• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.746-752
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• 2015

This study investigates the effects of aspect ratio (transport length-to-width) on diffusive-convection for physical vapor transport processes of $Hg_2Cl_2-NO$ system. For a system with the temperature difference of 20 K between an interface at the source material region and growing crystal interface, the linear temperature profiles at walls, the total molar fluxes at Ar = 2 are much greater than Ar = 5 as well as the corresponding nonuniformities in interfacial distributions due to the effect of convection. The maximum total molar flux at the gravitational acceleration of 1 $g_0$ is greater twice than at the level of 0.1 $g_0$, where g0 denotes the gravitational acceleration on earth. With increasing aspect ratio from 2 to 5, a diffusive-convection mode is transited into the diffusion mode, and then the strength of diffusion is predominant over the strength of diffusive-convection.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.3
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• pp.115-125
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• 1992

혼합 대류 이상 유동 시스템에 부유된 슈트와 미분탄과 같은 고흡수, 방사하는 입자의 열확산적 입자이동에 대한 복사 및 부력효과를 수치적으로 검토하였다. 기체 및 입자유동의 지배방정식 들은 Euler 관점의 two-fluid model의 근간에서 수행되었으며, 에너지 보존식의 비선형 복사 생 성항은 P-1 근사방법에 의해 계산되었다. 혼합 대류 유동에서의 입자의 열확산 현상은 복사 열 전달과 커플링되며, 복사효과의 증가는 부력효과를 상대적으로 감소시켜 부력효과에 의한 입자 부착율을 완화시켰다. 복사효과가 무시될 때 Grashof 수의 증가에 따라 입자의 확산효과는 감 소되었으며, 복사효과가 함께 작용될 때 입자 부착율은 증가됨을 보였다.

• Journal of Ocean Engineering and Technology
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• v.13 no.1 s.31
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• pp.121-129
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• 1999

Double-diffusive convection with verical temperature and concentration gradients in thermally stratified fluids has been investigated experimentally using an electrochemical technique. Cupric sulfuric-sulffuric acid solution confined between two horizontal copper electrodes was used. The change of thermal and solutal buoyance has no influence on the range of voltage for the limiting current. Due to Soret effect, the onset time of natural convection is delayed as the stabilizing thermal buoyancy decreases. Also it is found that the shrinkage of the unstabilizing solutal buoyancy makes the onset of natural convection retard. Multi-layered convective phenomena do not appear because cupric sulfate-sulfuric acid solution is thermally stratified, and heat diffuses faster than cupric sulfate solfate solution.

• Journal of Environmental Impact Assessment
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• v.11 no.3
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• pp.173-187
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• 2002

토양 속에서 발생될 수 있는 용질과 용매의 복합 수송시스템을 대상으로 한 연구 중 회석상태로부터 포화상태에 이르기까지의 넓은 농도분포를 가지는 토양 용액에 적용될 수 있는 물리 화학적 이론에 입각한 지배방정식을 발표한 연구는 전무한 실정이다. 본 연구는 용매와 토양기체간 그리고 용질과 결정간의 상변화를 고려한 연립물질수지방정식을 제시하고, 여기에 타율적 대류를 포함하는 상호확산 분산수송방정식을 도입하여 대류와 확산에 관한 프럭스를 분리, 결정하는 것을 목적으로 한다. 대류 플럭스의 결정은 타율적으로 이루어지는 것이 이론적으로 타당하며, 이러한 타율적 대류 플럭스가 제공된다면 본 연구에서 제시된 지배방정식을 이용해서 토양용액의 복합수송 시스템을 범용적으로 해석, 예측할 수 있을 것으로 판단된다.

• Applied Chemistry for Engineering
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• v.27 no.3
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• pp.335-341
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• 2016

In this study, impurity effects on diffusive-convection flow fields by physical vapor transport under terrestrial and microgravity conditions were numerically analyzed for the mixture of $Hg_2Cl_2-I_2$ system. The numerical analysis provides the essence of diffusive-convection flow as well as heat and mass transfer in the vapor phase during the physical vapor transport through velocity vector flow fields, streamlines, temperature, and concentration profiles. The total molar fluxes at the crystal regions were found to be much more sensitive to both the gravitational acceleration and the partial pressure of component $I_2$ as an impurity. Our results showed that the solutal effect tended to stabilize the diffusive-convection flow with increasing the partial pressure of component $I_2$. Under microgravity conditions below $10^{-3}g_0$, the flow fields showed a one-dimensional parabolic flow structure indicating a diffusion-dominant mode. In other words, at the gravitational levels less than $10^{-3}g_0$, the effects of convection would be negligible.

