垂向振荡浮子装置掺气的水气二相动力行为及增氧机理研究

Dissolved oxygen concentration is an important index of seawater quality，and its low value results in a serious environment and ecology problem. In recent years, the artificial aeration and oxygen supply method has been used in environmental protection practice, but the high energy consumption and poor economy efficiency is a great disadvantage. The research aims at enhancing the dissolved oxygen concentration in hypoxic seawater with natural aeration and oxygen supply method economically and efficiently as the application background. Physical experiment, numerical calculation, field test and theoretical analysis are employed respectively to investigate the water-air two-phase flow hydrodynamic behavior and oxygen supply mechanics on aeration of a wave floater device oscillating vertically. The hydraulic parameters of aeration and the dissolved oxygen concentration are measured respectively. The intrinsic relationship between hydrodynamic behavior of floater, oxygen supply performance of the device and its geometry, wave parameters is explored. On the basis of bubbly population balance theory, a 3-D mathematical model of bubbly jet flow with buoyancy and a 3-D mathematical model of dissolved oxygen transport are established to compute the hydraulic parameters and dissolved oxygen concentration considering the effect of bubbly coalescence and breakup. The rates of bubbly coalescence and breakup are introduced into the calculation of oxygen transfer coefficient between water and bubbles, which considers the complex influence of bubbly behavior on mass transfer more accurately. The sensitivities of oxygen transfer coefficient and oxygen supply efficiency to water temperature are analyzed so as to promote the water and air mass transfer research process. The geometric parameters of the device are optimized to obtain the economical and efficient conditions. The objective is to provide a strong technology support on oxygen supply research and engineering application in hypoxic seawater economically and efficiently.

溶解氧浓度是重要的海水水质指标，过低会带来严重的环境生态问题。近年来，人工掺气增氧已在环保工程中应用，但能源消耗高，经济性差。本项目以缺氧海域经济、高效的自然掺气增氧为应用背景，以垂向振荡浮子装置掺气的水气二相动力行为及增氧机理为研究对象，采用室内试验、数值计算、海上测试和理论分析的方法进行研究。观测掺气的水力参数及溶解氧浓度；探究浮子等构件水动力行为、装置增氧性能与波参数、浮子体型和几何尺寸的内在关联；基于气泡群平衡理论，建立考虑气泡聚并与破碎影响的气泡浮射流动和溶解氧输移扩散三维数学模型；将气泡聚并和破碎速率引入气泡界面氧传质系数，精确反映气泡群复杂动力行为对水气二相传质的影响；分析氧传质系数和增氧效率对水温的敏感性，推进水气二相界面传质的研究进程；开展装置体型与几何尺寸的优化研究，阐明其经济、高效运行条件。本项目目标是为缺氧海域经济、高效增氧研究和工程应用提供有力的技术支持。

溶解氧浓度是重要的海水水质指标之一，过低会带来严重环境生态问题。近年来，受海水富营养化和气候变化共同影响，全球近岸缺氧海域面积逐渐增加，形势日趋严峻。项目组提出了一套波浪驱动的垂荡浮子掺气增氧装置，具有结构简单、运行中无需消耗化石电力能源、经济性好及无二次污染等优点。项目组利用室内试验、数值模拟和理论分析等方法，对波浪作用下单浮子和阵列式四浮子装置水动力学机理和溶解氧输移扩散行为特性进行了观测和计算分析。发现：（1）随着入射规则波周期增加，单浮子和阵列式浮子垂荡幅度与平均掺气流量均相应增加；后排浮子垂荡幅度小于前排浮子对应值。当波周期增加到较大值时，单浮子相对垂荡幅度基本趋于稳定，平均掺气流量甚至呈现下降趋势。（2）随着入射波高增加，单浮子和阵列式浮子平均掺气流量、单浮子相对垂荡幅度和阵列式浮子垂荡幅度均相应增加。（3）掺气深度较小时，单浮子和阵列式浮子平均掺气流量较大。随着掺气深度增加，单浮子相对垂荡幅度和平均掺气流量均降低。（4）随着浮子相对高度增加，单浮子相对垂荡幅度与平均掺气流量呈现先增加后减小趋势，而阵列式浮子相对垂荡幅度呈下降趋势。（5）随着浮子密度增加，单浮子相对垂荡幅度与平均掺气流量缓慢增加，增幅远小于密度增幅；阵列式浮子垂荡幅度呈下降趋势。浮子密度对垂荡运动和平均掺气流量的影响相对较小。（6）随着阵列式浮子装置等效阻尼系数增加，前后排浮子运动相位差减小，垂荡幅度呈下降趋势。（7）随着入射波周期、波高、掺气深度和平均掺气流量增加，气泡界面氧传质系数相应增加。随着掺气源面积增加，气泡界面氧传质系数呈现轻微下降趋势。（8）分别建立并验证了由无量纲波参数和装置几何体型等一系列变量表达的气泡界面氧传质系数和阵列式前后排浮子相对垂荡幅度预测公式，其精度较高。上述结论可以为缺氧海域经济、高效和环境友好的人工增氧研究和工程实践提供有力的技术支持和参考依据。