Influence of waves on air-water gas transfer

Experiments on air-water gas transfer were performed in a flume with a mechanical wave maker for the determination of the gas-transfer coefficient with waves. Oxygen was used as the transferred gas. The experiments indicate that nonbreaking deep-water gravity waves significantly influence air-water gas transfer. The gas-transfer coefficient was correlated with the wave characteristics. A renewal model was used for the analysis of the data, and the renewal rate was dependent on a wave Reynolds number. The gas-transfer coefficient was linearly dependent upon the product of wave height and wave frequency. This is also equivalent to the gas-transfer coefficient being directly proportional to the wave velocity at the water surface. Comparison with data reported in the literature indicates that a significant portion of the observed gas transfer in wind-wave flume experiments can be attributed to nonbreaking waves. The presence of bubbles or bubble-entraining breaking waves enhances the gas-transfer coefficient considerably. Visual correlation between breaking intensity and the transfer coefficient was good, although the relation has not been quantified.