Bubble Production Research Articles

Dynamics of bubble formation in yield stress fluids in parallelized microchannels

The bubble formation in yield stress fluids in parallelized microchannels is investigated experimentally. Nitrogen and Carbopol gel are used as the dispersed and continuous phases, respectively. Due to the feedback effect of the downstream microchannels, the uniformity and stability of bubble formation strongly depends on the properties of gels and operating conditions. The effect of yield stress on the interface evolution during bubble formation is investigated under different mass factions of Carbopol (0.2 %, 0.13 %, 0.05 %) and flow rates of gas (0.1–400 mL·min−1) and liquid (0.03–0.2 mL·min−1). The activation rate of parallel microchannels for bubble production increases with the decrease in the concentrations of Carbopol. The increase of liquid flow rate and the decrease of gas flow rate benefit the uniformity of bubble formation frequency. However, under the double-channel bubble-generation flow pattern, reducing the liquid flow rate significantly improves the stability of bubble formation.

Experimental observations and modelling of sub-Hinze bubble production by turbulent bubble break-up

We present experiments on large air cavities spanning a wide range of sizes relative to the Hinze scale$d_{H}$, the scale at which turbulent stresses are balanced by surface tension, disintegrating in turbulence. For cavities with initial sizes$d_0$much larger than$d_{H}$(probing up to$d_0/d_{H} = 8.3$), the size distribution of bubbles smaller than$d_{H}$follows$N(d) \propto d^{-3/2}$, with$d$the bubble diameter. The capillary instability of ligaments involved in the deformation of the large bubbles is shown visually to be responsible for the creation of the small bubbles. Turning to dynamical, three-dimensional measurements of individual break-up events, we describe the break-up child size distribution and the number of child bubbles formed as a function of$d_0/d_{H}$. Then, to model the evolution of a population of bubbles produced by turbulent bubble break-up, we propose a population balance framework in which break-up involves two physical processes: an inertial deformation to the parent bubble that sets the size of large child bubbles, and a capillary instability that sets the size of small child bubbles. A Monte Carlo approach is used to construct the child size distribution, with simulated stochastic break-ups constrained by our experimental measurements and the understanding of the role of capillarity in small bubble production. This approach reproduces the experimental time evolution of the bubble size distribution during the disintegration of large air cavities in turbulence.

Effect of Gas Sources on the Oxygen Transfer Efficiency Produced by Fine Bubbles Generator

Fine bubbles (micro to nanometer-sized) have rapidly gained popularity in academia and industry due to their unique properties, such as their high surface area, stability, and longevity. In this study, the performance of oxygen transfer rate efficiency in fine bubbles with high purity oxygen and atmospheric air was analyzed. In this study, the developed fine bubbles generator with power requirement 300 watt was used to evaluate the production of fine bubbles and oxygen transfer efficiency at two type gas sources i.e., ambient air and high-purity oxygen in the small bench aqueous media (5 L water tank). The fine bubbles generator was set up at the pressure in 50 psi and gas flow rate at 0.3 L/min to produce fine bubbles in water medium. The effect of water recirculation process in the bubbles production was measured using particles size analyzer (PSA), zeta potential and dissolved oxygen (DO) meter to measure temperature and dissolved oxygen on the water. Dissolved Oxygen (DO) measurement shows the saturation value of oxygen concentration in water, for high purity oxygen is 30 mg/L higher than air which has a value of 8.64 mg/L. This causes the efficiency of gas transfer in high-purity oxygen to reach 72.09% higher than ambient air at 35.39%. The particle size distribution shows that the mean size of bubbles after 10 minutes recirculation was 465.5 nm and 599.9 nm correspondingly for ambient air and oxygen gas source. High purity oxygen also affect to the zeta potential value tends to be more negative than in ambient air. The type of high-purity oxygen gas can increase the efficiency of the oxygen transfer rate so that the gas containing high-purity oxygen increases the volumetric oxygen transfer rate coefficient which is 2 times higher than using ambient air.

Bubbles spray aerosols: Certitudes and mysteries.

