• 설비공학논문집
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• 제12권1호
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• pp.95-101
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• 2000

The effect of surface contact angle on the behavior of frost formation in a fin-tube heat exchanger is investigated experimentally. It is shown that both heat exchangers with hydrophilic and hydrophobic surfaces appear to have a better thermal performance than bare aluminium heat exchanger, but the improvements are very small. There is a little increase in the amount of the frost deposited onto the heat exchanger with both hydrophilic and hydrophobic surface. However, the effect of contact angle on the frost density is observed ; the frost with high density forms on the heat exchanger with hydrophilic surface ; and the frost with low density is deposited onto the heat exchanger with hydrophobic surface when compared with the frost deposited onto the heat exchanger with bare aluminium surface. This may be attributed to the fact that the shape of water droplets which condense on the surface of heat exchanger at the early stage of frosting varies with contact angle, and thus makes a difference on the structure of frost formation. From the experiments with different relative humidity of inlet air, it is shown that the variations of operating parameter make no influence on the effect of surface contact angle on the frosting behavior in the heat exchanger.

• Tribology and Lubricants
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• 제35권2호
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• pp.94-98
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• 2019

The riblet structure like shark skin has been widely studied owing to its drag reduction and anti-fouling properties. In this study we simulated the wettability of an oil droplet on a riblet surface. We developed a numerical analysis method using the Wenzel equation and Cassie-Baxter equation that can estimate the contact angle with a penetrated depth of the droplet on rough surfaces. Riblet surfaces with nine scales composed of five hemi-elliptical ribs are generated numerically. The variation of contact angles with fractional depth of penetration for the generated riblet surfaces with and without coatings is demonstrated in the condition of solid-air-oil and solid-water-oil interfaces. The contact angle for the uncoated surface decreases with increasing fractional depth of penetration more drastically than that for the coated surface. For the effect of surface roughness on the contact angle of the droplet, the oleophilic surface gives lower contact angle when the surface is rougher, whereas the oleoophobic surface gives higher contact angle with higher roughness To verify the analysis results, the wetting angle was measured in the solid-air-oil interface and solid-water-oil interface for the shark-skin template and shark-skin replica. The effects of teflon coating were also evaluated. It is shown that the simulation results cover the experimental ones.

• 한국정밀공학회지
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• 제31권2호
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• pp.171-178
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• 2014

In this study, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micropillars was studied. The previous researches showed that the Wenzel equation and the Cassie-Baxter equation were thermodynamically derived for the rough hydrophilic/hydrophobic surfaces and generally referenced on the field of wetting phenomena. For the verification of both equations, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micro-pillars was measured. In the comparison between the measured and estimated apparent contact angles with the equations, the differences between the apparent contact angles were analyzed. Conclusively, the available range and limitation of theoretical equations were investigated and further researches about the apparent contact angle on the rough surfaces were proposed.

• 대한정형도수물리치료학회지
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• 제12권2호
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• pp.1-10
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• 2006

The purpose are to assess the efficacy of a contact lateral-wedged insole with strapping on the femorotibial angle in patients with varus deformity osteoarthritis of the knee after treatment period. 25 outpatients with knee osteoarthritis (OA) were randomized to be treated with a contact lateral-wedge insole with strapping. Standing radiographs were used to analyze the femorotibial angle for each subject. The result of repeated two-way ANOVA's reveled that a contact lateral-wedged insole with strapping produced significantly differences in the femorotibial angle between groups after treatment period (P<0.05). and repeated one-way ANOVA's reveled that it produced significantly differences in the femorotibial angle between experimental groups after treatment period (P<0.05). We suggest that these results may be beneficial for manufacturing foot orthotic devices, such as wedged insoles, to control medial and later compartment forces in the knee varus-valgus deformity.

