Cervantes-Álvarez A M, Escobar-Ortega Y Y, Sauret A, Pacheco-Vázquez F
Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apartado Postal J-48, Puebla 72570, Mexico.
Department of Mechanical Engineering, University of California, Santa Barbara, CA, 93106 USA.
J Colloid Interface Sci. 2020 Aug 15;574:285-292. doi: 10.1016/j.jcis.2020.04.009. Epub 2020 Apr 14.
A water jet penetrating into a water pool produces air entrainment and bubbles that rise to the surface and disintegrate. A similar scenario can be expected when a granular jet enters into water. This phenomenon is common in natural and industrial processes but remains so far unexplored.
A collimated jet of monodisperse silica beads was poured into water and the process was filmed with a high-speed camera. The grain size, jet impact velocity, and the liquid physical properties were systematically varied.
For grains of ~50-300μm in diameter, the granular jet deforms the air-water interface, penetrates the pool and produces air entrainment. Most of the entrained air is contained in the interstitial space of the jet, and its volume is linearly proportional to the volume of grains. The bubbles formed in this process are covered by a layer of grains attached to the bubble air-water interface due to capillary-induced cohesion. These "granular bubbles" are stable over time because the granular shell prevents coalescence and keeps the air encapsulated, either if the bubbles rise to the surface or sink to the bottom of the pool, which is determined by the competition of the buoyancy and the weight of the assembly.
水射流穿透水池会产生空气夹带现象，形成的气泡会上升至水面并破裂。当颗粒射流进入水中时，预计会出现类似情况。这种现象在自然和工业过程中很常见，但迄今为止尚未得到探索。
将准直的单分散二氧化硅珠粒射流倒入水中，并用高速摄像机记录该过程。系统地改变颗粒尺寸、射流冲击速度和液体物理性质。
对于直径约为50 - 300μm的颗粒，颗粒射流会使空气 - 水界面变形，穿透水池并产生空气夹带。大部分夹带的空气包含在射流的间隙空间中，其体积与颗粒体积成线性比例。在此过程中形成的气泡由于毛细作用引起的内聚力，被一层附着在气泡空气 - 水界面的颗粒所覆盖。这些“颗粒气泡”随时间保持稳定，因为颗粒壳阻止了合并，并使空气保持封装状态，气泡是上升到水面还是沉到水池底部，这取决于浮力与组件重量之间的竞争。
