English  |  正體中文  |  简体中文  |  Items with full text/Total items : 69561/69561 (100%)
Visitors : 23151299      Online Users : 755
RC Version 7.0 © Powered By DSPACE, MIT. Enhanced by NTU Library IR team.
Scope Tips:
  • please add "double quotation mark" for query phrases to get precise results
  • please goto advance search for comprehansive author search
  • Adv. Search
    HomeLoginUploadHelpAboutAdminister Goto mobile version

    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/72468

    Title: 液滴及塞流熱毛細遷移之數值模擬;Numerical Simulation of Thermocapillary Migration of Silicone Droplet and Plug
    Authors: 李昇隆;Long,Le Thanh
    Contributors: 機械工程學系
    Keywords: 溫度梯度;液滴驅動;表面張力;熱毛細流;微流道;Temperature gradient;Droplet actuation;Surface tension;Thermocapillary flow;Microchannel
    Date: 2016-08-26
    Issue Date: 2016-10-13 14:58:13 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 在微流體的應用開發中,了解溫度梯度來控制與操縱液滴之運動行為是很重要的。在本研究中,採用數值計算方式來探討微流道與毛細管中的熱毛細遷移現象。透過COMSOL Multiphysics軟件開發的有限元素方法,以two-phase level set技術來求解Navier-Stokes 與能量方程式,並以conservative level set的方法,配合arbitrary Lagrangian Eulerian(ALE)運動描述法和連續的表面力學法(CSF)來追蹤液體/氣體界面,並確保該自由界面附近良好的分辨率。在液氣界面上考慮兩種力量的作用,如界面曲率法線方向上的毛細力以及作用在自由表面切線方向上的熱毛細力。
    ;An understanding of the transport behavior of a liquid droplet controlled and manipulated by the thermal gradient is very important for the development of microfluidic applications. In this study, a numerical computation is utilized to investigate the thermocapillary actuation behavior of a liquid with two different physical problems: microchannel and capillary tube. The finite element method with the two-phase level set technique, developed by Comsol Multiphysics, is used to solve the incompressible Navier-Stokes equations coupled with the energy equation. The conservative level set method, the arbitrary Lagrangian Eulerian (ALE), and the continuum surface force (CSF) method are used to track the liquid/gas interface and ensure good resolution near the free interface. Two forces are considered at the liquid/gas interface such as the capillary force acting in the normal direction, and the thermocapillary force acting in the tangential direction to the free surface.
    For modeling of a liquid droplet in microchannel, the lower wall of the microchannel is subjected to a uniform temperature gradient, while the upper one is adiabatic, isothermal or heated wall. When the upper wall is set to be adiabatic, a pair of asymmetric thermocapillary convection vortices initially occurs inside the droplet but these turn into a sole thermocapillary vortex once enough time has passed. For the isothermal case, a pair of asymmetric thermocapillary convection vortices always appears inside the droplet. For the case of the upper wall temperature higher than the bottom one, the net thermocapillary momentum generated by two pairs of thermocapillary vortices assists the droplet migration during the initial stage. When time reaches a certain value, it turns to go against the droplet migration. The droplet initially accelerates for all cases. The droplet velocity then decreases dramatically for the adiabatic case while it decreases slowly for the isothermal one. For the heated upper wall case, the droplet velocity decelerates to zero velocity after it gets the maximal value. The actuation velocity of the droplet is affected by temperature gradients, contact angles and microchannel heights for adiabatic, isothermal or heated wall cases.
    For a silicone plug migration inside a capillary tube, flow motion is affected by the thermocapillary effect generated by the temperature gradient along the gas-liquid interface near the receding side and the capillary force caused by the temperature difference between the ends of the liquid plug. When time is long enough, the flow mainly moves horizontally from the hot side to the cold side near the tube wall and then returns to the hot side near the center of the tube due to the capillary force effect. There is a smaller clockwise circulation near the receding contact angle caused by the thermocapillary convection. The flow motion causes significant distortion of the isotherms inside the silicone plug. The temperature gradient along the tube is enhanced by the flow motion inside the capillary tube. The liquid plug accelerates rapidly in the initial stage and then decelerates after it reaches the maximum speed. During the migration process, the receding contact angle is always greater than the advancing one. An increase in the input heat flux leads to a higher migration velocity due to the higher temperature gradient along the tube wall. When the initial contact angle is smaller, the migration velocity moves faster due to the higher capillary force. A liquid plug with a lower viscosity moves faster owing to the lower viscous force. The numerical simulation results are in good agreement with the results from previous experiments.
    Appears in Collections:[機械工程研究所] 博碩士論文

    Files in This Item:

    File Description SizeFormat

    All items in NCUIR are protected by copyright, with all rights reserved.

    社群 sharing

    ::: Copyright National Central University. | 國立中央大學圖書館版權所有 | 收藏本站 | 設為首頁 | 最佳瀏覽畫面: 1024*768 | 建站日期:8-24-2009 :::
    DSpace Software Copyright © 2002-2004  MIT &  Hewlett-Packard  /   Enhanced by   NTU Library IR team Copyright ©   - Feedback  - 隱私權政策聲明