• 한국가시화정보학회지
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• 제22권1호
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• pp.61-67
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• 2024

In this study, the behavior of water droplets on a solid-infused surface was evaluated by quantifying a water droplet's contact angle, sliding angle, and terminal velocity. The contact angle hysteresis and sliding angle of water on the solid-infused surface were measured to be lower than those of the hydrophobic PTFE surface. It led to the enhancement of the initiation of the water droplet's movement. When the capillary number was lower than Ca < 0.004, the terminal velocity of the water droplet on the solid-infused surface was higher than the PTFE surface due to the low contact line resistance. However, the transition of the droplet morphology from a hemispherical shape to a streamlined teardrop shape beyond Ca > 0.004 lost the effect of reducing frictional resistance on the solid-infused surface.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.155-158
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• 2009

We developed a numerical method to analyze the contact-line problems, incorporating a dynamic contact angle model. We used level set method to capture free surface. The method is applied to the analysis of dynamic behavior of a droplet in DC electrowetting. The result is compared with an experimental data and result of perturbation method.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2003년도 The Korea-Japan Joint Symposium
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• pp.103-103
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• 2003

A newly developed contact angle measurement instrument by laser beam projection allows for rapid and direct determination of contact angles. From the result of comparative experiment and questionnaire, the laser contact angle.

• 한국토양비료학회지
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• 제36권5호
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• pp.263-271
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• 2003

$CO_2$ 가스 존재여부와 pH가 Pb(II)와 sodium dodecyl sulfonate(SDS, $C_{12}H_{25}SO_3Na$) 흡착에 따른 silca 표면의 특성 변화에 미치는 영향을 contact angle 과 AFM을 이용한 힘 측정을 통하여 살펴보았다. 대기와 접촉하여 $CO_2$가 용해되는 조건에서 Pb와 SDS가 $10^{-4}M$ 씩 들어 있는 혼합용액을 처리하였을 때, fused silica 표면의 contact angle은 $PbCO_3$의 침전 때문에 최대 $46^{\circ}$로 낮았다. 반면에 $N_2$ 개스를 불어넣는 $CO_2$ 부재조건에서는 $PbCO_3$의 침전이 없었기 때문에 contact angle이 최대 $90^{\circ}$로 크게 증가되었다. $CO_2$ 부재조건에서 pH에 따른 contact angle과 AFM에서 측정한 점착력($F_{ad}$) 변화 양상은 $PbOH^+$ 화학종 분포와 유사하였으므로, Pb(II)의 silica 표면 흡착형태는 $PbOH^+$ 로 판단되었다. 한편 contact angle 과 AFM 측정결과 모두 Pb 단독처리에서 소수성을 발현하였다. 이 결과는 현재까지의 알려진 이론으로 설명할 수 없었으며 이를 위하여 원자수준에서의 심도 깊은 연구가 필요하다고 판단되었다.

• 접착 및 계면
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• 제23권3호
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• pp.87-93
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• 2022

섬유와 기지 간 계면 특성을 분석하기 위해 일반적으로 접촉각을 활용하여 계산된 접착일을 활용한다. 접촉각 측정 방식으로 동적접촉각과 정적접촉각이 있으며, 본 논문에서는 보다 정확도가 높은 접촉각 측정 방법이 무엇인지 모색하였다. 각각 4가지 종류의 에폭시 수지와 유리섬유를 사용하였고, 유리섬유와 에폭시의 표면 에너지 결과를 기반으로 접착일, W_a을 계산하여 계면강도를 예측하였다. 접착일과 계면 전단강도는 이론상 비례관계이며, 이를 확인하기 위해 조성이 다른 에폭시와 유리섬유 간의 계면강도를 마이크로드롭렛 시험법을 이용하여 측정하였다. 정적접촉각 결과의 경우 접착일과 계면 전단강도 사이에는 일치하지 않는 경향을 보였다. 이는, 동적 접촉각 평가 방법은 정적접촉각에 비해, 드롭 크기에 따른 최소 표면적을 이루는 에러와 미니스커서에서 접선 측정에 따른 에러를 최소화할 수 있다는 점이다.

• 한국생산제조학회지
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• 제22권1호
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• pp.15-21
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• 2013

In this paper, a high-speed imaging and an image processing technique have been applied to detect the position of a meniscus as a function of time in the micro capillary flows. Two fluids with low and high viscosities, ethylene glycol and glycerin, were dropped into the entrance well of a circular capillary tube. The filling times of the meniscus in both cases of ethylene glycol and glycerin were compared with the theoretical models - Washburn model and its modified model based on Newman's dynamic contact angle equation. To evaluate the model coefficients of Newman's dynamic contact angle, time-varying contact angles under the capillary flows were measured using an image processing technique. By considering the dynamic contact angle, the estimated filling time from the modified Washburn model agrees well with the experimental data. Especially, for the lower-viscosity fluid, the consideration of dynamic contact angle is more significant than for the higher-viscosity fluid.