• Title/Summary/Keyword: Receding Contact Angle

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DIRECT NUMERICAL SIMULATION OF IMMISCIBLE GAS BUBBLE DISPLACEMENT IN 2D CHANNEL (2차원 관내 유동에서 불활성 기체 제거과정의 직접 수치 해석)

  • Shin, S.
    • Journal of computational fluids engineering
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    • v.12 no.3
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    • pp.41-46
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    • 2007
  • Dynamic behavior of immiscible gas bubble attached to the wall in channel flow plays very important role in many engineering applications. Special attention has been paid to micro direct methanol fuel cell(${\mu}$DMFC) where surface tension becomes dominant factor with minor gravitational effect due to its reduced size. Therefore, displacement of $CO_2$ bubble generating on a cathode side in ${\mu}$DMFC can be very difficult and efficient removal of $CO_2$ bubbles will affect the overall machine performance considerably. We have focused our efforts on studying the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We used Level Contour Reconstruction Method(LCRM) which is the simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

Fabrication of Super Water Repellent Surfaces by Vacuum Plasma (진공 플라즈마 처리를 통한 초소수성 표면 제작 및 특성 평가)

  • Rha, Jong-Joo;Jeong, Yong-Soo;Kim, Wan-Doo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.32 no.2
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    • pp.143-147
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    • 2008
  • Super-hydrophobic surfaces showed that contact angle of water was higher than 140 degrees. That surface could be made several methods such as Carbon nano tubes grown vertically, PDMS asperities arrays, hydrophobic fractal surfaces, and self assembled monolayers coated by CVD and so on. However, we fabricated super-hydrophobic surfaces with plasma treatments which were very cost efficient processes. Their surfaces were characterized by static contact angles, advancing, receding, and stability against UV irradiation. Optimal surfaces showed static contact angles were higher than 150 degrees. Super-hydrophobic property was remained after UV irradiation for one week.

Surface modification of polypropylene membrane to improve antifouling characteristics in a submerged membrane-bioreactor: Ar plasma treatment

  • Zhou, Jin;Li, Wei;Gu, Jia-Shan;Yu, Hai-Yin
    • Membrane and Water Treatment
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    • v.1 no.1
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    • pp.83-92
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    • 2010
  • To improve the antifouling characteristics of polypropylene hollow fiber microporous membranes in a submerged membrane-bioreactor for wastewater treatment, the surface-modification was conducted by Ar plasma treatment. Surface hydrophilicity was assessed by water contact angle measurements. The advancing and receding water contact angles reduced after the surface modification, and hysteresis between the advancing and receding water contact angles was enlarged after Ar plasma treatment due to the increased surface roughness after surface plasma treatment. After continuous operation in a submerged membrane-bioreactor for about 55 h, the flux recovery after water cleaning and the flux ratio after fouling were improved by 20.0 and 143.0%, while the reduction of flux was reduced by 28.6% for the surface modified membrane after 1 min Ar plasma treatment, compared to those of the unmodified membrane. Morphological observations showed that the mean membrane pore size after Ar plasma treatment reduced as a result of the deposition of the etched species; after it was used in the submerged membrane-bioreactor, the further decline of the mean membrane pore size was caused by the deposition of foulants. X-ray photoelectron spectroscopy and infrared spectroscopy confirmed that proteins and polysaccharide-like substances were the main foulants in the precipitate.

Experimental Study of Heating Surface Angle Effects on Single Bubble Growth

  • Kim, Jeong-Bae;Kim, Hyung-Dae;Lee, Jang-Ho;Kwon, Young-Chul;Kim, Jeong-Hoon;Kim, Moo-Hwan
    • Journal of Mechanical Science and Technology
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    • v.20 no.11
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    • pp.1980-1992
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    • 2006
  • Nucleate pool boiling experiments were performed using pure R11 for various surface angles under constant heat flux conditions during saturated pool boiling. A 1-mm-diameter circular heater with an artificial cavity in the center that was fabricated using a MEMS technique and a high-speed controller were used to maintain the constant heat flux. Bubble growth images were taken at 5000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of the surface angle on the bubble growth behavior were analyzed for the initial and thermal growth regions using dimensional scales. The parameters that affected the bubble growth behavior were the bubble radius, bubble growth rate, sliding velocity, bubble shape, and advancing and receding contact angles. These phenomena require further analysis for various surface angles and the obtained constant heat flux data provide a good foundation for such future work.

