Showing papers on "Bubble published in 2020"
29 Sep 2020
TL;DR: Wang et al. as mentioned in this paper studied implicit knowledge in industrial Internet of things (IIoT) by using collaborative learning techniques, considering the increased dimensions and dynamics of IoT devices, and explored the possible relationships between users and between APIs.
Abstract: The industrial Internet of things (IIoT), a new computing mode in Industry 4.0, is deployed to connect IoT devices and use communication technology to respond to control commands and handle industrial data. IIoT is typically employed to improve the efficiency of computing and sensing and can be used in many scenarios, such as intelligent manufacturing and video surveillance. To build an IIoT system, we need a collection of software to manage and monitor each system component when there are large-scale devices. Application programming interface (API) is an effective way to invoke public services provided by different platforms. Developers can invoke different APIs to operate IoT devices without knowing the implementation process. We can design a workflow to configure how and when to invoke target APIs. Thus, APIs are a powerful tool for rapidly developing industrial systems. However, the increasing number of APIs exacerbates the problem of finding suitable APIs. Current related recommendation methods have defects. For example, most existing methods focus on the relation between users and APIs but neglect the valuable relations among the users or APIs themselves. To address these problems, this article studies implicit knowledge in IIoT by using collaborative learning techniques. Considering the increased dimensions and dynamics of IoT devices, we explore the possible relationships between users and between APIs. We enhance the matrix factorization (MF) model with the mined implicit knowledge that are implicit relationships on both sides. We build an ensemble model by using all implicit knowledge. We conduct experiments on a collected real-world dataset and simulate industrial system scenarios. The experimental results verify the effectiveness and superiority of the proposed models.
140 citations
TL;DR: In this article, the authors analyzed the Higgs condensate bubble expansion during a first-order electroweak phase transition in the early Universe and found that the scaling of the thermal pressure exerted against the wall to be $P\sim \gamma^2T^4$, independent of the particle masses, implying a significantly slower terminal velocity than previously suggested.
Abstract: We analyze Higgs condensate bubble expansion during a first-order electroweak phase transition in the early Universe. The interaction of particles with the bubble wall can be accompanied by the emission of multiple soft gauge bosons. When computed at fixed order in perturbation theory, this process exhibits large logarithmic enhancements which must be resummed to all orders when the wall velocity is large. We perform this resummation both analytically and numerically at leading logarithmic accuracy. The numerical simulation is achieved by means of a particle shower in the broken phase of the electroweak theory. The two approaches agree to the 10\% level. For fast-moving walls, we find the scaling of the thermal pressure exerted against the wall to be $P\sim \gamma^2T^4$, independent of the particle masses, implying a significantly slower terminal velocity than previously suggested.
123 citations
TL;DR: In this paper, a review of studies of the regulation of bubble size is presented, where the bubble generation, evolution, and action mechanism of different factors on the bubble size are elucidated.
Abstract: During the flotation process, hydrophobic minerals are transferred to the foam by bubbles. The size of bubbles has a significant influence on the capture probability of the bubbles and particles, hence affecting the flotation efficiency. Effective regulation of the bubble size is a premise for achieving a controllable flotation index. This paper reviews studies of the regulation of bubble size. The bubble generation, evolution, and action mechanism of different factors on the bubble size are elucidated. It is shown that mechanical stirring, variable pressure (dissolved air, jet, and vacuum), porous medium, ultrasound, and electrolysis are usually used to generate bubbles during flotation. The bubbles generated continuously evolve (i.e., deform, break up and coalesce) to form bubbles of a stable size in the flotation cell, and the bubble size depends on the equilibrium of the breakup and coalescence. The frother, collector, slurry properties, mechanical energy input, and air flow rate are the main factors influencing the bubble size, and bubble size has been regulated using a single factor. This review proposes that research on the regulation of the bubble size should focus on the industrial application of micron-sized bubble generation technology and the effect of multi-factor coupling on the bubble size.
107 citations
TL;DR: In this paper, a multi-scale Euler-Lagrange method was developed and applied to numerically assess cavitation-induced erosion based on the collapse dynamics of Lagrangian bubbles.
