Contact-line behavior in boiling on a heterogeneous surface: Physical insights from diffuse-interface modeling

We simulate the moving contact line in two-dimensional chemically patterned channels using a diffuse-interface model with the generalized Navier boundary condition. The motion of the fluid–fluid interface in confined immiscible two-phase flows is modulated by the chemical pattern on the top and bottom surfaces, leading to a stick–slip behaviour of the contact line. The extra dissipation induced by this oscillatory contact-line motion is significant and increases rapidly with the wettability contrast of the pattern. A critical value of the wettability contrast is identified above which the effect of diffusion becomes important, leading to the interesting behaviour of fluid–fluid interface breaking, with the transport of the non-wetting fluid being assisted and mediated by rapid diffusion through the wetting fluid. Near the critical value, the time-averaged extra dissipation scales as U, the displacement velocity. By decreasing the period of the pattern, we show the solid surface to be characterized by an effective contact angle whose value depends on the material characteristics and composition of the patterned surfaces.

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LES Eulerian diffuse-interface modeling of fuel dense sprays near- and far-field

International Journal of Multiphase Flow ◽

10.1016/j.ijmultiphaseflow.2020.103272 ◽

2020 ◽

Vol 127 ◽

pp. 103272 ◽

Cited By ~ 1

Author(s):

J.M. Desantes ◽

J.M. García-Oliver ◽

J.M. Pastor ◽

I. Olmeda ◽

A. Pandal ◽

...

Keyword(s):

Diffuse Interface ◽

Far Field ◽

Interface Modeling

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Sliding, pinch-off and detachment of a droplet on a wall in shear flow

Journal of Fluid Mechanics ◽

10.1017/s0022112009992217 ◽

2010 ◽

Vol 644 ◽

pp. 217-244 ◽

Cited By ~ 38

Author(s):

HANG DING ◽

MOHAMMAD N. H. GILANI ◽

PETER D. M. SPELT

Keyword(s):

Shear Flow ◽

Contact Line ◽

Contact Angle Hysteresis ◽

Stress Singularity ◽

Local Maximum ◽

Diffuse Interface ◽

Moving Contact Line ◽

Moving Contact ◽

Effective Slip Length ◽

Maximum Angle

We investigate here what happens beyond the onset of motion of a droplet on a wall by the action of an imposed shear flow, accounting for inertial effects and contact-angle hysteresis. A diffuse-interface method is used for this purpose, which alleviates the shear stress singularity at a moving contact line, resulting in an effective slip length. Various flow regimes are investigated, including steadily moving drops, and partial or entire droplet entrainment. In the regime of quasi-steadily moving drops, the drop speed is found to be linear in the imposed shear rate, but to exhibit an apparent discontinuity at the onset of motion. The results also include the relation between a local maximum angle between the interface and the wall and the instantaneous value of the contact-line speed. The critical conditions for the onset of entrainment are determined for pinned as well as for moving drops. The corresponding critical capillary numbers are found to be in a rather narrow range, even for quite substantial values of a Reynolds number. The approach to breakup is then investigated in detail, including the growth of a ligament on a drop, and the reduction of the radius of a pinching neck. A model based on an energy argument is proposed to explain the results for the rate of elongation of ligaments. The paper concludes with an investigation of detachment of a hydrophobic droplet from the solid wall.

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