Motion Of Air Bubbles Research Articles

Design of electrical energy harvesting devices utilizing air bubbles sliding along a fluoropolymer immersed in water

Recent research has shown that it is possible to utilize contact electrification combined with electrostatic induction to harvest electrical energy from the mechanical motion of air bubbles sliding along a charged solid surface immersed in water. The working principle of these devices is simple, but the design is usually complicated as transduction efficiency depends on a number of interdependent parameters. Here we propose a simple analytical model and demonstrate how it can be used to determine the optimal energy per bubble for a given resistive load. The model allows one to estimate the optimal energy harvested per bubble in terms of polymer thickness, electrode separation and load resistance. It is shown that the model provides a good fit to experimental data. The model may be used as an initial step when designing energy harvesting devices utilizing air bubbles sliding along a solid surface.

Motion of Air Bubbles in a Cement Slurry.

The dynamics of air (gas) bubbles in a column of cement slurry is examined numerically. The air injected at the bottom of a laboratory-scale column through a porous distributor plate spatially distributes and migrates as a swarm of bubbles throughout the slurry toward the freeboard. The two-phase system of the cement slurry and the air bubbles is modeled using the conservation equations of mass and linear momentum in the framework of the volume-of-fluid (VOF) approach. The cement slurry is modeled using the Herschel-Bulkley and Bingham fluid models. Results show that the mean Sauter diameter and the mean rise velocity of the bubbles decrease with the gas flow rate. Meanwhile, it is found that the rising of the bubbles is controlled by breakup events, along with relatively weak path instabilities of the bubbles resulting in relatively straight trajectories, independent of the gas flow rate. The extent of the yielded region appears larger for the Herschel-Bulkley model compared to the Bingham fluid model (by approximately 10%).

Single-Bubble Rising in Shear-Thinning and Elastoviscoplastic Fluids Using a Geometric Volume of Fluid Algorithm.

The motion of air bubbles within a liquid plays a crucial role in various aspects including heat transfer and material quality. In the context of non-Newtonian fluids, such as elastoviscoplastic fluids, the presence of air bubbles significantly influences the viscosity of the liquid. This study presents the development of an interface-capturing method for multiphase viscoelastic fluid flow simulations. The proposed algorithm utilizes a geometric volume of fluid (isoAdvector) approach and incorporates a reconstructed distance function (RDF) to determine interface curvature instead of relying on volume fraction gradients. Additionally, a piecewise linear interface construction (PLIC) scheme is employed in conjunction with the RDF-based interface reconstruction for improved accuracy and robustness. The validation of the multiphase viscoelastic PLIC-RDF isoAdvector (MVP-RIA) algorithm involved simulations of the buoyancy-driven rise of a bubble in fluids with varying degrees of rheological complexity. First, the newly developed algorithm was applied to investigate the buoyancy-driven rise of a bubble in a Newtonian fluid on an unbounded domain. The results show excellent agreement with experimental and theoretical findings, capturing the bubble shape and velocity accurately. Next, the algorithm was extended to simulate the buoyancy-driven rise of a bubble in a viscoelastic shear-thinning fluid described by the Giesekus constitutive model. As the influence of normal stress surpasses surface tension, the bubble shape undergoes a transition to a prolate or teardrop shape, often exhibiting a cusp at the bubble tail. This is in contrast to the spherical, ellipsoidal, or spherical-cap shapes observed in the first case study with a bubble in a Newtonian fluid. Lastly, the algorithm was employed to study the buoyancy-driven rise of a bubble in an unbounded elastoviscoplastic medium, modeled using the Saramito-Herschel-Bulkley constitutive equation. It was observed that in very small air bubbles within the elastoviscoplastic fluid, the dominance of elasticity and capillary forces restricts the degree of bubble deformation. As the bubble volume increases, lateral stretching becomes prominent, resulting in the emergence of two tails. Ultimately, a highly elongated bubble shape with sharper tails is observed. The results show that by applying the newly developed MVP-RIA algorithm, with a tangible coarser grid compared to the algebraic VOF method, an accurate solution is achieved. This will open doors to plenty of applications such as bubble columns in reactors, oil and gas mixtures, 3D printing, polymer processing, etc.