Abstract: A multi-scale Euler–Lagrange method was developed and applied to numerically assess cavitation-induced erosion based on the collapse dynamics of Lagrangian bubbles. This approach linked macroscopic and microscopic scales and captured large vapour volumes on an Eulerian frame, while small vapour volumes were treated as spherical Lagrangian bubbles. Interactions between vapour bubbles and the liquid phase were considered via a two-way coupling scheme. A verification and sensitivity study of the developed procedure to transform vapour volumes between Eulerian and Lagrangian frames was performed. First, the developed method was validated for bubble dynamics, using analytical and experimental data. Second, the cavitating flow through an axisymmetric nozzle was simulated using a measurement-based distribution of cavitation nuclei. Details of single bubble collapses were used to assess cavitation erosion. Based on well-recognised fundamental experiments and theoretical considerations from the literature, model assumptions were derived to account for the effects of a bubble’s stand-off distance on the bubble’s motion and its radiated pressure during an asymmetric near-wall bubble collapse. Computed maximum collapse radii of bubbles correlated well with diameters of measured erosion pits. Considering a nonlinear dependence of erosion on impact pressure, calculated erosion potentials compared well to measured erosion depths.
99 citations
23 Sep 2020
TL;DR: In this paper, the authors studied bubble expansion and collapse in a Newtonian liquid for a range of dimensionless initial distances from a solid boundary, and showed that for bubbles very close to the solid, a different jet mechanism leads to the formation of very fast, thin jets.
Abstract: Bubble expansion and collapse in a Newtonian liquid is studied numerically for a range of dimensionless initial distances from a solid boundary. Bubbles farther from the solid develop the well-known microjet during collapse. However, for bubbles very close to the solid, a different jet mechanism leads to the formation of very fast, thin jets. The results are relevant for a better understanding of cavitational erosion.
93 citations
TL;DR: In this article, a simulation of the dynamics of a collapsing cavitation bubble near a resilient metal surface was performed. But the simulation was performed using finite volume based flow solver CavitatingFOAM.
86 citations
TL;DR: The inadequacy of the traditional 5-equation model for spherical bubble collapse problems is demonstrated and the corresponding advantages of the augmented model of Kapila et al.
82 citations
TL;DR: In this article, the dynamics of the relativistic bubble expansion during the first order phase transition focusing on the ultra-relativistic velocities was analyzed and it was shown that fields much heavier than the scale of the phase transition can significantly contribute to the friction and modify the motion of the bubble wall leading to interesting phenomenological consequences.
Abstract: We analyse the dynamics of the relativistic bubble expansion during the first order phase transition focusing on the ultra relativistic velocities $\gamma\gg 1$. We show that fields much heavier than the scale of the phase transition can significantly contribute to the friction and modify the motion of the bubble wall leading to interesting phenomenological consequences. NLO effects on the friction due to the soft vector field emission are reviewed as well.
82 citations
TL;DR: In this paper, the ice breaking caused by a pair of interacting collapsing bubbles was studied by an experimental approach, where bubbles were generated by an underwater electric discharge simultaneously, positioned either horizontally or vertically below a floating ice plate and observed via high-speed photography.
Abstract: In this work ice breaking caused by a pair of interacting collapsing bubbles was studied by an experimental approach. The bubbles were generated by an underwater electric discharge simultaneously, positioned either horizontally or vertically below a floating ice plate and observed via high-speed photography. The bubble-induced shock waves, which turn out to be crucial to the fracturing of the ice, were visualized using a shadowgraph method and also measured using pressure transduces. Unique bubble behaviour was observed, including bubble coalescence, bubble splitting, inclined counter-jets and asymmetric toroidal bubble collapse. Bubble dynamic properties, such as jet speed, jet energy and bubble centre displacement, were measured. Shock wave emission and ice breaking capability of the two bubbles were investigated over a range of inter-bubble and bubble–boundary distances. Regions where the damaging potential of the bubble pair are strengthened or weakened were summarized and possible reasons for the variation in the ice breaking capability were analysed based on bubble morphology, jet characteristics and shock wave pressure. The findings may contribute to more efficient ice breaking and also inspire new ways to manipulate cavitation bubble damage.
80 citations
TL;DR: In this paper, the molecular dynamics simulation method is conducted to investigate the bubble nucleation on grooved substrates with different wettability, and the results show that the groove has significant impacts on bubble nucleations from two aspects: improving thermal energy transfer efficiency and supporting an initial bubble nucleus.
78 citations
TL;DR: A high performance manipulation strategy for gas bubbles is proposed by utilizing ferrofluid-infused laser-ablated microstructured surfaces (FLAMS) and shows terrain compatibility, programmable design and fast response, which will find potential applications in water treatment, electrochemistry and so on.
