Draining phenomenon in closed narrow tubes pierced at the top: an experimental and theoretical analysis

Abstract

The phenomenon of draining, although ubiquitous in nature, has received scant attention especially in the meso-scale. We observe that closed top tubes drain by the inception of an axisymmetric 'Taylor finger' while a minute pierce of the top closure results in an altogether different physics with air entry from the top pushing the liquid out. Again, a coupled mechanism comprising full bore followed by film draining is observed for "too small" a top pierce at "high enough" Eotvos number. Top pierce initiates draining in dimensions which would not drain otherwise and finger entry hastens the process of draining. The myriad of phenomena thus exhibited is depicted as phase diagrams in vertical and inclined conduits. A mechanistic model has been proposed to predict draining and the onset of finger entry in vertical tubes.

Enhanced liquid retention capacity within plastic food packaging through modified capillary recesses

“…However, the liquid retention capacity decreased for lower liquid surface tensions as the liquid menisci exhibited less stability and pressure barrier. The reduction in liquid surface tension reduced the resistance to the liquid drainage by facilitating the propagation of air finger as explained by Kumar et al (2018). The PET recesses with the very low surface tension liquid (γ: 31.5 mN/m) lacked retention capabilities.…”

“…6a. This phenomenon is called Taylor finger, which can propagate into the liquid leading to liquid draining out from the capillarity opening (Davies and Taylor, 1950;Extrand, 2017;Kumar et al, 2018). However, geometrical valves usually introduced to capillary systems improve the liquid pinning on their expanded walls leading to increases in the pressure barrier.…”

“…These openings allow the liquid to be pinned on their edges, and hence the capillary pressure generates a local pressure barrier to prevent liquid drainage (Wang et al, 2013). This results in more stable menisci and improved resistance to air finger formation that causes the liquid drainage (Kumar et al, 2018). The capillary pressure and stability of the liquid menisci significantly improved with the decrease in recess sizes.…”

“…This could reduce the menisci stability and undermine the liquid pinning on the recess openings. Thus, the air finger was initiated since the pressure barrier was not sufficient to resist the growing local hydrostatic pressure during the recess inclination (Extrand, 2017(Extrand, , 2018Kumar et al, 2018). This resulted in liquid drainage of the recess cavities as manifested in the reduced liquid retention of larger sized recesses, notably for recesses with no rim.…”

“…The capillary valve functionality has widely been studied for controlling the liquid flow in open capillary systems (Chen et al, 2008;Leu and Chang, 2004;Zimmermann et al, 2008), and liquid drainage in closed capillary systems, such as inclined tube with one closed end and container with small open orifice. Liquid drainage in an inclined tube with large opening is initiated by air finger evolving into the liquid meniscus (Kumar et al, 2018). This drainage mechanism is attributed to Taylor fingering phenomenon (Davies and Taylor, 1950).…”