Effect of platy gangue minerals in sulfide flotation: Part 2: Mechanisms

The presence of the usually unwanted, hydrophilic ore particles (gangue) in a mineral flotation froth plays a critical role. While they reduce the grade of the concentrate, they are also an important influence on the dynamical structure of the froth and its ability to transport value particles into the launder for ultimate recovery. This paper discusses how the shape and size of these gangue particles affect their transport through the froth zone under conditions typical of commercial sulfide flotation, but without hydrophobic ore particles present.Advective transport of gangue particles via entrainment depends on slurry drag due to the upward motion of air bubbles and the drainage effects of gravity on the liquid and solid phases confined in the network of fluid channels in the froth. In a companion paper (Bhambhani et al., 2023a) a significant increase in gangue transport rates through the froth zone was observed when a copper sulfide ore was mixed with platy mica (higher aspect ratio) compared to when the same ore was mixed with globular (lower aspect ratio) silica. It was hypothesized that this increased upwards transport rate was related to the greater upward drag experienced by the platy mica particles as compared to the lower aspect-ratio silica particles of comparable size. This hypothesis was tested by conducting froth sampling experiments, reported here, under increased upward drag conditions for the suspension and thus increased upward advective forces on the particles. It was observed that the entrainment vs particle size curves shifted upwards for the coarser sizes for both mica and silica. This was unexpected. It was additionally hypothesized that as the particle size approached the size of the channels (Plateau borders), through which settling particles must pass if they are to move downward, the particles become more confined and on average experience less downward motion. Platy mica particles of a certain sieve size are more susceptible to confinement in the channels than their lower aspect-ratio counterparts due to their reduced mass per particle. This was suggested from froth sampling experiments where drag and drainage were balanced in one case, and more drag dominated in the other.

Influence of air velocity and powder bed height on local density and float–sink of spheres in a gas–solid fluidized bed

Depending on their density, large objects will either float or sink in a gas–solid fluidized bed due to the liquid–like properties and density of the fluidized bed. The float–sink technology has been applied to dry density separations in industry. It is important for optimized industrial application to understand how the air velocity and the powder bed height affect the float–sink as the key operating factors. In this study, we investigated the float–sink of spheres of various density by varying the air velocity and the powder bed height. Also, we obtained the local fluidized bed density and the buoyancy force working on the sphere at various heights. We used the weight of a stainless-steel sphere in the fluidized bed to estimate the local fluidized bed density and the buoyancy force based on Archimedes principle. We found that the spheres float–sink behavior changes dramatically with the air velocity and the powder bed height and that the spheres float–sink behavior is correlated to ΔF = Fb – Fg, where Fb is the buoyancy force and Fg is the gravity force acting on the sphere. We also found that the fluidized bed density is not constant as a function of height when the air velocity is relatively large; the local fluidized bed density is interestingly either minimal at approximately mid-height or surprisingly, gradually increases with height within the fluidized bed at higher air velocities. The possible reasons are discussed by considering the local variation of the motion of air bubbles and the fluidized medium which affect the fluid force acting on the sphere in the fluidized bed.

