Abstract
The purpose of this study is to obtain basic knowledge of the heat and mass transfer processes in the absorber, as affected by Marangoni convection induced by surfactant addition. We apply a nonflowing bulk absorption model and assume that a dropwise surfactant is fixed on the absorbent surface. The surface-tension difference between the surfactant (n-octanol) and the absorbent solution (H2O/LiBr) is considered to be of a constant value (Δσ=20x10-3N/m). Four governing equations-continuity, laminar momentum, energy, and diffusion-are solved numerically to obtain the unsteady temperature and concentration distributions from the time when Marangoni convection starts until dimensionless time is t=10, for various aspect ratios (AR=thickness of absorbent solution/length of model cell). The influence of the absorbent-solution depth on the occurrence of Marangoni convection is quantified in terms of a mean Sherwood number and a mean Nusselt number for several AR values. As a result of these calculations, absorption-enhancement ratios are obtained for each calculation parameter AR by comparison of the surfactant-added and nonadded conditions (vapor-absorption amount with surfactant addition/vapor-absorption amount without surfactant addition).
