Experimental Study of Water Drops with Additive Impact on Wood Surfaces

Huang, Xianjia; Chen, Pingping; Lan, Meijuan; Wang, Xishi; Liao, Guangxuan

doi:10.1016/j.proeng.2013.08.135

Cited by 8 publications

(1 citation statement)

References 28 publications

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“…Microribs are structures, which resemble the surface structure of a cut wood surface, where the sliced cell walls are represented by the ribs and the cellular voids are represented by the space in between the ribs. The impact of liquid drops on wood surfaces has been a topic of a few experimental studies in the literature. − However, to the best of our knowledge, in comparison to evaporation on micropillar arrays, ,− there is no effort in the literature to study liquid drop evaporation on rib structures in terms of both distance and size of the ribs as performed in this study. Further, the computation of the Gibbs free energy of an evaporating droplet includes all terms involved in this paper, namely, the interfacial energy, pressure term, and viscous dissipation.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of Contact Line Pinning and Depinning of Droplets Evaporating on Microribs

2018

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The contact line dynamics of evaporating droplets deposited on a set of parallel microribs is analyzed with the use of a recently developed entropic lattice Boltzmann model for two-phase flow. Upon deposition, part of the droplet penetrates into the space between ribs because of capillary action, whereas the remaining liquid of the droplet remains pinned on top of the microribs. In the first stage, evaporation continues until the droplet undergoes a series of pinning-depinning events, showing alternatively the constant contact radius and constant contact angle modes. While the droplet is pinned, evaporation results in a contact angle reduction, whereas the contact radius remains constant. At a critical contact angle, the contact line depins, the contact radius reduces, and the droplet rearranges to a larger apparent contact angle. This pinning-depinning behavior goes on until the liquid above the microribs is evaporated. By computing the Gibbs free energy taking into account the interfacial energy, pressure terms, and viscous dissipation due to drop internal flow, we found that the mechanism that causes the unpinning of the contact line results from an excess in Gibbs free energy. The spacing distance and the rib height play an important role in controlling the pinning-depinning cycling, the critical contact angle, and the excess Gibbs free energy. However, we found that neither the critical contact angle nor the maximum excess Gibbs free energy depends on the rib width. We show that the different terms, that is, pressure term, viscous dissipation, and interfacial energy, contributing to the excess Gibbs free energy, can be varied differently by varying different geometrical properties of the microribs. It is demonstrated that, by varying the spacing distance between the ribs, the energy barrier is controlled by the interfacial energy while the contribution of the viscous dissipation is dominant if either rib height or width is changed. Main finding of this is study is that, for microrib patterned surfaces, the energy barrier required for the contact line to depin can be enlarged by increasing the spacing or the rib height, which can be important for practical applications.

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