Air Bubbles Research Articles

Experimental investigation on the characteristics of the shock wave emitted by the cavitation bubble near the air bubble

This study explores the mitigation of cavitation damage in hydraulic engineering through air entrainment. The primary aim is to experimentally analyze the shock wave characteristics emitted by cavitation bubbles adjacent to air bubbles affixed to a tube nozzle. The schlieren optical system is utilized to visualize the shock wave, while a hydrophone measures its pressure. Experiments are conducted on cavitation bubbles induced by the spark-generated method in the vicinity of air bubbles, varying the dimensionless distances and sizes of the air bubbles. The results indicate that (1) The introduction of an air bubble noticeably changes the morphology, kinematic behavior, and shock wave features of the cavitation bubble. (2) Four distinct shock wave patterns are identified based on the quantity and shape of the shock wave, with variations in the cavitation bubble's collapsing behavior and shock wave characteristics across different patterns. (3) The dimensionless distance γ and size δ exert significant influence on the shock wave's quantity, pressure peak, shape, and energy. With γ decreases or δ increases, the shock wave quantity increases while the shock wave intensity decreases. This investigation of the interaction between cavitation bubbles and air bubbles is essential for elucidating the mechanism through which air entrainment mitigates cavitation damage.

Acoustic observations of individual bubble release events from melting glacier ice in an arctic fjord

Melting below the waterline of marine-terminating glaciers and ice sheets has the potential to remove ice that is holding back land-based ice upstream, and increase the rate of global mean sea level rise. It is difficult to observe this melting directly, and the physical processes involved remain an active area of study. As glacier ice melts, the air bubbles trapped in the ice are released into the water. The air bubbles are often at greater pressure than the surrounding hydrostatic pressure in the water, causing them to be released explosively and generate sound through resulting monopole oscillations. Studying this sound at the level of individual bubbles provides an opportunity to learn more about the role of the bubbles in affecting heat flux across the ice-water boundary layer. It is also essential for proposed efforts to use acoustic emissions as a tool to quantify glacier-scale submarine melting. We will present and discuss observations made at the ice-water interface of floating pieces of glacier ice in an Arctic fjord. These observations included measurements of the water thermal structure, velocity, and salinity, as well as ablation of the ice face, made concurrently with acoustic measurements of bubble release pulses from a 2-element hydrophone array.

Influence of hydrophobic particles on the film drainage during bubble–solid interaction

In this article, we investigate the complex drainage behavior of liquid (“dimple”) films entrapped between hydrophilic glass substrates and air bubbles in water and aqueous suspensions of polystyrene (PS) particles. The film drainage was monitored by capturing the evolution of spatial-temporal thicknesses using interferometry. Faster drainage of the entrapped film is observed in the PS colloid suspensions compared to the water. The film drainage strongly depends on the interface boundary conditions. Our experiments reveal that the air–liquid interface of the entrapped film becomes partially mobile in the PS suspensions, which results in faster drainage. The hydrophobic PS particles tend to migrate toward the air–water interface and form an ordered layer. We argue that the adsorbed layer of PS particles makes the bubble surface elastic, delaying the formation of the immobile interface.

Wall effect on single bubble rising in a Hele–Shaw cell

Single air bubble rising near vertical wall in a Hele–Shaw cell was investigated experimentally. Bubbles with a large range of size from 4.46 mm to 21.68 mm were generated. A vertical wall was introduced in the cell, and the initial distance between the wall and the bubble releasing position was varied systematically to study the wall effect on the rising dynamics. Rising trajectory, bubble morphology, and rising characteristics were analyzed. Bubble will migrates away from the wall, and the trajectory transits from rectilinear path to zigzag. Two mechanisms of zigzag were revealed as “rigid zigzag” for the small bubble and “contracting zigzag” for the large bubble. It is always easier to zigzag for a more rounded bubble, and migration is always stronger with a smaller normalized initial distance.

Performance and exergy analysis of vacuum-assisted sweeping air membrane distillation and bubble column dehumidifier

This study provides a comprehensive theoretical analysis of an integrated Sweeping Gas Membrane Distillation (SGMD) and Bubble Column Dehumidifier (BCD) system for cost-effective water desalination. Analytical investigations on this novel system are not available in the literature which represents a knowledge gap. The current analytical study offers insights into the efficiency of the integrated SGMD-BCD system, identifies optimal operational conditions, and provides benchmark data for future scaling-up and commercialization. The theoretical model, based on solving heat and mass transfer equations, is validated against the experimental data. An exergy analysis of the integrated SGMD-BCD is considered to explore the possible improvements in the design and operation for enhanced performance. Results reveal a peak GOR of 0.41 under maximal tested feed flow rates and temperatures, coupled with minimal air flow rates and air channel pressures. The BCD achieves maximum effectiveness in the range of 0.95–0.98 at feed temperature of 90 °C. Exergetic efficiency reaches its peak at 3.25%, observed at the lowest feed flow rate (1 L/min) and temperature (40 °C). Notably, the SGMD process exhibits 18 to 20 times the exergy destruction compared to the BCD at a 90 °C feed temperature, highlighting the need for improvements in its design and operation.

