• Title/Summary/Keyword: 마랑고니 유동

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Study of the Internal Flow and Evaporation Characteristic Inside a Water Droplet on a Vertical Vibrating Hydrophobic Surface (수직 진동을 이용한 가열된 고체표면 위 증발하는 액적의 내부유동 제어연구)

  • Park, Chang-Seok;Lim, Hee-Chang
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.41 no.1
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    • pp.37-46
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    • 2017
  • Thermal Marangoni flow has been observed inside droplets on heated surfaces, finally resulting in a coffee stain effect. This study aims to visualize and control the thermal Marangoni flow by employing periodic vertical vibration. The variations in the contact angle and internal volume of the droplet as it evaporates is observed by using a combination of continuous light and a still camera. With regard to the internal velocity, the particle image velocimetry system is applied to visualize the internal thermal Marangoni flow. In order to estimate the internal temperature gradient and surface tension on the surface of a droplet, the theoretical model based on the conduction and convection theory of heat transfer is applied. Thus, the internal velocity increases with an increase in plate temperature. The flow directions of the Marangoni and gravitational flows are opposite, and hence, it may be possible to control the coffee stain effect.

Surfactant-Induced Suppression of the Thermocapillary Flow in Evaporating Water Droplets (증발하는 물방울의 계면활성제에 의한 열모세관 유동 억제)

  • Yun, Sungchan;Kim, Tae Kwon;Lim, Hee Chang;Kang, Kwan Hyoung;Lim, Geunbae
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.7
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    • pp.695-701
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    • 2013
  • The suppression of a thermocapillary flow (Marangoni flow) by a nonionic surfactant is experimentally investigated for evaporating pure water droplets on hydrophobic substrates. The experiment shows that as the initial concentration of the surfactant increases, the velocity and lifetime of the flow monotonically decrease. The result confirms the no-slip boundary condition at a liquid-air interface, which is explained on the basis of the previous model regarding the effect of surfactants on the no-slip condition. Interestingly, at an initial concentration much less than a critical value, it is found that depinning of the contact line occurs during the early stage of evaporation, which is ascribed to a reduction in the contact angle hysteresis owing to the presence of the Marangoni flow.

Reverse tracking method for concentration distribution of solutes around 2D droplet of solutal Marangoni flow with artificial neural network (인공신경망을 통한 2D 용질성 마랑고니 유동 액적의 용질 농도 분포 역추적 기법)

  • Kim, Junkyu;Ryu, Junil;Kim, Hyoungsoo
    • Journal of the Korean Society of Visualization
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    • v.19 no.2
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    • pp.32-40
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    • 2021
  • Vapor-driven solutal Marangoni flow is governed by the concentration distribution of solutes on a liquid-gas interface. Typically, the flow structure is investigated by particle image velocimetry (PIV). However, to develop a theoretical model or to explain the working mechanism, the concentration distribution of solutes at the interface should be known. However, it is difficult to achieve the concentration profile theoretically and experimentally. In this paper, to find the concentration distribution of solutes around 2D droplet, the reverse tracking method with an artificial neural network based on PIV data was performed. Using the method, the concentration distribution of solutes around a 2D droplet was estimated for actual flow data from PIV experiment.

A Droplet-Manipulation Method using Opto-thermal Flows on Amorphous Silicon Thin Film (비결정질 실리콘 박막 상에서의 광열 유동을 이용한 액적 조작)

  • Lee, Horim;Yoon, Jin Sung;Kim, Dong Sung;Lim, Geunbae
    • Journal of the Korean Society for Precision Engineering
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    • v.31 no.1
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    • pp.91-96
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    • 2014
  • We present a droplet-manipulation method using opto-thermal flows in oils. The flows are originated from Marangoni and buoyancy effects due to temperature gradient, generated by the adsorption of light on an amorphous silicon thin film. Using this method, we can transport, merge and mix droplets in an extremely simple system. Since the temperature rise during the operation is small, this method can be used for biological applications without the damage on cell viability.

