Experimental Investigation of Marangoni Convection in Aqueous LiBr Solution With Additives

Abstract

The most crucial and expensive component in commercial absorption machines is the absorber where the refrigerant vapor is absorbed into the absorbent solution. The absorption performance can be improved by mechanical or chemical means. As the mechanical means, efficient heat transfer mechanisms, such as falling film or bubble-type modes, are suggested by using enhanced surfaces. As the chemical means, the performance of heat and mass transfer has been significantly enhanced by adding heat transfer additives to the working solution pairs. A small addition of heat transfer additives causes interfacial turbulence by the Marangoni effect, leading to a higher heat and mass transfer performance. It is generally known that Marangoni convection is caused by the surface tension gradient that is originated from the concentration and temperature dependence of the surface tension. The primary objective of this paper is to establish a general model on the onset of Marangoni convection based on experimental results. The experimental data of the surface tension and interfacial tension of aqueous LiBr solution with heat transfer additives are provided. The effects of the LiBr concentration, the additive concentration, and the solution temperature on the surface tension and interfacial tension gradients are studied and compared quantitatively.