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Fluids
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Dynamics of Droplets and Bubbles
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Dynamics of Droplets and Bubbles

A special issue of Fluids (ISSN 2311-5521). This special issue belongs to the section "Flow of Multi-Phase Fluids and Granular Materials".

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 15277

Special Issue Editor

Dr. Hua Tan

E-Mail Website
Guest Editor
School of Engineering and Computer Science, Washington State University-Vancouver, Vancouver, WA 98686, USA
Interests: computational fluid dynamics (CFD); finite element analysis (FEA); multiphase flows; porous media flow; microfluidics; additive manufacturing; manufacturing process for fiber reinforced polymer (FRP) composites
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The droplets and bubbles are ubiquitously present in natural and engineering processes including raindrops on soil, jet droplets from breaking waves, transmission of respiratory diseases, inkjet printing, combustion, spray cooling, anti-icing, additive manufacturing, and surface coating. The dynamics of droplets and bubbles play critical roles in these processes, therefore understanding of droplet and bubble dynamics in various types of fluids is of great significance.  This Special Issue aims to gather a wide variety of papers that focus on the dynamics of droplets and bubbles. Potential topics include but are not limited to droplet deformation, rising droplets, droplet coalescences, droplet breakup, bubble collapse, droplet media interaction, droplet/bubble produced from capillary focusing phenomena, and droplet/bubble transport in microsystem.

Dr. Hua Tan
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fluids is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • droplet deformation
  • rising droplets
  • droplet coalescences
  • droplet breakup
  • bubble collapse
  • droplet media interaction
  • droplet/bubble produced from capillary focusing phenomena
  • droplet/bubble transport in microsystem

Published Papers (6 papers)