A study of drop spreading between moving solid plates (움직이는 고체판 사이에서 액적의 퍼짐에 관한 연구)

  • Kwon, Hyuk-Min;Kim, Ho-Young
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2967-2970
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    • 2007
  • In a usual painting process, a liquid drop spreads on canvas by being dragged along a paintbrush. To obtain the fundamental understanding of the painting process from the mechanical point of view, we experimentally investigate various dynamic behavior of a liquid drop that spreads between moving solid plates. It is shown that three distinct types of drop spreading take place, i.e. shearing, spreading, and intact dragging, depending on the liquid viscosity and surface tension, the plate speed, and the wettability. We suggest a regime map based on the capillary number and the receding contact angle, which indicates the boundaries between different types of spreading behavior in a dimensionless space.

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Direct Numerical Analysis of $CO_2$ degassing process in ${\mu}DMFC$ (마이크로 DMFC 에서 $CO_2$ degassing 과정의 직접 수치 해석)

  • Shin, Seung-Won;Shim, Jung-Ik;Wi, Wan-Seok;Jo, Sung-Won
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2648-2653
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    • 2007
  • Recently, increasing demand on not only lighter but also extremely mobile battery make micro fuel cell device very attractive alternative. By reducing the size of fuel cell, surface tension becomes dominant factor with minor gravitational effect. Therefore, it is very difficult to detach the $CO_2$ bubble generating on a cathode side in ${\mu}DMFC$ (micro direct methanol fuel cell). The degassing of a $CO_2$ bubble has drawn quite attention especially for ${\mu}DMFC$ due to its considerable effect on overall machine performance. Our attention has been paid to the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We use Level Contour Reconstruction Method (LCRM) which is simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

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Heat Transfer Characteristics under Saturated Nucleate Pool Boiling for Various Heating Surface Angles using Heater with Artificial Cavity (인공 캐비티를 가진 히터를 이용한 가열면 경사각에 따른 포화상태 풀 핵비등 열전달 기초연구)

  • Kim, Jeong-Bae
    • Journal of the Korean Solar Energy Society
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    • v.29 no.4
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    • pp.7-14
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    • 2009
  • Nucleate pool boiling experiments with constant heat flux condition were performed using pure R11 and R113 for various surface angles under saturated pool condition. A circular heater of 1 mm diameter, with artificial cavity in the center, fabricated using MEMS technique and the high-speed controller were used to maintain the constant heat flux. Images of bubble growth were taken at 5,000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of surface angles on the bubble growth behaviors were analyzed as dimensional scales for the initial and thermal growth regions. The parameters for the bubble growth behaviors were bubble radius, bubble growth rate, sliding velocity, bubble shape and advancing and receding contact angles. These phenomena require further analysis for various surface angles, but this study will provide good experimental data with constant heat flux boundary condition for such works.

Hydrophobic Characteristics of a Silicone Resin Surface Produced by Replicating an Electric Discharge Machined Surface (방전가공면을 복제한 실리콘수지 표면의 발수특성연구)

  • Kim, Y.H.;Hong, S.K.;Lee, S.Y.;Lee, S.H.;Kim, K.H.;Kang, J.J.
    • Transactions of Materials Processing
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    • v.22 no.1
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    • pp.23-29
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    • 2013
  • In this study, a micro/nano-random-pattern-structure surface was machined by electric discharge machining (EDM) followed by replicating the EDM surface with a silicone elastomer having low energy and greater hydrophobicity. The variation of hydrophobicity was of prime interest and was examined as a function of the surface roughness of the replicated silicone elastomer. The hydrophobicity was evaluated by the water contact angle (WCA) measured on the relevant surface. For the experiments, the original surfaces were machined by die sinking electric discharge machining (DS-EDM) and wire cutting electric discharge machining (WC-EDM). The ranges of surface roughness were Ra $0.8{\sim}19{\mu}m$ for the DS-EDM and Ra $0.5{\sim}4.7{\mu}m$ for the WC-EDM. In order to fabricate a hydrophobic surface, the EDM surfaces were directly replicated using a liquid-state silicone elastomer, which was thermally cured. The measured WCA on the replicated surfaces for DS-EDM was in the range of $115{\sim}130^{\circ}$ and for WC-EDM the WCA was in the range of $123{\sim}150^{\circ}$. Additionally, the dynamic hydrophobicity was evaluated by measuring an advancing and a receding WCA on the replicated silicone elastomer surfaces.