Bubble Distribution Research Articles

Accurate models of the added mass force of a uniform random distribution of spherical particles or bubbles

Accurate models of the added mass force of a uniform random distribution of spherical particles or bubbles

Bubble distribution in shaped sapphire grown from molybdenum crucibles using the micro-pulling down technique

Mo crucibles can be used for micro-pulling down to grow undoped sapphire fibers and rods. The bubble distribution was investigated.

Insights into cavitation enhancement: Numerical simulation and spectrum analysis of a novel dual-frequency octagonal ultrasonic reactor.

Ultrasonic reactors, widely applied in process intensification, face limitations in their industrial application due to a lack of theoretical support for their structural design and optimization, particularly concerning the uniformity of the cavitation zone. Addressing this gap, our study introduces a novel approach to design a multi-frequency octagonal ultrasonic reactor of capacity 9.5 L through numerical simulation and spectrum analysis. The effects of reactor shape, transducer position, and multi-frequency ultrasound interaction on the sound pressure distribution in the reactor were simulated, employing a linear wave equation that accounts for the inhomogeneous distribution of bubbles. The accuracy of sound pressure amplitude predictions has been validated through a multi-frequency simulation method, exhibiting good consistency with experimental data. The results revealed that an octagonal structure with transducers positioned at the bottom and sides enhances the uniformity and distribution of the cavitation area compared to traditional rectangular designs. Notably, the combination of 20 and 40kHz frequencies at a driving pressure of 3bar significantly enhances cavitation rates to 69.2%, surpassing the single frequency of 40kHz by an increase of 16.5%. The enhanced cavitation rate can be attributed to the dual-frequency operation, which facilitates larger bubble radii, along with higher collapse temperatures and pressures, as determined through bubble dynamics calculations. Moreover, spectrum analysis method enables energy separation, showing that the introduction of a 40kHz transducer into a 20kHz field markedly strengthens both steady and transient cavitation intensities. These findings offer practical insights for their structural design and optimization, paving the way for their broader industrial application.

Exploring salting-out phenomena in air-assisted solvent extraction of Cu

ABSTRACT Air-assisted solvent extraction (AASX) has been introduced as an alternative method with a high potential for recovering metals from dilute solutions in alignment with sustainable development goals. This research investigates the effect of salting out using KCl, NaCl, CaCl2, NaNO3, and Na2SO4 on the efficiency of the AASX process (Cu recovery and organic-phase recycling). This study uses thermodynamic coefficient and bubble size values to interpret the relationship between AASX efficiency results and ions present in the aqueous phase (type and concentration of electrolytes). It was observed that salting out up to the inhibition concentration increases bubble size and distribution while decreasing bubble coalescence. The trend of anion effects (from highest to lowest) on copper recovery and organic-phase recycling was determined as NO3−>SO4 2−>Cl− and SO4 2− > Cl− > NO3 −, respectively. It was also found that the bubble-specific surface area, the retention time of fluids in the column, and the proportion of uncoated organic phase play significant roles in this process. This research emphasizes the potential of establishing the AASX process for extracting copper from dilute solutions containing barrier anions and cations in various industries.

Influence of speed on the internal flow characteristics of a multiphase pump based on a coupled CFD-PBM model

Under the influence of the characteristic behavior of the bubbles, the flow pattern in the multiphase pump suffers a serious deterioration and the pressurization performance is significantly reduced. In order to be more close to the engineering practice, the CFD-PBM (Computational Fluid Dynamics-Population Balance Model) coupling model is established and verified on the basis of considering the bubble coalescence and breakup behavior, revealing the bubble distribution characteristics in the pressurization unit, and studying the influence of speed on the internal flow characteristics of the multiphase pump. The results show that the volume fraction of large bubbles in the pressurization unit of the multiphase pump decreases significantly with increasing speed, and the bubble coalescence zone shrinks parallel to the blade profile along the flow direction. The volume fraction of small bubbles increases sharply with speed, and the bubble breakup zone covers almost the entire fluid domain at high speed conditions. The speed has a significantly greater influence on the distribution of the gas phase and the vortex structure in the diffuser domain than in the impeller domain. In the diffuser domain, a pair of mutually separate vortices are formed, and a large number of gas phases are sucked near the vortex center. With the increase of speed, the velocity slip in impeller domain is weakened, but in diffuser domain is intensified. The results of the study can accurately predict the performance variation of the multiphase pump and are important for their optimal design and engineering application.