Abstract: Manipulation of gas bubbles in an aqueous ambient environment is fundamental to both academic research and industrial settings. Present bubble manipulation strategies mainly rely on buoyancy or Laplace gradient forces arising from the sophisticated terrain of substrates. However, these strategies suffer from limited manipulation flexibility such as slow horizontal motion and unidirectional transport. In this paper, a high performance manipulation strategy for gas bubbles is proposed by utilizing ferrofluid-infused laser-ablated microstructured surfaces (FLAMS). A typical gas bubble ( 150 mm/s2 and reach an ultrafast velocity over 25 mm/s on horizontal FLAMS. In addition, diverse powerful manipulation capabilities are demonstrated including antibuoyancy motion, "freestyle writing", bubble programmable coalescence, three-dimensional (3-D) controllable motion and high towing capacity of steering macroscopic object (>500 own mass) on the air-water interface. This strategy shows terrain compatibility, programmable design, and fast response, which will find potential applications in water treatment, electrochemistry, and so on.
TL;DR: In this article, the Eulerian finite element method is introduced to continuously simulate the shock wave and non-spherical bubble evolution stages near a horizontal solid wall with the volume of fluid method and pressure balance technique used to resolve the multi-medium flow.
TL;DR: In this paper, the influence of viscosity and surface tension on bubble dynamics and gas liquid mass transfer has been examined experimentally in a model bubble column using optical measurement methods.
TL;DR: The results show that the surface tension of air–liquid interface exerts a huge impact on bubble stability by reducing surface free energy and Plateau drainage, as well as increasing the Gibbs surface elasticity.
Abstract: In order to improve the stability of air bubbles in fresh concrete, it is of great significance to have a better understanding of the mechanisms and main influencing factors of bubble stability. In the present review, the formation and collapse process of air bubbles in fresh concrete are essentially detailed; and the advances of major influencing factors of bubble stability are summarized. The results show that the surface tension of air-liquid interface exerts a huge impact on bubble stability by reducing surface free energy and Plateau drainage, as well as increasing the Gibbs surface elasticity. However, surface tension may not be the only determinant of bubble stability. Both the strength of bubble film and the diffusion rate of air through the membrane may also dominate bubble stability. The application of nano-silica is a current trend and plays a key role in ameliorating bubble stability. The foam stability could be increased by 6 times when the mass fraction of nano-particle reached 1.5%.
10 Mar 2020
TL;DR: In this article, the authors simulate the bursting of a single bubble by direct numerical simulations of the axisymmetric two-phase liquid-gas Navier-Stokes equations, and describe the number, size and velocity of all the ejected droplets, for a wide range of control parameters, defined as non-dimensional numbers, the Laplace number which compares capillary and viscous forces and the Bond number, which compares gravity and capillarity.
Abstract: When a bubble bursts at the surface of a liquid, it creates a jet that may break up and produce jet droplets. This phenomenon has motivated numerous studies due to its multiple applications, from bubbles in a glass of champagne to ocean/atmosphere interactions. We simulate the bursting of a single bubble by direct numerical simulations of the axisymmetric two-phase liquid-gas Navier-Stokes equations. We describe the number, size and velocity of all the ejected droplets, for a wide range of control parameters, defined as non-dimensional numbers, the Laplace number which compares capillary and viscous forces and the Bond number which compares gravity and capillarity. The total vertical momentum of the ejected droplets is shown to follow a simple scaling relationship with a primary dependency on the Laplace number. Through a simple evaporation model, coupled with the dynamics obtained numerically, it is shown that all the jet droplets (up to fourteen) produced by the bursting event must be taken into account as they all contribute to the total amount of evaporated water. A simple scaling relationship is obtained for the total amount of evaporated water as a function of the bubble size and fluid properties. This relationship is a first important step toward building a physics-based model of the ocean-atmosphere water vapour fluxes controlled by bubbles bursting at the surface.
TL;DR: In this article, a new model that takes into account liquid compressibility, heat transfer, and non-equilibrium evaporation and condensation was proposed to predict the radius of the single laser-induced cavitation bubble over one or two growth and collapse cycles.
TL;DR: In this paper, the dynamics of cavitation bubbles and induced jets in a thin liquid gap bounded by two rigid walls are compared to simulations, and it is shown that the impact velocity of the liquid jets onto the walls can reach more than and strongly depends on the gap height and bubble position.
Abstract: We study the dynamics of cavitation bubbles and induced jets in a thin liquid gap bounded by two rigid walls. The bubbles are generated experimentally with a focused laser pulse and are compared to simulations. The gap height and the distance of the position of bubble nucleation with respect to the nearest wall are varied. The bubble dynamics is recorded at 500 000 frames per second and is compared to simulation results from the compressible volume of fluid solver based on OpenFOAM that takes into account viscosity and surface tension. Good agreement of the spatio-temporal bubble dynamics between experiments and simulations is obtained. The findings are that the parameter space consists of three regions with distinct jetting dynamics that are characterized by two dimensionless parameters: the normalized gap height, , where is the spherical equivalent radius of the bubble at maximum expansion, and the normalized stand-off distance of the bubble measured from the centre of the gap, . The three qualitatively distinct jetting behaviours are the transferred jet impacting on the distant wall, the double jet as a result of a bubble splitting and impacting on both walls and the directed jet from a conically shaped bubble impacting on the closest wall. The impact velocity of the liquid jets onto the walls can reach more than and strongly depends on the gap height and bubble position. The simulations reveal that the viscous boundary layers affect the bubble splitting and therefore the directions of jetting. Additionally, we found that with increasing length of the thin gap the bubble oscillation period increases and converges for sufficiently large gaps.
