Arrangement Of Bubbles Research Articles

Micromixer driven by bubble-induced acoustic microstreaming for multi-ink 3D bioprinting.

Recently, the 3D printing of cell-laden hydrogel structures, known as bioprinting, has received increasing attention owing to advances in tissue engineering and drug screening. However, a micromixing technology that efficiently mixes viscous bioinks under mild conditions is needed. Therefore, this study presents a novel method for achieving homogeneous mixing of multiple inks in 3D bioprinting through acoustic stimulation. This technique involves generating an acoustic microstream through bubble oscillations inside a 3D bioprinting nozzle. We determined the optimal hole design for trapping a bubble, hole arrangement, and voltage for efficient mixing, resulting in a four-fold increase in mixing efficiency compared to a single bubble arrangement. Subsequently, we propose a nozzle design for efficient mixing during bioprinting. The proposed nozzle design enabled the successful printing of line structures with a uniform mixture of different viscous bioinks, achieving a mixing efficiency of over 80% for mixing 0.5-1.0 wt% sodium alginate aqueous solutions. Additionally, acoustic stimulation had no adverse effects on cell viability, maintaining a high cell viability of 88% after extrusion. This study presents the first use of a bubble micromixer in 3D bioprinting, demonstrating gentle yet effective multi-ink mixing. We believe this approach will broaden 3D printing applications, particularly for constructing functional structures in 3D bioprinting.

Interpretation of Chemical Compositions and Making Techniques for Ancient Glass Beads from Suchonri Tomb Complex in Gongju, Korea

The Suchonri tomb complex in Uidang of Gongju has been excavated several times, and the remains and artifacts from various periods have been unearthed. Tomb No. 8, known as a Baekje Kingdom, collected a large quantity of blue-colored glass beads, quartz bead and gold-gilded glass beads. In this study, we analyzed the occurrences, internal textures and chemical compositions of representative glass beads, and interpreted the making techniques based on the study. As a result, quartz bead, which are different from glass, were confirmed, and the glass beads were classified into potassium, sodium and gold-gilded beads. The internal texture of the glass beads contained a mixture of bubbles and unmelted additives. The additives consisted of fluxes, stabilizers and colorants compositions, and were observed in various crystals and shapes. Based on internal textures, arrangement of bubbles and shape of impurities within the glass beads, it seems that various making techniques such as the winding, the drawing and the molding methods were applied. In this way, the glass beads used in a single location have slightly different characteristics suggests the diversity of the manufacturing site, materials used and producers, as well as the possibility of external introduction. It can also be interpreted that the beads were likely procured and assembled for the funeral rites to serve the purpose of the interred individual.

Study on the violent splitting and coalescence characteristics of large-scale rising bubbles

Large-scale rising bubbles exist in some extreme marine engineering fields, such as the exploitation of combustible ice and submarine volcanism. The violent splitting and coalescence process of large-scale rising bubbles with internal pressure comparable to ambient pressure differs greatly from that of the normal small-scale bubbles and high-pressure bubbles. In this paper, the complex splitting and coalescence characteristics of large-scale rising bubbles are studied with a multi-phase smoothed particle hydrodynamics approach. The effects of the arrangement of bubbles, initial centroid distance, and the ratios of bubble radii on the bubble splitting and coalescence characteristics are investigated. The results show that the arrangement of the bubbles dictates whether or not the two bubbles coalesce and influences the coalescence mode of the bubbles further. When two large-scale bubbles are arranged horizontally, the initial spacing of bubbles has minimal influence on the coalescence features, and they always bounce off each other. When the bubbles are not placed horizontally, the bubbles can coalesce in two modes: direct-absorption coalescence and penetrating reverse-absorption coalescence. When arranged vertically, the initial centroid distance affects the coalescence extent of bubbles, and when the vertical distance exceeds five times the bubble radius, the two bubbles do not interact with each other. When the leading bubble is too large relative to the trailing bubble, the large ratios of bubble radii play negative roles in the coalescence of bubbles.

