Fluid Mechanical Studies on Heat and Mass Transfer Mechanism across the Sheared Air-Water Interface
Grant-in-Aid for Scientific Research (B)
|Allocation Type||Single-year Grants|
|Research Institution||KYOTO UNIVERSITY(1998)|
KOMORI Satoru Kyoto Univ., Dept.of Mech.Eng., Professor, 工学研究科, 教授 (60127082)
SHIMADA Takashi Japan Society of Promotion of Sci., Research Scientist, 特別研究員
NAGATA Kouji Kyoto Univ., Dept.of Mech.Eng., Research Associate, 工学研究科, 助手 (50274501)
|Project Period (FY)
1997 – 1998
Completed(Fiscal Year 1998)
|Budget Amount *help
¥8,200,000 (Direct Cost : ¥8,200,000)
Fiscal Year 1998 : ¥3,300,000 (Direct Cost : ¥3,300,000)
Fiscal Year 1997 : ¥4,900,000 (Direct Cost : ¥4,900,000)
|Keywords||Mass Transfer / Air-Water Interface / Turbulence Structure / Shear / Thermal Stratification / Similarity / 直接数値計算|
It is of great importance to get precise heat and mass transfer velocities across the air-water interface for estimating the global atmospheric CO2 budget and unusual climate and for designing industrial equipment with the air-water interface.
The purpose of this study is, therefore, to investigate the heat and mass transfer mechanism across the sheared air water interface with breaking waves due to the strong wind shear and to discuss the similarity between the heat and mass transfer velocities. The CO2 and heat transfer velocities were measured in a wind-wave tank by carrying Out the CO2 desorption and evaporation experiments. Further, to clarify the effects of both droplets due to the wave breaking and thermal stratification on the mass transfer the fundamental experiments and numerical simulations were conducted.
The main results from this study can be summarised as follows.
(1) The trends of the CO2 transfer velocity against wind velocity are quite different from the previous measure
ments with big errors and they can be elucidated by considering the effects of the surface renewal eddies and tiny surface-active impurities.
(2) The similarity between heat and mass transfer velocities at the sheared air-water interface can be seen in the high wind speed region where the effects of the tiny surface-active impurities are removed by intense wave-breaking, However, the similarity disappears in the lower wind speed region with the non-breaking interface. The damping effect of the surface-active impurities on the heat transfer is larger than that on the mass transfer.
(3) The behaviours of the lift and drag coefficients for spherical particles with large particle Reynolds numbers are different from the conventional models. To predict the motions of the droplets due to the wave breaking a method for exactly estimating the drag and lift forces acting droplets was proposed.
(4) Stable stratification causes the large difference in eddy diffusivities between passive mass and active heat. The difference suggests that an assumption of the same eddy diffusivity for passive mass and active heat, used in conventional turbulence models, gives a serious error in estimating heat and mass transfer in a plume in a stable thermally-stratified flow. Less
Research Output (17results)