A study of capillary flow from a pendant droplet

作者：Radiom Milad; Chan Weng Kong; Yang Chun^*

来源：Microfluidics and Nanofluidics, 2009, 7(5): 697-707.

DOI：10.1007/s10404-009-0429-2

• Capillary flow
• Finite reservoir effect
• Pendant droplet
• Egg-shaped model
• Dynamic contact angle

Surface tension driven capillary flow from a pendant droplet into a horizontal glass capillary is investigated in this paper. Effect of the droplet surface on dynamic behavior of such capillary flow is examined and compared with surface tension driven capillary flow from an infinite reservoir. In the experiment, capillaries of 300-700 mu m in diameter were used with glycerol-DI water mixture solutions having viscosities ranging from 80 to 934 mPa s. It is observed that compared to the capillary flow from an infinite reservoir, the capillary flow from a droplet exhibits higher rates of meniscus displacement. This is due to an additional driving force resulted from change in droplet surface area (or curvature). The two main parameters influencing the flow are the dimensionless droplet geometry parameter (k) and the dynamic contact angle (theta (D)). The molecular kinetics theory of Blake and De Coninck's model [Adv Colloid Interface Sci 96(1-3):21-36, 2002] is used to interpret the dynamic contact angle. This theory considers a molecular friction coefficient (zeta) at the liquid front flowing over a solid surface. Moreover, three models are proposed to describe the shape of the pendant droplet during capillary action. It is found that the egg-shaped model provides a more realistic model to compute the shape of the pendant droplet deformed during the capillary action. Thus the predictions by the egg-shaped model are in good agreement with the experimental data.

• 出版日期2009-11
• 单位南阳理工学院