Influence Of Bubble Size Research Articles

Influence of bubble size on perfluorooctanesulfonic acid degradation in a pilot scale non-thermal plasma treatment reactor

A 25L working volume non-thermal plasma-based treatment reactor was trialled to destroy per- and polyfluoroalkyl substances (PFAS) utilising argon bubbles to transport PFAS to the surface to be destroyed with plasma interaction at the argon-liquid interface. The breakdown rate of PFAS and the system's overall energy efficiency could be improved while minimising gas usage by utilising small bubbles (0.6–0.7 mm d32) to maximise the transport of PFAS to the plasma discharge for destruction. Vertically scaling the treatment reactor dimensions increases the overall liquid height and dwell time for bubbles to contact and transport PFAS molecules to the surface. The removal rate of perfluorooctane sulfonate (PFOS) correlated with the total surface area of the gas. Significant concentration gradients of PFOS could be observed when sampling from different liquid heights within the 25 L reactor. A one-dimensional model of mass transfer to the surface of rising bubbles was developed and gave good predictions of the overall rates of PFOS breakdown with modelled time constants of 0.14–0.18 min−1 versus 0.16 ± 0.01 min−1 for the fine bubble diffuser, and 0.048–0.053 min−1 versus 0.06 min−1 for the medium bubble diffuser. The time constant compared favourably with similar experiments at the 2 L scale of 0.11 min−1.

Potential response of single successive constant-current-driven electrolytic hydrogen bubbles spatially separated from the electrode

The presence of bubbles in gas-evolving electrolytic processes can heavily alter the mass transport of gaseous products and can induce severe overpotential penalties at the electrode through the action of bubble coverage (hyperpolarization) and electrolyte constriction (Ohmic shielding). However, bubble formation can also alleviate the overpotential by lowering the concentration of dissolved gas in the vicinity of the electrode. In this study, we investigate the latter by considering the growth of successive hydrogen bubbles driven by a constant current in alkaline-water electrolysis and their impact on the half-cell potential in the absence of hyperpolarization. The bubbles nucleate on a hydrophobic cavity surrounded by a ring microelectrode which remains free of bubble coverage. The dynamics of bubble growth does not adhere to one particular scaling law in time, but undergoes a smooth transition from pressure-driven towards supply-limited growth. The contributions of the different bubble-induced phenomena leading to the rich behaviour of the periodic fluctuations of the overpotential are identified throughout the different stages of the bubble lifetime, and the influence of bubble size and applied current on the concentration and Ohmic overpotential components is quantified. We find that the efficiency of gas absorption, and hence the concentration-lowering effect, increases with increasing bubble size and also with increasing current. However, the concentration-lowering effect is always eventually countered and overcome by the effect of Ohmic shielding as the bubble size outgrows and eclipses the electrode ring beneath.

Influence of Bubble Size on the Foaming Behavior of Molten Slag Containing FeO

Influence of Bubble Size on the Foaming Behavior of Molten Slag Containing FeO

Influence of bulk nanobubble concentration on the intensity of sonoluminescence

The present study mainly examined the effects of the volumetric concentration of nanobubbles (ultrafine bubbles) on the intensity of sonoluminescence (SL). The addition of nanobubbles at high acoustic amplitude enhanced the SL intensity for various bubble concentrations in comparison with that in pure water. This probably means that the resulting high amplitude is over the Blake threshold, and accordingly nanobubbles expand to some extent, leading to higher SL intensity. Therefore, nanobubbles have the potential to provide nucleation sites for sonochemistry. The influence of bubble size on the intensity of SL was also evaluated.

The influence of bubble size on chondrogenic differentiation of adipose-derived stem cells in gelatin microbubble scaffolds.

In human bodies, cartilage tissue lacks the ability to heal when it encounters trauma or lesions. This inability of cartilage tissue to self-repair motivates all sorts of studies on autologous chondrocyte transplantation; however, the drawback of high chondrocyte concentration is hard to overcome due to the loss of differentiated chondrocyte phenotype during cell culture. The differentiation of stem cells into chondrocytes is a possible solution to provide a large number of differentiated chondrocytes. In this study, human adipose-derived stem cells (hASCs) have been chosen as a model for further differentiation into chondrocytes. Studies on the influence of porous biomaterials on cell behavior have been performed to determine the best conditions for stem cell differentiation. Among these conditions, bubble or pore size is a factor that is commonly discussed. In our study, we fabricated four gelatin microbubble scaffolds with different pore sizes, but uniform spherical shapes by microfluidic techniques. Then, we compared the influence of pore size on cell growth and differentiation. Previously, we have examined adipogenesis and osteogenesis of hASCs in this scaffold. In this study, we focused on the influence of pore size on chondrogenesis. According to the experimental results of immunofluorescence staining, GAG content, and qPCR, the largest pore size, which is 200 μm in diameter, shows the best chondrogenesis result.