Mothers, Household Bubbles, and Social Support During the First Wave of the COVID-19 Pandemic

Parents of young children experienced many stressors due to stay-at-home directives in the first wave of the COVID-19 pandemic. Bubbles were implemented by some governments, allowing households to connect with another household while minimizing contagion risk, but little is known about their effectiveness. We explored the social support experiences of Canadian mothers living in Nova Scotia during this first wave, focusing on whether they perceived household bubbles to be helpful in reducing parenting stress. In-depth interviews were completed with 18 mothers (aged 21–49) who had at least one child under the age of 12 during the first shutdown. Interviews focused on how they coped during the initial shutdown period, the immediate time after they paired up with another household, and what was happening for them currently (approximately eight to ten months later). Data were analyzed using qualitative description and content analysis through application of topic, descriptive, and analytical coding; memo writing; and matrix analysis. Deciding who to bubble with typically focused on direct support for parents or having playmates for children. Having a bubble arrangement reduced the pressure of the situation, and perceptions of future emergency backup support also reduced anxiety levels. Support from family members who lived far away, however, was still key for some families. Household bubbles play an important role in reducing stress levels during a pandemic through received and perceived support. As the COVID-19 pandemic evolves, policy directives and support interventions need to enhance social support for parents and peer interactions for young children.

Numerical investigations on the effect of bubble injection on heat transfer of natural convection in laminar flows

AbstractIt was found that the injection of bubbles into liquid can effectively improve heat transfer efficiency, so it is important for industrial applications to investigate the effect of bubble injection on heat transfer. The effect of bubble injection on natural convective heat transfer in steady laminar flows in a vertical channel is investigated using the volume of fluid (VOF) method, and the effects of bubble diameter, Eötvös number (Eo), bubble arrangement, and bubble distance from a hot wall on the heat transfer between the hot wall and liquid are studied, respectively. The results show that bubble injection can effectively improve the heat transfer between the hot wall and liquid; an increase in bubble diameter and Eo can improve the enhancement effect of heat transfer and can expand the enhancement area of heat transfer; the closer to the hot wall a bubble is, the better the enhancement of heat transfer is; and the spacing and arrangement of bubbles also have important effects on the heat transfer between the hot wall and liquid. The comparison shows that the enhancement of heat transfer is the best for the vertical arrangement of double bubbles, which increases the local heat transfer coefficient by 3.2 times. The enhancement of heat transfer generated by bubble injection is related to the degree of disturbance of the local liquid phase caused by bubble injection. The more strongly the local liquid is disturbed, the thinner the local temperature boundary layer becomes, and the better the enhancement of heat transfer is.

Numerical Investigation on Effect of Bubbles Arrangement and Volume Fraction on Apparent Viscosity of Bubbly Suspensions

Background:: Bubbly suspensions can be often run into in natural and industrial processes. The addition of bubbles with different sizes can lead to a significant change in the rheological properties of a matrix liquid. It is extremely significant to fully understand the rheological properties of bubbly suspensions for improving process efficiencies and optimizing productive processes. background: Bubbly suspensions can be often run into in natural and industrial processes. The addition of bubbles of different sizes can greatly change the rheological properties of matrix liquid. It is extremely significant to fully understand the rheological properties of bubbly suspensions for improving process efficiencies and optimizing productive processes. Objective:: The objective of this study is to explore qualitatively the physical law and internal mechanism of the apparent viscosity of suspensions formed by a Newtonian liquid containing different bubbles. Methods:: Based on the parallel plate model of shear flow, the volume of fluid method (VOF) was used to investigate the effect of bubble arrangement and volume fraction on the apparent viscosity of bubbly suspensions at low volume fractions. The piecewise linear interface calculation (PLIC) method was applied to reconstruct the interface based on the phase function. Results:: The present results show that the relative viscosity (ηr) of bubbly suspensions shows a nonlinear change with an increase in bubble volume fraction (ϕ). When the capillary number (Ca) is less than 0.6, ηr shows a nonlinear increase with an increase in ϕ (ηr increases from 1 to 1.03 with an increase in ϕ from 0 to 2.94% at Ca=0.1). However, Ca is greater than or equal to 0.6, ηr shows a nonlinear decrease with an increase in ϕ (ηr decreases from 1 to 0.92 with an increase in ϕ from 0 to 2.94% at Ca=2.5). Even if ϕ is the same, different arrangements of bubbles can lead to different magnitudes of apparent viscosity of bubbly suspensions Conclusion:: As ϕ increases, the region of low shear rate increases, which leads to a non−linear decrease in the relative viscosity. When ϕ is the same, the different arrangements of bubbles can lead to different effects on bubble dynamics and flow fields. This results in different viscous dissipation in bubbly suspensions. Thus, the apparent viscosity of bubbly suspensions is different. other: Nothing

