Gravity-driven unsteady-state slug fall in capillaries – modeling and experimental verification

Kaiyin Zhang, Qiuling Wang*, Shigang Li, Shan Wu, Rony Wallach

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Infiltration of liquid droplets into dry porous media often occurs in industrial and natural settings, which has been widely modeled as liquid slug flow in capillaries. This work focuses on gravity-driven slug motion in vertically oriented capillary tubes. To model the propagation and evolution of the slug, a mathematical model was set on the basis of Newton’s second law and the law of conservation of mass. The model includes terms like slug’s inertia, deposited film, dynamic contact angle, slug’s advancing and receding menisci hysteresis, and it particularly highlights the direct effect of the trailing film on the change of slug mass. In order to verify this model, experiments on water slug with different lengths of initial slugs were conducted in two Pyrex glass capillaries that are partially wettable. It was found that both the length and the velocity of the slug vary during the slug motion in every case. Then the experimental results were simulated with the established model by carefully presetting two fitting parameters, αa and αh, that are related to the dynamic contact angle at the advancing meniscus and the thickness of the trailing film, respectively. The good agreement between the experimental and theoretical results demonstrates that the present model is capable of describing the unsteady-state dynamics of slugs fall in porous media.

Original languageAmerican English
Pages (from-to)2146-2156
Number of pages11
JournalJournal of Adhesion Science and Technology
Issue number19
StatePublished - 1 Oct 2016

Bibliographical note

Publisher Copyright:
© 2016 Informa UK Limited, trading as Taylor & Francis Group.


  • Slug dynamics
  • capillary
  • trailing film
  • unsteady-state


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