Three-dimensional Marangoni convection in electrostatically positioned droplets under microgravity
Three-dimensional Marangoni convection in electrostatically positioned droplets under microgravity
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DOI：
10.1016/j.ijheatmasstransfer.2004.01.021
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发表时间：
2004-07-01
影响因子：
5.2
通讯作者：
Li, BQ
中科院分区：
文献类型：
--
作者：
Huo, Y;Li, BQ
静电悬浮液滴中稳态和瞬态三维Marangoni对流和传热的数值研究。分析是基于Navier-Stokes方程和能量方程的Galerkin有限元解。本文在有限元和微分几何的框架内讨论了一般曲线坐标系中表面驱动流的数值计算问题。结果表明，在变形较小的实际微重力条件下，单光束和双光束加热装置在两极或赤道平面上产生近似轴对称的流动剖面和温度分布，其对称轴由通过激光束和液滴中心的线定义。因此，轴对称模型可以提供相当好的描述，并且当激光束被放置在一个极点或一个光束被放置在两个极点时是精确的。当应用四面体或八面体加热布置时，出现复杂的3-D流动结构，这是由与每个激光束相关联的流动运动的相互作用引起的。对于研究的情况下，四面体加热的安排似乎并没有产生显着减少内部速度，在感知相反，但温度更均匀。这一现象可以用2-和4-梁布置导致近似相同大小的表面温度梯度的事实来解释。然而，六束加热放置产生更显著的速度和温度不均匀性降低。冷却过程中的瞬态衰减的特点是温度场和速度场的演变以一种相当复杂的方式演变，初始阶段主要是由显着的热和流动混合的液滴的表面层。强烈的表面混合很快带来了轴对称的表面温度分布，而三维结构仍然占主导地位，直到很久以后。在衰减期间，在已经由4束或6束激光加热的液滴中也观察到流动反转，并且在流动反转发生时，速度和温度存在尖峰。(C)2004爱思唯尔有限公司保留所有权利。
A numerical study of steady-state and transient 3-D Marangoni convection and heat transfer in electrostatically levitated droplets. The analysis is based on the Galerkin finite element solution of the Navier-Stokes and energy equations. Numerical aspects for the computation of surface driven flows in general curvilinear coordinate system are discussed within the framework of finite elements and differential geometry. Results show that for practical micro-gravity conditions under which the deformation is small, the single and double beam heating arrangements, when placed at the poles or equator plane, produce an approximately axisymmetric flow profile and temperature distribution with the axis of symmetry defined by the line passing through the centers of the laser beam and the droplet. Thus, an axisymmetric model could provide a reasonably good description, and an exact one when the laser beam is placed at a pole or one beam is placed at both poles. When a tetrahedral or octahedral heating arrangement is applied, complex 3-D flow structures occur, which result from interaction of flow motions asociated with each laser beam. For the case studied, the tetrahedral heating arrangement does not seem to produce a significant reduction in internal velocity, in contrast to perception, but the temperature is more uniform. This phenomenon is explained by the fact that the 2- and 4-beam arrangements result in a surface temperature gradient of approximately the same magnitude. The six-beam heating placement produces, however, a much more significant reduction in both velocity and temperature non-uniformity. The transient decaying during cooling is characterized by the evolution of both temperature and velocity fields evolve in a rather complex fashion, with the initial stage dominated by the pronounced thermal and flow mixing on the surface layer of a droplet. The strong surface mixing quickly brings out a surface temperature distribution of axi-symmetry, while a 3-D structure still prevails inside until much later. The flow reversal is also observed in the droplets that have been heated by 4- or 6-beam lasers during the decay, and there is a spike in velocity and temperature at the time when the flow reversal occurs. (C) 2004 Elsevier Ltd. All rights reserved.