Dynamic motion of air bubble on micro-structured surfaces by novel dynamic wettability evaluation method under liquid media

Dynamic motion of air bubble on micro-structured surfaces by novel dynamic wettability evaluation method under liquid media

Air Bubbles Displacement in Yield Stress Fluids

The motion of air bubbles in a yield stress fluid is analyzed numerically using a 2D approach and the finite volume technique. The multiphase flow is simulated using the volume of fluid method (VoF), which solves the conservation equations of mass and momentum coupled to a transport equation for the volume fraction of the fluids. The effects of yield stress, bubble size, number and position of bubbles rising in a viscoplastic fluid confined between vertical parallel plates are analyzed and discussed. The results indicate that the yield stress has great impact on the rising velocity. In the case of multiple bubbles flowing vertically, it is observed that the displacement of one bubble influences the rising velocity of the others, causing them to approach each other. As the distance between the bubbles increases the interference is reduced and the bubbles begin to flow as single ones. When two bubbles are horizontally positioned, they can approach or move away from each other, depending on the initial distance between them. Furthermore, the bubbles shape is analyzed as a function of the governing parameters. It is observed that for lower Reynolds number the bubbles present a circular shape, but as inertia increases the bubble becomes ellipsoidal.

Development of suitable product recovery systems of continuous hybrid jig for plastic-plastic separation

A modified jig called the hybrid jig was recently developed to separate mixed-plastics with similar specific gravities effectively using the concepts of bubble attachment, surface wettability and gravity separation. This method was effective in a batch-type jig setup, but when applied to a continuous-type jig setup, the efficiency of the process dramatically decreased. This drop in efficiency was attributed to the unintended negative effects of air bubbles on separation especially close to the screw-type extractor at the product end though this type of product recovery system was successfully applied to the RETAC and reverse jigs. To address this problem, a better product recovery system for continuous-type hybrid jig is proposed in this study, and the effects of air injection rate at different positions of the hybrid jig separation chamber were evaluated. The results showed that fluidization behavior of particles in the hybrid jig was influenced by not only water pulsation but also the rising motion of air bubbles. To improve the purity of heavy materials in the bottom layer products, two product recovery systems are proposed: (1) a screw-type extractor with one “separating” single-screen, and (2) a screw-type extractor with modified air injection and water pulsation (i.e., upward flow period was shortened).

Step-Wise Velocity of an Air Bubble Rising in a Vertical Tube Filled with a Liquid Dispersion of Nanoparticles.

The motion of air bubbles in tubes filled with aqueous suspensions of nanoparticles (nanofluids) is of practical interest for bubble jets, lab-on-a-chip, and transporting media. Therefore, the focus of this study is the dynamics of air bubbles rising in a tube in a nanofluid. Many authors experimentally and analytically proposed that the velocity of rising air bubbles is constant for long air bubbles suspended in a vertical tube in common liquids (e.g. an aqueous glycerol solution) when the capillary number is larger than 10-4. For the first time, we report here a systematic study of an air bubble rising in a vertical tube in a nanofluid (e.g. an aqueous silica dioxide nanoparticle suspension, nominal particle size, 19 nm). We varied the bubble length scaled by the diameter of the tubes (L/D), the concentration of the nanofluid (10 and 12.5 v %), and the tube diameter (0.45, 0.47, and 0.50 cm). The presence of the nanoparticles creates a significant change in the bubble velocity compared with the bubble rising in the common liquid with the same bulk viscosity. We observed a novel phenomenon of a step-wise increase in the air bubble rising velocity versus bubble length for small capillary numbers less than 10-7. This step-wise velocity increase versus the bubble length was not observed in a common fluid. The step-wise velocity increase is attributed to the nanoparticle self-layering phenomenon in the film adjacent to the tube wall. To elucidate the role of the nanoparticle film self-layering on the bubble rising velocity, the effect of the capillary number, the tube diameter (e.g. the capillary pressure), and nanofilm viscosity are investigated. We propose a model that takes into consideration the nanoparticle layering in the film confinement to explain the step-wise velocity phenomenon versus the length of the bubble. The oscillatory film interaction energy isotherm is calculated and the Frenkel approach is used to estimate the film viscosity.

