Bubble System Research Articles

Influence of the pandemic on the best Romanian handball leagues for seniors

The current paper aims to present the situation of COVID-19 cases recorded among the teams participating in Liga Florilor MOL and Liga Zimbrilor (the best senior leagues in Romania), the monthly distribution of the number of no-shows due to coronavirus and the analysis of teams’ adaptability to the new anti-COVID-19 regulations as regards the number of sanctions received for non-compliance with these rules. The novel coronavirus affected all teams participating in Liga Florilor MOL and Liga Zimbrilor. In total, 365 people including players and staff were infected with SARS CoV-2 during this season. Eight teams were in the situation of not being able to participate in handball tournaments, and 24 games were decided at the green table due to COVID-19, meaning 5.86% of the total number of games scheduled for the best men’s and women’s leagues in the 2020-2021 season. The Romanian Handball Federation organized 207 “bubble system” tournaments for all competitive categories, of which 31 were organized for Liga Florilor MOL (17) and Liga Zimbrilor (14). Throughout the season, the teams successfully adapted to the new rules against the spread of the SARS CoV-2 virus. The sanctions imposed for non-compliance with these rules, excepting the games ended 10:0, were extremely low in numbers. A single pecuniary penalty was applied, which was doubled by an exclusion from that tournament. In addition, a single warning was given to a team that violated the ban on using the locker room inside the sports hall.

Large-scale 3D-PTV measurement of Ahmed-body wake in crossflow

The near wake of the Ahmed body at zero-yaw has been extensively studied in the literature, but comparatively little is known about the wake flow in crossflow condition. In this investigation, we characterize the near wake of a square-back Ahmed body at a Reynolds number of ReH = 9.2 × 104 for three yaw angles of β = 0°, 5°, and 10°. The measurements are carried out using 3D particle tracking velocimetry utilizing an innovative helium-filled soap bubble (HFSB) system for seeding a large domain of approximately 35 × 30 × 18 cm3. The results showed that increasing the yaw angle shifted the separation bubble towards the windward side and enlarged the recirculating region of the leeward side. The downwash motion from the top-edge and the spanwise motion from the leeward edge of rear-face also strengthened. A vortex ring formed in the periphery of the mean separation bubble. With increasing the yaw, the ring skewed toward the leeward edge and its windward potion became weaker. For the yaw cases, streamwise vortices appeared originating from the windward portion of the vortex ring. Spectral analysis showed that the overall energy of oscillations increased with yaw while the Strouhal numbers of the spanwise and wall-normal flow motions remained relatively constant. Proper orthogonal decomposition of the velocity field showed that the first spatial mode contained 32.8% of the total kinetic energy for the zero-yaw case. The energy of the first spatial mode reduced to approximately 10% for the β = 5° and 10° wakes due to the disappearance of the bi-stability mode. The energetic flow motions within the yawed wakes were primarily on the windward side of the body.

An insightful analysis of dimethyl phthalate degradation by the collaborative process of DBD plasma and Graphene-WO3 nanocomposites

In this paper, the prepared graphene-WO3 nanocomposites (rGO-WO3) were added into a dielectric barrier discharge (DBD) plasma system with spiral discharge electrode to set up a collaborative process to treat the dimethyl phthalate (DMP) in water. Degradation of the DMP under different experimental conditions were studied to illustrate the catalysis of the rGO-WO3 in the DBD plasma system. The obtained results proved that there was the catalysis of the rGO-WO3 for the DMP degradation within the studied DMP concentration, solution initial pH values and conductivities. From the results of the energy utilization efficiency (G50) analysis, the catalysis was more apparent in the case of the oxygen bubbling system than that in the nitrogen or the air bubbling system, which was due to the higher oxygen constitution in the oxygen bubbling system. The reduction of the measured liquid phase ozone concentrations in the DBD/rGO-WO3 system bubbled with air as well as oxygen than those measured in the sole DBD system, which verified the consumption of the ozone by the catalysis of the rGO-WO3. Furthermore, the UV–Vis and the three-dimensional fluorescence spectra analysis were also carried out to state the catalytic effect of the rGO-WO3 for the DMP degradation. Toxicity analysis for the degradation byproducts confirmed the collaborative process could reduce the negative effect of the original DMP on the environment.

