纳米阵列中气体驱替液体的流动特征

纳米尺度下气体驱动液体流动特征在纳流控芯片及页岩气开发中具有广泛的应用前景. 利用管径规格为292.8 nm,206.2 nm,89.2 nm,67.0 nm,26.1 nm的氧化铝膜为纳米阵列,进行气驱水实验和单相气体流动实验,分析纳米尺度下气驱水流动特征. 实验表明,纳米阵列中气驱水时气体流量随驱动压力变化经历三个阶段:第一阶段流量缓慢增大,且比单相气体流量降低约一个数量级;第二阶段纳米阵列中的水被大量驱替出,流量迅速增大;第三阶段纳米阵列中的水全部被驱替出,流动特征与单相气体流动保持一致. 分析表明,气驱水第一阶段存在气液界面毛细管力的“钉扎”作用及固液界面相互作用力的影响,是产生非线性流动的主要原因;而一旦“钉扎”作用破坏,气体进入管道推动界面运动,气柱与液柱之间的毛细曲面曲率变化,毛细管力减小,气体流量急剧增大,其中毛细管力随驱替压力增大急剧变化,是造成第二阶段气体流量突变的主要原因. 

THE CHARACTERISTICS OF WATER FLOW DISPLACED BY GAS IN NANO ARRAYS

The two-phase flow characteristics of water flow displaced by gas at nanometer scale have a wide application in the development of nano-fluidic chips and shale gas. In this paper, experiments of water flow displaced by gas and single-phase flow was carried out to study the flow characteristics of water flow displaced by gas at nanoscale of alumina membranes with diameters of 292.8 nm, 206.2 nm, 89.2 nm, 67.0 nm and 26.1 nm. The experiments show that there are three flow stages for water flow displaced by gas at nanoscale: firstly, the flow rate increases slowly with increasing the driving pressure in the first stage, and the gas flux is decreased about one order of magnitude when compared with gas single-phase flow; secondly, gas flux increases rapidly with increasing the driving pressure as water in nano arrays are largely driven out in the second stage; thirdly, gas flow characteristics are consistent with the single-phase flow when water in nano arrays are all displaced out in the third stage. The analysis results show that due to the “pinning" effect of capillary pressure at the gas-liquid interface and the interaction of solid-liquid interface, gas flux increase slowly in the first stage of water flow displaced by gas. And the larger driving pressure is required to increase the gas flux in nano arrays, which is the main reason of the nonlinear flow characteristics. Once the “pinning" effect is destroyed, the gas will enter the pipeline to promote the movement of the interface, which will change the capillary curvature between capillary column and liquid column. As a result, the capillary force reduces rapidly with the increase of displacing pressure and gas flux will increase sharply, which is the main reason of the sudden change of water flow displaced by gas in the second stage.