Two-dimensional spin coating technology and the effect of artificial gravity on film’s air-bubbling

This article mathematically and experimentally investigates the effects of increased artificial gravity acceleration on a film's air-bubbling defect. The controllable artificial gravity is generated using a two-dimensional (2D) spin coating method. In order to conduct these studies a 2D spin coater was designed and manufactured. The mathematics of particle motion in fluids (Stokes' Law) is investigated in order to analyze the motion of air-bubbles along the thickness of the film. The mathematic of particle motion in fluids is simulated using MATLAB in a wide range of variation of related parameters. These simulations illustrate that increasing the artificial gravity acceleration increases the velocity of air-bubbles motion and decreases the decay time of the air-bubble release. Simulations also show that the fluid viscosity and size of air-bubbles are effective factors which can affect the decay time of air-bubble release and their velocity along the thickness of the film. To investigate the simulation results, a high viscous photoresist (SU8-3050) is used as the coating material. The mentioned photoresist is coated with the both conventional and 2D spin coating methods and their results are compared. The surface and cross section of coated substrates are imaged with an SEM device. The natural results of mathematic simulations are in agreement with our experimental comparisons.

Effect of air bubble injection on the performance of a horizontal helical shell and coiled tube heat exchanger: An experimental study

This paper aims to study experimentally the effects of air bubble injection on the performance of a horizontal helical shell and coiled tube heat exchanger. The variations of number of thermal units (NTU), exergy loss and effectiveness due to the air bubbles injection with different air flow rates are evaluated. A new procedure for injecting the air bubbles into the shell side flow of the heat exchanger is proposed. The results exhibited a significant increase in the effectiveness and NTU of the heat exchanger as the air bubbles were injected. It is suggested that the disturbance and perhaps the turbulence intensity of the shell side flow are increased due to the motion of air bubbles resulting in an increment in the value of NTU and exergy loss. In addition, the mixing effect of the bubbles and the interaction with the thermal boundary layer can increase the velocity (hence the Reynolds number) of the shell side flow.

Spiral Motion of Air Bubbles in Multiphase Mixing for Wastewater Treatment

Vortex flow forms due to spiral motion of the air bubbles around water in the aeration tank. The formation of vortices would indicate the mixing pattern of water and air in the aeration tank. The mixing of two phases such as air-water or water-air flow systems in the aeration tank is important to increase oxygen transfer efficiency in aeration process. With different process parameters of the aeration tank such as the diameter of pore size of the membrane, diameter of diffuser and air mass flow rate are simulated using ANSYSTM CFD software. When the air mass flow rate increasing, the diameter of pore size decreasing, the air-water or vice versa are mixed homogenously and increases the oxygen transfer efficiency. The air-water mixing efficiency increases if the diameter of membrane pore size decreases at higher mass flow rate and the diameter of diffuser is in the practical range which is between 4 to 12. An improvement of vortices occurs in an aeration tank when higher strength of air velocity curl occurs.

Transurethral prostate thermotherapy: filtering the bowel motion during MR-thermometry processing

Magnetic resonance imaging (MRI)-guided transurethral ultrasound therapy is a minimally-invasive image-guided treatment for localized prostate cancer offering precise targeting of tissue within the gland. The accuracy of MR thermometry is critical for precise on-line feedback control as well as for monitoring potential thermal injury of surrounding tissues, especially the rectum wall. The PRFS thermometry method used is sensitive to tissue motion and change in the local magnetic susceptibility which might be related to the motion of air bubbles in the rectum in the particular case of MR controlled prostate cancer therapy.