Analysis of attachment process of bubbles to high-density oil: Influence of bubble size and water chemistry

The interaction studies between high-density oil and bubbles were investigated to understand the bubble attachment behaviour on oil with respect to bubble size, pH and temperature. An increase in the bubble size from 350µm (microbubbles) to 1000µm (macrobubbles) demonstrated a decrease in the attachment force due to the reduction in contact angle by 7%. The results were in good agreement with the bubble-strength visualization tests, as the retraction of microbubble attached onto oil demonstrated a significant change in shape from concave to convex, as opposed to constant shape of macrobubble attachment-retraction from the oil layer. This was attributed to a higher cross sectional area to volume ratio (IA:V) of 12.3 for oil-microbubble attachment compared to IA:V of 4.9 for oil-macrobubble attachment. Due to the higher IA:V, microbubble is more firmly attached onto the oil layer compared to macrobubbles. Therefore, microbubbles could help to enhance the flotation process as it would preferentially attach to the oil contaminant as opposed to macrobubbles. The results also indicate that increase in pH is detrimental for oil-bubble attachment due to the production of natural surfactants, while the increase in temperature does not appear to affect the bubble attachment on the oil layer.

Influence of bubble size, diffuser width, and flow rate on the integral behavior of bubble plumes

AbstractA large‐eddy simulation based Eulerian‐Lagrangian model is employed to quantify the impact of bubble size, diffuser diameter, and gas flow rate on integral properties of bubble plumes, such as the plume's width, centerline velocity, and mass flux. Calculated quantities are compared with experimental data and integral model predictions. Furthermore, the LES data were used to assess the behavior of the entrainment coefficient, the momentum amplification factor, and the bubble‐to‐momentum spread ratio. It is found that bubble plumes with constant bubble size and smaller diameter behave in accordance with integral plume models. Plumes comprising larger and non‐uniform bubble sizes appear to deviate from past observations and model predictions. In multi‐diameter bubble plumes, a bubble self‐organisation takes place, i.e., small bubbles cluster in the center of the plume whilst large bubbles are found at the periphery of the plume. Multi‐diameter bubble plumes also feature a greater entrainment rate than single‐size bubble plumes, as well as a higher spread ratio and lower turbulent momentum rate. Once the plume is fully established, the size of the diffuser does not appear to affect integral properties of bubble plumes. However, plume development is affected by the diffuser width, as larger release areas lead to a delayed asymptotic behavior of the plume and consequently to a lower entrainment and higher spread ratio. Finally, the effect of the gas flow rate on the integral plume is studied and is deemed very relevant with regards to most integral plume properties and coefficients. This effect is already fairly well described by integral plume models.

Direct Numerical Simulations of spherical bubbles in vertical turbulent channel flow. Influence of bubble size and bidispersity

The paper presents two Direct Numerical Simulations of bubble swarms in a vertical turbulent channel flow and is intended as a complement to the companion paper, Santarelli and Fröhlich (2015). Both swarms addressed here are composed of spherical bubbles in contaminated fluid with a void fraction of 2.14%, as for the reference case in the companion paper. The first simulation reported is done for a monodisperse swarm of larger bubbles while in the second case a bidisperse swarm is considered. The influence of the bubble size and of the bidispersity is investigated by means of flow visualizations and quantitative statistical analysis. Due to the higher Reynolds number, the behavior of the larger bubbles differs from the one of the small bubbles and this impacts the turbulence of the carrier phase. The results show that for the parameter range considered both swarms induce elongated flow structures in the streamwise direction and that the liquid turbulence is enhanced by the bubbles, as quantified by the budget of the turbulence kinetic energy. In both cases the tendency of bubbles to align horizontally is confirmed while the analysis of mixed pairs in the bidisperse swarm allows elucidating the complex interaction of bubbles of different size.

Influence of bubble size and thermal dissipation on compressive wave attenuation in liquid foams

Acoustic or blast wave absorption by liquid foams is especially efficient and bubble size or liquid fraction optimization is an important challenge in this context. A resonant behavior of foams has recently been observed, but the main local dissipative process is still unknown. In this paper, we evidence the thermal origin of the dissipation, with an optimal bubble size close to the thermal boundary layer thickness. Using a shock tube, we produce typical pressure variation at time scales of the order of the millisecond, which propagates in the foam in linear and slightly nonlinear regimes.

