into the 60 wt% lithium bromide solution with alcohol additives were investigated by using a simple stagnant pool absorber. The experimental apparatus could be used with good confidence and accuracy particularly for studying mass transfer enhancement. The surfactants are added in different state: in liquid, in vapor and both in liquid and in vapor.Most surfactant additives used in the experiment can significantly improve absorption rates and a vigorous interfacial turbulence is observed during absorption process. The effect of two additives together is near to the better one. The additives vapor have significant improvement to the absorption. When a surfactant is added both in liquid and in vapor, the absorption enhancement is close to the case when surfactant is added in vapor only, so is the phenomenon.