The effects of ripples, bubbles, droplets and contamination on mass transfer across tne breaking air-water interfaces

通过剪切气-水界面的传质速率的精确估算在与大气和海洋之间的二氧化碳交换有关的全球变暖问题中引起了特别的兴趣。本文通过实验和数值模拟研究了波纹、气泡和破碎分散液滴对气液界面传质的影响。在实验室格栅水池中，研究了重油表面污染对CO_2气-水界面传输的影响。采用相位多普勒测速仪（PDA）和激光多普勒测速仪（LDV）测量了气泡夹带率和气泡与液体之间的相对速度。在此基础上，采用直接数值模拟方法，在较宽的颗粒雷诺数Re_p范围内，对气泡与液体之间的传质速度进行了估算，得到了气泡的尺寸分布 ...更多信息 用PDA测量了波浪破碎时分散液滴的运动和平均速度，结果表明，即使在U= 18 m/s的自由流风速下，在波浪破碎强烈的情况下，气泡对破碎气-水界面总传质的净贡献最多为7%.这一结果支持了我们以前的研究，即在高风速区的快速增加的传输速度与破碎波是由于波纹状涡的表面更新频率的增加和非常微小的表面活性杂质的表面污染的消失波破碎。当含3.5wt%重油的盐水（或天然海水）中CO_2在非破裂界面上的传输速度比不含重油的盐水中的传输速度衰减46%。当界面强烈破裂时，CO_2在含重油的气-水界面上的传输速度接近于无重油污染的自来水或盐水的传输速度。少

The accurate estimation of the mass transfer rate across the sheared air-water interface has attracted a special interest in the global warming problem related to the exchange of carbon dioxide between atmosphere and ocean. The purpose of this study is to experimentally and numerically investigate the effects of ripples, bubbles entrained into water and dispersed droplets by wave breaking on the mass transfer across the air-water interface. The effects of heavy-oil surface contamination on the CO_2 transfer across the air-water interface were also investigated through laboratory experiments in an oscillating-grid tank. The bubble entrainment rate and relative velocity between a bubble and liquid were measured using both a phase Doppler anemometer (PDA) and a laser Doppler velocimeter (LDV). Further, the mass transfer velocity between a bubble and liquid was estimated by means of direct numerical simulation (DNS) over the wide range of the particle Reynolds number Re_p. The size distrib … More utions and mean velocities of dispersed droplets by wave breaking were measured using a PDA.The results show that the net contribution of the bubbles to the total mass transfer across the breaking air-water interface is at most 7% even at the free stream wind velocity of U=18m/s where wind waves are intensively broken. This result supports our previous study that the rapid increase of the transfer velocity in the high wind speed region with breaking waves is due to both the increase of the surface renewal frequency of ripple-like eddies and the disappearance of surface contamination of very tiny surface-active impurities by wave breaking. The CO_2 transfer velocity across the non-breaking interface for 3.5wt% saltwater(or natural seawater)contaminated with heavy-oil is damped to 46% of that for 3.5wt% saltwater without heavy-oil contamination. When the interface is intensively broken, the CO_2 transfer velocity across the air-water interface contaminated with heavy-oil approaches to that for tap water or saltwater without heavy-oil contamination. Less