Influence of bubble size on the fluid dynamic behavior of a DAF tank: A 3D numerical investigation

Abstract With computational fluid dynamics (CFD) methods, the influence of bubble size on the fluid dynamic behavior in a dissolved air flotation tank is investigated in this study. The choice of multiphase flow model between Euler–Euler and Euler–Lagrange approach is first addressed by comparing with the experimental results. The results indicate that Euler–Euler multiphase model is more suitable for the simulation of air/water flow in the DAF tank as it makes better performance in predicting air distribution. With the aid of Euler–Euler model, a systematic study was carried out to investigate the flow pattern and air distribution in the separation zone under bubble diameter from 30 μm to 70 μm. The results demonstrate that larger bubbles are conducive to the formation of stratified flow when bubble diameter ranges from 30 μm to 50 μm and show little impact on flow patterns when bubble diameter exceeds 50 μm. Bubble size has a significant influence on air distribution. Decreasing bubble size enlarges the height of “white water zone”.

Three-phase Contact Expansion During the Bubble Adhesion on an Inclined Plane

The bubble attachment onto a collecting surface is a common natural phenomenon and the bubble-particle interactions are used in numerous industrial applications. The adhesion process between a small single rising bubble and a stationary solid particle with hydrophobic surface in stagnant liquid is studied in this project. The real particle is replaced by a prism with an inclined plane representing a spherical particle with infinite diameter. Experiments were performed using a freely rising bubble method. The influence of bubble size and type of bubble surface mobility was studied and described both experimentally and theoretically. The molecular-kinetic and hydrodynamic models were used for theoretical description of the TPC expansion. According to our results, hydrodynamic model is not appropriate for the TPC line calculation. The value of its adjustable parameter is not in accordance with physical assumption. The molecular-kinetic model gives better results. Two adjustable parameters (the frequency of the molecular displacement and the average jumping distance) were calculated and their values correspond to the physical assumptions. It was found that the bubble size is the most important parameter influencing the TPC line expansion. The influence of bubble surface mobility is surprisingly low. Only the frequency of the molecular displacement differs for bubbles with mobile or immobile surface. This conclusion corresponds to the theoretical assumption that the presence of surface active agents decelerates the bubble motion.

CFD simulation of gas and solids mixing in FCC strippers

AbstractThe gas and solid mixing in fluid catalytic cracking strippers with and without internals were investigated using computational fluid dynamics simulations. The Eulerian–Eulerian two‐fluid model coupled with the modified Gidaspow drag model was used to simulate the gas‐solid flow behavior. The grid independency study and the comparison of 2D and 3D simulations were carried out first. The residence time distribution model and axial dispersion model were utilized to obtain the parameters indicating the back‐mixing degree, such as mean residence time, dimensionless variance and Peclet number of gas and solids. Moreover, the influence of bubble size and gas/solid flow distribution on the mass transfer between the bubble and emulsion phase were also analyzed. The results show that the baffles in the V‐baffle stripper can efficiently enhance the gas and solids mixing, reduce the back‐mixing degree of gas and solids, strengthen the mass transfer between the bubble and emulsion phase, and hence improve the stripping efficiency. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Phenomenological Simulation Model for the Prediction of Hydrodynamic Parameters of an Internal Loop Airlift Reactor

Airlift reactors are pneumatically agitated reactors finding wide applications in chemical and biotechnology industries as well as in the treatment of wastewater. The design and scale-up of an airlift reactor is difficult and largely based on empirical approaches. The bubble size, distribution, and concentration are important parameters that influence the gas holdup and interfacial area. However, the influence of bubble size and distribution are not taken into account by any of the empirical correlations. In the present investigation, a phenomenological approach has been developed to predict the gas holdup in an internal loop airlift reactor. This approach considers the effect of bubble dynamics such as bubble breakup and bubble coalescence in the column and employs a population balance approach to determine bubble concentration in the column. From the knowledge of number and size of the bubbles, gas holdup in the reactor was obtained. A reasonably good agreement was observed between the simulation model ...

The limits of fine particle flotation

Understanding the limits of fine particle flotation is the key to the selective separation of fine mineral particles. Fine particles have low collision efficiencies with gas bubbles and float slowly. There has been a great deal of work aimed at overcoming the inefficient collision of small particles with rising air bubbles. This review deals with the influence of bubble size, particle aggregation, different flow conditions, particle induction time, as well as the action of surface and capillary forces on fine particle–bubble capture. Recommendations for practice are given.

