Unsteady motion of a long bubble or droplet in a self-rewetting system
Unsteady motion of a long bubble or droplet in a self-rewetting system
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DOI：
10.1103/physrevfluids.3.123603
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发表时间：
2018-12
影响因子：
2.7
通讯作者：
B. Duffy;Stephen K. Wilson;J. Conn;K. Sefiane
中科院分区：
文献类型：
--
作者：
B. Duffy;Stephen K. Wilson;J. Conn;K. Sefiane
受自再润湿流体的潜在用途的启发（即表现出表面张力随温度的非单调变化的流体）在各种传热应用中，在目前的工作中，我们制定和分析的非稳态运动的自再润湿系统中的长气泡或液滴的理论模型，由于表面张力随温度变化引起的马兰戈尼效应，由于两种流体之间的密度差引起的重力效应，以及沿管沿着施加的背景流。我们发现，气泡或液滴的形状（而不是位置）的演变完全由Marangoni效应驱动，并取决于其半径的初始值与临界值的关系。在不存在马兰哥尼效应的情况下，气泡或液滴总是以恒定速度运动而不改变形状。在仅存在马兰戈尼效应的情况下，气泡或液滴总是远离或总是朝向最小表面张力的位置移动;在后一种情况下，其最终在最终静止位置处填充管的整个横截面，该最终静止位置比其原始位置更接近最小表面张力的位置。在仅存在Marangoni效应和重力效应或仅存在Marangoni效应和背景流效应的情况下，这两种效应之间的竞争可导致气泡或液滴的质心位置的非单调演变。在本工作中描述的自再润湿系统的行为是定性地不同于普通流体，在这种情况下，气泡或液滴总是以恒定的速度移动，而不改变形状。
Motivated by the potential use of self-rewetting fluids (i.e. fluids that exhibit a non-monotonic variation of surface tension with temperature) in various heat transfer applications, in the present work we formulate and analyse a theoretical model for the unsteady motion of a long bubble or droplet in a self-rewetting system in a non-uniformly heated tube due to a combination of Marangoni effects due to the variation of surface tension with temperature, gravitational effects due to the density difference between the two fluids, and an imposed background flow along the tube. We find that the evolution of the shape (but not of the position) of the bubble or droplet is driven entirely by Marangoni effects, and depends on the initial value of its radius in relation to a critical value. In the case in which Marangoni effects are absent the bubble or droplet always moves with constant velocity without changing shape. In the case in which only Marangoni effects are present the bubble or droplet either always moves away from or always moves towards the position of minimum surface tension; in the latter case it ultimately fills the entire cross-section of the tube at a final stationary position which is closer to the position of minimum surface tension than its original position. In the cases in which either only Marangoni effects and gravitational effects or only Marangoni effects and background-flow effects are present the competition between the two effects can lead to a non-monotonic evolution of the position of the centre of mass of the bubble or droplet. The behaviour of a self-rewetting system described in the present work is qualitatively different from that for ordinary fluids, in which case the bubble or droplet always moves with constant velocity without changing shape.