Development and validation of a comprehensive 1-D model to simulate gas hold-up and gas–liquid transfer in deep air–water bubble columns

This study proposed to develop a model coupling hydrodynamics and mass transfer in order to gain an understanding of measurements taken on air–water bubble columns with low gas hold-up. Three experimental datasets with various operating conditions (water quality, liquid height, air flow range) were chosen. The model analyzes and interprets the significant impact of the local hydrostatic pressure and the effects of contamination on hydrodynamic and mass transfer parameters. The oxygen concentration in gas significantly depletes with the distance from diffusers, which explains the difference between the calculated mean of the local <kLa> and global KLa coefficients. This difference is highly significant for a high bubble column and/or systems with a low mean bubble size. The impact of water quality on mass transfer can be characterized by the contamination angle using comprehensive 1-D modeling and highlights a differentiated impact on the hydrodynamic or mass transfer parameters.

Bubble characteristics in subcooled flow boiling of seawater

Bubble characteristics are important to the two-phase flow dynamics and two-phase flow simulation. Different from the known slug flow in subcooled flow boiling of de-ionized water, fined bubbly flow and foam flow are found to be dominant in that of artificial seawater at high temperatures. Through image analysis, the present study conducts bubble characteristics measurements of such bubbly/foam flow of subcooled flow boiling in artificial seawater, including bubble Sauter mean diameters, bubble equivalent diameters and distributions of bubble sizes, bubble shapes and bubble orientations. The data set is compared with that in de-ionized water. The images for analysis are acquired from the high-speed camera with 4000 frame/s. The results indicate the Sauter mean diameters of de-ionized water could be larger than that of artificial seawater by 16–30%. Good agreements with two existing correlations prove the accuracy of current measurements and provide a way to predict the bubble characteristic in such fined bubble systems. Moreover, the results reveal the two-phase foam flow structure in artificial seawater is comparatively rigid and inflexible, compared to that in the de-ionized water. Increasing liquid temperature to 85℃ may keep the Sauter mean diameter of bubbles in artificial seawater at a stable value. The only peak of the unimodal bubble size distributions of artificial seawater is at 0.15–0.36 mm, while the possible other peak of bimodal bubble size distributions of de-ionized water is at 0.78–0.99 mm or 0.57–0.78 mm. Bubbles are mostly either nearly/perfectly parallel to the heated surface or perpendicular to the heated surface. Spherical shape for bubbles smaller than 0.2–0.25 mm, rigid ellipsoid shape for intermediate bubbles with diameter greater than 0.40 mm and less than 1.0 mm −2.7 mm, and distorted large bubbles, depending strongly on the liquid temperature, are observed. The data of bubble aspect ratio appear to be quite scattering due to the complicated nature of subcooled flow boiling. However, its general variation trend with Eötvös number or the product of Eötvös number and vapor Reynolds number agrees fairly well with some well-known correlations in the literature. Moreover, the bubble shape can also be predicted well with an extrapolated boundary of the Grace diagram on the plane of gas Reynolds number versus Eötvös number.

Efficient Mesh Interface Engineering: Insights from Bubble Dynamics in Electrocatalysis.

Electrochemical catalysis offers great potential in energy and mass conversion in academy and industry. However, bubble dynamics and its influence on gas-evolving electrode systems remain ambiguous. Detailed information on the local transport process between different phases and the underlying mechanism are required for the full understanding of two-phase flow evolution and distribution. Here, we construct a three-electrode water splitting reaction system to study the bubble dynamics and system efficiency of titanium electrodes with different morphologies. The dynamics of a gas bubble at an electrode with a plate and 100-mesh, 150-mesh, and 300-mesh structures is systematically investigated with respect to applied voltage conditions. Parameters and underlying mechanisms that influence the two-phase flow evolution and electrochemical reaction performance are carefully discussed. Finally, the underlying dynamic force balance on the gas bubble is analyzed to illustrate the mechanism and experimental observations. Our study provides insights in gas-evolving electrocatalysis and offers opportunities for the design and fabrication of high-performance electrocatalytic reactors.