Effect of colloidal nano silica on the freeze-thaw resistance and air void system of portland cement concrete

The present study investigates the impact of colloidal nano silica (CNS) on the freeze-thaw durability of concrete, with a particular focus on understanding the fundamental mechanism via a systematic analysis of the air void system. Experimental results suggest that the incorporation of CNS increases the total air content of the sample while reducing the average void size. This phenomenon can be attributed to the remarkable capacity of CNS to stabilize air bubbles within the concrete matrix, by a heightened viscosity and lower surface tension of the fresh concrete mixture. The increase in air void chambers facilitates the release of internal stress during freezing expansion, thereby enhancing the freeze-thaw resistance of the concrete. Additionally, the inclusion of CNS results in the formation of a denser cement matrix that improves the water impermeability of the concrete and prevents the ingress of water and other potentially corrosive substances.

Biofilm removal effect of diatom complex on 3D printed denture base resin

For patients who have difficulty in mechanical cleaning of dental appliances, a denture cleaner that can remove biofilm with dense extracellular polymeric substances is needed. The purpose of this study is to evaluate the efficacy of diatom complex with active micro-locomotion for removing biofilms from 3D printed dentures. The diatom complex, which is made by doping MnO2 nanosheets on diatom biosilica, is mixed with H2O2 to generate fine air bubbles continuously. Denture base resin specimens were 3D printed in a roof shape, and Pseudomonas aeruginosa (107 CFU/mL) was cultured on those for biofilm formation. Cleaning solutions of phosphate-buffered saline (negative control, NC), 3% H2O2 with peracetic acid (positive control, PC), denture cleanser tablet (DCT), 3% H2O2 with 2 mg/mL diatom complex M (Melosira, DM), 3% H2O2 with 2 mg/mL diatom complex A (Aulacoseira, DA), and DCT with 2 mg/mL DM were prepared and applied. To assess the efficacy of biofilm removal quantitatively, absorbance after cleaning was measured. To evaluate the stability of long-term use, surface roughness, ΔE, surface micro-hardness, and flexural strength of the 3D printed dentures were measured before and after cleaning. Cytotoxicity was evaluated using Cell Counting Kit-8. All statistical analyses were conducted using SPSS for Windows with one-way ANOVA, followed by Scheffe’s test as a post hoc (p < 0.05). The group treated with 3% H2O2 with DA demonstrated the lowest absorbance value, followed by the groups treated with 3% H2O2 with DM, PC, DCT, DCT + DM, and finally NC. As a result of Scheffe’s test to evaluate the significance of difference between the mean values of each group, statistically significant differences were shown in all groups based on the NC group. The DA and DM groups showed the largest mean difference though there was no significant difference between the two groups. Regarding the evaluation of physical and mechanical properties of the denture base resin, no statistically significant differences were observed before and after cleaning. In the cytotoxicity test, the relative cell count was over 70%, reflecting an absence of cytotoxicity. The diatom complex utilizing active micro-locomotion has effective biofilm removal ability and has a minimal effect in physical and mechanical properties of the substrate with no cytotoxicity.

3D Foaming Printing Biomimetic Hierarchically Macro-Micronanoporous Hydrogels for Enhancing Cell Growth and Proliferation.

Hydrogel, recognized as a promising biomaterial for tissue engineering, possesses notable characteristics, including high water uptake, an interconnected porous structure, and excellent permeability. However, the intricate task of fabricating a hierarchically macro-micronanoporous structure, essential for providing adequate space for nutrient diffusion and cell growth within hydrogels, remains a formidable challenge. In response to these challenges, this study introduces a sustainable and straightforward three-dimensional (3D) foaming printing strategy to produce hierarchically macro-micronanoporous hydrogels (HPHs) without the utilization of porogens and post-etching process. This method entails the controlled generation of air bubbles within the hydrogels through the application of optimal mechanical stirring rates. Subsequent ultraviolet (UV) cross-linking serves to effectively stabilize the macropores within the HPHs. The resulting hierarchically macro-micronanoporous structures demonstrate a substantial improvement in the viability, adhesion, and proliferation of human umbilical vein endothelial cells (HUVECs) when incubated with the hydrogels. These findings present a significant advancement in the fabrication of hierarchically macro-micronanoporous hydrogels, with potential applications in the fields of tissue engineering and organoid development.

