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.

通过剪切的空气水界面上的质量转移机制，由于波浪破裂而没有气泡夹带，根据风波储罐中界面区域的有组织运动的湍流结构进行了实验研究。通过CO_2的重新实验测量了水侧二氧化碳（CO_2）的转移速度，并使用热线电仪和激光射击器速度计测量空气和水流中的流体速度。结果表明，与未切除的界面相比，在风剪中更强烈地促进了跨剪切空气水界面的传质。然而，风剪对质量转移的影响趋于在当前的风波储罐中的高剪切区域饱和，在这种风波储罐中，随着风剪切速度的增加速度的增加速度迅速下降。可以根据空气水界面附近的湍流结构来很好地解释风剪的影响。也就是说，通过在界面上方的空气流中产生的强组织运动的强烈有组织的运动，通过在空气水界面上的高风剪诱导表面续订涡流，而更新涡流控制着横跨剪切界面的质量转移。传质速度与表面更新涡流的出现频率相关，因为它处于带有未切换接口的开放通道流中，并且与表面续订频率的根部大约增加。表面更新频率随着风剪切的增加而增加，但对于高剪切速度的增加速度。这导致了风剪对当前风波储罐高剪切区域中质量转移的饱和作用。根据表面更新发生时时间分数的概念，可以通过表面续订涡流模型来很好地估算传质速度。