Mesoscale simulation on bimodal distribution of nano-sized intragranular fission bubbles in UO2

UO2 is widely used as a nuclear fuel in the light water reactors. Irradiated UO2 nuclear fuel exhibits an intriguing bimodal distribution of bubble number and size at the nanoscale. To uncover the underlying mechanisms, we investigate bubble characteristics under varying damage events using the continuum phase-field method. Our findings suggest that the occurrence of bimodal pattern is primarily due to the biased trapping of supersaturated vacancies and gas atoms by bubbles, rather than gas resolution effect.

Effects of ethanol addition on the quality and stability of Pickering emulsions: Developing Baijiu-infused ice cream

The application of Pickering emulsions in real food systems has attracted increasing research interest. Similarly, the tendency of incorporation of Chinese Baijiu into food products is also increasing. This study aimed to investigate the effects of ethanol addition (3 %–15 %, v/v) on the physicochemical, rheological properties and microstructure of Pickering emulsions. The results showed that ethanol resulted in a decrease in particle size, an increase in the apparent viscosity and in the proportion of adsorbed proteins at the oil-water interface of Pickering emulsions, resulting in an increase in emulsion stability. The results obtained from cryo-scanning electron microscopy showed that the incorporation of Baijiu improve the interaction between the fat globules at the interface, enhanced the film around the bubbles, and led to a reduction in the size and a more uniform distribution of air bubbles in the ice cream. These results indicate that the incorporation of a moderate amount (<15 %, v/v) of ethanol into the Pickering emulsion enhances its stability. Adding Baijiu to the preparation of plant-based ice cream resulted in a mellow texture, fine organization, and suitable hardness. These findings provide valuable information for potential application of ethanol, particularly Baijiu, in Pickering emulsion-based applications, including frozen products.

Quantitative Relationship Between Strength and Porosity of Nano-Silica-Modified Mortar Based on Fractal Theory

Nano-silica (NS) is an ideal modifier for mortar materials, and exploring the evolution of the fractal dimension of the pore structure in NS-modified mortar is crucial for elucidating the mechanism by which NS enhances mortar strength. In this study, NS reinforced mortar was prepared using an NS sol solution, which inhibited the aggregation of NS particles. The relationship between the strength and pore structure of NS-modified mortar was quantitatively analyzed based on fractal dimension theory and gray correlation degree. The experimental system evaluated the mortar strength, pore structure distribution, and micro-morphology. Based on this evaluation, the fractal dimension of the mortar pore volume was calculated in detail. Subsequently, models for mortar strength and NS content were further established using grey analysis. The results indicate that NS significantly enhances the strength of mortar while also increasing its porosity due to reduced fluidity. NS can improve the compressive strength of mortar by up to 35%. The curve fitting of volume fractal dimension and box dimension is effective and can accurately reflect the complexity of the pore structure. The calculation of the grey correlation analysis model shows that the impact of varying silica content on the mechanical properties of mortar specimens is not linear; the distribution and quantity of bubbles are the main factors affecting the strength of the specimen.

