Experimental study of droplet shedding on laser-patterned substrates

Moghtadernejad, Sara; Jadidi, Majid; Ahmmed, K. M. Tanvir; Lee, Christian; Dolatabadi, Ali; Kietzig, Anne‐Marie

doi:10.1063/1.5126048

Cited by 19 publications

(7 citation statements)

References 45 publications

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“…Furthermore, air shear flow has a significant influence on the impact, splashing, and coalescence dynamics. The effect of air shear flow on a single droplet's dynamics on a surface has been reported in [33,34] for different wettability conditions.…”

Section: Modes Of Droplet Transportmentioning

confidence: 99%

Droplet Dynamics on a Wettability Patterned Surface during Spray Impact

et al. 2021

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Wettability patterning of a surface is a passive method to manipulate the flow and heat transport mechanism in many physical processes and industrial applications. This paper proposes a rational wettability pattern comprised of multiple superhydrophilic wedges on a superhydrophobic background, which can continuously remove the impacted spray droplets from the horizontal surface. We observed that the spray droplets falling on the superhydrophilic wedge region spread and form a thin liquid film, which is passively transported away from the surface. However, most of the droplets falling on the superhydrophobic region move towards the wedge without any flooding. The physics of the passive transport of the liquid film on a wedge is also delved into using numerical modelling. In particular, we elucidate the different modes of droplet transport in the superhydrophobic region and the interaction of multiple droplets. The observed droplet dynamics could have profound implications in spray cooling systems and passive removal of liquid from a horizontal surface. This study’s findings will be beneficial for the optimization of efficient wettability patterned surfaces for spray cooling application.

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Section: Modes Of Droplet Transportmentioning

confidence: 99%

Droplet Dynamics on a Wettability Patterned Surface during Spray Impact

et al. 2021

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“…For the low air speed of 5 m/s, the coalescence of droplets resulted in successive rebounds of the merged droplet on the substrate. In another study by Moghtadernejad et al, 8 they also evaluated the effect of air shear flow on different liquid properties depositing on a lasermicromachined surface with superhydrophobic properties substrates. They observed that droplet dynamics are affected by both surface tension and viscosity properties.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Mobility of sessile droplets occurs when there is an imbalance in droplet contact line forces. This might be attributed to the conditions in which there is a thermal gradient, air shear flow, , mechanical vibration, and electrowetting . Among mobility-driven forces, the air shear flow scenario has attracted significant attention in various natural and industrial applications.…”

Section: Introductionmentioning

confidence: 99%

“…Droplet incipient movement occurs when the drag force (due to air shear flow) overcomes the adhesion force between the droplet and the substrate. The drag force and adhesion force are illustrated as F drag ∝ (1/2)ρ l V air 2 SC D and F adh ∝ L w σ(cos θ min – cos θ max ) , where ρ l , V air , S , and C D are the droplet density, air speed, front area of the droplet facing the airflow, and drag coefficient, respectively. L w and σ are the droplet-wetting length and surface tension coefficient.…”

Section: Introductionmentioning

confidence: 99%

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Droplet Mobility on Slippery Lubricant Impregnated and Superhydrophobic Surfaces under the Effect of Air Shear Flow

et al. 2021

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The focus of this study is to investigate and compare the behavior of a droplet on superhydrophobic (SHS) and slippery lubricant impregnated (SLIPS) surfaces under the effect of air shear flow. In this regard, both experimental and numerical analyses have been conducted to compare their performance on droplet mobility under different air speeds. Two different lubricants have been utilized to scrutinize their effect on droplet movement. The numerical simulations have been performed based on the volume of fluid method coupled with the large eddy simulation turbulent model in conjunction with the dynamic contact angle method in addition to a model that can represent the effect of lubricants on slippery surfaces. The numerical simulations are compared with the experimental study in order to shed light on the underlying mechanisms. The results showed that under the same conditions, the critical velocity for droplet movement on the superhydrophobic surfaces is lower than that on the slippery lubricant impregnated surfaces due to the smaller droplet base diameter and the larger contact angle. The hydrodynamics of droplet mobility on superhydrophobic surfaces exhibits a rolling behavior while for the slippery lubricant impregnated surfaces a combination of rolling and sliding is observed. Beyond the critical airflow speed, a complete droplet shedding on all surfaces occurs. The wetting length and position of the droplet on superhydrophobic and slippery surfaces have been measured. On slippery surfaces, the speed of droplets is greatly affected by the lubricant properties while similar behavior in the wetting lengths is observed.

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“…More specifically, static and dynamic interactions of water with surface can occur that induce hydrolysis, erosion, and icing, which ultimately lead to premature or catastrophic failure of structural parts over time 13–18 . In particular, big droplets or jets, create small satellite droplets that are combined with high water‐hammer pressure, and are responsible for severe erosion wear and eventual destruction of surfaces 19,20 . Besides, in cold regions ice is accumulated on the surface of structures such as aircraft wings, and wind turbine blades due to rain droplets impact on these components.…”

Section: Introductionmentioning

confidence: 99%

Effect of thermo‐oxidative aging on surface characteristics of benzoxazine and epoxy copolymer

Moghtadernejad

Barjasteh

Johnson

et al. 2020

J of Applied Polymer Sci

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The copolymer of bisphenol A‐based benzoxazine and cycloaliphatic epoxy resin possesses greater processability and glass‐transition temperature compared to that of benzoxazine homopolymer, making it suitable for high‐temperature aerospace applications. The aim of this work is to investigate the behavior of the copolymers under thermos‐oxidative aging conditions using the surface characterization techniques. The benzoxazine homopolymer and copolymer samples were thermally aged in an air‐circulating oven under controlled temperatures of 180 and 200°C for various periods of time up to 24 weeks. The thermo‐oxidative‐induced weight change and surface cracking were monitored for samples during the aging period. As an alternative method to characterize thermal aging, static contact angle, and contact angle hysteresis of samples were measured over time. Moreover, droplet impact tests using deionized water were performed on stationary and moving samples to investigate the effects of aging time and temperature on impact dynamics of droplets. In addition, FTIR analysis was performed to evaluate the chemical changes on the surface of samples. The results indicated the extent of degradation of aged samples increased with increasing the aging time and temperature. In addition, the copolymer of cycloaliphatic epoxy and benzoxazine showed a greater amount of thermos‐oxidative degradation than the one for benzoxazine homopolymer. More importantly, the results obtained from the surface analysis measurements (e.g., contact angle) followed a similar trend to the one obtained from the traditional aging experiments (e.g., weight change). This showed the former nondestructive and simple method can be used to monitor thermal aging of materials in service.

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Experimental study of droplet shedding on laser-patterned substrates

Cited by 19 publications

References 45 publications

Droplet Dynamics on a Wettability Patterned Surface during Spray Impact

Droplet Dynamics on a Wettability Patterned Surface during Spray Impact

Droplet Mobility on Slippery Lubricant Impregnated and Superhydrophobic Surfaces under the Effect of Air Shear Flow

Effect of thermo‐oxidative aging on surface characteristics of benzoxazine and epoxy copolymer

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