微重力条件下与容器连通的毛细管中的毛细流动研究

利用落塔的短时微重力条件, 实验研究了与容器连通的毛细管中的流体在微重力条件下的毛细流动过程, 并通过理论分析建立了相应的毛细管中弯月液面高度随时间变化的微分方程. 结果表明, 对于不同的接触角和不同的容器/毛细管参数, 由建立的理论公式得到的数值解结果都与实验结果在定量上较为一致. 此外, 实验中发现, 改变乙醇和去离子水混合液的比例可以明显地改变接触角参数, 但对毛细流动的影响很小, 建立的理论公式也对这一现象给出了合理的解释. 该研究对于预测和分析微流道及空间微重力条件下的毛细流动行为具有明显的应用价值.

Capillary-driven flow in tubes connected to the containers under microgravity condition

The capillary-driven liquid flow in tubes connected to containers under a microgravity condition is systematically studied in a drop tower experimentally. The microgravity time lasts up to 3.6 s and the working liquids are mixtures of ethanol and deionized water with different ratios. Theoretically, based on the previous theory for tubes directly immersed in fluid, a modified formula is developed to describe the change tendency of the height of meniscus with microgravity time for such a container/tube system exposed to a microgravity environment. From the theoretical formula, the numerical results of meniscus height at different microgravity time can be obtained, utilizing the geometrical parameters of container/tube systems and the relevant physical quantities of Eth/H₂O mixtures with different ratios. By comparing the numerical results with experimental results for different contact angles between working liquid and container in different container/tube systems, we show that the theoretical model is able to quantitatively predict the capillary-driven flow in tubes connected to containers, and the numerical results have good consistence with the experimental results. In addition, the experimental results also show that though the ratio of ethanol to deionized water can change the contact angle remarkably, it has little influence on the capillary flow if the geometrical parameters of the container/tube systems are the same. This is because not only the contact angle, but also the surface tension and viscosity coefficient of the working liquid change with the ratio of ethanol to deionized water. It is found that when the contact angle increases from 42° to 66°, the surface tension increases from 0.0328 N/m to 0.0443 N/m correspondingly, but the viscosity coefficient decreases from 2.11 cSt to1.49 cSt. As a result, the changes of surface tension and viscosity coefficient offset the influence of the change of contact angle, which can be explained by our theoretical model. Compared with the extensively studied system in which tubes are directly immersed into liquid, the container/tube system studied in this paper is more similar to many actual systems such as fluid transfer systems in the microgravity condition and in micro-fluidic devices. Therefore, this study is useful for predicting and analyzing the capillary flows of these actual systems.