Ocean spray aerosol formed by bubble bursting are at the core of a broad range of atmospheric processes: they are efficient cloud condensation nuclei and carry a variety of chemical, biological, and biomass material from the surface of the ocean to the atmosphere. The origin and composition of these aerosols is sensibly controlled by the detailed fluid mechanics of bubble bursting. This perspective summarizes our present-day knowledge on how bursting bubbles at the surface of a liquid pool contribute to its fragmentation, namely to the formation of droplets stripped from the pool, and associated mechanisms. In particular, we describe bounds and yields for each distinct mechanism, and the way they are sensitive to the bubble production and environmental conditions. We also underline the consequences of each mechanism on some of the many air-sea interactions phenomena identified to date. Attention is specifically payed at delimiting the known from the unknown and the certitudes from the speculations.

Planetary nebulae with Wolf–Rayet-type central stars – IV. NGC 1501 and its mixing layer

ABSTRACT Theory predicts that the temperature of the X-ray-emitting gas (∼106 K) detected from planetary nebulae (PNe) is a consequence of mixing or thermal conduction when in contact with the ionized outer rim (∼104 K). Gas at intermediate temperatures (∼105 K) can be used to study the physics of the production of X-ray-emitting gas, via C iv, N v, and O vi ions. Here, we model the stellar atmosphere of the CSPN of NGC 1501 to demonstrate that even this hot H-deficient [WO4]-type star cannot produce these emission lines by photoionization. We use the detection of the C iv lines to assess the physical properties of the mixing region in this PNe in comparison with its X-ray-emitting gas, rendering NGC 1501 only the second PNe with such characterization. We extend our predictions to the hottest [WO1] and cooler [WC5] spectral types and demonstrate that most energetic photons are absorbed in the dense winds of [WR] CSPN and highly ionized species can be used to study the physics behind the production of hot bubbles in PNe. We found that the UV observations of NGC 2452, NGC 6751, and NGC 6905 are consistent with the presence mixing layers and hot bubbles, providing excellent candidates for future X-ray observations.

A yearlong record of acoustic propagation and ambient sound in a seagrass meadow

Seagrasses are sentinel species whose structures are sensitive to variations in environmental conditions and thus reliable indicators of long-term changes in sea level and regional climate. The biological and physical characteristics of seagrasses are known to affect acoustic propagation. Gas bodies contained within the seagrass tissue as well as photosynthetic-driven bubble production result in free gas bubbles attached to the plants and in the water. The detachment of gas bubbles from the plants is also a source of ambient sound. In this work, we deployed a measurement system in a shallow (1.3 m deep) seagrass meadow that included an acoustic projector, a set of receiving hydrophones, an instrumentation pressure vessel that housed the electronics controlling the acoustic data acquisition and data storage, and a suite of environmental sensor loggers. Acoustic propagation and ambient sound were collected every ten minutes for a period of one year. Coincident measurements of water temperature, salinity, dissolved oxygen, and photosynthetically active radiation were also collected and used to interpret the acoustic data. We present preliminary results from the yearlong deployment of the acoustic system in a moderately dense seagrass bed dominated by Thalassia testudinum (turtle grass) in Corpus Christi Bay, Texas. [Work supported by NSF.]

Research on nano H2/O2 bubble generating mechanism and characteristics.

In this research, electrolysis water is used to produce hydrogen and oxygen for carrying out the vertical cutting through high-speed water in order that the bubbles will be refined for generating the nano H2/O2 bubble liquid. In the meantime, a Nanobubble Generator is developed to verify the basic characteristics of the produced nano H2/O2 bubbles. Its purpose is to identify the maximum concentration of bubbles in the nano H2/O2 bubble liquid, the bubble production efficiency and bubble electrification characteristics as well as the effect of reducing the pipe flow friction resistance together with the characteristics of nanobubbles containing varied gases. By verifying the nano H2/O2 bubbles, it is hoped that the flowing rate of the hollow electrode can be elevated.

Capillary driven fragmentation of large gas bubbles in turbulence

Bubble fragmentation drives up to 40% of the CO2 transfer from the atmosphere to the ocean. However, the small size bubble distribution, mainly responsible for gas dissolution, is still poorly understood. Combining experimental and numerical calculations, we find that capillary effects set small bubble production rate which physically explains the origin of their size distribution.

