Dynamics of Passive Filling of Fluids in Cylindrical Capillaries

As a passive driving method for liquids, capillary flow has important value in the design of passive microfluidic chips and microreactors. To predict the behavior of fluid's flow in vertical capillaries, this paper studies the different stages of passive filling of microfluidics in capillaries through numerical simulation and experimental verification, with a focus on the dynamic law of passive filling in vertical capillaries. The theoretical derivation is combined with numerical simulation, which not only obtains the conditions for the occurrence of the liquid's surface oscillation in the capillaries but also gives the theoretical and predictive formulas for the flow law in vertical capillaries. This further clarifies whether a single factor in fluid's properties and pipeline characteristics has an impact on capillary flow and quantified the magnitude of its impact. The simulation results are verified by experiments, and the reasons for the difference between the simulation results and the experimental data are explored; that is, when the fluid flows in the tube, the dynamic contact angle will affect the actual flow process. The statistical variation of the contact angle with fluid's flow provides a certain reference value for the measurement and prediction of the dynamic contact angle in capillaries.