Compression of Porous Transport Layers Enhanced Bubble Transport in Polymer Electrolyte Membrane Water Electrolyzers

At high current densities, oxygen bubble formation limits the performance of polymer electrolyte membrane (PEM) water electrolyzers, particularly due to bubble accumulation at the porous transport layer (PTL)/catalyst layer (CL) interface. Efficient bubble removal from the PTL/CL interface is therefore crucial for PEM water electrolyzers1,2. Bubble transport at the PTL/CL interface is dominated by mechanical compression 3,4. However, it is still unclear how mechanical compression impacts bubble transport at the PTL/CL interface, due to difficulties in capturing the multiphase flow and differentiating liquid/gas in the pores of the titanium PTL. Thanks to its spatial resolution and high transmissivity for titanium, neutron imaging enables visualization of the bubble distribution in the PTL hence allowing for the identification of the role of compression in the bubble transport.We conducted operando neutron imaging for PEM water electrolyzers and examined the relationship between compression ratio and electrochemical performance. Neutron imaging results showed that the through-plane bubble distributions became more homogeneous as compression increased. Additionally, pore network modelling simulations indicated that compression-induced catalyst coated membrane intrusion homogenized the bubble distribution in the PTL. We identified an optimal compression condition for enhanced interfacial bubble transport that can contribute to the next-generation material development to improve the efficiency of PEM water electrolyzers at high current densities with low mass transport losses. References J. K. Lee and A. Bazylak, Joule, 5, 19–21 (2021).S. Yuan et al., Prog. Energy Combust. Sci., 96, 101075 (2023).T. Schuler, T. J. Schmidt, and F. N. Büchi, J. Electrochem. Soc., 166, F555–F565 (2019).A. Martin et al., J. Electrochem. Soc., 169, 014502 (2022).

Elucidating 3D Water Distributions in PEM Water Electrolyzers Via Neutron Imaging

A key challenge in polymer electrolyte membrane (PEM) water electrolysis stems from product oxygen bubble accumulation in the titanium (Ti) porous transport layer (PTL), which limits hydrogen production at high current densities. To design the next generation of PTLs with efficient porous structures that enhance bubble removal, obtaining three-dimensional (3D) water and gas distributions in an operating electrolyzer is critical. Previous works have demonstrated that neutron [1,2] and X-ray [3] imaging techniques can be used to quantify gas and water content, but capturing these phenomena with 3D imaging remains a challenge due to low transmission through metallic cell hardware, limitations in spatial and temporal resolutions, and low contrast between reactant water and product gas bubbles.In this work, we used the high flux neutron beam at the NeXT instrument of the Institut Laue-Langevin to perform operando radiography during electrolysis and to acquire tomography scans of the steady-state water and gas distributions. We designed a custom PEM electrolysis cell with a Ti PTL and serpentine flow field design for neutron radiography and tomography to reveal the water distribution and its evolution in the PTL. To correlate electrochemical losses to reactant distributions, polarization curves and EIS measurements were acquired. Operando radiography was employed to reveal changes in water distributions over time with increasing current density. Additionally, to elucidate the steady-state water and gas distributions at a variety of current densities, neutron tomography was utilized. Within our analysis, we reveal the impact of water and bubble distributions through the PTL on activation, ohmic, and mass transport overpotentials, particularly at the PTL and catalyst layer interface. The insights provided will aid in identifying performance degradation mechanisms and desirable reactant distributions for the next generation of PTL design. References J. K. Lee et al., Energy Convers Manag, 226, 113545 (2020)CH. Lee et al., J Power Sources, 446, 227312 (2020)S. De Angelis et al., J Mater Chem A Mater, 9, 22102–22113 (2021)

Towards reliable subharmonic-aided pressure estimation: Simulation and experimental validation of microbubble dynamics