TRAVEL BUBBLE POLICY IN INDONESIA: OPPORTUNITIES AND CHALLENGES

The COVID-19 pandemic has hurt the world economy. The tourism industry of Indonesia was the most sector affected by the air travel restrictions policy during the COVID-19 era. After the first wave of COVID-19 moved slowly, several countries began to think about how to recover their economy through travel arrangements. The term travel bubble is increasingly popular to revive the economy through cooperation in the tourism sector between countries. Indonesia has launched travel bubble arrangement in Batam and Bintan with Singapore in January, 2022. This study aims to analyze the opportunities and challenges of the Travel Bubble policy in Indonesia. Data collection techniques used secondary data such as documentation and literature study. Data analysis was carried out in three stages, namely condensing data, displaying data, verifying data, and drawing conclusions. The results of this study are opportunities and challenges related to the application of the travel bubble in Indonesia. The opportunities are (1) travel bubble able to increase tourism activities, (2) travel bubble has had success in island-based countries, (3) travel bubble procedure suitable to be tested and adopted, and (4) as momentum for cooperation with neighboring countries. Then the challenges are (1) public sentiment related to the increase in covid cases, (2) there are travel anxiety to travel to Indonesia rank in transmission COVID-19 cases, (3) the opinion of epidemiologists regarding the variants and waves of covid, and (4) the difficulty of collaborating with neighboring countries.
 Keywords: travel bubble, tourism, foreign tourists, economic recovery.

Analysis of bubble dynamics and thermal destratification induced by gas bubbles in cylindrical liquid storage tanks

• OpenFOAM code is modified to incorporate temperature-dependent transport properties. • A new parameter to estimate the extent of the destratification is introduced. • The destratification index increased by 25.29% as the diameter ratio is increased. • Bubble in square pitch with p/d =4 gives higher effectiveness for thermal destratification. • The destratification index increased by 44.65% as the gravity ratio is increased. Thermal stratification is of great concern for liquid propellant storage tanks of space vehicles. The present study's primary objective is to better understand the bubble dynamics on thermal destratification, quantify the extent of destratification and propose a scheme for destratification. This study investigates the effect of different geometric parameters on the destratification of thermally stratified layers of liquid using the volume of fluid and interface compression method of OpenFOAM CFD code. The OpenFOAM code is modified to incorporate temperature-dependent fluid properties. Different values of bubble diameter, spacing between the bubbles, and arrangement of bubbles in triangular and square fashion with different pitches are considered. The effect of gravitational forces on thermal destratification is also reported. For all these cases, the effectiveness of thermal destratification is quantified in terms of the destratification index ( I d ). The average destratification index ( I davg ) value increased by 25.29% as the ratio of bubble diameter to tank diameter ( d/D ) increased from 0.10 to 0.16. When the pitch to bubble diameter ratio ( p/d ) of triangular and square arrangements is reduced from 8 to 4, the I davg increases by 14.59% and 22.97%, respectively. The average destratification index increased by 44.65% when the g/g e ratio changed from 0.3 to 3. These studies give an overall idea of the sparger design for getting the correct gas flow rate for thermal destratification within the liquid propellant storage tanks.

Role of Contamination in Optimal Droplet Production by Collective Bubble Bursting

AbstractGas bubbles bursting at the sea surface produce drops, which contribute to marine aerosols. The contamination or enrichment of water by surface‐active agents, of biological or anthropogenic origin, has long been recognized as affecting the bubble bursting processes and the spray composition. However, despite an improved understanding of the physics of a single bursting event, a quantitative understanding of the role of the physico‐chemical conditions on assemblies of bursting bubbles remains elusive. We present experiments on the drop production by millimetric, collective bursting bubbles, under varying surfactant concentration and bubble density. We demonstrate that the production of supermicron droplets (with radius larger than 35 μm) is non‐monotonic as the surfactant concentration increases. The bursting efficiency is optimal for short‐lived, sparsely distributed and non‐coalescing bubbles. We identify the combined role of contamination on the surface bubble arrangement and the modification of the jet drop production process in the bursting efficiency.

Droplet size distributions in cryogenic flash atomization

Flash atomization can occur in rocket thrusters operated at near vaccum conditions just prior to ignition when cryogenic propellants are injected into the reaction chamber. Although the morphology of flashing sprays has been widely studied, empirical observations of the primary breakup mechanisms at the micro-scale are currently not feasible. Still, further analysis of the micro-scales is necessary for development of closure models in both empirical and numerical models. In this work direct numerical simulations are performed to provide insight into the microscopic processes that dominate the dynamics of the primary atomization. We use a multiphase solver (FS3D) based on the volume of fluid method and PLIC reconstruction to track the liquid-vapour interface with high fidelity, fully resolving viscous and capillary effects. Thermodynamic effects are introduced by calibration of the fluid properties and evaporation rate to a target range of thermodynamic conditions and nuclei number density. The use of an affordable incompressible scheme allows for highly resolved simulations comprising up to thousand bubbles across a range of Weber and Ohnesorge numbers. Using a randomized bubble arrangement it is generally observed that the qualitative characterization of the breakup dynamics corroborates previous results using regular bubble arrays. However, these differ substantially from the simplified mechanics hypothesised in the literature. A temporal analysis of the breakup provides estimates for the rate of change in the spray surface area and volume fraction. The droplet size distributions are compared in terms of droplet number, surface area and volume fraction. A model based on the thermodynamic conditions is proposed to estimate the SMD for different Weber numbers.

