Orthogonal liquid-jet impingement on wettability-patterned impermeable substrates

Abstract

Liquid jet impingement on flat, impermeable substrates is important for a multitude of applications, ranging from electronic equipment cooling, to fuel atomization, and erosion of solid surfaces. On a wettable surface, where a sufficient downstream liquid depth can be sustained after axisymmetric impingement, the jet forms a thin film on the substrate up to a radial distance where the film height suddenly increases, forming a hydraulic jump. On a superhydrophobic surface, where a downstream liquid depth is not naturally sustained, the thin film expands and breaks up into droplets, which are subsequently ejected in a random fashion outward, as carried by their radial momentum. In the present work, a facile, scalable, wettability-patterning approach is presented for delaying or even eliminating droplet breakup in the case of jet impingement on horizontal superhydrophobic surfaces. An analytical expression for predicting the hydraulic jump and droplet breakup locations is developed to designate the proper wettability patterns that facilitate alteration and control of the post-impingement liquid behavior. The axisymmetric model is extended to evaluate the radial variation of the competing forces responsible for film breakup, and a design criterion for the effective wettability patterns is proposed.

The circular capillary jump

“…Despite this experimental evidence several other recent papers (Fernandez-Feria, Sanmiguel- Rojas & Benilov 2019;Scheichl 2019;Sen et al 2019;Wang & Khayat 2019) continue to support the previous gravity-based theory. For example, Fernandez-Feria et al (2019) performed numerical simulations of the downward vertical impingement of a liquid jet onto a horizontal plate and compared their results with the experimental data from Button et al (2010), which were obtained for an upward directed jet onto a ceiling.…”

Circular hydraulic jumps: where does surface tension matter?

“… stationary impact of a jet on a dry surface, possibly superhydrophobic (fully or partially as in Sen et al. 2019), without formation of the outer film (atomization ring); stationary impact of a jet on a dry surface in inverse gravity (impact of a jet on a ceiling); transient regime of circular hydraulic jump formation for low-viscosity liquids in partial wetting. …”

“…stationary impact of a jet on a dry surface, possibly superhydrophobic (fully or partially as in Sen et al. 2019), without formation of the outer film (atomization ring);…”

“…2011; Sen et al. 2019). In this regime the force opposed to fluid inertia at the boundaries is dictated only by surface tension and not by gravity; there is no developed shock, no liquid ‘wall’.…”

“…The second, in figure 1( b ), is its equivalent on a ‘dry’ surface (atomization rim), obtained by superhydrophobic treatment (Maynes, Johnson & Webb 2011; Sen et al. 2019). A related, but different, configuration can be reached by simply impinging a vertical jet from below on a horizontal ceiling (Button et al.…”