Two-Layer Model to Simulate the Effect of Marangoni Enhancement of Absorption

Abstract

Abstract Absorption of vapor into a laminar film of liquid is a well-known problem that has received considerable interest in the literature. In many practical systems, the mass transfer process in the liquid phase is a limiting factor because the diffusion of mass is much slower than the diffusion of energy. Enhancement of absorption usually involves some scheme to mix the liquid, causing the effective diffusivities to increase. One such enhancement method is the use of surfactants that drive Marangoni flow in the liquid. This method is used very effectively in absorption chillers based on aqueous lithium bromide. The complexity of the resulting liquid flow is significant and this may explain why there are few studies of this effect found in the literature. In the present paper, a model is described which treats the liquid film as composed of two-layers: the inner layer is laminar and the outer layer is fully mixed. The relative thickness of the two layers is a parameter that must be known to enable use of the model. The layer thickness was determined from comparisons between the model results and absorption data from a vertical tube absorber. The layer thickness is found to be a function of liquid flow rate and surfactant concentration.