Magneto-Elastic Effect in Non-Newtonian Ferrofluid Droplets Impacting Superhydrophobic Surfaces

Prasad, Gudlavalleti V V S Vara; Dhar, Purbarun; Samanta, Devranjan

doi:10.1021/acs.langmuir.1c00885

Cited by 11 publications

(9 citation statements)

References 36 publications

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“…A height-alterable droplet dispenser coupled with a digitized controller unit has been used to generate and release the droplets from different heights. As similar to our previous studies, , we have performed experiments at different Weber numbers ( ), i.e., the ratio of inertial forces to surface tension forces, and Ohnesorge numbers ( ) i.e., the ratio of viscous forces to both inertial and capillary forces, where ρ, U , D o , and σ represent the density, impact velocity, preimpact droplet diameter, and surface tension of the fluid, respectively. The Reynolds number is denoted as Re in the definition of the Ohnesorge number.…”

Section: Methodsmentioning

confidence: 95%

Augmenting the Leidenfrost Temperature of Droplets via Nanobubble Dispersion

et al. 2022

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Droplets may rebound/levitate when deposited over a hot substrate (beyond a critical temperature) due to the formation of a stable vapor microcushion between the droplet and the substrate. This is known as the Leidenfrost phenomenon. In this article, we experimentally allow droplets to impact the hot surface with a certain velocity, and the temperature at which droplets show the onset of rebound with minimal spraying is known as the dynamic Leidenfrost temperature (T DL ). Here we propose and validate a novel paradigm of augmenting the T DL by employing droplets with stable nanobubbles dispersed in the fluid. In this first-of-itskind report, we show that the T DL can be delayed significantly by the aid of nanobubble-dispersed droplets. We explore the influence of the impact Weber number (We), the Ohnesorge number (Oh), and the role of nanobubble concentration on the T DL . At a fixed impact velocity, the T DL was noted to increase with the increase in nanobubble concentration and decrease with an increase in impact velocity for a particular nanobubble concentration. Finally, we elucidated the overall boiling behaviors of nanobubble-dispersed fluid droplets with the substrate temperature in the range of 150− 400 °C against varied impact We through a detailed phase map. These findings may be useful for further exploration of the use of nanobubble-dispersed fluids in high heat flux and high-temperature-related problems and devices.

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Section: Methodsmentioning

confidence: 95%

Augmenting the Leidenfrost Temperature of Droplets via Nanobubble Dispersion

et al. 2022

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“…Ferrofluid has demonstrated a wide range of studies, including encapsulation, mixing, droplet manipulation, evaporation, and cell sorting . The impact dynamics of magnetic droplets on a nonmagnetic substrate is widely studied in the literature, which involves the effect of magnetic field on the dynamics of droplet spreading and postimpact self-assembly. − In this regard, Shyam et al have studied the impact dynamics of a water-based ferrofluid on PDMS substrate. It is found that upon impact, the ferrofluid droplet undergoes Rosensweig instability and exhibits several regimes of equilibrium configurations .…”

Section: Introductionmentioning

confidence: 99%

Magnetic Control of Water Droplet Impact onto Ferrofluid Lubricated Surfaces

2023

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Controlling the impact process of a droplet impacting a liquid film has remained a wide-open challenge. The existing passive techniques lack precise on-demand control of the impact dynamics of droplets. The present study introduces a magnet-assisted approach to control water droplets’ impact dynamics. We show that by incorporating a thin, magnetically active ferrofluid film, the overall droplet impact phenomena of the water droplets could be controlled. It is found that by modifying the distribution of the magnetic nanoparticles (MNPs) present inside the ferrofluid using a permanent magnet, the spreading and retraction behavior of the droplet could be significantly controlled. In addition to that, we also show that by altering the impact Weber number (We i), and the magnetic Bond number (Bo m), the outcomes of droplet impact could be precisely controlled. We reveal the role of the various forces on the consequential effects of droplet impact with the help of phase maps. Without the magnetic field, we discovered that the droplet impact on ferrofluid film results in no-splitting, jetting, and splashing regimes. On the other hand, the presence of magnetic field results in the no-splitting and jetting regime. However, beyond a critical magnetic field, the ferrofluid film gets transformed into an assembly of spikes. In such scenarios, the droplet impact only results in no-splitting and splashing regimes, while the jetting regime remains absent. The outcome of our study may find potential applications in chemical engineering, material synthesis, and three-dimensional (3D) printing where the control and optimization of the droplet impact process are desirable.

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“…The impact hydrodynamics of liquid droplets, Newtonian fluids or otherwise, on different surfaces in the presence of external electric or magnetic fields [1] has great importance in many applications, such as inkjet printing [2], ferrohydrodynamic three-dimensional inkjet printing [3], magnetic drug targeting in microfluidic applications [4], spray painting, spray cooling [5], controlling the liquid metal droplet deposition during welding or soldering [6], electrohydrodynamic (EHD) droplet-on-demand inkjet printing [7], electro spraying [8,9], electrowetting [10] electrohydrodynamic jet (E-jet) [11] printing and so forth.…”

Section: Introductionmentioning

confidence: 99%

Triggering of electro-elastic anti-superhydrophobicity during non-Newtonian droplet collision

2023

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The present article discusses the electrohydro-dynamics of impacting non-Newtonian dielectric droplets on superhydrophobic (SH) surfaces. The role of important parameters like electric Eotvos number ( Eo e ), Weber number ( We ), dielectric particle concentration ( TiO 2 ) and polymer concentration ( PEG-400 ) were elucidated in this experimental study. Due to the interplay of non-Newtonian effects and electric field, we had observed the suppression of drop rebound on SH surfaces at much lower Eo e compared to its Newtonian counterpart. It has been observed that with an increase in both polymer concentration or dielectric particle concentration, the suppression of drop rebounds was observed at lower Eo e. In order to encapsulate the combined effects of electric field and non-Newtonian dynamics on drop rebound suppression, we have introduced the ‘electro-elastic effect’. Contrary to the common observations of drop rebound on SH surfaces, this electro-elastic effect induces inhibition of drop rebound, thereby resulting in anti-superhydrophobicity. Subsequently, we also established a scaling relationship to show that the rebound suppression is observed as a manifestation of the onset of electro-elastic instability, when a proposed electric Weissenberg number ( Wi e ) exceeds unity. Finally, we demarcated the rebound and rebound suppression regimes of droplet dynamics through a detailed phase map.

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Magneto-Elastic Effect in Non-Newtonian Ferrofluid Droplets Impacting Superhydrophobic Surfaces

Cited by 11 publications

References 36 publications

Augmenting the Leidenfrost Temperature of Droplets via Nanobubble Dispersion

Augmenting the Leidenfrost Temperature of Droplets via Nanobubble Dispersion

Magnetic Control of Water Droplet Impact onto Ferrofluid Lubricated Surfaces

Triggering of electro-elastic anti-superhydrophobicity during non-Newtonian droplet collision

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