Eccentricity effect on horizontal capillary emptying. (10th September 2022)

• Record Type: Journal Article
• Authors: Tan, Dongwen; Zhou, Xinping; Zhang, Gang; Zhu, Chengwei; Fu, Chenyu
• Is Part Of: Journal of fluid mechanics. Volume 946(2022)
• Publication Date: 2022-09-10
• Subjects: capillary flows; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2022.567
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Abstract : This paper theoretically studies the effect of eccentricity on the conditions of capillary emptying (determined by critical Bond number) in a horizontal annular tube in a downward gravity field. Experiments are conducted to compare with theoretical results. We find that non-horizontal eccentricity can lead to the occurrence of a re-entrant liquid-state transition (from liquid non-occlusion to liquid plug to liquid non-occlusion) with increasing Bond number, when the eccentricity ( e ) or inner-to-outer radius ratio ( χ ) is large enough, and the two liquid non-occlusion states correspond to different emptying mechanisms dominated by the gravity effect and the 'wedge' effect, respectively. Existence of the re-entrant transition is accompanied by occurrence of unconditional liquid non-occlusion at large enough or small enough contact angles regardless of Bond numbers. The critical Bond numbers at a contact angle γ for vertical upward eccentricity are equal to those at a contact angle 180° − γ for vertical downward eccentricity. In a parameter space ( γ, e /(1 − χ )), the region with the re-entrant transition becomes larger with the eccentric angle varying from 0° (horizontal) to 90° (vertical). Optimization of geometrical parameters and inner and outer contact angles can lead to better effect of capillary emptying. This paper provides a very effective scheme for removing a liquid blockage from a capillary in optofluidics/microfluidics.