Effect of Closure Characteristics of Annular Jet Mixed Zone on Inspiratory Performance and Bubble System

In the flotation process, gas-liquid properties and the bubble system greatly influence bubble mineralization. In order to clarify how the mechanism applies to the closure characteristics of an annular jet mixed flow zone on the inspiratory performance and the bubble system, different degrees of closure on the velocity field and gas-liquid ratio in the mixed flow zone were investigated using numerical simulation. The variations in the characteristics of bubble size distribution, rising velocity, and gas content under different closure levels were measured with a high-speed dynamic camera technology. The results confirmed that when the closure degrees of the mixed flow zone improved, the inlet jet could gradually overcome the static pressure outside the nozzle effectively. It formed a gas-liquid mixing zone with high turbulence first, and a large pressure difference at the gas-liquid junction second. This helped to increase the inspiratory capacity. At the same time, the gas-liquid ratio rose gradually under conditions of constant flow. When the nozzle outlet was completely closed, the gas-liquid ratio gradually stabilized. For the bubble distribution system, an enhancement in the closure degrees can effectively reduce the bubble size, and subsequently, the bubble size distribution became more uniform. Due to the improved gas-liquid shear mixing, the aspect ratio of the bubbles can be effectively changed, consequently reducing the bubble rising speed and increasing the gas content and bubble surface area flux of the liquid.

Liquid metal bubbles

Classical bubbles are ubiquitous in nature, throughout industrial production and daily life. So far, tremendous researches on bubbles are mostly focused on aqueous or lipid systems. In this study, a new conceptual bubble system based on liquid metals, whose surface tension is nearly eight times larger than that of water, is proposed and demonstrated. Such liquid metal bubbles display a series of completely different features over the existing bubbles generated via common liquids, especially those composed of conventional aqueous solutions. Through delivering fluids inside the interior of liquid metal system, we successfully achieved the regulation of liquid metal surface with diverse morphologies, including forming single bubble, hole and multi-bubble clusters etc. For more precise manipulations, the solution environment where liquid metal is immersed into can be divided into “film-forming” and “remover” species, enabling the control of generation and vanishing of oxide on the metal surface in particular area through different combinations, resulting in the complicated administration and control of liquid metal matters. Further, the electrical characteristics of these morphologies were justified and disclosed to be capable of building logic circuits. Along this way, a display device was developed to exhibit various patterns, showing or even storing information inside. Overall, the liquid metal bubble as well as its periodic excitation opens applications in diverse areas, including but not limited to soft robotics, logic system, or underwater circuits.

Intensification of Ozone Mass Transfer and Generation of Hydroxyl Radicals by Ceramic Membrane

ABSTRACT The strengthening ability of ozone to treat the reverse osmosis concentrate (ROC) of landfill leachate is a crucial issue. From the standpoint of coupling intensification, a ceramic membrane/ozone (CM/O3) system was developed to improve the oxidation performance of ozone. The results showed that CM/O3 system could significantly improve the ozone concentration and the generation of hydroxyl radicals (·OH) when compared to the traditional O3 bubble system. The reaction condition, such as inlet ozone concentration and ozone flow, ceramic membrane pore size, transmembrane pressure, and temperature on the concentration of ozone in the liquid phase and the formation of ·OH, has been considered. Experimental results showed that the concentration of ozone and OH in the liquid increased with the increase in the inlet ozone concentration and ozone flow. Moreover, a certain degree of reduction in membrane pores was facilitated to intensify the mass transfer of ozone. The increase of pressure was able to raise the concentration of ozone. However, there was a slight effect on ·OH concentration. As for the temperature, a low-temperature situation was conducive to strengthen ozone dissolution. In terms of the generation of ·OH, a high-temperature situation was a better favorable environment. In order to evaluate the performance of the reactor system, three treatment processes (CM/O3, CM alone and O3 alone) were compared to treat ROC. In the CM/O3 system, the final removal efficiency of Chemical Oxygen Demand (COD) was 81.9%, and the final removal efficiency of Total Organic Carbon (TOC) was 62.6%.

Improving the Performance of Surface Flow Generated by Bubble Plumes

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.

Dynamics of the delay-coupled bubble system combined with the stochastic term

The purpose of this paper is to study the mechanisms of the delay-coupled bubble system combined with the stochastic term from a mathematical point of view. Firstly, the dynamic behaviors of the bubble system were studied with the normal form theory, center manifold and stochastic averaging method. The stochastic bifurcation behaviors (P-bifurcation and D-bifurcation) of the bubble system were analyzed. Besides, the relationship between the dynamic behaviors of the interaction between the time delay term and the stochastic term and the stability of the bubble was numerically simulated. Finally, we compared the joint probability density curves of the bubble system and Ito^ equation. The numerical simulation results are consistent, which indicated that it is feasible to study the stochastic bifurcation behaviors of the bubble system by using the Ito^ stochastic differential equation.