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Research

22 pages, 5552 KiB  
Article
Suitability of the VOF Approach to Model an Electrogenerated Bubble with Marangoni Micro-Convection Flow
by Florent Struyven, Zhenyi Guo, David F. Fletcher, Myeongsub (Mike) Kim, Rosalinda Inguanta, Mathieu Sellier and Philippe Mandin
Fluids 2022, 7(8), 262; https://doi.org/10.3390/fluids7080262 - 2 Aug 2022
Cited by 2 | Viewed by 1845
Abstract
When a hydrogen or oxygen bubble is created on the surface of an electrode, a micro-convective vortex flow due to the Marangoni effect is generated at the bottom of the bubble in contact with the electrode. In order to study such a phenomenon [...] Read more.
When a hydrogen or oxygen bubble is created on the surface of an electrode, a micro-convective vortex flow due to the Marangoni effect is generated at the bottom of the bubble in contact with the electrode. In order to study such a phenomenon numerically, it is necessary to be able to simulate the surface tension variations along with a liquid-gas interface, to integrate the mass transfer across the interface from the dissolved species present in the electrolyte to the gas phase, and to take into account the moving contact line. Eulerian methods seem to have the potential to solve this modeling. However, the use of the continuous surface force (CSF) model in the volume of fluid (VOF) framework is known to introduce non-physical velocities, called spurious currents. This paper presents an alternative model based on the height function (HF) approach. The use of this method limits spurious currents and makes the VOF methodology suitable for studying Marangoni currents along with the interface of an electrogenerated bubble. Full article
(This article belongs to the Special Issue Dynamics of Droplets and Bubbles)
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14 pages, 753 KiB  
Article
Quantifying Uniform Droplet Formation in Microfluidics Using Variational Mode Decomposition
by Michael Izaguirre, Luke Nearhood and Shima Parsa
Fluids 2022, 7(5), 174; https://doi.org/10.3390/fluids7050174 - 18 May 2022
Cited by 1 | Viewed by 1976
Abstract
Using variational mode decomposition, we analyze the signal from velocities at the center of the channel of a microfluidics drop-maker. We simulate the formation of water in oil droplets in a microfluidic device. To compare signals from different drop-makers, we choose the length [...] Read more.
Using variational mode decomposition, we analyze the signal from velocities at the center of the channel of a microfluidics drop-maker. We simulate the formation of water in oil droplets in a microfluidic device. To compare signals from different drop-makers, we choose the length of the water inlet in one drop-maker to be slightly shorter than the other. This small difference in length leads to the formation of satellite droplets and uncertainty in droplet uniformity in one of the drop-makers. By decomposing the velocity signal into only five intrinsic modes, we can fully separate the oscillatory and noisy parts of the velocity from an underlying average flow at the center of the channel. We show that the fifth intrinsic mode is solely sufficient to identify the uniform droplet formation while the other modes encompass the oscillations and noise. Mono-disperse droplets are formed consistently and as long as the fifth mode is a plateau with a local standard deviation of less than 0.02 for a normalized signal at the channel inlet. Spikes in the fifth mode appear, coinciding with fluctuations in the sizes of droplets. Interestingly, the spikes in the fifth mode indicate non-uniform droplet formation even for the velocities measured upstream in the water inlet in a region far before where droplets form. These results are not sensitive to the spatial resolution of the signal, as we decompose a velocity signal averaged over an area as wide as 40% of the channel width. Full article
(This article belongs to the Special Issue Dynamics of Droplets and Bubbles)
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24 pages, 2707 KiB  
Article
Improving the Performance of Surface Flow Generated by Bubble Plumes
by Hassan Abdulmouti
Fluids 2021, 6(8), 262; https://doi.org/10.3390/fluids6080262 - 21 Jul 2021
Cited by 1 | Viewed by 2001
Abstract
Gas–liquid two-phase flow is widely used in many engineering fields, and bubble dynamics is of vital importance in optimizing the engineering design and operating parameters of various adsorptive bubble systems. The characteristics of gas–liquid two-phase (e.g., bubble size, shape, velocity, and trajectory) remain [...] Read more.
Gas–liquid two-phase flow is widely used in many engineering fields, and bubble dynamics is of vital importance in optimizing the engineering design and operating parameters of various adsorptive bubble systems. The characteristics of gas–liquid two-phase (e.g., bubble size, shape, velocity, and trajectory) remain of interest because they give insight into the dynamics of the system. Bubble plumes are a transport phenomenon caused by the buoyancy of bubbles and are capable of generating large-scale convection. The surface flow generated by bubble plumes has been proposed to collect surface-floating substances (in particular, oil layers formed during large oil spills) to protect marine systems, rivers, and lakes. Furthermore, the surface flows generated by bubble plumes are important in various types of reactors, engineering processes, and industrial processes involving a free surface. The bubble parameters play an important role in generating the surface flow and eventually improving the flow performance. This paper studies the effects of temperature on bubble parameters and bubble motion to better understand the relationship between the various bubble parameters that control bubble motion and how they impact the formation of surface flow, with the ultimate goal of improving the efficiency of the generation of surface flow (i.e., rapidly generate a strong, high, and wide surface flow over the bubble-generation system), and to control the parameters of the surface flow, such as thickness, width, and velocity. Such flow depends on the gas flow rate, bubble size (mean bubble diameter), void fraction, bubble velocity, the distance between bubble generator and free surface (i.e., water height), and water temperature. The experiments were carried out to measure bubble parameters in a water column using the image visualization technique to determine their inter-relationships and improve the characteristics of surface flow. The data were obtained by processing visualized images of bubble flow structure for the different sections of the bubble regions, and the results confirm that temperature, bubble size, and gas flow rate significantly affect the flow structure and bubble parameters. Full article
