title: Different regimes in vertical capillary filling.
abstract: In this paper, we identify that the different regimes encountered in a vertical capillary filling or a capillary-rise problem are determined entirely by two dimensionless parameters: Ohnesorge number (Oh) and Bond number (Bo). The initial universal inertial regime, which has been analyzed in our recent paper [Das et al., Phys. Rev. E 86, 067301 (2012)], is followed by any one of three possible regimes, dictated by the ratio Oh/Bo. For Oh/Bo>>1, the viscous effects dominate the gravitational effects, and one encounters the classical Washburn regime. For the other limit, i.e., Oh/Bo<<1, the viscous effects are insignificant and there is no Washburn regime. On the contrary, the inertial regime transits to the oscillatory regime with the filling length ℓ oscillating about the Jurin height (~1/Bo), which is the maximum height attained by a liquid column in vertical capillary filling, with the viscous effects (~Oh) dictating the nature of the oscillations. For Oh/Bo~1, we get a behavior intermediate of these two extreme regimes. Finally, we identify the correct force picture that drives the oscillatory regime and in the process achieve quantitative match with the experimental results, that was precluded in the previous studies.
authors.affiliation: Micro & Nano-scale Transport Laboratory, Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G8.
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Das
authors.forename: Sushanta K
authors.initials: SK
authors.lastname: Mitra