TL;DR: In this article, the effect of different inlet gas flow rates on bed hydrodynamics parameters such as bed height, equivalent bubble diameter, and particle ejection were studied by the high-speed photography technology and numerical simulation methods.
TL;DR: High-speed photography and schlieren method are applied to investigate the bubble dynamics between the free surface and a rigid wall to show the formation and propagation of shock waves, which explains the radiative process of bubble collapse energy.
TL;DR: The details of bubble interface interaction (deformation, penetration) are investigated and as predicted, by the anisotropy parameter the bubble always jets toward the interface if it grows in the lighter liquid and correspondingly away from the interfaces if it is initiated inside the denser liquid.
TL;DR: In this paper, the bubble departure diameter and the bubble location were controlled through the variation of the size and pitch of hydrophobic patterns on the biphilic surface, and the critical heat flux (CHF) and heat transfer coefficient (HTC) were enhanced.
TL;DR: In this article, the influence of nanolites on bubble nucleation and growth dynamics was investigated in a degassing nanolite-bearing silicic magma, and it was shown that an increase in the resulting bubble number density associated with nanolitic materials could push an eruption that would otherwise be effusive into the conditions required for explosive behavior.
Abstract: Degassing dynamics play a crucial role in controlling the explosivity of magma at erupting volcanoes Degassing of magmatic water typically involves bubble nucleation and growth, which drive magma ascent Crystals suspended in magma may influence both nucleation and growth of bubbles Micron- to centimeter-sized crystals can cause heterogeneous bubble nucleation and facilitate bubble coalescence Nanometer-scale crystalline phases, so-called “nanolites”, are an underreported phenomenon in erupting magma and could exert a primary control on the eruptive style of silicic volcanoes Yet the influence of nanolites on degassing processes remains wholly uninvestigated In order to test the influence of nanolites on bubble nucleation and growth dynamics, we use an experimental approach to document how nanolites can increase the bubble number density and affect growth kinetics in a degassing nanolite-bearing silicic magma We then examine a compilation of these values from natural volcanic rocks from explosive eruptions leading to the inference that some very high naturally occurring bubble number densities could be associated with the presence of magmatic nanolites Finally, using a numerical magma ascent model, we show that for reasonable starting conditions for silicic eruptions, an increase in the resulting bubble number density associated with nanolites could push an eruption that would otherwise be effusive into the conditions required for explosive behavior
TL;DR: In this article, the attachment process of the oil droplet onto the gas bubble was described in detail, and it was shown that the spreading of an oil film on the bubble surface precedes the entire droplet during the spread phase, and the induction time increases with decreasing oil spreading coefficient and increasing bubble size and oil viscosity.
TL;DR: In this article, a modified gas feeding bubble column photo-bioreactor was utilized for microalgae cultivation and CO2 capturing, and the optimum values of temperature, pH, light intensity, aeration rate, light-dark cycle and time were determined as 25 ° C, 8, 2700※lx, 0.5
Abstract: In this study, a modified gas feeding bubble column photo-bioreactor was utilized for microalgae cultivation and CO2 capturing. By applying response surface methodology, the optimum values of temperature, pH, light intensity, aeration rate, light-dark cycle and time were determined as 25 ° C, 8, 2700 lx, 0.5 LPM and 16−8 h, respectively. Two air spargers (with different aperture size) were used to study the effect of the bubble size on the CO2 removal and microalgae growth rate. Besides, the inlet air was humidified to avoid the evaporation from the photo-bioreactor. For the smaller bubbles and 7% CO2 concentration, the maximum values for the CO2 fixation rate, productivity and concentration of microalgae were determined to be 633.73 mg L−1d−1, 337 mg L−1d−1 and 4244 mg L−1, respectively. CO2 utilization efficiency was 35% for the smaller bubbles, showing a 15% increase over that for the larger bubbles.
TL;DR: In this paper, the cavitation-vortex-pressure fluctuation interaction in a centrifugal pump under partial load with experimental validation was investigated, and the authors used the improved unsteady calculation model based on bubble-rotation-based Zwart-Gerber-Belamri (BRZGB) cavitation model.
