Laboratory experiments on interfacial heat and gas exchange promoted by surface cooling: novel simultaneous thermal imaging and optical oxygen-concentration measurement

为了能够正确模拟全球碳循环（以及全球热量收支），需要详细了解大型水体吸收或释放的温室气体量。目前，大多数用于估算气-水界面气体传输的模型只考虑风切变，而没有考虑浮力，浮力是低至中等风速下的主要贡献因素。为了提高预测的准确性，详细研究浮力驱动的气体传输在深沃茨是必要的。由于低至中等可溶性气体（例如二氧化碳、氧气、甲烷）的界面传质的特征在于极薄的气体浓度边界层，因此阐明该过程的物理机制是非常困难的。尽管先进的光学测量技术的发展，详细的同时映射的高度动态的温度和气体浓度分布促进良好控制的实验室条件下的对流还没有报道。因此，我们建议通过非侵入式（光学）和同时测量气体（氧气）浓度和温度场（i）在水面和（ii）在液体侧的垂直平面上，调查由表面冷却触发的对流不稳定性驱动的热和气体传递过程。一个完整的基于寿命的激光诱导荧光系统，适用于解决包括在扩散子层的氧动力学将被开发。为了捕获表面热结构的分布，将使用高精度红外摄像机，而基于强度的LIF测温系统将用于获得水柱内的2D热场。结果将提供前所未有的实验数据的形式天气的二维热量和气体浓度映射下对流驱动的流动条件下，在一个相对较深的水体。将研究热羽流和气体饱和羽流之间的相关性，并探讨它们在水面和水柱中的几何特征，以及与热通量和气体通量的关系。一系列的气体传输速度（k）的测量在大范围的空气和水的大部分之间的温度差将进行允许k相关的散装瑞利数和k相比，从我们的新的详细的同时测量。此外，为了提供流场信息，还将对选定的情况进行粒子图像测速（PIV）测量，主要侧重于提供整体（批量）视图。

To be able to properly model the global cycling of carbon (and thus the global heat budget), detailed knowledge is needed on the amount of greenhouse gases absorbed or released by large bodies of water. At present, most models used to estimate gas transfer across the air-water interface only consider wind-shear and do not take buoyancy into account, which is a major contributor at low to moderate wind speeds. To improve the accuracy of the predictions, a detailed study of buoyancy-driven gas transfer in deep waters is necessary. As the interfacial mass transfer of low to moderate soluble gases (e.g. carbon dioxide, oxygen, methane) is characterized by an extremely thin gas concentration boundary layer, elucidating the physical mechanisms of the process is immensely difficult. Despite advanced development in optical measurement techniques, detailed simultaneous mappings of the highly dynamic temperature and gas concentration distributions promoted by buoyant-convection under well-controlled laboratory conditions have not been reported yet. We therefore propose to investigate the heat and gas transfer process driven by a buoyant-convective instability triggered by surface cooling through non-intrusive (optical) and simultaneous measurements of gas (oxygen) concentration and temperature fields (i) at the water surface and (ii) in a vertical plane on the liquid side. A complete lifetime-based laser induced fluorescence system suitable for resolving the oxygen dynamics including in the diffusive sublayer will be developed. To capture the distribution of the thermal structures at the surface, a high-precision infrared camera will be used, while an intensity-based LIF-thermometry system will be employed to obtain 2D thermal fields within the water column. The results will provide unprecedented experimental data in the form of synoptic two-dimensional thermal and gas concentration mappings under buoyant-convectively driven flow conditions in a relatively deep water body. The correlation between the thermal and gas-saturated plumes will be studied and their geometrical characteristics both at the water surface and in the water column will be explored and related to the heat and gas fluxes. A series of gas transfer velocity (k) measurements over a wide range of temperature differences between the bulk of the air and of the water will be carried out allowing k to be related to the bulk Rayleigh number and compared with k obtained from our new detailed simultaneous measurements. In addition, to provide information on the flow-field, particle image velocimetry (PIV) measurements will also be carried out for selected cases, which mainly focus on providing an overall(bulk)-view.