This study examines the reliability of subharmonic-aided pressure estimation (SHAPE) using polydisperse microbubbles. SHAPE utilizes the subharmonic response of ultrasound contrast agent microbubbles to estimate pressure non-invasively. Despite its potential, gaps in theoretical understanding and experimental inconsistencies with polydisperse microbubbles necessitate further investigation. This research explores the impact of microbubble distribution, excitation parameters, and contrast-enhanced ultrasound imaging modes on SHAPE’s signal consistency, measurement linearity, and sensitivity. A one-dimensional microbubble population model was developed to simulate microbubble behavior and the Hilbert transform demodulation technique was applied for subharmonic analyses. Variability in SHAPE was further assessed through flow phantom experiments using Sonazoid agents and a commercial SHAPE scanner. Findings indicate that bubble distribution in both size and location, microbubble interactions, and CEUS imaging modes significantly influence subharmonic responses. An excitation frequency of 3.5 MHz is recommended for robust SHAPE. Monte Carlo simulations confirmed the inherent variability of subharmonic amplitude signals due to dynamic bubble distributions. Using monodisperse microbubbles enhanced SHAPE sensitivity and consistency, without markedly reducing signal variability. These results underscore the necessity of further research to optimize SHAPE for clinical applications, focusing on microbubble characteristics and excitation conditions to enhance consistency and reliability.

Improvement of bubble distribution characteristics through multi-objective optimization of flow characteristics of a swirling flow type microbubble generator with fixed blades

Swirling flow type microbubble generators with fixed blades (hereafter referred to as "bubblers") can be easily downsized and upsized and can be easily integrated into existing facilities. For this reason, bubblers have been used for mercury targets; however, there is a need to improve the bubble distribution characteristics. The objective of this study is to establish a technique to rapidly improve bubble distribution characteristics through multi-objective optimization of the flow characteristics of this bubbler using single-phase flow computational fluid dynamics (CFD) analysis. Therefore, design variables for the bubbler blades were defined by applying turbomachinery design methods, and four flow characteristics were subjected to multi-objective optimization using single-phase flow CFD analysis and the response surface methods. While the resulting optimized bubbler increased the pressure loss coefficient by 0.9 %, it improved the wall shear stress by 3.4 %, the swirl number by 10.0 %, and the pressure reduction coefficient by 14.3 % compared to the original bubbler. Furthermore, experiments showed that the optimized bubbler produced smaller bubbles than the original bubbler, demonstrating that the multi-objective optimization design method can significantly improve the bubble distribution characteristics while maintaining the same pressure loss coefficient.

Two-phase flows downstream, upstream and within Plate Heat Exchangers

Air-water flows were assessed within Plate Heat Exchangers (PHE) with the aid of fast camera imaging. Tests occurred in transparent setups with three chevron angle arrangements (30o/30o, 30o/60o and 60o/60o), representative of low, in-between and high pressure drop channels. Evaluation upstream the PHE inlet happened with Electrical Capacitance Tomography. Three patterns were tested: bubbly, slug and stratified. The effects of flow direction, superficial fluid velocities, two-phase pattern, and chevron angle arrangement on air-water distributions were assessed. The PHE channel outlet is characterized by intense flow recirculation. Bubble entrapment occurs in the core of the recirculation zones. Energy dissipation processes along the PHE channel flow affect the inlet gaseous content, intensifying the mixing process of air and water phases, particularly at flow distribution areas owing to the occurrence of flow acceleration and deceleration. Bubble distribution is wide since the break-up process is rather heterogeneous. Prediction of the maximum bubble diameter was obtained with a modification to Hinze's model. Coalescence can occur with small liquid superficial velocities. At the exit manifold, the recirculation zones affect the two-phase pipe flow. In addition to swirling decay, two-phase flow features and gravitational forces need to be accounted to determine the necessary pipe length to attain stationary process.

