Shen Feng, Ai Mingzhu, Ma Jianfeng, Li Zonghe, Xue Sen
Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing 100124, China.
Beijing Key Laboratory of Advanced Manufacturing Technology, Beijing University of Technology, Beijing 100124, China.
Micromachines (Basel). 2020 Sep 30;11(10):914. doi: 10.3390/mi11100914.
Pressure is one basic parameter involved in microfluidic systems. In this study, we developed an easy capillary-based method for measuring fluid pressure at one or multiple locations in a microchannel. The principal component is a commonly used capillary (inner diameter of 400 μm and 95 mm in length), with one end sealed and calibrated scales on it. By reading the height () of an air-liquid interface, the pressure can be measured directly from a table, which is calculated using the ideal gas law. Many factors that affect the relationship between the trapped air volume and applied pressure () have been investigated in detail, including the surface tension, liquid gravity, air solubility in water, temperature variation, and capillary diameters. Based on the evaluation of the experimental and simulation results of the pressure, combined with theoretical analysis, a resolution of about 1 kPa within a full-scale range of 101.6-178 kPa was obtained. A pressure drop (Δ) as low as 0.25 kPa was obtained in an operating range from 0.5 kPa to 12 kPa. Compared with other novel, microstructure-based methods, this method does not require microfabrication and additional equipment. Finally, we use this method to reasonably analyze the nonlinearity of the flow-pressure drop relationship caused by channel deformation. In the future, this one-end-sealed capillary could be used for pressure measurement as easily as a clinical thermometer in various microfluidic applications.
压力是微流体系统中涉及的一个基本参数。在本研究中，我们开发了一种基于毛细管的简易方法，用于测量微通道中一个或多个位置的流体压力。主要部件是一根常用的毛细管（内径400μm，长度95mm），一端密封并带有校准刻度。通过读取气液界面的高度（），可以直接从一个表格中测量压力，该表格是根据理想气体定律计算得出的。已经详细研究了许多影响捕获空气体积与施加压力（）之间关系的因素，包括表面张力、液体重力、空气在水中的溶解度、温度变化和毛细管直径。基于对压力实验和模拟结果的评估，结合理论分析，在101.6 - 178kPa的满量程范围内获得了约1kPa的分辨率。在0.5kPa至12kPa的工作范围内，获得了低至0.25kPa的压力降（Δ）。与其他基于新型微结构的方法相比，该方法不需要微加工和额外设备。最后，我们使用该方法合理分析了由通道变形引起的流动 - 压力降关系的非线性。未来，这种一端密封的毛细管在各种微流体应用中可以像临床温度计一样轻松用于压力测量。
