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

小颗粒有着广泛的应用，从药物输送和传感到作为填料改变材料的性质。颗粒尺寸和尺寸分布通常是关键的，因此通常寻求从具有各种尺寸的颗粒的混合物中按尺寸分离颗粒。作为一个例子是血液，其中通常期望将大的白色血细胞与稍微较小的柔性红细胞和甚至更小的血小板分离。在许多情况下进行这种分离仍然是一个挑战。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尺寸的分离。气泡的运动是一个很好理解的流体动力学问题，我们以一种新的方式加以利用。特别是，我们表明，气泡的速度选择一个临界尺寸的较小的颗粒，可以流过气泡，而较大的颗粒仍然在前面的气泡。因此，气泡充当颗粒的过滤器。这个问题的几个变种进行了研究，为不同的通道几何形状和新的分离过程的效率将characteristic.Technologies的需要，从悬浮液中分离颗粒的大小，它仍然是一个挑战，以分离颗粒在微米和亚微米范围。如流体力学文献中所公知的，在管中平移的长气泡通过薄液膜与边界分离，所述薄液膜的厚度随着流速而变化。在这里，这种薄膜被证明是作为一个速度依赖性的过滤器，用于分离颗粒的大小从悬浮液。 因此，该构造被用于（1）研究气泡平移通过填充有双分散悬浮液的水平通道的尺寸分离效率，（2）研究当一个或多个气泡在弯曲通道中平移时形成的薄膜，以及（3）研究气泡平移通过填充悬浮液的弯曲通道和垂直通道的分离效率，该奖项反映了NSF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.