Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
Lab Chip. 2011 Dec 7;11(23):3970-8. doi: 10.1039/c1lc20444k. Epub 2011 Oct 14.
This paper describes the behavior of bubbles suspended in a carrier liquid and moving within microfluidic networks of different connectivities. A single-phase continuum fluid, when flowing in a network of channels, partitions itself among all possible paths connecting the inlet and outlet. The flow rates along different paths are determined by the interaction between the fluid and the global structure of the network. That is, the distribution of flows depends on the fluidic resistances of all channels of the network. The movement of bubbles of gas, or droplets of liquid, suspended in a liquid can be quite different from the movement of a single-phase liquid, especially when they have sizes slightly larger than the channels, so that the bubbles (or droplets) contribute to the fluidic resistance of a channel when they are transiting it. This paper examines bubbles in this size range; in the size range examined, the bubbles are discrete and do not divide at junctions. As a consequence, a single bubble traverses only one of the possible paths through the network, and makes a sequence of binary choices ("left" or "right") at each branching intersection it encounters. We designed networks so that, at each junction, a bubble enters the channel into which the volumetric flow rate of the carrier liquid is highest. When there is only a single bubble inside a network at a time, the path taken by the bubble is, counter-intuitively, not necessarily the shortest or the fastest connecting the inlet and outlet. When a small number of bubbles move simultaneously through a network, they interact with one another by modifying fluidic resistances and flows in a time dependent manner; such groups of bubbles show very complex behaviors. When a large number of bubbles (sufficiently large that the volume of the bubbles occupies a significant fraction of the volume of the network) flow simultaneously through a network, however, the collective behavior of bubbles-the fluxes of bubbles through different paths of the network-can resemble the distribution of flows of a single-phase fluid.
本文描述了悬浮在载体液体中并在具有不同连通性的微流控网络中移动的气泡的行为。单相连续流体在网络中的通道中流动时，会在连接入口和出口的所有可能路径之间进行分配。不同路径上的流速取决于流体与网络整体结构之间的相互作用。也就是说，流量分布取决于网络中所有通道的流体阻力。悬浮在液体中的气体气泡或液滴的运动与单相液体的运动可能有很大的不同，尤其是当它们的尺寸略大于通道时，因此气泡（或液滴）在通过通道时会增加通道的流体阻力。本文研究了处于这个尺寸范围内的气泡；在研究的尺寸范围内，气泡是离散的，在交界处不会分裂。因此，单个气泡仅通过网络中的一条可能路径穿过，并且在遇到每个分支交点时都会做出一系列二进制选择（“左”或“右”）。我们设计了网络，以便在每个交点处，气泡进入载体液体体积流量最高的通道。当网络中一次只有一个气泡时，气泡所走的路径不是直觉上的最短或最快的连接入口和出口的路径。当少量气泡同时通过网络移动时，它们会通过改变流体阻力和流量在时间上相互作用；这样的气泡群表现出非常复杂的行为。当大量气泡（足够大，以至于气泡的体积占据了网络体积的很大一部分）同时流过网络时，气泡的集体行为——气泡通过网络不同路径的通量——可以类似于单相流体的流量分布。