Bubble formation by argon injection through the down-leg snorkel with Ruhrstahl–Heraeus (RH) circulating flow

The objective for bubble refining is to control the production of plentiful, tiny and dispersed bubbles. For this, the rapid downward stream in the down-leg snorkel of an RH vessel can separate the injected gas into fine bubbles. In this work, the formation behavior of bubbles generated by argon injection through the down-leg is investigated by combining physical simulation experiments and multiphase flow simulations. A physical model was first established to investigate the formation behavior of argon bubbles. A Volume of Fluid model (VOF) was then developed and the results from the physical simulation used to validate the mathematical model. Subsequently, the validated VOF model was expanded to include the prediction of bubble formation behavior in liquid steel. From the results obtained, it was found that with a wetting orifice, separated bubbles are obtained under most conditions. When the orifice is non-wettable, the injected gas forms a curtain. When the separated bubbles are carried down into the ladle, they can be compressed to 70 % of their initial value, which enhances collision, promotes adherence to inclusions and facilitates their removal.

Ultrasound single-phase CBE imaging for monitoring radiofrequency ablation of the liver tumor: A preliminary clinical validation.

Radiofrequency ablation (RFA) is an alternative treatment for early-stage hepatocellular carcinoma (HCC). The production of gas bubbles by RFA indicates threshold temperature of tissue necrosis and results in changes in backscattered energy (CBE) when ultrasound monitors RFA. In this study, ultrasound single-phase CBE imaging was used as a means of monitoring RFA of the liver tumor by analyzing the backscattering of ultrasound from gas bubbles in the liver. A total of 19 HCC patients were enrolled in the study. An ultrasound system was used during RFA to monitor the ablation process and acquire raw image data consisting of backscattered signals for single-phase CBE imaging. On the basis of single-phase CBE imaging, the area corresponding to the range of gas bubbles was compared with the tumor sizes and ablation zones estimated from computed tomography. During RFA, ultrasound single-phase CBE imaging enabled improved visualization of gas bubbles. Measured gas bubble areas by CBE were related to tumor size (the Spearman correlation coefficient r s = 0.86; p < 0.05); less dependent on the ablation zone. Approximately 95% of the data fell within the limits of agreement in Bland-Altman plots, and 58% of the data fell within the 95% CI. This study suggests that single-phase CBE imaging provides information about liver tumor size because of the abundant vessels in liver tumors that promote the generation of gas bubbles, which serve as natural contrast agents in RFAs to enhance ultrasound backscattering. Ultrasound single-phase CBE imaging may allow clinicians to determine if the required minimum RFA efficacy level is reached by assessing gas bubbles in the liver tumors.

Hunting, Fighting, or Playing with Bubbles: Possible Usage and Acoustic Characteristics of Bubble Burst Sounds Produced by the Amazon River Dolphin (Inia geoffrensis)

Acoustic characteristics of bubble production by an odontocete were documented for the first time. Bubble sounds produced by the Amazon river dolphin (Inia geoffrensis) were recorded incidentally as part of a survey of fish sounds in the Pacaya–Samiria National Reserve of Peru on six dates between 4 and 24 July 2012. Dolphins were observed to periodically produce large clouds of bubbles underneath or near the survey boat (averaging 7/survey or 8/h) as it drifted through areas of actively foraging dolphins. The bubble production was classified as bubble bursts due to their similarity to bubble bursts produced by other cetaceans. Bubble burst sounds had a mean peak frequency of 402 Hz and duration of 8.9 s (n = 51). Bubble bursts were temporally clustered with an average interval of 169 s (0.1 to 1,187 s) between bursts. Bubble bursts were disproportionately more likely to be present when fish sounds were also present, but it is not known if the association was due to predation or other factors. A review of the literature finds similar bubble production has been reported in at least 14 other species of cetaceans (4 mysticetes and 10 odontocetes). Most are commonly associated with play, surprise, agonistic, and foraging behaviors. We discuss each of these possibilities and conclude that Amazon river dolphin bubble burst behavior is most likely related to foraging or aggressive behavior because the behavior occurred in feeding areas and appeared to be directed at the drifting boat. We further propose a novel hypothesis that the bubble bursts are a hunting strategy used to disperse prey associated with floating vegetation mats and other forms of drifting materials used by fishes for shelter. Future research is needed to better understand the behavior associated with bubble production by the Amazon river dolphin.