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.129-137
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• 1999

The time of the onset of double-diffusive convection in time-dependent, nonlinear concentration fields is investigated theoretically. The initially quiescent horizontal fluid layer with a uniform temperature gradient experiences a sudden concentration change from below, but its stable thermal stratification affects concentration effects in such way to invoke convective motion. The related stability analysis, including Soret effect, is conducted on the basis of the propagation theory. Under the linear stability theory the concentration penetration depth is used as a length scaling factor, and the similarity transform for the linearized perturbation equations. The newlly obtained stability equations are solved numerically. The resulting critical time to mark the onset of regular cells are obtained as a function of the thermal Rayleigh number, the solute Rayleigh number, and the Soret effect coefficient. For a certain value of the Soret effect coefficient, the stable thermal gradient promote double-diffusive convective motion.

• Journal of the Korean Electrochemical Society
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• v.2 no.2
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• pp.98-105
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• 1999

In the present study, buoyant force and its stabilizing effects in an electrostatic field were examined systematically in order to reduce the effect of natural convection with thermal stratification in a horizontal fluid-saturated porous layer. The correlation of ionic mass transport induced by double-diffusive convection in a horizontal porous layer has been derived theoretically. And the theoretical model was examined by electrochemical experiments. The theoretical correlation for mass transport which is satisfying Forchheimer's flow equation and based on the micro-turbulence model is derived as a function of soltual Darcy-Rayleigh number, thermal Darcy-Rayleigh number and Lewis number. In the experiment, the mass transport of copper ions in $CuSO_4-H_2SO_4$ solution is measured by electrochemical technique. By assembling theoretical correlation and experimental results, the mass transport correlation induced by double-diffusive convection is proposed as $$Sh=\frac{0.03054(Rs_D-LeRa_D)^{1/2}}{1-3.8788(Rs_D-LeRa_D)^{-1/10}}$$ The present correlation looks flirty reasonable with comparing experimental results, and very promising for the applications of its prototype into various systems involving heat transfer as well as mass transfer, in order to control the effects of natural convection effectively.

• Journal of Energy Engineering
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• v.4 no.1
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• pp.126-139
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• 1995

저속의 압축성 유동장에서의 원형 실린더 주위의 유동 및 열전달특성을 해석하였다. 비압축성 유동장에서의 실린더 주위의 유동 및 열전달현상에 대하여는 실험과 수치해석을 포함한 광범위한 연구가 진행되어 왔으며 매우 잘 알려져 있다. 실린더 벽면과 주위 유동장의 온도차가 큰 경우, 밀도의 변화가 커지므로 유동장은 압축성 유체가 되나 지배 방정식의 복잡함과 적절한 수치해석 방법의 부족으로 실린더 주위의 유동장을 압축성유체로 해석한 경우는 매우 드물다. 현재 압축성유동 해석에 널리 사용되는 time marching algorithm은 저속의 유동장 해석시 지배방정식에 나타나는 eigenvalue들의 괴리에 의하여 수렴속도가 현저히 떨어지게 된다. 본 연구에서는 이와 같은 난점을 극복할 수 있는 time-derivative preconditioning 방법을 사용하여 온도차가 큰 유동장에서의 강제 및 혼합대류에 대한 계산을 수행하였고 이들의 열전달특성을 비교하였다. 강제대류의 경우 실린더 벽면 온도의 증가에 따른 밀도 감소의 영향은 유동장의 Re수를 감소시켜 확산의 영향을 증가시키면서, 혼합대류의 경우 부력의 영향은 가열되는 유동장의 범위와 재순환 영역을 강제대류에 비해 현저히 감소시킨다.

• Proceedings of the Korea Water Resources Association Conference
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• 1985.07a
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• pp.77-83
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• 1985

• Fire Protection Technology
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• s.58
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• pp.18-26
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• 2015