Symmetry break in the eight bubble compaction

Geometry and mechanics have both a relevant role in determining the three-dimensional packing of $ 8 $ bubbles displayed in a similar foam structure. We assume that the spatial arrangement of bubbles obeys a geometrical principle maximizing the minimum mutual distance between the bubble centroids. The compacted structure is then obtained by radially packing the bubbles under constraint of volume conservation. We generate a polygonal tiling on the central sphere and peripheral bubbles with both flat and curved interfaces. We verify that the obtained polyhedra is optimal under suitable physical criteria. Finally, we enforce the mechanical balance imposing the constraint of conservation of volume.We find an anisotropy in the distribution of the field of forces: surface tensions of bubble-bubble interfaces with normal oriented in the circumferential direction of bubbles aggregate are larger than the ones with normal unit vector pointing radially out of the aggregate. We suggest that this mechanical cue is key for the symmetry break of this bubbles configuration.

Scattering of acoustic waves by a nonlinear resonant bubbly screen

Abstract

Dynamics of bubbles in cavitation cloud based on lattice model

A lattice model is introduced to deal with the dynamics of bubbles in cavitation cloud driven by ultrasound, which makes it possible to extend the study of a finite number of bubbles to cloud with an infinite number of bubbles. In this model, the arrangement of bubbles in cloud is assumed to be a cubic lattice. The central bubble in one lattice cell is representative of all the bubbles in cloud. The numerical simulation shows that the bubble in cloud can be severely suppressed by other bubbles under a cubic lattice structure. An interesting phenomenon is found that the maximum radius of bubbles would be saturated when the driving amplitude exceeds a threshold in cavitation cloud, which makes it easy to understand that the sonoluminescence in a single bubble is always brighter than that in cloud.

A study of the collapse speed of bubble clusters

The collapse process of bubble cluster is closely related to bubble–bubble interaction. Theoretical analysis and numerical simulation are adopted to study the collapse of bubble cluster with various distributions. The key parameters for bubble collapse, including bubble quantity, volume fraction, and dimensionless pressure, are acquired by dimensional analysis. The effects of key parameters on collapse of bubble cluster are investigated by direct numerical simulation. The numerical result shows that the collapsing speed of bubble cluster increases with the increase of bubble quantity and dimensionless pressure, decreases with the increase of volume fraction. A condensation rate is considered on the basis of bubble cluster with primitive cubic distributions. Square pyramid arrangement and random arrangement of bubbles are also simulated. A parameter study of the dimensionless bubble distance bubble cluster with random arrangement shows that a larger distance generally results in a larger collapse speed of bubble cluster.

Analysis of bubble formation during injection molding of polymeric foams by computational fluid dynamics simulations

AbstractFoam injection molding processes have received special attention in polymer industry. The size distribution of bubbles is an important parameter on the molding piece, which depends on the characteristics of the blowing process. This work proposes a computational fluid dynamics (CFD) methodology to analyze the formation and distribution of bubbles in a foamed polymer piece. The birth, coalescence, and breakup of bubbles during the filling process were included and related to the azodicarbonamide (ACA) decomposition. The results agree with experimental data and allow the prediction of shape, location, and predominant size of bubbles. The proposed methodology could also be used to study arrangements of bubbles in more complex geometries, which are directly related to the mechanical properties of the piece.

Periodic Trends in Two-Phase Flow Through a Vertical Minichannel: Wavelet and Multiscale Entropy Analyses Based on Digital Camera Data

Abstract By changing the air and water flow relative rates in the two-phase (air-water) flow through a minichannel, we observe aggregation and partitioning of air bubbles and slugs of different sizes. An air bubble arrangement, which show non-periodic and periodic patterns. The spatiotemporal behaviour was recorded by a digital camera. Multiscale entropy analysis is a method of measuring the time series complexity. The main aim of the paper was testing the possibility of implementation of multiscale entropy for two-phase flow patterns classification. For better understanding, the dynamics of the two-phase flow patterns inside the minichannel histograms and wavelet methods were also used. In particular, we found a clear distinction between bubbles and slugs formations in terms of multiscale entropy. On the other hand, the intermediate region was effected by appearance of both forms in non-periodic and periodic sequences. The preliminary results were confirmed by using histograms and wavelets.