Process to Reduce Particulate Matter in Ambient Air Using Bubbles of Sodium Palmitate

AbstractMining is a significant dust‐generating activity, and almost every major process in mining contributes to the atmospheric load of total suspended particulate matter (TSPM). Prolonged exposure to TSPM is known to cause various respiratory diseases, including pneumoconiosis among miners. Thus, the generation of airborne TSPM and its subsequent movement into the surrounding environment is a significant problem for the mining industry. The present study describes a possible approach for removing SPM from air by the environmentally friendly approach of releasing bubbles of a salt of a long‐chain fatty acid. More specifically, the study examined the production of bubbles of sodium palmitate and releasing them into the air to capture and remove SPM. TPSM was reduced by using this method at laboratory scale.

Experimental Investigation of a Cavitating Water Flow With the Addition of Drag- Reducing Agents

Local reduction of the pressure in a flow field to levels lower than the saturation pressure triggers the production of tiny vaporous bubbles and causes the cavitation phenomenon. Higher pressure reductions significantly increase the cavitation bubbles’ population, which can coalesce and generate large-scale cavitation structures such as cloud cavitation that shed downstream of the flow channel. The chaotic collapse of cavities produces strong shockwaves in regions with a recovered pressure which causes serious erosion on solid surfaces and high levels of noise. Hence, there is a growing interest in cavitation control methods. In this study, drag-reducing polymer additives are utilized as cavitation reducing (CR) agents in a converging-diverging mesoscale nozzle to verify the applicability of these agents in the control of the cavitation process. Analysis of high-speed images of the cavitating flow fields reveals that the viscoelastic flow of a 400 ppm polymer solution reduced the cavitation intensity by nearly 60 % relative to the pure water flow at a similar Reynolds number. Ultra-high-speed imaging of single cavitating bubbles at the inception showed that in a viscoelastic flow, the collapse period of cavities is longer, and their sizes are shrunk at a lower rate relative to their counterparts in the puer water. Particle image velocimetry (PIV) was used to study the near-wall turbulent flow fields at the flow conditions close to the cavitation inception, at different flow locations with non-zero pressure gradients present on the curved surfaces. Preliminary analysis of the results reveals that viscoelasticity alters the near-wall turbulence and distribution of the pressure gradient fluctuations, which might link to the significant reduction of cavitation intensity in polymeric flows.

Enhanced Contrast of WO3-Based Smart Windows by Continuous Li-Ion Insertion and Metal Electroplating.

The electrochromic WO3 smart window based on an aqueous electrolyte shows an excellent liquid/solid interface and thus can achieve a fast electrochromic response, while the aqueous electrolyte has a limited electrochemical window, which probably induces the H+ reduction and degrades the practical application. Here, we propose a strategy to modify the traditional Li+ acidic aqueous electrolyte by adding some selective inert metal ions, which not only improve the electrochromic performance but also avoid the possible production of hydrogen bubbles due to the broadened electrochemical window. Furthermore, reversible electroplating of inert metal ions will occur, leading to an enhanced optical transmission change of up to 77.5% at 500 nm and 70.4% at 700 nm. This combination of Li-ion insertion and metal electroplating in the ESW device makes it superior to all of the previous reports. The device also demonstrates high stability and high electrochromic efficiency after 1000 cycles. The current study not only emphasizes the rational design for aqueous electrolytes but also demonstrates a practical way to realize an excellent electrochromic window for practical applications.

