• Title/Summary/Keyword: Dynamics Contact Angle

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Numerical Study of Droplet Motion in a Microchannel with defferent contact angles (접촉각에 따른 마이크로채널 내에서의 액적 거동에 대한 수치적 연구)

  • Choi, Ji-Young;Son, Gi-Hun
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.656-657
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    • 2008
  • The droplet dynamics in a hydrophilic/hydrophobic microchannel, which is applicable to a typical proton exchange membrane fuel cell (PEMFC), is studied numerically by solving the equations governing conservation of mass and momentum. The liquid-gas interface or droplet shape is determined by a level set method which is modified to treat contact angles. The matching conditions at the interface are accurately imposed by incorporating the ghost fluid approach based on a sharp-interface representation. The effects of contact angle, inlet flow velocity, droplet size and side wall on the droplet motion are investigated parametrically. Based on the numerical results, the droplet dynamics including the sliding and detachment of droplets is found to depend significantly on the contact angle. Also, a droplet removal process is demonstrated on the combination of hydrophilic and hydrophobic surfaces.

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A Molecular Dynamics Simulation for the Moving Water Droplet on Atomistically Smooth Solid Surface (원자적으로 균일한 평판 위에서 움직이는 물 액적에 대한 분자동역학 시뮬레이션)

  • Hong, Seung-Do;Ha, Man-Yeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.8
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    • pp.559-564
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    • 2009
  • The variation in the shape of water droplet moving on atomistically smooth solid surface in the presence of a constant body force is simulated using molecular dynamics simulation. We investigated how the advancing and receding contact angle of the moving water droplet changes on a solid surface having various characteristic energies. From the MD simulation results, we obtained the density profile defined as the number of water molecules at a given position. Then, assuming the water droplet periphery to be a circle, we calculated the contact angles by using a nonlinear fitting of the half-density contour line. The present simulation clearly shows the different profile of the advancing and receding contact angle for these three different interaction potential between the water droplet and the solid surface.

ANALYSIS OF ELECTROWETTING DYNAMICS WITH CONSERVATIVE LEVEL SET METHOD (레벨셋 기법을 이용한 전기습윤 현상의 동적 거동에 대한 해석)

  • Park, J.K.;Hong, J.W.;Kang, K.H.
    • 한국전산유체공학회:학술대회논문집
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    • 2009.11a
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    • pp.84-87
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    • 2009
  • Electrowetting is a versatile tool to handle tiny droplets and forms a backbone of digital microfluidics. Numerical analysis is necessary to fully understand the dynamics of electrowetting, especially in designing electrowetting-based devices, such as liquid lenses and reflective displays. We developed a numerical method to analyze the general contact-line problems, incorporating dynamic contact angle models. The method is based on the conservative level set method to capture the interface of two fluids without loss of mass. We applied the method to the analysis of spreading process of a sessile droplet for step input voltages and oscillation of the droplet for alternating input voltages in electrowetting. The result was compared with experimental data. It is shown that contact line friction significantly affects the contact line motion and the oscillation amplitude. The pinning process of contact line was well represented by including the hysteresis effect in the contact angle models.

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A molecular dynamics simulation for the moving water droplet on a solid surface (평판 위에서 움직이는 물방울에 대한 분자동역학 시뮬레이션)

  • Hong, Seung-Do;Ha, Man-Yeong
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.1891-1895
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    • 2008
  • Water covers 70% of the earth's surface and the human body consist of 75% of it. It is clear that water is one of the prime elements responsible for life on earth. Over the last 30 years or so, numerous studies have attempted to find out more about the water microscopically. In this paper, we investigated how the receding and advancing contact angle of the moving water droplet changes on a solid surface having various LJ epsilon parameters. To observe the dynamic contact angle history, a body force applied to all water molecules after obtained the water droplet in equilibrium with the solid surface. We obtained the density profile and receding and advancing contact angle of the moving water droplet

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A Study for the Water Droplet on a Stripe-patterned Surface (주기적 줄무늬 구조물 위의 물 액적에 관한 연구)

  • Choi, Ho-Jin;Hong, Seung-Do;Ha, Man-Yeong;Yoon, Hyun-Sik
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.22 no.2
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    • pp.64-69
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    • 2010
  • We investigated the variation in contact angle of a nano-sized water droplet on a nano stripe-patterned surface using molecular dynamics simulation. By changing the height and width of the stripe pillar, and the gap width of the stripes, we observed the contact angle of water droplet in equilibrium. When the surface energies were 0.1 and 0.3 kcal/mol, the calculated contact angles were in good agreement with the Cassie and Baxter equation. However, when the surface energy is 0.5 kcal/mol, the contact angles are observed to be perturbed along the Cassie and Baxter equation.

Surface wettability and contact angle analysis by dissipative particle dynamics

  • Lin, Tzung-Han;Shih, Wen-Pin;Chen, Chuin-Shan
    • Interaction and multiscale mechanics
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    • v.5 no.4
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    • pp.399-405
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    • 2012
  • A dissipative particle dynamics (DPD) simulation was presented to analyze surface wettability and contact angles of a droplet on a solid platform. The many-body DPD, capable of modeling vapor-liquid coexistence, was used to resolve the vapor-liquid interface of a droplet. We found a constant density inside a droplet with a transition along the droplet boundary where the density decreased rapidly. The contact angle of a droplet was extracted from the isosurfaces of the density generated by the marching cube and a spline interpolation of 2D cutting planes of the isosurfaces. A wide range of contact angles from $55^{\circ}$ to $165^{\circ}$ predicted by the normalized parameter ($|A_{SL}|/B_{SL}$) were reported. Droplet with the parameters $|A_{SL}|>5.84B{_{SL}}^{0.297}$ was found to be hydrophilic. If $|A_{SL}|$ was much smaller than $5.84B{_{SL}}^{0.297}$, the droplet was found to be superhydrophobic.

