Non-isothermal absorption in stagnant films under the influence of surfactants

This study numerically examines the influence of surfactants on non-isothermal vapor absorption into a liquid contained within a shallow two-dimensional rectangular cavity. The surfactant is assumed to exist as an insoluble monomeric film, and the equation of state for the surface tension is taken to be linear in temperature, solute concentration, and adsorbed surfactant concentration. The model predicts the system development in response to interfacial disturbances. Results indicate that the presence of a surfactant is required for non-uniform absorption to induce a strong capillary flow that can alter the otherwise diffusional nature of the absorption process. Furthermore, it is shown that the effect of the surfactant is to generate an initially strong flow near the perturbation location, but that the strength of this motion quickly decays with time. The dynamic behavior of the flow field is characterized by a dependence on the surfactant elasticity number, with higher elasticity number producing an oscillatory flow pattern. The effect of surfactant on the absorption heat and mass transfer is quantified in terms of normalized average Nusselt and Sherwood numbers.