Bubble flushing effect in micro EDM drilling and its relation with debris

In micro electrical discharge machining (EDM) drilling with a liquid dielectric, the bubble flushing effect is significant to the dielectric exchange and debris evacuation. Clarifying its mechanism is critical to guild the machining and avoid the deterioration of machining environment, which is a common problem in deep hole drilling with micro EDM. However, the investigation of bubble flushing is always disturbed by debris, which affects bubble production through disturbing the discharge process, because the debris is always conductive as a byproduct of metal materials. In this paper, the bubble flushing effect is systematically investigated from the in situ observation to statistical analysis to clarify the driven force for bubble movement or escape in the narrow gap and assess the evolution of bubble flushing effect with increasing hole depth. Moreover, the influence of debris on the bubble flushing effect is quantitatively analyzed through the contrast experiments in single crystal SiC and stainless steel SUS304 (SS304). It is confirmed in this paper that the debris of SiC has nearly no effect on the discharge due to its special material property. The visible and quantitative investigations reveal the nature bubble flushing effect in micro EDM drilling. The contrast analysis of bubble flushing effect under two cases (with/without influence of debris) clarifies how bubble and debris affect one another and their influences on the drilling process. This study provides new insights into the mechanism of micro EDM drilling and benefits to optimize the actual machining processes for the industry and manufacturer.

Optimisation on the Performance of Bubble-Bursting Atomisation for Minimum Quantity Lubrication with Vegetable Oil Using Computational Fluid Dynamics Simulation

Sustainable and green machining technologies have become a welcomed topic in the manufacturing industries. One of the emerging sustainable technologies is minimum quantity lubrication (MQL). In this study, the optimisation and study of the bubble-bursting atomisation system applied to MQL machining is carried out through the computational fluid dynamics (CFD) simulation approach. Vegetable oil is selected as the cooling lubricant in this study. The performance of the bubble-bursting atomisation system is improved by alternating air inlet velocity and the gap distance between the inlets of bubble production. A velocity of 0.1 ms−1 is suitable for the air at the inlets for the bubble production, whereas 10 ms−1 is suitable for the velocity of the air at the inlet, where the droplets of vegetable oil are guided to the nozzle. Besides that, a 50 mm gap distance between the air inlets for the production of bubbles is able to avoid the occurrence of bubble coalescence. Under these conditions, optimal bubble sizes of 2–3 mm can be achieved, with a higher probability of nano-sized droplets being present in these ranges. Furthermore, a higher rate and smaller size of vegetable oil droplets escaping the atomisation chamber and reaching the machining zone will be generated. Thus, the performance of the MQL machining can be improved.

Implications of Microstructure in Helium-Implanted Nanocrystalline Metals.

Helium bubbles are known to form in nuclear reactor structural components when displacement damage occurs in conjunction with helium exposure and/or transmutation. If left unchecked, bubble production can cause swelling, blistering, and embrittlement, all of which substantially degrade materials and—moreover—diminish mechanical properties. On the mission to produce more robust materials, nanocrystalline (NC) metals show great potential and are postulated to exhibit superior radiation resistance due to their high defect and particle sink densities; however, much is still unknown about the mechanisms of defect evolution in these systems under extreme conditions. Here, the performances of NC nickel (Ni) and iron (Fe) are investigated under helium bombardment via transmission electron microscopy (TEM). Bubble density statistics are measured as a function of grain size in specimens implanted under similar conditions. While the overall trends revealed an increase in bubble density up to saturation in both samples, bubble density in Fe was over 300% greater than in Ni. To interrogate the kinetics of helium diffusion and trapping, a rate theory model is developed that substantiates that helium is more readily captured within grains in helium-vacancy complexes in NC Fe, whereas helium is more prone to traversing the grain matrices and migrating to GBs in NC Ni. Our results suggest that (1) grain boundaries can affect bubble swelling in grain matrices significantly and can have a dominant effect over crystal structure, and (2) an NC-Ni-based material can yield superior resistance to irradiation-induced bubble growth compared to an NC-Fe-based material and exhibits high potential for use in extreme environments where swelling due to He bubble formation is of significant concern.

Long-term monitoring of a seagrass meadow using wideband acoustic measurements

Seagrasses are sentinel species whose sensitivity to changing water conditions makes them an indicator for sea level rise and climate change. The biological processes and physical characteristics associated with seagrass are known to affect acoustic propagation due to gas bodies contained within the seagrass tissue as well as photosynthesis-driven bubble production that results in free gas bubbles in the water. In this work, acoustical methods are applied to monitor seagrass biomass and gas ebullition with an autonomous field-deployed system using broadband acoustic measurements. Supporting environmental measurements including water temperature and salinity, dissolved oxygen, and photosynthetically active radiation (PAR) were also collected and used to interpret the acoustic data. A ray-based propagation model that includes losses due to the dispersion, absorption, and scattering of sound is applied to relate the measured acoustic signals to the gas bodies in the seagrass tissue and free bubbles in the water. This talk will present preliminary results from the first six months of a year-long deployment of the acoustic system in a dense seagrass meadow dominated by Thalassia testudinum (turtle grass) in Corpus Christi Bay, Texas (Gulf of Mexico). [Work supported by NSF.]

