Fluid Mechanical Studies on Heat and Mass Transfer Mechanism across the Sheared Air-Water Interface

准确获得气-水界面传热传质速率对于估算全球大气CO2收支和异常气候以及设计具有气-水界面的工业设备具有重要意义。研究了风切变引起的破波作用下剪切气-水界面的热质交换机理，并讨论了风切变引起的破波作用下剪切气-水界面的热质交换机理。传热速度和传质速度之间的相似性。在风浪箱中进行了CO2解吸和蒸发实验，测定了CO2的解吸速度和传热速度。此外，为了阐明由于波浪破碎和热分层引起的液滴对传质的影响，进行了基础实验和数值模拟。(1)CO2传输速度随风速的变化趋势与以前的测量结果有很大的不同 ...更多信息 误差较大的部分，考虑表面更新涡和微小的表面活性杂质的影响，可以得到解释。(2)在高风速区，由于强烈的波浪破碎作用，微小的表面活性杂质的影响被去除，剪切界面处的传热传质速度具有相似性，而在低风速区，由于剪切界面处的非破碎界面，这种相似性消失了。表面活性杂质对传热的阻尼作用大于对传质的阻尼作用。(3)大颗粒雷诺数下球形颗粒的升阻系数的变化规律与常规模型不同。为了预测波浪破碎时液滴的运动，提出了一种精确估算液滴阻力和升力的方法。(4)稳定层结导致被动质量和主动热量之间的涡动扩散率的巨大差异。这种差异表明，被动质量和主动热相同的涡流扩散率的假设，在传统的湍流模型中使用，在估计热和质量传递在一个稳定的热分层流的羽流中给出了严重的错误。少

It is of great importance to get precise heat and mass transfer velocities across the air-water interface for estimating the global atmospheric CO2 budget and unusual climate and for designing industrial equipment with the air-water interface.The purpose of this study is, therefore, to investigate the heat and mass transfer mechanism across the sheared air water interface with breaking waves due to the strong wind shear and to discuss the similarity between the heat and mass transfer velocities. The CO2 and heat transfer velocities were measured in a wind-wave tank by carrying Out the CO2 desorption and evaporation experiments. Further, to clarify the effects of both droplets due to the wave breaking and thermal stratification on the mass transfer the fundamental experiments and numerical simulations were conducted.The main results from this study can be summarised as follows.(1) The trends of the CO2 transfer velocity against wind velocity are quite different from the previous measure … More ments with big errors and they can be elucidated by considering the effects of the surface renewal eddies and tiny surface-active impurities.(2) The similarity between heat and mass transfer velocities at the sheared air-water interface can be seen in the high wind speed region where the effects of the tiny surface-active impurities are removed by intense wave-breaking, However, the similarity disappears in the lower wind speed region with the non-breaking interface. The damping effect of the surface-active impurities on the heat transfer is larger than that on the mass transfer.(3) The behaviours of the lift and drag coefficients for spherical particles with large particle Reynolds numbers are different from the conventional models. To predict the motions of the droplets due to the wave breaking a method for exactly estimating the drag and lift forces acting droplets was proposed.(4) Stable stratification causes the large difference in eddy diffusivities between passive mass and active heat. The difference suggests that an assumption of the same eddy diffusivity for passive mass and active heat, used in conventional turbulence models, gives a serious error in estimating heat and mass transfer in a plume in a stable thermally-stratified flow. Less