Two-phase flow pattern recognition inside tubes by a novel diagnostic technique

Abstract A two-phase (liquid-gas) flow represents a highly complex regime influenced by factors such as the mass flow rate of each phase, fluid dynamic and thermal conditions, viscosity, density, and surface tension. The presence and distribution of bubbles within the liquid phase significantly impact heat transfer mechanisms and the performance of components like pumps, valves, and nozzles. This study aims to develop and validate a method for identifying the flow regime within a horizontal duct and accurately quantifying flow parameters. The authors have developed a sensing methodology and instrumentation capable of detecting and analysing the vibrational modes of ducts. This approach enables the identification of flow patterns and serves as a sensor for two-phase flow in Direct Steam Generation (hereafter DSG) solar fields. In the experimental by regulating the pump’s rotational speed, inlet gas pressure, and volumetric flow rate, various two-phase flow configurations were replicated. The flow patterns were characterized using independent statistical indices such as crest factors, shape factors, medians, and modes, to define an objective function capable of describing bubble cluster behaviour on a phase diagram (Poincare map), in which more than 76 % of cases were correctly processed. This analysis employs Poincare’s topological theory and the “within-between approach” in multivariate analysis.

The Effect of Channel Surface Roughness on Two–Phase Flow Patterns: A Review

This review article highlights the critical impact of surface roughness in modifying the structure of two-phase flow within mini- and microchannels, particularly in processes such as boiling and condensation. Channel surface roughness enhances flow resistance, affects the distribution of vapor bubbles, and enhances heat transfer by providing additional nucleation sites. Several experiments have shown that while increased surface roughness enhances the efficiency of heat transfer, increased flow resistance may hurt system performance. This is so because too high a surface roughness negatively impacts flow resistance, a factor of importance in the optimization for a balance between heat transfer and flow resistance, especially in high-performance compact heat exchangers. Furthermore, the review identifies that higher-degree measurement and characterization techniques of the surface roughness are increasingly required, as traditional 2D parameters may not fully represent the actual physics of complex surface interactions in two-phase flow systems. Consequently, the article calls for further research that can examine the exact relationship between roughness, flow structure, and thermal performance with the aim of improving design strategies for future heat exchanger technologies.

Study on Cavitation Erosion Mechanism of Ultra-High Molecular Weight Polyethylene (UHMWPE) and Polytetrafluoroethylene (PTFE)

Polymer materials possess low density, high strength, corrosion resistance, and excellent cavitation erosion resistance. As a result, they are widely used in marine, water conservancy, and other engineering equipment as replacements for metal materials. However, polymer friction pairs working in a water environment for an extended period are easily damaged by cavitation erosion. In this work, the cavitation behavior of polytetrafluoroethylene (PTFE) and ultra-high molecular weight polyethylene (UHMWPE) in deionized water and seawater is investigated through experiments and computational fluid dynamics (CFD) simulations. The results indicate that the cavitation erosion resistance of UHMWPE is significantly better than that of PTFE, and the UHMWPE has four cavitation process stages, while the PTFE has only three cavitation stages. 316 L counterparts in the seawater corrosion and cavitation coupling effect of a large number of metal particles off and wash polymer material surface, so that the cavitation erosion of PTFE and UHMWPE is more serious in seawater environment. CFD simulation demonstrates that the cavitation erosion zone under the radiator shows a semicircular distribution. Meanwhile, the formation of ring-shaped cavitation pit is related to the distribution of bubbles on the surface of the radiator. The cavitation rate of PTFE and UHMWPE is slowed down by the “water cushion effect.”

Evolutionary mechanism of Y-branches in acoustic Lichtenberg figures just below the water surface

The acoustic Lichtenberg figure (ALF) in an ultrasonic cleaner with a frequency of 28 kHz at different power levels was observed using high-speed photography. The nonlinear response of the cavitation structure was analyzed by the entropy spectrum in the ALF images, which showed the modulation influence of the primary acoustic field, exhibiting the fluctuations of the bubble distribution with time. Typical Y-branches predict the paths by which surrounding bubbles are attracted and converge into the structure, the branches are curved due to bubble-bubble interactions, and the curvature increases as the bubbles are approaching the main chain. The average travelling speed of bubbles along the branches is about 1.1 m/s, almost independent of power level of the ultrasonic cleaner. A theoretical model consisting of free bubbles and a straight bubble chain of finite length was developed to explore the evolutionary mechanism of branching. It was found that the bubble trajectories showed a bending tendency similar to the experimentally observed Y-branches, and the stationary straight bubble chain parallel to the main chain could evolve into a curved chain and eventually become a branch of the main chain. The theoretical predictions agree well with the experimental results, verifying the evolutionary mechanism of Y-branches in ALF.

