基于气泡细观尺度的过饱和溶解气体释放机理研究

The presence of elevated dissolved gas downstream of a spillway may result in an increased incidence of gas bubble disease; even cause large scale death in fish. The dissipation process of dissolved gas is affected by water depth, velocity, sediment, aeration, wind and temperature, while the mechanism of how to affect the dissipation is not ascertained. Based on the frame of subregion theory for supersaturated dissolved gas dissipation which was formed from last sponsored foundation, mechanical experiments and theoretical analysis will conducted on the micro level, by employing high-speed camera system, aeration measure system and dissolved gas measure system. The relations between bubble formation and developing characteristics, such as bubble concentration, scale, distribution and lifting velocity, and water body characteristics, such as dissolved gas supersaturation, pressure, embedded medium will be investigated as pioneers. Then the mechanism of the dissolved gas dissipation will be explored based on them. The critical condition for the bubble formation will be determined. The mass transfer mechanism of air bubble surface in dissolved gas supersaturation water will be investigated. And the calculated method for the wall sorption function of embedded medium in dissolved gas supersaturation water will be explored. Finally, an ultimate model of supersaturated dissolved gas dissipation will be proposed, whose key parameters are independent of analogy according to field or experimental results. The project extends the research about supersaturated dissolved gas from macro impact to micro mechanism. It is of great importance in improving the prediction of supersaturated dissolved gas and accelerating the study of mitigation measures. Also, it is of theoretical value and practical significance in developing eco-environmentally friendly hydropower projects.

高坝泄水会产生溶解气体过饱和并可能导致鱼类患气泡病甚至规模性死亡。过饱和溶解气体的释放过程受水深、流速、介质等众多因素影响，但其根本作用机制尚未探明。项目在已有过饱和溶解气体分区释放模型框架上，利用高速图像采集系统、掺气和溶解气体饱和度测量系统，从细观层面开展机理试验和理论分析，以溶解气体析出形成气泡及其发展特性（气泡密度、尺寸、分布、上浮速度等）与水体溶解气体饱和度、压力、植入介质等的关系入手探究过饱和溶解气体释放的根本机制。确定溶解气体析出发生条件，揭示溶解气体过饱和水体内气泡表面的气-液传质关系，探求植入介质壁面吸附作用的计算方法，建立不依赖于试验和原观成果类比确定参数的过饱和溶解气体释放模型体系。本项目研究将以往宏观层面探讨影响因素的研究拓展至细观层面的机理研究中，对于显著提高过饱和溶解气体预测水平，有效促进减缓措施研究，建设环境友好型水利工程具有重要的理论价值和现实意义。

高坝泄水会产生溶解气体过饱和并可能导致鱼类患气泡病甚至规模性死亡。过饱和溶解气体的释放过程受水深、流速、介质等众多因素影响，但其根本作用机制尚未探明，制约了过饱和溶解气体释放过程的深入认识和河库系统过饱和气体传输的精细模拟。项目研发构建利用减压环境生成TDG过饱和水体的新方法并构建了无多余掺气影响的过饱和TDG释放过程研究实验系统，实现了过饱和TDG特性研究实验手段的创新。解构过饱和TDG释放过程为自由液面水气传质、壁面TDG吸附和内部TDG释放等三个过程，针对关键的壁面吸附与内部释放过程提出了过饱和TDG释放系数的计算方法，完善了过饱和TDG释放预测方法。研究发现阻水介质的壁面材料属性是决定释放快慢的关键。致密类阻水介质表面粗糙度和接触角为影响过饱和TDG释放的关键因素，多孔类阻水介质比表面积和总孔容为影响过饱和TDG释放的关键因素。分别建立了致密类阻水介质面积吸附系数与接触角的定量关系和多孔类材料质量吸附系数与比表面积和总孔容的定量关系。提出了附壁气泡体积随时间变化过程以及不同相对真空度下的附壁气泡界面传质系数。建立了附壁气泡生消模型，揭示了附壁气泡生消规律与壁面对过饱和TDG吸附量之间的定量关系。在气泡二维图像处理的基础上重构气泡体积，以实现传质通量的计算。针对内部释放过程提出了过饱和TDG气泡界面传质通量与压力条件和TDG饱和度条件的定量关系，为精细的过饱和TDG生成、释放模拟提供关键参数的确定方法。结合鱼类耐受性研究成果提出了对过饱和TDG释放非恒定过程下的鱼类风险评估方法，量化了不同释放促进材料使用下的风险指数与鱼类致死度。项目研究将以往宏观层面探讨影响因素的研究拓展至细观层面的机理研究中，对于显著提高过饱和溶解气体预测水平，有效促进减缓措施研究，建设环境友好型水利工程具有重要的理论价值和现实意义。