Internal flow visualization of an evaporating droplet placed on heated metal plate (가열된 금속표면에 놓인 증발하는 액적의 내부유동 가시화)

  • Park, Chang-Seok;Lim, Hee-Chang
    • Journal of the Korean Society of Visualization
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    • v.15 no.1
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    • pp.25-31
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    • 2017
  • This study aims to visualize the Marangoni flow inside a droplet placed on heated hydrophobic surface and to measure its internal velocity field. The experimental result shows that the internal velocity increases with the increase of the plate temperature. In addition, the temperature difference induces the initial flow and drives the Marangoni circulation inside the droplet as soon as the evaporation starts (i.e. the thermal Marangoni flow). The fluorescence particles in the droplet trace two large-scale counter-rotating vortex pairs yielding the downwards flow along the vertical central axis. These vortex pairs gradually become small and move towards the contact line as time goes by, and this Marangoni flow sustains only for a half of the total evaporation time.

Effect of axial rotation on oscillatory thermocapillary flow in half-zone of high Prandtl number fluid (높은 Prandtl 수 유체에서 축회전이 열모세관 유동의 진동에 미치는 영향)

  • Jeon, Seung-Won;Lee, Kyu-Jung
    • Proceedings of the KSME Conference
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    • 2008.11b
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    • pp.2248-2253
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    • 2008
  • A numerical study on oscillatory thermocapillary flow in half-zone has performed to understand the effect of axial rotation. 2d unsteady code is developed to observe the onset of oscillation. 2cs Silicone oil with Prandtl number of 26.5 is used as a working fluid. The critical temperature difference at onset of oscillation is investigated under the different aspect ratios and rotation modes. It is shown that the onset of oscillation is delayed when aspect ratio reduces and rotating speed increases. The oscillatory flow is strongly reduced under top rotation and co-rotation modes, while it is augmented under bottom rotation and counter-rotation modes. It is thought that interaction between return flow and bottom wall is important to explain the oscillatory flow.

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Experimental Study on Rayleigh-Benard-Marangoni Natural Convection using IR Camera (열화상카메라를 이용한 Rayleigh-Benard-Marangoni 자연대류 실험 연구)

  • Kim, Jeongbae
    • Journal of ILASS-Korea
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    • v.26 no.2
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    • pp.67-72
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    • 2021
  • Rayleigh-Benard-Marangoni (RBM) convection have been artificially made for application of various engineering fields. For a relatively larger circular container, natural convection experiments were carried out to reveal and show the flow characteristics with engine oil (SAE30) using IR camera. IR camera has captured the temperature distribution on the free surface. From these experiments, it was confirmed that it was possible to quantitatively analyze the occurrence characteristics of RBM flow clearly from the thermal images taken with IR camera. As the aspect ratio increased, both the number of internal and external cavities increased. And found that the criteria of RBM flow generation proposed through previous experiments performed for small-sized containers are also very effective with the results on larger circular container.

The Effect of Microdroplet Shape on the Evaporation (미세액적의 형상이 증발에 미치는 효과)

  • Song, Hyun-Soo;Lee, Yong-Ku;Jin, Song-Wan;Yoo, Jung-Yul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.6 s.261
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    • pp.558-565
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    • 2007
  • Many studies of microdroplet evaporation from solid surfaces were made with priority given to inkjet printing and dye painting techniques. The objective of these studies is how to evaporate a droplet quickly and uniformly. Also it is necessary to prevent evaporation of a droplet to observe cells in a droplet generated through cell-patterning. In general, an identical volume of a water droplet on hydrophobic surfaces evaporates slower than that on hydrophilic surfaces. In this study, we observe the evaporation process of a droplet on various hydrophobic surfaces and calculated the evaporation rate considering the droplet geometry such as contact angle and height. This study also proposes a new model based on the fact that evaporation mode at the edge of a droplet is different from that at the outer surface of a droplet as the contact angle changes during evaporation. Finally, we reveal the cause fur the increase of evaporation flux and show that the ratio of edge evaporation to total evaporation increases with time.