Mechanical & Industrial Engineering Department, Montana State University, Bozeman, Montana, USA.
Lab Chip. 2022 Nov 8;22(22):4306-4316. doi: 10.1039/d2lc00648k.
Pressure is important in virtually all problems in fluid dynamics from macro-scale to micro/nano-scale flows. Although technologies are well developed for its measurement at the macroscopic scale, pressure quantification at the microscopic scale is still not trivial. This study reports the design and fabrication of an on-chip sensor that enables quantification of pressure in microfluidic devices based on a novel technique called astigmatic particle tracking. With this technique, thin membranes that sense pressure variations in the fluid flow can be characterized conveniently by imaging the shapes of the particles embedded in the membranes. This innovative design only relies on the reflected light from the back of the microchannel, rendering the sensor to be separate and noninvasive to the flow of interest. This sensor was then applied to characterize the pressure drop in single-phase flows with an accuracy of ∼70 Pa and good agreement was achieved between the sensor, a commercial pressure transducer and numerical simulation results. Additionally, the sensor successfully measured the capillary pressure across an air-water interface with a 7% deviation from the theoretical value. To the best of our knowledge, this pore-scale capillary pressure quantification is achieved for the first time using an on-chip pressure sensor of this kind. This study provides a novel method for quantification of local pressure and thus opens the door to a renewed understanding of pore-scale physics of local pressure in multi-phase flow in porous media.
压力在从宏观到微观/纳米尺度的几乎所有流体动力学问题中都很重要。虽然在宏观尺度上已经开发出了测量压力的成熟技术，但在微观尺度上对压力的定量测量仍然不是一件简单的事情。本研究报告了一种基于一种称为像散粒子跟踪的新技术的片上传感器的设计和制造，该传感器能够实现微流控设备中压力的定量。通过这种技术，可以通过对嵌入在膜中的粒子的形状进行成像，方便地对感应流体流动中压力变化的薄膜进行表征。这种创新设计仅依赖于微通道背面的反射光，使得传感器与感兴趣的流是分离的且不会对其产生干扰。然后，该传感器被应用于对单相流中的压降进行表征，其精度约为 70Pa，并且传感器、商业压力传感器和数值模拟结果之间具有良好的一致性。此外，该传感器还成功地测量了空气-水界面的毛细压力，与理论值的偏差为 7%。据我们所知，这是首次使用这种片上压力传感器实现了这种孔尺度毛细压力的定量。本研究为局部压力的定量提供了一种新方法，从而为多孔介质中多相流局部压力的孔尺度物理特性的重新认识打开了大门。