Er:YAG laser-induced cavitation can activate irrigation for the removal of intraradicular biofilm

We investigated the biofilm removal effects of laser activated irrigation (LAI) using a pig model, focusing on the impact of the fiber tip position, and used a high-speed camera to observe the occurrence and positioning of the cavitation associated with laser irradiation. A total of 16 roots of deciduous mandibular second premolars from 4 pigs were used. After a pulpectomy, the canals were left open for 2 weeks and sealed for 4 weeks to induce intraradicular biofilm. Root canal irrigation was then performed with Er:YAG laser activation. The fiber tip was inserted at two different positions, i.e., into the root canal in the intracanal LAI group and into the pulp chamber in the coronal LAI group. Intracanal needle irrigation with saline or 5% NaOCl was utilized in the positive control and conventional needle irrigation (CNI) groups. SEM and qPCR were carried out to evaluate treatment efficacy. Statistical analysis was performed using ANOVA and a Tukey–Kramer post-hoc test for qPCR and with a Steel–Dwass test to compare the SEM scores, with α = 0.05. A high-speed camera was used to observe the generation of cavitation bubbles and the movement of the induced bubbles after laser irradiation. The intracanal and coronal LAI groups showed significantly lower amounts of bacteria than either the positive control or CNI groups. There was no significant difference found between the intracanal and coronal LAI groups. SEM images revealed opened dentinal tubules with the destruction of biofilm in both LAI groups. High-speed camera images demonstrated cavitation bubble production inside the root canal after a single pulse irradiation pulse. The generated bubbles moved throughout the entire internal multi-rooted tooth space. Coronal LAI can generate cavitation in the root canal with a simply placed fiber inside the pulp chamber, leading to effective biofilm removal. This method could thus contribute to the future development of endodontic treatments for refractory apical periodontitis caused by intraradicular biofilm.

Unprecedented roles of submillimetric interelectrode distances and electrogenerated gas bubbles on mineral cathodic electro-precipitation: Modeling and interface studies

• New mechanisms of mineral scaling on cathode at various interelectrode distances. • New model on Mg(OH) 2 and CaCO 3 depositions at various interelectrode gap. • Crucial roles of cathode potential, H 2 and O 2 gas evolutions on mineral scaling. • A decrease of internal ohmic resistance did not imply a reduction of mineral scaling. • Modeling of charge transfer resistance and double-layer capacitance at interface. For the first time, the roles of submillimetric interelectrode distances ( d elec ) and electrogenerated gas on cathodic mineral electro-precipitation have been investigated, particularly under advanced electro-oxidation condition with boron-doped diamond (BDD) anode. The main objective was to understand how to limit or favor the magnesium hydroxide (Mg(OH) 2 ) and calcium carbonate (CaCO 3 ) deposits that progressively passivate the cathode surface during the electrolysis of effluent initially containing calcium (Ca 2+ ), magnesium (Mg 2+ ) and bicarbonate/carbonate (HCO 3 – /CO 3 2– ). As predicted by a new model taking into account the concomitant H 2 evolution reaction (HER), more mineral scaling (Mg(OH) 2 and CaCO 3 ) was observed in decreasing order of d elec from 3 mm to 100 μm at 4 mA cm −2 . Contrastingly, no deposit was present at the lowest d elec (50 μm), which was due to non-faradaic condition. The applied cathode potential ( E C ) decreased with increase of d elec , which intensified the H 2 gas bubbles production and minimized the electro-precipitation. Supplementary experiments with identical E C highlighted the additional involvement of O 2 evolution at the anode towards the cathodic mineral scaling, whose role was intensified at submillimetric distances. Finally, novel predictive correlations have been proposed from impedance spectroscopy studies at cathode/electrolyte interface in order to link the charge transfer resistance ( R CT ) and the double-layer capacitance ( C DL ) with d elec .