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수직이동하는 평판위 박막유동의 근사해

Approximations of Thin Liquid Film Flows in Dip Coating

HWAHAK KONGHAK, June 1986, 24(3), 237-246(10), NONE
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Abstract

유동현상 자체보다는 액막의 전체 모양에 보다 관심이 있을 때 시도되는 일반적 방법은, 지배방정식의 변환 및 결함에 의하여 액막형태 방정식, y방향 운동량 적분방정식, x방향 운동량 적분방정식의 이용 등으로 나누어진다. 이들은 보통 박막가정과 함께 액막을 가로질러 이차의 속도분포를 가정하게 되는데, 근사의 과정을 통하며 각 방정식들은 액막의 자유표면 부근과 고체표면 부근이 강조되거나, 두 표면사이의 유동정보가 평균적으로 수용되는 등 특성이 나타나고 있다. 근래 적분법이라는 명칭아래 많이 쓰이는 것은 이들 중 세 번째의 x 방향 운동량 적분방정식이다. 그러나 dip coating공정의 모사과정을 면밀히 검토한 결과, 적분법은 표면장력이 크고 평판의 이동속도가 느려 액막이 충분히 얇을 경우에만 안전하게 적용될 수 있었다. 기존의 Ca수나 Re수 대신 M, Uo계로써 모사결과를 해석하였으며, 최종 액막두께와 도입길이, 액막의 발달에 관한 보다 명확한 경향이 관찰되었다.
When the meniscus is shape important and the velocity distribution itself is not required in high accuracy, the basic equations have been transformed and combined to yield a meniscus shape equation, an integral-y-momentum equation and an integral-x-momentum equation. Although their original forms were exact as they were, thin film assumption with a parabolic velocity profile across the film rendered the working equation to emphasize the flow characteristics near the free surface or on the solid surface, or to accomodate these two flow patterns. Most frequently used in recent times is the integral-x-momentum equation designated by the integral method in the literature. But a critical examination of simulated results for the dip coating process revealed that the integral method could be applied safely to the limited case of employing the liquid of large surface tension and small withdrawal speed. Simulation was carried out in terms of M and Uo instead of the capillary and Reynolds numbers, and distinct tendencies of the final film thickness, the entrance length and the dynamic meniscus profile could be observed.

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