Mixing and internal dynamics of droplets impacting and coalescing on a solid surface

Castrejón‐Pita, J. R.; Kubiak, Krzysztof; Castrejón‐Pita, Alfonso A.; Wilson, Mark C. T.; Hutchings, I.M.

doi:10.1103/physreve.88.023023

Cited by 54 publications

(40 citation statements)

References 49 publications

(73 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…This model produces a non-ideal equation of state supporting the coexistence of a heavy phase of density ρ h and a light phase of density ρ l " [11].…”

Section: Numerical Simulations By Lattice Boltzmann Methodsmentioning

confidence: 99%

Anisotropic Wetting of Hydrophobic and Hydrophilic Surfaces–Modelling by Lattice Boltzmann Method

Kubiak¹,

Mathia²

2014

Procedia Engineering

View full text Add to dashboard Cite

Anisotropic wetting on unidirectionally textured surfaces was investigated by Lattice Boltzmann Method. Previously published experimental data were used to validate the numerical model. New analysis were carried out by changing static contact angle of grooved surfaces from hydrophilic to hydrophobic (θ s = 50 − 150 • ). Presented results suggests that anisotropic wetting on unidirectionally textured surfaces is governed by spreading along the grooves by capillary action and mainly is dominant in Wenzel state on hydrophilic surfaces. Transition to Cassie-Baxter state on hydrophobic surfaces (θ s > 90 • ) significantly reduces the effect of anisotropic wetting. Structured texture and/or chemical heterogeneity can be potentially used to manipulate droplets in case of hydrophobic surfaces.

show abstract

“…This model produces a non-ideal equation of state supporting the coexistence of a heavy phase of density ρ h and a light phase of density ρ l " [11].…”

Section: Numerical Simulations By Lattice Boltzmann Methodsmentioning

confidence: 99%

Anisotropic Wetting of Hydrophobic and Hydrophilic Surfaces–Modelling by Lattice Boltzmann Method

Kubiak¹,

Mathia²

2014

Procedia Engineering

View full text Add to dashboard Cite

show abstract

“…Unless otherwise stated, the following parameters were used in all of lattice Boltzmann simulations described in this work: G= -6, L =0.0734 H =2.65, =0.54, x=2.5x10 -6 m, t=2.86x10 -7 s. These parameters correspond to dynamic conditions of water with surface tension =0.0727 σ/m and dynamic viscosity =4.3x10 -3 Pa.s. A detailed description of this lattice Boltzmann solver may be found in [17].…”

Section: Lattice Boltzmann Methodsmentioning

confidence: 99%

Dropwise condensation heat transfer process optimisation on superhydrophobic surfaces using a multi-disciplinary approach

Khatir

Kubiak

Jimack

et al. 2016

Applied Thermal Engineering

View full text Add to dashboard Cite

Dropwise condensation has superior heat transfer efficiency than filmwise condensation; however condensate evacuation from the surface still remains a significant technological challenge. The process of droplets jumping, against adhesive forces, from a solid surface upon coalescence has been studied using both experimental and Computational Fluid Dynamics (CFD) analysis. Both Lattice Boltzmann (LBM) and Volume of Fluid (VOF) methods have been used to evaluate different kinematic conditions of coalescence inducing a jump velocity. In this paper, an optimisation framework for superhydrophobic surface designs is presented which uses experimentally verified high fidelity CFD analyses to identify optimal combinations of design features which maximise desirable characteristics such as the vertical velocity of the merged jumping droplet from the surface and energy efficiency. A Radial Basis Function (RBF)-based surrogate modelling approach using design of experiment (DOE) technique was used to establish near-optimal initial process parameters around which to focus the study. This multidisciplinary approach allows us to evaluate the jumping phenomenon for superhydrophobic surfaces for which several input parameters may be varied, so as to improve the heat transfer exchange rate on the surface during condensation. Reliable conditions were found to occur for droplets within initial radius range of r=20-40 m and static contact angle s~160º. Moreover, the jumping phenomenon was observed for droplets with initial radius of up to 500 m. Lastly, our study also reveals that a critical contact angle for droplets to jump upon coalescence is c~1 40º. KeywordsCondensation heat transfer, Super-hydrophobic surface, Jumping droplets velocity, Multi-disciplinary optimisation. IntroductionDrop-wise condensation processes, where condensation occurs through small droplets on a solid surface, has been demonstrated to significantly improve heat transfer rates in comparison to filmwise condensation (where a whole surface is covered by a thin film of liquid) [1,2]. Drop-wise condensation usually takes place on hydrophobic or super-hydrophobic surfaces as demonstrated by Boreyko and Chen [3]. One of the main technological challenges is to create such a surface, so as to allow condensation and evacuation of the droplets to take place in a continuous manner. Droplet coalescence is a complex physical phenomenon and optimisation of kinematic conditions leading to surface dewetting and jumping of droplets is of paramount importance for processes like heat transfer, de-icing, atmospheric water harvesting or dehumidification [4][5][6]. Dropwise condensation heat transfer performance can be enhanced by allowing condensed droplets to be removed rapidly from the surface to minimize the thermal barrier [7]. Recently, researchers showed that superhydrophobic surfaces provide a higher mobility of condensates, which may enhance the heat transfer performance [1][2][3][4][5][6][7]. Coalescence-induced jumping phenomena occur on superhydrophobic surfa...

show abstract

“…Note that such internal flow is not observed in the ostensibly similar experiments of Ref. [14], primarily due to higher Ohnesorge number utilized (Oh ≈ 0.25) in that work which yields a reduced influence of surface tension and much greater viscous dissipation.…”

Section: A Lateral Separationmentioning

confidence: 58%

Surface jets and internal mixing during the coalescence of impacting and sessile droplets

Sykes

Castrejón‐Pita

et al. 2020

Phys. Rev. Fluids

View full text Add to dashboard Cite

The internal dynamics during the coalescence of a sessile droplet and a subsequently deposited impacting droplet, with either identical or distinct surface tension, is studied experimentally in the regime where surface tension is dominant. Two color high-speed cameras are used to capture the rapid internal flows and associated mixing from both side and bottom views simultaneously by adding an inert dye to the impacting droplet. Given sufficient lateral separation between droplets of identical surface tension, a robust surface jet is identified on top of the coalesced droplet. Image processing shows this jet is the result of a surface flow caused by the impact inertia and an immobile contact line. By introducing surface tension differences between the coalescing droplets, the surface jet can be either enhanced or suppressed via a Marangoni flow. The influence of the initial droplet configuration and relative surface tension on the long-term dynamics and mixing efficiency, plus the implications for emerging applications such as reactive inkjet printing, are also considered. * mm13tcs@leeds.ac.uk † M.Wilson@leeds.ac.uk

show abstract

Mixing and internal dynamics of droplets impacting and coalescing on a solid surface

Cited by 54 publications

References 49 publications

Anisotropic Wetting of Hydrophobic and Hydrophilic Surfaces–Modelling by Lattice Boltzmann Method

Anisotropic Wetting of Hydrophobic and Hydrophilic Surfaces–Modelling by Lattice Boltzmann Method

Dropwise condensation heat transfer process optimisation on superhydrophobic surfaces using a multi-disciplinary approach

Surface jets and internal mixing during the coalescence of impacting and sessile droplets

Contact Info

Product

Resources

About