Visual detection of thermal microvariation characteristics of transparent layer of quartz crucible

Aiming at detecting and locating bubbles in transparent layer of quartz crucible during the growth of monocrystalline silicon, an improved YOLOv5s model algorithm is proposed in this paper to achieve efficient and accurate crucible bubble detection. Optimize the anchor box through the K-means algorithm to adapt to the bubble dataset before and after the use of the crucible. Utilize the FasterNet backbone network to extract contextual information, enhancing target detection effectiveness. Additionally, the ECA attention mechanism is added to enhance information exchange and improve the accuracy of small target detection. Experimental results show that the improved algorithm performs significantly in bubble detection. For bubble detection before and after use, mAP increased by 2.1 % and 3.29 %, respectively. As usage time increases, the size, shape, and distribution of bubbles in the transparent layer of the quartz crucible change significantly, directly affecting the crucible’s effectiveness. Regular monitoring and evaluation of crucible bubble changes are crucial for maintaining stability and safety in the production process. Further research could explore how these findings can optimize crucible design and usage, improving performance and longevity.

Numerical simulation of fluid flow characteristics and ultrasonic cavitation performance in novel-designed stirred tank sonoreactor

A novel-designed stirred tank sonoreactor was developed to well solve large-scale dispersion of nanoparticles in liquid phase system. The fluid flow characteristics and ultrasonic cavitation performance in the sonoreactor were numerically simulated by CFD method. By comparing the pressure, cavitation bubble and velocity distribution under different situations, it is found that larger ultrasonic amplitude, relatively smaller ultrasonic frequency, higher saturated vapor pressure and lower viscosity of liquid medium are beneficial to ultrasonic cavitation. Besides, the acoustic flow action is strengthened with the increase of ultrasonic frequency and decrease of gas-liquid mixture's average density. For the designed sonoreactor, it is critical that high-frequency transducers should be determined near the bottom and upper region of the kettle, and large-amplitude transducers can be confirmed in the middle position. The research findings will provide theoretical and technical supports for developing state-of-the-art sonoreactors and optimizing ultrasonic process parameters in the industrialized preparation of nanocomposites.

Design of Aerated Oleogel-Hydrogel Mixtures for 3D Printing of Personalized Cannabis Edibles.

Cannabis seed oil oleogel structured with Glycerol Monostearate (20% w/w) was mixed with xanthan gum hydrogel (2% w/w) at different ratios ranging from 0% w/w hydrogel to 75% w/w hydrogel, using a syringe-to-syringe apparatus, for the preparation of 3D-printable food inks. This process enabled the simultaneous blend of oleogel and hydrogel phases and the incorporation of air in a reproducible and accurate manner. The printability of bigel inks with different mass ratios was evaluated by using a conventional benchtop food 3D printer. The printability of the inks was found to be negatively affected by the presence of higher portions of the hydrogel phase, while the printing performance of pure cannabis seed oil oleogel was superior compared to the printing performance of the bigel inks. The physicochemical properties of hybrid gels were investigated with rheological studies, thermophysical studies (Differential Scanning Calorimetry), Polarized Light Microscopy, and Confocal Laser Scanning Microscopy. The microstructure of the aerated inks was affected by the presence of a higher oleogel fraction, in terms of air bubble shape and distribution. The addition of hydrogel at concentrations higher than 50% w/w had a strong negative effect on the mechanical properties of the inks leading to a partial collapse of the printed structures and subsequently to poor printing performance.