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HEAT AND MASS TRANSFER MECHANISM ACROSS THE AIR-SEA INTERFACE

海气界面的传热传质机制

基本信息

批准号：
02455016
负责人：
KOMORI Satoru
金额：
$ 4.61万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1992
项目状态：
已结题

项目摘要

The mass transfer mechanism across a sheared air-water interface without bubble entrainment due to wave breaking was experimentally investigated in terms of the turbulence structure of the organized motions in the interfacial region in a wind-wave tank. The transfer velocity of the carbon dioxide (CO_2) on the water side was measured through reaeration experiments of CO_2, and the fluid velocities in the air and water flows were measured using both a hot-wire anemometer and a laser-Doppler velocimeter. The results show that the mass transfer across a sheared air-water interface is more intensively promoted in wind shear, compared to an unsheared interface. However, the effect of the wind shear on the mass transfer tends to saturate in the high-shear region in the present wind-wave tank, where the increasing rate of mass transfer velocity with the wind shear decreases rapidly. The effect of the wind shear on the mass transfer can be well explained on the basis of the turbulence structure near the air-water interface. That is, surface-renewal eddies are induced on the water side through the high wind shear on the air-water interface by the strong organized motion generated in the air flow above the interface, and the renewal eddies control the mass transfer across a sheared interface. The mass transfer velocity is correlated with the frequency of the appearance of the surface-renewal eddies, as it is in open-channel flows with unsheared interfaces, and it increases approximately in proportion to the root of the surface-renewal frequency. The surface-renewal frequency increases with increasing the wind shear, but for high shear the rate of increase slows. This results in the saturated effect of the wind shear on the mass transfer in the high-shear region in the present wind-wave tank. The mass transfer velocity can be well estimated by the surface-renewal eddy-cell model based on the concept of the time fraction when the surface renewal occurs.

根据风浪水池中界面区域有组织运动的湍流结构，实验研究了无波浪破碎气泡夹带的剪切空气-水界面的传质机理。通过CO2复氧实验测量了CO2在水侧的传递速度，并用热线风速仪和激光多普勒测速仪测量了空气和水流中的流体速度。结果表明，与未发生剪切的气液界面相比，风切变对空气-水界面的传质有更强的促进作用。然而，在现有的风浪水槽中，风切变对传质的影响在高切变区趋于饱和，此时传质速度随风切变的增加速率迅速减小。根据气液界面附近的湍流结构，可以很好地解释风切变对传质的影响。也就是说，由于界面上方的气流产生强烈的有组织运动，通过气水界面上的高风切变在水侧诱导了表面更新涡，更新涡控制了剪切界面上的质量传递。传质速度与表面更新涡的出现频率有关，与无剪切界面的明渠水流一样，传质速度与表面更新频率的根近似成正比地增加。地面更新频率随着风切变的增加而增加，但对于高切变，地面更新频率的增加速度变慢。这导致了风切变对现有风浪水池高切变区传质的饱和效应。基于表面更新时间分数概念的表面更新涡胞模型可以很好地估算传质速度。