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

波纹、气泡、液滴和污染物对穿过空气-水界面的传质的影响

基本信息

批准号：
11450077
负责人：
KOMORI Satoru
金额：
$ 9.02万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11450077/
关键词：
Wind-driven turbulence Mass transfer Bubble Droplet Ripple

项目摘要

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

对穿过剪切空气-水界面的传质速率的准确估计引起了人们对与大气和海洋之间二氧化碳交换相关的全球变暖问题的特别兴趣。本研究的目的是通过实验和数值研究波纹、夹带到水中的气泡以及波浪破碎分散的液滴对空气-水界面上的传质的影响。还通过振荡网格罐中的实验室实验研究了重油表面污染对CO_2穿过空气-水界面传输的影响。使用相位多普勒风速计（PDA）和激光多普勒测速仪（LDV）测量气泡夹带率和气泡与液体之间的相对速度。此外，通过直接数值模拟（DNS）在较宽的粒子雷诺数Re_p范围内估计了气泡和液体之间的传质速度。利用PDA测量了波浪破碎分散液滴的尺寸分布和平均速度。结果表明，即使在风浪强烈破碎的自由流风速U=18m/s下，气泡对破碎空气-水界面总传质的净贡献最多为7%。这一结果支持了我们之前的研究，即高风速区破碎波传递速度的快速增加是由于波纹状涡流表面更新频率的增加和极微小表面活性杂质的表面污染因波浪破碎而消失所致。受重油污染的3.5wt%盐水(或天然海水)穿过非破裂界面的CO_2传输速度衰减至无重油污染的3.5wt%盐水的46%。当界面强烈破坏时,重油污染的空气-水界面上的CO_2传输速度与无重油污染的自来水或盐水接近。较少的