Bubbles for Separating Particles from Suspensions: Thin Films and Curved Channels

小颗粒有广泛的应用，从药物输送和传感到作为改变材料性质的填料。粒度和粒度分布通常是至关重要的，因此通常寻求从不同粒度的颗粒混合物中按粒度分离颗粒。以血液为例，通常需要将大的白细胞与稍小的有弹性的红细胞与更小的血小板分离开来。在许多情况下，执行这种分离仍然是一项挑战。在这里，研究人员展示了一种新的想法，通过在充满悬浮液的圆柱形管中流动一个长气泡来实现这种颗粒大小的分离。气泡的运动是一个众所周知的流体动力学问题，我们以一种新的方式加以利用。特别是，我们表明气泡的速度选择了一个临界尺寸的小颗粒，这些小颗粒可以流过气泡，而大颗粒则留在气泡前面。这样，气泡就充当了粒子的过滤器。针对不同的通道几何形状，研究了该问题的几种变体，并对新分离过程的效率进行了表征。根据悬浮液的大小分离颗粒需要技术，而在微米和亚微米范围内分离颗粒仍然是一个挑战。在流体力学文献中众所周知，在管中移动的长气泡被一层薄的液膜与边界隔开，而液膜的厚度随流速的变化而变化。在这里，这种薄膜被显示为一个速度依赖的过滤器，用于从悬浮液中按大小分离颗粒。因此，利用这种结构可以(1)研究气泡通过充满双分散悬浮液的水平通道时的大小分离效率，(2)研究一个或多个气泡在弯曲通道中转换时形成的薄膜，以及(3)研究气泡通过充满悬浮液的弯曲通道和垂直通道转换的分离效率，垂直通道可能为这种分离提供最有效的连续流动过程。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Small particles find a wide range of applications, from drug delivery and sensing to serving as fillers for altering the properties of materials. The particle size and the size distribution are often critical and so it is common to seek to separate particles by size from a mixture of particles with various sizes. As one example is blood, where it is often desired to separate the large white blood cells from the somewhat smaller flexible red blood cells from the even smaller platelets. It remains a challenge to perform such separations in many circumstances. Here the investigators demonstrate a new idea for accomplishing such particle-size separations by flowing a long gas bubble in a cylindrical tube filled with a suspension. The motion of the bubble is a well-understood fluid dynamics problem that we exploit in a new way. In particular, we show that the speed of the bubble selects a critical size of smaller particles that can flow past the bubble while larger particles remain in front of the bubble. Thus, the bubble acts as a filter for particles. Several variants of this problem are studied for different channel geometries and the efficiency of the new separation process will be characterized.Technologies are needed to separate particles by size from a suspension, and it remains a challenge to separate particles in the micron and sub-micron range. A long bubble translating in a tube is separated from the boundaries by a thin liquid film, whose thickness varies with flow speed, as is well known in the fluid mechanics literature. Here this thin film is shown to act as a speed-dependent filter for separating particles by size from a suspension. Thus, this configuration is exploited to (1) study the efficiency of separation by size for a bubble translating through a horizontal channel filled with a bidisperse suspension, (2) study the thin films formed when one or more bubbles translates in curved channels, and (3) study the separation efficiency of bubbles translating through suspension-filled curved channels and vertical channels, the latter potentially allowing the most effective continuous flow process for such separations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.