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

精确的空气-水界面传热传质速度对于估算全球大气CO2收支和异常气候以及设计具有空气-水界面的工业设备具有重要意义。因此，本研究的目的是探讨在强风切变作用下，具有破碎波的剪切气水界面的传热传质机制，并讨论传热传质速度的相似性。在风浪箱中进行了CO2的解吸和蒸发实验，测量了CO2和换热速度。此外，为了阐明破波液滴和热分层对传质的影响，进行了基础实验和数值模拟。本研究的主要结果可以总结如下。(1) CO2传输速度随风速的变化趋势与以往的测量结果有很大的不同，误差较大的因素较多，可以通过考虑地表更新涡流和微小的地表活性杂质的影响来解释。(2)在剪切气水界面处，在高风速区域，微小的表面活性杂质的影响被强烈的破波去除，传热传质速度与剪切气水界面处的传质速度相似，而在低风速区域，在非破波界面处，这种相似性消失。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)大雷诺数球形颗粒的升力和阻力系数的变化规律与常规模型不同。为了准确预测波浪破碎时液滴的运动，提出了一种准确估计液滴阻力和升力的方法。(4)稳定分层导致被动质量和主动热涡动扩散系数差异较大。这一差异表明，传统湍流模型中对被动质量和主动热量采用相同涡流扩散率的假设，在估计稳定热分层流中羽流的传热和传质时存在严重误差。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