Experimental studies on the shape and motion of air bubbles in viscous liquids

This paper is concerned with single bubble dynamics over a wide experimental data set in stagnant water and glycerol aqueous solution. The bubble trajectory in three-dimensional space was deduced by analyzing the bubble characteristics in two-dimensional plane captured by a single high-speed camera and the bubble trajectory in the water was ascertained by this method. Bubble shape, trajectory and terminal velocity in water, which closely related and strongly influenced by each other, are not only determined by bubble diameter, but also dramatically influenced by nozzle diameters, i.e. the bubble dynamics is sensitive to the disturbance of detachment process. The bubbles remain spherical and rise up rectilinearly when their diameters are small enough. Otherwise, the bubbles begin to deform to ellipsoidal, oblate ellipsoidal, or cap shape, with surface wobbling strongly, and proceed in a zigzagging, helical, nearly zigzagging or helical motion. In this case, periodic oscillations occur at the velocity and aspect ratio of the bubbles. Moreover, there exists an inverse function relationship between them, a large deformation, i.e. a small aspect ratio will lead to a high velocity and vice versa. However, in glycerol aqueous solution, bubble shape, trajectory and velocity is stable under a certain bubble diameter. In the water, bubble shape is mainly dominated by the inertial force and surface tension, and the influence caused by the viscous force could be neglected. The influence of gravity should be taken into consideration if the bubble diameter is large enough. However, the bubble shape is mainly dominated by the viscous force, surface tension and inertial force in the glycerol aqueous solution. Available correlations in the literature do not give fully satisfactory results in predicting aspect ratio, and new correlations combined Weber number with Eötvös number and Weber number with Reynolds number were proposed to correlate bubble shape in water and glycerol aqueous solution, respectively, showing that a good relevance between them in the range of the present experimental data set.

Spatiotemporal filtering of MR-temperature artifacts arising from bowel motion during transurethral MR-HIFU.

Transurethral MR-HIFU is a minimally invasive image-guided treatment for localized prostate cancer that enables precise targeting of tissue within the gland. The treatment is performed within a clinical MRI to obtain real-time MR thermometry used as an active feedback to control the spatial heating pattern in the prostate and to monitor for potential damage to surrounding tissues. This requires that the MR thermometry measurements are an accurate representation of the true tissue temperature. The proton resonance frequency shift thermometry method used is sensitive to tissue motion and changes in the local magnetic susceptibility that can be caused by the motion of air bubbles in the rectum, which can impact the performance of transurethral MR-HIFU in these regions of the gland. A method is proposed for filtering of temperature artifacts based on the temporal variance of the temperature, using empirical and dynamic positional knowledge of the ultrasonic heating beam, and an estimation of the measurement noise. A two-step correction strategy is introduced which eliminates artifact-detected temperature variations while keeping the noise level low through spatial averaging. The filter has been evaluated by postprocessing data from five human transurethral ultrasound treatments. The two-step correction process led to reduced final temperature standard deviation in the prostate and rectum areas where the artifact was located, without negatively affecting areas distal to the artifact. The performance of the filter was also found to be consistent across all six of the data sets evaluated. The evaluation of the detection criterion parameter M determined that a value of M = 3 achieves a conservative filter with minimal loss of spatial resolution during the process. The filter was able to remove most artifacts due to the presence of moving air bubbles in the rectum during transurethral MR-HIFU. A quantitative estimation of the filter capabilities shows a systematic improvement in the standard deviation of the corrected temperature maps in the rectum zone as well as in the entire acquired slice.

Development of combined salt- and air-assisted liquid–liquid microextraction as a novel sample preparation technique

A new, simple and sensitive method based on a combination of salt-assisted liquid–liquid microextraction (SALLME) with an aeration process, namely, salt- and air-assisted liquid–liquid microextraction (SAALLME), coupled with high-performance liquid chromatography (HPLC), has been developed for the quantitative analysis of β-naphthol, naphthalene and anthracene as model analytes. In this new technique, the centrifugation step has been replaced with an aeration process. In the proposed technique, the extraction solvent and salt are added into the aqueous sample solution and dissolved using a vortex. Phase separation is performed via motion of air bubbles from the bottom to the top of extraction tube, which promotes the transfer of analytes into the supernatant organic phase. Various parameters that affect the extraction efficiency, such as the extraction solvent and its volume, salt and its concentration, the volume of injected air, vortex time and sample pH, were evaluated and optimized. The calibration curves showed good linearity (r2 > 0.9959) and precision (RSD < 7.2%) in the working concentration ranges. The limit of detection (LOD) for β-naphthol, naphthalene and anthracene were 4.25, 8.34 and 0.22 ng mL−1, respectively. The recoveries were in the range of 92.0–99.0% with RSD values ranging from 4.8% to 7.2%.

