Current lithography methods allow facile fabrication of microfluidic conduits where not only the shape of the bounding walls can be arbitrarily varied but also the internal conduit space can be laden with a variety of microstructures and wetting properties. This virtually infinite design space of microfluidic geometries brings in the challenge of how to quantify fluid resistance in a large number of microfluidic conduits, while maintaining operational simplicity. We report a versatile experimental technique referred to as microfluidic bypass manometry for measurement of pressure drop versus flow rate (ΔP–Q) relations in a parallelized manner. The technique involves introducing co-flowing laminar streams into a microfluidic network that contains a series of loops, where each loop is comprised of a test geometry and a bypass channel as a flow-rate sensing element. We optimize the network geometry and present operational considerations for microfluidic bypass manometry. To demonstrate the power of our technique, we used single-phase fluids and measured ΔP–Q relations simultaneously for forty test geometries ranging from linear to contraction–expansion to serpentine to pillar-laden microchannels. To expand the capabilities of the method, we measured ΔP–Q relations for similar-sized oil droplets trapped in microcavities where the cavity geometry spans from prisms of 3–10 sides to circular disks. We found in all cases, the ΔP–Q relation is nonlinear and the flow resistance of droplets is sensitive to confinement. At high flow rates, the drop resistance depends on the cavity geometry and is higher in a triangular prism compared to a circular disk. We compared the measured flow resistance of single-phase fluids and droplets in different microfluidic geometries to that from computational fluid dynamics simulations and found them to be in excellent agreement. Given the simplicity and versatility of the microfluidic bypass manometry method, we anticipate that it may find broad application in several areas including design of lab-on-chip devices, laminar drag reduction and mechanics of deformable particles.

中文翻译：

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微流体旁路测压法：高度并行地测量复杂通道几何形状和捕获的液滴的流阻†

当前的光刻方法允许容易地制造微流体导管，在该微流体导管中，不仅可以任意地改变边界壁的形状，而且还可以使内部导管空间充满各种微结构和润湿特性。实际上，微流体几何形状的无限设计空间带来了挑战，即如何在保持操作简便性的同时，量化大量微流体导管中的流体阻力。我们报告了一种称为微流体旁路测压法的通用实验技术，用于测量压降与流速（ΔP – Q）关系的并行化。该技术涉及将同流层流引入到包含一系列回路的微流体网络中，其中每个回路都由测试几何形状和作为流量传感元件的旁路通道组成。我们优化了网络几何形状，并提出了微流旁路测压的操作注意事项。为了证明我们技术的力量，我们使用了单相流体并同时测量了ΔP – Q关系，对40种测试几何形状进行了测试，这些几何形状从线性，收缩，膨胀，蛇形到充满柱的微通道。为了扩展该方法的功能，我们测量了ΔP – Q困在微腔中的相似大小的油滴的几何关系，腔的几何形状从3–10边的棱柱延伸到圆盘。我们发现在所有情况下，ΔP – Q这种关系是非线性的，液滴的流动阻力对约束敏感。在高流速下，抗滴落性取决于型腔的几何形状，并且与圆形圆盘相比，三角形棱镜的抗滴落性更高。我们比较了在不同微流体几何形状中测得的单相流体和液滴的流阻与计算流体动力学仿真所得的流阻，发现它们具有极好的一致性。鉴于微流体旁路测压法的简单性和多功能性，我们预计它会在包括芯片实验室设备设计，层流减阻和可变形颗粒力学在内的多个领域中得到广泛应用。