A study of capillary flow from a pendant droplet |
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Authors: | Milad Radiom Weng Kong Chan Chun Yang |
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Affiliation: | (1) School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore; |
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Abstract: | 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 μm 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 (θ
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 (ζ) 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. |
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