Experimental and numerical evidence of intensified non-linearity at the microscale: The lipid coated acoustic bubble

A lipid coated bubble (LCB) oscillator is a very interesting non-smooth oscillator with many important applications ranging from industry and chemistry to medicine. However, due to the complex behavior of the coating intermixed with the nonlinear behavior of the bubble itself, the dynamics of the LCB are not well understood. In this work, lipid coated Definity® microbubbles (MBs) were sonicated with 25 MHz 30 cycle pulses with pressure amplitudes between 70 and 300 kPa. Here, we report higher order subharmonics in the scattered signals of single MBs at low-amplitude high-frequency ultrasound excitations. Experimental observations reveal the generation of period 2, period 3, and two different period 4 oscillations at low excitation amplitudes. Despite the reduced damping of the uncoated bubble system, such enhanced nonlinear oscillations have not been observed and cannot be theoretically explained for the uncoated bubble. To investigate the mechanism of the enhanced non-linearity, the bifurcation structure of the lipid coated MBs is studied for a wide range of MBs sizes and shell parameters. Consistent with the experimental results, we show that this unique oscillator can exhibit chaotic oscillations and higher order subharmonics at excitation amplitudes considerably below those predicted by the uncoated oscillator. Buckling or rupture of the shell and the dynamic variation of the shell elasticity cause the intensified non-linearity at low excitation pressure amplitudes. The simulated scattered pressure by single MBs is in good agreement with the experimental signals.

A deterministic model for bubble propagation through simple and cascaded loops of microchannels in power-law fluids

This paper investigates the path selection of bubbles suspended in different power-law carrier liquids in microfluidic channel networks. A finite volume-based numerical method is used to analyze the two-dimensional incompressible fluid flow in microchannels, while the volume of fluid method is used to capture the gas–liquid interface. To instill the influences of shear thinning, Newtonian, and shear-thickening fluids, the range of power-law indices (n) is varied from 0.3 to 1.5. We have validated our numerical model with the available literature data in good agreement. We have investigated the nonlinearity in the hydrodynamic resistance which arises due to single-phase non-Newtonian fluid flow. The path selection of a bubble in power-law fluids is examined from the perspective of velocity distribution and bubble deformation. We have found that the bubble indeed goes to the channel with a higher flow rate for all power-law fluids, but interestingly it did not always take the shorter route channel at a junction for n = 0.3. Our results suggest that long channels need not be more resistant for every fluid and that the longest arm becomes the least resistant resulting in the bubble leading into the long arm at a junction for shear-thinning fluid. We have proposed a deterministic model that enables predicting the second bubble path in a single bubble system for any location of the first bubble. We believe that the present study results will help design future generation microfluidic systems for efficient drug delivery and biomedical and biochemical applications.

Enhancement of Oscillation Amplitude of Cavitation Bubble Due to Acoustic Wake Effect in Multibubble Environment

Acoustic cavitation occurs in ultrasonic treatment causing various phenomena such as chemical synthesis, chemical decomposition and emulsification. Nonlinear oscillations of cavitation bubble are assumed to be responsible for these phenomena. Therefore, bubble oscillations have been studied especially focusing on single bubble system while those in multi-bubble systems have not been analyzed yet despite their importance for the actual ultrasonic processing. In the present study, we numerically investigated the dynamic behavior of cavitation bubbles in multi-bubble systems. The results reveal that the oscillation amplitude of bubbles becomes larger in multi-bubble environment compared with that in the single-bubble case. It is found that this is caused by an acoustic wake effect, which reduces the pressure near a bubble surrounded by other bubbles and increases the time delay between the bubble contraction/expansion cycles and sound pressure oscillations. A new parameter, called “cover ratio” is introduced to quantitatively evaluate the variation in the bubble oscillation amplitude and time delay.