Image Processing Techniques in Foam Characterization

Foam is one of the most widely used energized fluids in petroleum industry at fracturing and drilling operations. The influence of bubble size and texture on foam rheology has been observed for years. However, no mathematical description has been introduced yet. This study aims to consider the effects of bubble size and texture in determining the rheological parameters. Rheological analysis using digital image processing techniques and conventional methods are compared using information acquired from a developed set-up. It has been observed that by using digital image processing techniques, the rheological parameters of foam could be determined accurately.

Influence of bubble size on micro-bubble drag reduction

Micro-bubble drag reduction experiments were conducted in a turbulent water channel flow. Compressed nitrogen was used to force flow through a slot injector located in the plate beneath the boundary layer of the tunnel test section. Gas and bubbly mixtures were injected into a turbulent boundary layer (TBL), and the resulting friction drag was measured downstream of the injector. Injection into tap water, a surfactant solution (Triton X-100, 20 ppm), and a salt-water solution (35 ppt) yielded bubbles of average diameter 476, 322 and 254 μm, respectively. In addition, lipid stabilized gas bubbles (44 μm) were injected into the boundary layer. Thus, bubbles with d+ values of 200 to 18 were injected. The results indicate that the measured drag reduction by micro-bubbles in a TBL is related strongly to the injected gas volumetric flow rate and the static pressure in the boundary layer, but is essentially independent of the size of the micro-bubbles over the size range tested.

Flow patterns in gas-assisted injection molding process in a channel

The flow field of a long bubble steadily expelling a viscous fluid confined by two closely located parallel plates is examined. In order to investigate the influence of bubble size on the flow field, a theoretical bubble profile is used to replace the complicated procedure for computing simultaneously the interface between the gas surface and fluid flows. The present study showed the two typical flow patterns and also a third flow pattern of the stagnation point moving in the region of the bubble tip front during transformation of the two typical flow patterns. The vorticity patterns are also drawn for various bubble profiles and are examined for their effect on the flow. The velocity field is also presented from two different viewpoints and the phenomena is examined. The stagnation point located on the center line between the bubble tip to the upstream is only found in the small range of \(2/3 <\lambda < 0.685\) in a channel, where λ is ratio of the bubble width to the distance between two parallel plates.

Influence of bubble size and flow velocity on AC electrical breakdown characteristics of LN 2

To evaluate insulation design of high voltage for high T c superconducting (HTS) power apparatus, the effect of bubble and electrode arrangements on the AC breakdown characteristics of LN 2 were investigated. Supposing that an outbreak of quench, the three electrode models were employed for breakdown voltage measurement in LN 2 with bubbles. Experimental results for various quench conditions revealed that the breakdown voltage of LN 2 with increasing the bubble size, flow velocity and electrode distance. Then, the relationship between the bubble conditions and the AC breakdown characteristics of LN 2 were clarified. Also, bubble movement phenomena were observed with an electrode model which consist of plane to cylindrical needle electrode immersed LN 2 for the simulation of the insulation environment in HTS pancake type coils and others of the quenching state.

Influence of bubble size on the transition from low-Re bubbly flow to slug flow in a vertical pipe

An upward air–water bubbly flow in a pipe was studied experimentally, special attention being paid to the transition from bubbly flow to slug flow. The pipe diameter was 72 mm and the height 18 m. The Reynolds number based on liquid flow was low-to-moderate ( U sl<0.2 m s−1), so that bubble break-up due to turbulence was nearly absent. Three different inlet devices were used, which had a significant influence on the initial bubble size and initial bubble concentration distribution. The transition from bubbly flow to slug flow was shown to be strongly dependent on the inlet configuration, particularly on the bubble size. A number of theoretical models for the transition from bubbly flow to slug flow were reviewed. The Taitel et al. [2] approach was combined with a bubble-size-dependent critical void-fraction expression of Song et al. [7]. This new formulation for the transition from bubbly flow to slug flow was in good agreement with the measurements.

The influence of bubble size on void fraction distribution in subcooled flow boiling at low pressure

The effect of bubble size on void fraction distribution in subcooled flow boiling in a vertical annular channel at low pressure is studied numerically. It is found that a simple linear formula used by Anglart and Nylund [1] and adopted in Reference [2] for calculation of bubble size as a function of local subcooling lacks a physical and experimental basis limiting the general application of the model for predicting subcooled flow boiling. A bubble size correlation proposed by Zeitoun and Shoukri [3] has been employed in this study. The predictions of void fraction profiles and the bubble size distributions, after incorporating the above bubble size correction, show very good agreement with the experimental data.