Abstract:
Cavitation is a complicated phenomenon in the centrifugal pump. In this work, the improved unsteady calculation model based on bubble-rotation-based Zwart–Gerber–Belamri (BRZGB) cavitation model is used to investigate the cavitation-vortex-pressure fluctuation interaction in a centrifugal pump under partial load with experimental validation. Spatial–temporal evolution of cavitation can be classified into three stages: developing stage, shedding stage, and collapsing stage. The cavitation evolution period is found as 1/4T (T is impeller rotation period), corresponding to the frequency 4fi (fi is impeller rotation frequency). On the analysis of the relative vorticity transport equation, it is revealed that the cavity is stretched by the relative vortex stretching term (RVS) and developed by the relative vortex dilation term (RVD), and they have great influence on the cavity shedding. The peak value of pressure fluctuation intensity occurs near the vapor–liquid interface at cavity rear, and shifts downstream with the cavitation development. The hysteresis between the vapor volume fraction, vorticity, and pressure fluctuation is observed, and the variation of vapor volume fraction is the source of cavitation-vortex-pressure interaction.
TL;DR: In this paper, a small, spherical bubble of high internal pressure is inserted into water at constant ambient pressure as a model of a laser-induced bubble and its subsequent dynamics near a flat solid boundary is studied in dependence on the distance of the bubble to the boundary by numerically solving the Navier-Stokes equations with the help of the open source software environment OpenFOAM.
Abstract: A small, spherical bubble of high internal pressure is inserted into water at constant ambient pressure as a model of a laser-induced bubble. Its subsequent dynamics near a flat solid boundary is studied in dependence on the distance of the bubble to the boundary by numerically solving the Navier-Stokes equations with the help of the open source software environment OpenFOAM. Implemented is the finite volume method for discretization of the equations of motion and the volume of fluid method for capturing the interface between the bubble interior and exterior. The bubble contains a small amount of non-condensable gas that is treated as an ideal gas. The liquid is water obeying the Tait-equation. Surface tension is included where necessary. The evolution of the bubble shape and a selection of pressure and velocity fields are given for normalized distances $D^* = D/R_{\rm max}$ between 0 and 3 ($D$ = initial distance of the bubble centre to the boundary, $R_{\rm max}$ = maximum radius the bubble would attain without any boundary). $R_{\rm max} = 500 \mu$m is chosen for the study. Normal axial jet formation ($\sim 100$ m s$^{-1}$) by axial flow focusing is found for $0.24 \le D^* \le 3$ and the change to a different type of axial jet formation ($\sim 1000$ m s$^{-1}$) by annular-liquid-flow collision for bubbles very near to the solid boundary ($0 \le D^* \le 0.2$). The transition region ($0.2 < D^* < 0.24$) is characterized by additional inbound and outbound annular jets. Remarkably, the inclusion of the viscosity of the water is decisive to get the fast jets.
TL;DR: In this article, the authors evaluated the performance of a micro-scale Venturi channel as a bubble generator and analyzed the mechanisms dominating the bubble breakups based on observations, and identified a negative aspect associated with the bubble generator.
TL;DR: In this article, the authors investigated supercritical heat transfer by pseudo-boiling concept, where heat transfer is analogized between supercritical pressure and subcritical pressure to create a new non-dimensional supercriticalboiling number, representing the bubble expansion induced momentum force against the inertia force.
22 Mar 2020
TL;DR: Results show the bubble mechanism significantly improves ray-casting on both performance and preference, and the Bubble Ray technique with angular distance definition is competitive compared with other target acquisition techniques.
Abstract: Ray-casting, i.e., a ray cast from a hand-held controller to select targets, is widely used in 3D environments. Inspired by the bubble cursor [12] which dynamically resizes its selection range on 2D surfaces, we investigate a bubble mechanism for ray-casting in virtual reality. Bubble mechanism identifies the target nearest to the ray, with which users do not have to accurately shoot through the target. We first design the criterion of selection and the visual feedback of the bubble. We then conduct two experiments to evaluate ray-casting techniques with bubble mechanism in both simple and complicated 3D target acquisition tasks. Results show the bubble mechanism significantly improves ray-casting on both performance and preference, and our Bubble Ray technique with angular distance definition is competitive compared with other target acquisition techniques. We also discuss potential improvements to show more practical implementations of ray-casting with bubble mechanism.
TL;DR: In this article, strong nonlinear interactions of one and two underwater explosion bubbles with a free surface are numerically studied using an axisymmetrical fully compressible three-phase homogeneous model.