A Bubble‐Assisted Approach for Patterning Nanoscale Molecular Aggregates

AbstractWe demonstrate a new approach to pattern functional organic molecules with a template of foams, and achieve a resolution of sub 100 nm. The bubble‐assisted assembly (BAA) process is consisted of two periods, including bubble evolution and molecular assembly, which are dominated by the Laplace pressure and molecular interactions, respectively. Using TPPS (meso‐tetra(4‐sulfonatophenyl) porphyrin), we systematically investigate the patterns and assembly behaviour in the bubble system with a series of characterizations, which show good uniformity in nanoscale resolution. Theoretical simulations reveal that TPPS's J‐aggregates contribute to the ordered construction of molecular patterns. Finally, we propose an empirical rule for molecular patterning approach, that the surfactant and functional molecules should have the same type of charge in a two‐component system. This approach exhibits promising feasibility to assemble molecular patterns at nanoscale resolution for micro/nano functional devices.

A Bubble-Assisted Approach for Patterning Nanoscale Molecular Aggregates.

We demonstrate a new approach to pattern functional organic molecules with a template of foams, and achieve a resolution of sub 100 nm. The bubble-assisted assembly (BAA) process is consisted of two periods, including bubble evolution and molecular assembly, which are dominated by the Laplace pressure and molecular interactions, respectively. Using TPPS (meso-tetra(4-sulfonatophenyl) porphyrin), we systematically investigate the patterns and assembly behaviour in the bubble system with a series of characterizations, which show good uniformity in nanoscale resolution. Theoretical simulations reveal that TPPS's J-aggregates contribute to the ordered construction of molecular patterns. Finally, we propose an empirical rule for molecular patterning approach, that the surfactant and functional molecules should have the same type of charge in a two-component system. This approach exhibits promising feasibility to assemble molecular patterns at nanoscale resolution for micro/nano functional devices.

Analyses of production capacity of 89Sr and 90Sr in the 2 MW molten salt reactor

The production capacity of 89Sr and 90Sr in the 2 MW MSR are evaluated. The gaseous 89Kr and 90Kr are extracted from the core through the helium bubbling system, and then decay to 89Sr and 90Sr, respectively. In order to improve purity of 89Sr product, two cooling devices are adopted in the 89Sr and 90Sr production system. The annual yields of 89Sr and 90Sr are about 9000 Ci and 32 Ci, respectively, and the impurity of 89Sr product is less than 2 ppm which can meet the medical requirement.

Number density of bubbles under ultrasonic horn measured from stroboscopic images

Although image measurement is essential in the analysis of acoustic cavitation bubbles, it is impossible to determine the position of the bubble along the optical axis of the imaging system from the images. Thus, the number density of the bubbles cannot be measured from the image. This paper proposed a method to determine bubbles’ positions along the optical axis using the bubble image brightness. The relationship among the bubble position along the optical axis, the bubble diameter, and the bubble image brightness is clarified using the bubble in the single bubble system. A measurement method of the bubble number density based on this relationship is established. Using this method, the time-averaged spatial distribution of bubble number density under ultrasonic horn is revealed.

Comparative analysis of energy efficiency of ballast tank anti-freezing systems

Choosing the best way to deal with the internal icing of ballast tanks is the important task of the designing Arctic vessels. To prevent excessive ice formation in the ballast tank, various methods are used, the main of which are: heating the water and increasing of the water circulation intensity inside the tank (air and steam bubbling, forced water circulation). The report presents qualitative assessment of the heating method and air bubbling system and investigation of energy efficiency of anti-freezing systems.

Experimental investigations of three laser-induced synchronized bubbles

Herein, we investigated experimentally the dynamics of three laser-induced, same-sized, symmetrically aligned, and synchronized bubbles. Three synchronized laser beams split from the same beam using a Diffractive Optical Element splitter were focused on water, and then we obtained three bubbles. Another nanosecond laser pulse was used to probe the bubbles to obtain shadowgraphs. The exact delay of the excited and detected light was controlled using a delay generator. The results revealed that the maximum volumes of bubbles in arrays decrease as the normalized distance falls, while the lifetimes and translation increase. It was explained by the interaction between the acoustic radiation of bubbles and the surrounding bubbles. The shrinkage of linear bubble arrays exists an anomaly. The center bubbles were stretched, to ellipsoid, stick, even fractured, by the peripheral bubbles. The closer they are, the more distinct is the above phenomenon. However, when the normalized distance was sufficiently small, instead of being stretched, the center bubbles were compressed to disk shape and thus shrank with the whole array. Finally, the dependence of the distance on the energy transfer of the bubble system is also discussed.