Mass transfer enhancement by gravity waves at a liquid-vapour interface

Experimental results on mass transfer enhancement by large amplitude gravity waves at a liquid-gas/vapour interface are presented. The waves are sub-harmonically excited in a circular cylinder that is partially filled with liquid, by oscillating the cylinder in the direction normal to the liquid surface. The lowest asymmetric sloshing mode (1, 1) as well as the axisymmetric mode (0, 1) are considered in the limit of large fluid depth approximation and for wave amplitudes that include breaking. The fluids used are low viscosity and low surface tension liquids of low boiling point temperatures. In the mass transfer experiments the lower part of the test cell is filled with cold liquid and the upper part with gas, generally vapour, at a temperature above the saturation temperature. When the interface is at rest and the gas is vapour, the pressure decrease due to condensation is small. In the presence of large amplitude sloshing the condensation rate is large and the pressure decreases rapidly and substantially. A model is developed that expresses the pressure variation in terms of a Jacob number, interfacial temperature gradient and an effective diffusion coefficient. The effective dimensionless diffusion coefficient is the relevant similarity parameter and is determined in the experiments. In Appendix A results are presented for conditions of evaporation in the presence of a non-condensable gas. (C) 2008 Elsevier Ltd. All rights reserved.