Simulation of Capillary Flow Along a Slot-die Head for Stripe Coatings (Stripe 코팅용 슬롯 다이 헤드 모세관 유동 전산모사)

  • Yoo, Su-Ho;Lee, Jin-Young;Park, Jong-Woon
    • Journal of the Semiconductor & Display Technology
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    • v.18 no.1
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    • pp.92-96
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    • 2019
  • In the presence of ${\mu}-tip$ embedded in a slot-die head for stripe coatings, there arises the capillary flow that limits an increase of the stripe density, which is required for the potential applications in organic light-emitting diode displays. With an attempt to suppress it, we have employed a computational fluid dynamics software and performed simulations by varying the ${\mu}-tip$ length and the contact angles of the head lip and ${\mu}-tip$. We have first demonstrated that such a capillary flow phenomenon (a spread of solution along the head lip) observed experimentally can be reproduced by the computational fluid dynamics software. Through simulations, we have found that stronger capillary flow is observed in the hydrophilic head lip with a smaller contact angle and it is suppressed effectively as the contact angle increases. When the contact angle of the head lip increases from $16^{\circ}$ to $130^{\circ}$, the distance a solution can reach decreases sharply from $256{\mu}m$ to $44{\mu}m$. With increasing contact angle of the ${\mu}-tip$, however, the solution flow along the ${\mu}-tip$ is disturbed and thus the capillary flow phenomenon becomes more severe. If the ${\mu}-tip$ is long, the capillary flow also appears strong due to an increase of flow resistance (electronic-hydraulic analogy). It can be suppressed by reducing the ${\mu}-tip$ length, but not as effectively as reducing the contact angle of the head lip.

Analysis of Contact Stiffness and Bending Stiffness according to Contact Angle of Curvic Coupling (곡률 커플링 접촉각에 따른 접촉 강성 및 굽힘 강성해석)

  • Yu, Yonghun;Cho, Yongjoo;Lee, Donghyun;Kim, Young-Cheol
    • Tribology and Lubricants
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    • v.34 no.1
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    • pp.23-32
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    • 2018
  • Coupling is a mechanical component that transmits rotational force by connecting two shafts. Curvic coupling is widely used in high-performance systems because of its excellent power transmission efficiency and easy machining. However, coupling applications change dynamic behavior by reducing the stiffness of an entire system. Contact surface stiffness is an important parameter that determines the dynamic behavior of a system. In addition, the roughness profile of a contact surface is the most important parameter for obtaining contact stiffness. In this study, we theoretically establish the process of contact and bending stiffness analysis by considering the rough surface contact at Curvic coupling. Surface roughness parameters are obtained from Nayak's random process, and the normal contact stiffness of a contact surface is calculated using the Greenwood and Williamson model in the elastic region and the Jackson and Green model in the elastic-plastic region. The shape of the Curvic coupling contact surface is obtained by modeling a machined shape through an actual machining tool. Based on this modeling, we find the maximum number of gear teeth that can be machined according to the contact angle. Curvic coupling stiffness is calculated by considering the contact angle, and the calculation process is divided into stick and slip conditions. Based on this process, we investigate the stiffness characteristics according to the contact angle.

A Study of a Hydrophobic Surface: Comparing Pure Water and Contaminated Water

  • Ambrosia, Matthew Stanley;Lee, Chang-Han
    • Journal of Environmental Science International
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    • v.22 no.4
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    • pp.407-413
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    • 2013
  • The flow of sewage has been studied for hundreds of years. Reducing drag in pipes can allow sewer to be removed easily and quickly. Drag reduction is not only a macroscale issue. Physical and chemical properties of the nano-scale can affect flow at the macroscopic scale. In this paper the predictability of hydrophobicity at the nano-scale is studied. Molecular dynamics simulations were used to calculate the range of contact angles of water droplets in equilibrium on a pillared graphite surface. It was found that at a pillar height of two graphite layers there was the largest range of contact angles. It is observed that at this height the droplet begins to transition from the Wenzel state to the Cassie-Baxter state. Surfaces with larger pillar heights have much larger contact angles corresponding to a more hydrophobic surface. Silicon dioxide was also simulated in the water droplet. The contaminant slight decreased the contact angle of the water droplet.

NUMERICAL STUDY OF MULTIPLE DROPLET DYNAMICS IN A PEMFC AIR FLOW CHANNEL (고분자전해질막 연료전지의 공기유로 내에서의 다중 액적 거동에 대한 수치적 연구)

  • Choi, J.Y.;Son, G.
    • 한국전산유체공학회:학술대회논문집
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    • 2009.04a
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    • pp.159-164
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    • 2009
  • The water droplet motion and the interaction between the droplets in a PEMFC air flow channel with multiple pores, through which water emerges, is studied numerically by solving the equations governing the conservation of mass and momentum. The liquid-gas interface is tracked by a level set method which is based on a sharp-interface representation for accurately imposing the matching conditions at the interface. The method is modified to implement the contact angle conditions on the walls and pores. The dynamic interaction between the droplets growing on multiple pores while keeping the total water flow rate through pores constant is investigated by conducting the computations until the droplet motion exhibits a periodic pattern. The numerical results show that the droplet merging caused by increasing the number of pores is not effective for water removal and that the contact angle of channel wall strongly affects water management in the PEMFC air flow channel.

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