Effects of Fetch on Mass Transfer Across the Air-Water Interface in Wind-Driven Turbulence

Abstract

The effects of fetch on mass transfer across the wind-driven air-water interface was investigated through laboratory experiments in a large wind-wave tank. The CO2 transfer coefficient on the liquid-side, kL, was measured by applying the flux-profile method to the vertical distributions of wind velocity and CO2 concentration in air. The surface-renewal frequency fs that dominates mass transfer across the air-water interface was measured by applying the VITA method to the streamwise velocity fluctuation in water. The results show that both kL and fs are well correlated with free-stream wind velocity U∞ irrespective of fetch, whereas kL and fs are poorly correlated with the velocity at the center of entrance U∞. Furthermore, kL measured in both small and large wind-wave tanks is well correlated with U∞ whereas kL is poorly correlated with air friction velocity u*a.These results suggest that an outer parameter is a more suitable parameter for correlating kL.