Estimation of effective thermal conductivity in U-10Mo fuels with distributed xenon gas bubbles

We simulate the influence of distributed xenon gas bubbles on the effective thermal conductivity of irradiated U-10Mo fuel using a two-dimensional finite element method (FEM). The effective thermal conductivity of the inhomogeneous materials is estimated by solving the heat equation on a two-dimensional domain and estimating the mean temperature and heat flux. Bubble size distributions representative of both intra- and inter-granular fission gas bubbles are simulated. A distribution consistent with a gas bubble superlattice is compared to less-ordered bubble distributions in the intra-granular case. For inter-granular bubbles, the bubbles' spatial and size distribution was estimated from a two-dimensional scanning electron microscopy (SEM) image of fission gas bubbles that had collected on grain boundaries. The obtained results are compared with some theoretical models and experimental results. The results indicate that the pressure inside the bubbles has minimal influence on the overall thermal conductivity. The effect of krypton concentration is also negligible compared to pure xenon bubbles. Bubble arrangement is also insignificant unless a relatively wide bubble-free path through the metal exists. However, the area fraction of xenon bubbles has a significant impact on the overall thermal conductivity.

A Phononic Crystal-Based High Frequency Rheometer

Dynamic Mechanical Analysis (DMA) allows for the measurement of the complex shear modulus of an elastomer. Measurements at frequencies above the frequency range of the device can be reached thanks to the Time–Temperature Equivalence principle. Yet, frequencies higher than a few kHz are not attainable. Here, we propose a method exploiting the physics of bubble phononic crystals to measure the complex shear modulus at frequencies of a few tens of kHz. The idea is to fabricate a phononic crystal by creating a period arrangement of bubbles in the elastomer of interest, here PolyDiMethylSiloxane (PDMS), and to measure its transmission against frequency. Fitting the results with an analytic model provides both the loss and storage moduli. Physically, the shear storage modulus drives the position of the dip observed in transmission while the loss modulus controls the damping, and thus the level of transmission. Using this method, we are able to compare the high-frequency rheological properties of two commercial PDMS and to monitor the ageing process.

Subwavelength Localized Modes for Acoustic Waves in Bubbly Crystals with a Defect

The ability to control wave propagation is of fundamental interest in many areas of physics. Photonic and phononic crystals have proved very useful for this purpose but, because they are based on Bragg interference, these artificial media require structures with large dimensions. In [Ammari et al., Subwavelength phononic bandgap opening in bubbly media, J. Diff. Eq., 263 (2017), 5610--5629], it has been proved that a subwavelength bandgap opening occurs in bubbly phononic crystals. To demonstrate the opening of a subwavelength phononic bandgap, a periodic arrangement of bubbles is considered and their subwavelength Minnaert resonance is exploited. In this paper, this subwavelength bandgap is used to demonstrate cavities, very similar to those obtained in photonic and phononic crystals, albeit of deeply subwavelength dimensions. The key idea is to perturb the size of a single bubble inside the crystal, thus creating a defect. The goal is then to analytically and numerically show that this crystal has a localized eigenmode close to the defect bubble.

Long‐Lived Foams Stabilized by a Hydrophobic Dipeptide Hydrogel

A hydrogel of hydrophobic dipeptides can be used to create a wet foam with long‐term stability. The dipeptide molecules self‐assemble into fiber‐like networks (due to the presence of metal ions) both at air–water interfaces and in the continuous phase. The former creates an interfacial film stabilizing the air bubbles while the latter forms a bulk gel, which prevents bubble movement and retards growth. If the storage modulus (G′) of the bulk hydrogel is sufficiently high it can stop the coarsening of the air bubbles and thus dramatically improve the stability of the foam. Cryogenic scanning electron microscopy and Raman spectra reveals the width of the fibers (200 nm) and that they are held together by hydrogen bonds. In the absence of bubbles, phase separation is observed between a hydrogel and a water‐rich phase; in the foam this can be suppressed provided that the concentration of dipeptides and metal ions are sufficiently high. It is speculated that the resistance of the bubble arrangement to compaction and hence further drainage arrests the process of phase separation. This foam system has the advantages of long stability, low cost, as well as easy preparation; therefore, it has potential applications in food manufacturing, drug delivery, and personal care industries.