(This article belongs to the Special Issue Dynamics of Droplets and Bubbles)
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27 pages, 11164 KiB  
Article
Cavitation Bubble Cloud Break-Off Mechanisms at Micro-Channels
by Paul McGinn, Daniel Pearce, Yannis Hardalupas, Alex Taylor and Konstantina Vogiatzaki
Fluids 2021, 6(6), 215; https://doi.org/10.3390/fluids6060215 - 8 Jun 2021
Cited by 5 | Viewed by 2179
Abstract
This paper provides new physical insight into the coupling between flow dynamics and cavitation bubble cloud behaviour at conditions relevant to both cavitation inception and the more complex phenomenon of flow “choking” using a multiphase compressible framework. Understanding the cavitation bubble cloud process [...] Read more.
This paper provides new physical insight into the coupling between flow dynamics and cavitation bubble cloud behaviour at conditions relevant to both cavitation inception and the more complex phenomenon of flow “choking” using a multiphase compressible framework. Understanding the cavitation bubble cloud process and the parameters that determine its break-off frequency is important for control of phenomena such as structure vibration and erosion. Initially, the role of the pressure waves in the flow development is investigated. We highlight the differences between “physical” and “artificial” numerical waves by comparing cases with different boundary and differencing schemes. We analyse in detail the prediction of the coupling of flow and cavitation dynamics in a micro-channel 20 μm high containing Diesel at pressure differences 7 MPa and 8.5 MPa, corresponding to cavitation inception and "choking" conditions respectively. The results have a very good agreement with experimental data and demonstrate that pressure wave dynamics, rather than the “re-entrant jet dynamics” suggested by previous studies, determine the characteristics of the bubble cloud dynamics under “choking” conditions. Full article
(This article belongs to the Special Issue Dynamics of Droplets and Bubbles)
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12 pages, 3070 KiB  
Article
Jet Dynamics Associated with Drop Impact on Micropillared Substrate
by Brooklyn Asai, Anayet Ullah Siddique and Hua Tan
Fluids 2021, 6(4), 155; https://doi.org/10.3390/fluids6040155 - 12 Apr 2021
Cited by 5 | Viewed by 2205
Abstract
The jetting phenomenon associated with droplet impact upon a hydrophilic micropillared substrate was analyzed in detail using a high-speed camera. Viscosities of the fluids were varied using differing concentrations of glycerol in deionized water. This paper aims to connect similarities between this form [...] Read more.
The jetting phenomenon associated with droplet impact upon a hydrophilic micropillared substrate was analyzed in detail using a high-speed camera. Viscosities of the fluids were varied using differing concentrations of glycerol in deionized water. This paper aims to connect similarities between this form of capillary jetting and another well-known jetting phenomenon from the bubble bursting. Both experience a cavity collapse when opposing fluid fronts collide which causes a singularity at the liquid surface, thus leading to the occurrence of jetting. Following processes used to define scaling laws for bubble bursting, a similar approach was taken to derive scaling laws for the dimensionless jet height, jet radius, base height, and radius of the jet base with respect to dimensionless time for the jetting phenomenon associated with the droplet impact. The development of a top droplet before the breakup of the jet also allows the examination of a scaling law for the necking diameter. We find that with the proper scaling factors, the evolution of the jet profile can collapse into a master profile for different fluids and impact velocities. The time dependence of the necking diameter before the jet breakup follows the power law with an exponent of ~2/3. Contrastingly, for other jet parameters such as the radius and height, the power law relationship with time dependence was not found to have a clear pattern that emerged from these studies. Full article
(This article belongs to the Special Issue Dynamics of Droplets and Bubbles)
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13 pages, 2358 KiB  
Article
The Lifetimes of Evaporating Sessile Droplets of Water Can Be Strongly Influenced by Thermal Effects
by Feargus G. H. Schofield, David Pritchard, Stephen K. Wilson and Khellil Sefiane
Fluids 2021, 6(4), 141; https://doi.org/10.3390/fluids6040141 - 3 Apr 2021
Cited by 7 | Viewed by 2450
Abstract
The effect of the thermal properties of the system on the lifetime of an evaporating sessile droplet of water is analysed using a fully coupled model which involves determining the temperature of the droplet, the substrate and the atmosphere. The evolutions, and hence [...] Read more.
The effect of the thermal properties of the system on the lifetime of an evaporating sessile droplet of water is analysed using a fully coupled model which involves determining the temperature of the droplet, the substrate and the atmosphere. The evolutions, and hence the lifetimes, of droplets of water evaporating in both of the extreme modes are calculated. In particular, it is shown how the lifetimes of droplets of water can be strongly influenced by thermal effects. Droplets with larger initial contact angles or on less conductive substrates generally have longer lifetimes than those with smaller initial contact angles or on more conductive substrates, and the physical mechanism by which the thermal properties of the system influence the evaporation can be understood in terms of the thermal anchoring between the droplet and the lower surface of the substrate. Full article
(This article belongs to the Special Issue Dynamics of Droplets and Bubbles)
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