Vortex and air assisted liquid–liquid microextraction as a sample preparation method for high-performed liquid chromatography determinations

A novel, simple and sensitive method based on vortex and air assisted liquid–liquid microextraction (VAALLME) technique coupled with high-performance liquid chromatography (HPLC) has been developed for quantitative analysis of β-naphthol, naphthalene and anthracene as model analytes. Unlike the dispersive liquid–liquid microextraction (DLLME), dispersive solvent and centrifuging step were eliminated in proposed technique. In this technique, extraction solvent was dispersed into the aqueous sample solution by using vortex. Phase separation was achieved via motion of air bubbles from the bottom to top of the extraction tube, which promoted the analytes transfer into the supernatant organic phase. Influential parameters on the extraction efficiency such as type and volume of extraction solvent, salt type and its concentration, vortex and aeration times, and sample pH were evaluated and optimized. The calibration curves showed good linearity (r2>0.9947) and precision (RSD<5.0%) in the working concentration ranges. The limit of detection (LOD) for β-naphthol, naphthalene and anthracene were 10, 5.0 and 0.5ngmL−1, respectively. The recoveries were in the range of 97.0–102.0% with RSD values ranging from 2.2 to 5.2%.

Motions of Air Bubbles Trapped in Grooved and Plane Journal Bearings of Operating Fluid Dynamic Bearings

We investigated the motion of air bubbles trapped in grooved and plane journal bearings of operating fluid dynamic bearings (FDBs) by using the finite volume method and the volume of fluid method. The motion of a trapped air bubble in grooved journal bearing is mostly determined by surface tension and the pressure difference due to the wedge effect of the groove. Also, the motion of trapped air bubbles in plane journal bearing is mostly determined by surface tension and the Coutte flow. A novel design of FDBs was finally proposed to expel the air bubbles trapped in grooved journal and plane journal bearings out of operating FDBs.

J134 溶融プラスチック充填層の気泡挙動と熱伝導に対する実験的検討(一般講演(3))

J134 溶融プラスチック充填層の気泡挙動と熱伝導に対する実験的検討(一般講演(3))

Single- and two-phase numerical models of Dissolved Air Flotation: Comparison of 2D and 3D simulations

In this work single- and two-phase flow numerical models of a pilot DAF (Dissolved Air Flotation) tank are presented. In the latter framework, the mixture in the tank consists of water and air bubbles. The motion of air bubbles is resolved within the Lagrangian frame of reference. Interaction between bubbles is neglected in the present model. To account for turbulence in the tank, the realizable k– ɛ model is selected as a compromise between a need to correctly resolve the flow and the computational cost of the calculations. To validate the numerical simulations the results are compared with experimental results of an independent research group. The paper discusses the choice between performing two (2D)- or three-dimensional (3D) simulations of a flotation process. Our simulations show that a 3D hydrodynamic model of the flow pattern can well reproduce the single-phase flow in the pilot tank. Despite the major changes in the flow pattern that occur when the second phase (air bubbles) is introduced, the validated single-phase model provides a useful tool in the process of setting up the two-phase model. We show in the paper that a 2D two-phase model cannot resolve successfully the flow in the contact zone, whereas major flow characteristics in the separation zone can, to some extent, be described by a 2D approach (e.g. the stratification of the flow). In addition, two-phase simulations demonstrate that a 3D model is sensitive to the distribution of air and water from the needle valves, which, in turn, influences the stability of the solution obtained.