通过粒子图像测速法研究水桥中双向流自发排布的证据
Evidence for spontaneous arrangement of two-way flow in water bridge via particle image velocimetry
AI总结：
本研究通过粒子图像测速法等手段，发现百年经典问题中的水桥实为两股带不同电荷的反向同轴流，揭示了其自发排布机制与通量差异，为微型软壁流动研究提供了天然反例。
摘要：
通过重新探究水桥这一已有百年历史的问题，我们证明它实际上是动态的，由两股携带不同电荷、沿相反方向流动的同轴水流组成。这种自发分离是由水桥构建的不同阶段触发的。最初，由H⁺驱动的锥形射流促进了一股水流从正电极烧杯流出。随后来自负电极烧杯的反向锥形射流形成，并被迫沿外侧路径流动。我们通过使用荧光素和碳粉作为示踪剂，结合粒子图像测速法（Particle Image Velocimetry），揭示了这种双向流的自发排布。研究发现这两股反向流动的通量不相等，导致水向负电极烧杯净输送。我们成功估算了这些同轴流的流速和横截面积随时间及外加电压的变化关系。值得注意的是，外层的水起到了毫米级管道的作用，约束着内部流动并与其发生强烈相互作用。这为近期报道的、由铁磁流体构成的同等微型软壁中近乎无摩擦的流动，提供了首个天然却相反的例证。
英文摘要：
By revisiting the century-old problem of water bridge, we demonstrate that it is in fact dynamic and comprises of two coaxial water currents that carry different charges and flow in opposite directions. This spontaneous separation is triggered by the different stages to construct the water bridge. Initially, a flow is facilitated by the cone jet that is powered by H+ and flows out of the positive-electrode beaker. An opposing cone-jet from negative beaker is established later and forced to take the outer route. This spontaneous arrangement of two-way flow is revealed by using fluorescein and carbon powder as tracers, and the Particle Image Velocimetry, These two opposing flows are found to carry non-equal flux that results in a net transport of water to the negative beaker. We manage to estimate the flow speed and cross-sectional area of these co-axial flows as a function of time and applied voltage. Note that the water on the outer layer functions as a millimeter tube that confines and interacts strongly with the flow inside. This provides a first natural and yet counter example to the recently reported near-frictionless flow in an equally miniatureized soft wall made from ferrofluid.
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