Subjective Visual Floaters after Intravitreal Injection and Effect of the Inverse Tapping Technique

Purpose: To analyze the incidence of vitreous floaters after intravitreal antivascular endothelial growth factor injection and the effectiveness of the inverse tapping technique, which involves tapping the syringe with the needle downwards to prevent the entry of air bubbles during injection.Methods: The study enrolled patients undergoing their first intravitreal injection for exudative age-related macular degeneration or diabetic macular edema. The patients were divided into two groups: those who received an injection after inverse tapping (IT group) and controls who received the injection without tapping. Patients who consented to the study were randomly assigned to the IT group and the control group through block randomization. One week after injection, a questionnaire was used to assess the presence of vitreous floaters; those who reported them were examined via optical coherence tomography and wide fundus photography.Results: Of the 39 patients in the IT group, two (5.1%) reported floaters 1 week after injection. By contrast, eight (20.5%) of the 39 controls reported them, with a significant difference (&lt;i&gt;p&lt;/i&gt; = 0.042). Patients with floaters were significantly younger. Posterior vitreous detachment, as evaluated by pre-injection optical coherence tomography, was observed in 10.0% of those with floaters and 76.5% of those without them.Conclusions: The occurrence of vitreous floaters after intravitreal injection is related to age and the presence of posterior vitreous detachment. The use of the inverse tapping technique may help reduce these after intravitreal injection.

Inductive sensing of air bubbles in intravenous fluids: A novel approach for patient safety

In this study, a magnetic sensing approach is proposed for detecting air bubbles in intravenous fluids (IVs). To the author's knowledge, this is the first paper to apply magnetic sensing technology for the detection of air bubbles in an IV fluid. The approach is based on a compact, portable, and cost-effective sensor prototype that utilizes an LC resonator and a microcontroller. To validate the detecting system, an IV fluid containing air bubbles is passed through a medical tube, and the tube is passed over a planar coil. The magnetic interaction during the flow of the IV fluid with air bubbles is monitored and logging in real time. Air bubbles of 38, 44, 63 and 75 mm3 in IV fluid were successfully detected by the proposed sensing approach. Besides, the detection system is able to determine the flow direction, which is not encountered in alternatives such as capacitive sensing. The measurements from the established test setup, an average air bubble of 28 mm3 causes an inductance variation of approximately 2.8 nH.

Experimental study on the distribution and growth characteristics of trapped air bubbles in ice slices at different freezing temperatures

Icing is a phenomenon that exists widely in daily life and industry, and always brings some disadvantages. The dissolved air tends to become micro bubbles and trapped in ice, which have an effect on the physical properties of the ice. To explore the distribution and growth characteristics of trapped air bubbles in ice, experiments are carried out in a horizontal Hele-Shaw cell at different freezing temperatures. Results show that the trapped air bubbles in ice are classified into egg-shaped bubbles and needle-shaped bubbles according to an aspect ratio of bubble length to width larger and smaller than five. All the widths, lengths, and volumes of egg-shaped and needle-shaped bubbles increase with the distance from the cooler increasing and the freezing temperature decreasing. The length and volume of needle-shaped bubbles are larger than those of egg-shaped ones. The behaviors of trapped air bubbles are mainly affected by the freezing rate. When the bubble growth rate is greater than 20 μm/s, there are only egg-shaped bubbles in the ice, and when the bubble growth rate is less than 10 μm/s, there are only needle-shaped bubbles in the ice. The volumes of ESBs and NSBs both increase linearly with the bubble growth time at all freezing temperatures. These findings help deepen the understanding of trapped air bubbles in ice and provide guidance for improving icing and optimizing deicing strategies.

Characterization of microbubble aggregation in a double-T microfluidic chip

The coalescence phenomenon of air bubbles affects the flow field, bubble morphology, bubble velocity, and mass transfer efficiency in bioreactors, air bubble generators, and other devices. This article combines the level set method with COMSOL to simulate the formation process of two-phase fluid bubbles in microfluidic chips. The result shows that when the contact angle exceeds 90°, significant agglomeration occurs and the size of bubbles decreases with the increase in liquid flow velocity. However, as the gas velocity increases, agglomeration does not occur at liquid flow rates below 0.1 m/s. In addition, the agglomeration phenomenon occurs above the threshold, and when the gas flow rate is less than 0.02 m/s, there is no agglomeration phenomenon. The numerical simulation results exhibit an error rate of less than 10% compared to the experimental values, indicating that microfluidic chips can accurately predict the process of bubble coalescence.

Improving the longitudinal spot width of an optimizingly designed point-like scatterer-arrayed transcranial ultrasonic lens

As a non-invasive therapy to promote the effect of the thrombolytic agent in the acute phase of cerebral infarction, transcranial irradiation by ultrasonic waves at the site of the occlusion has been validated and is expected to achieve clinical application. Such irradiation may, however, cause damage to the brain by interference of reflected waves within the skull. In order to avoid such a phenomenon, we proposed a transcranial acoustic lens formed by optimizing the arrangement of point-like scatterers. The optimum arrangement of scatterers was determined so that the sound field vanishes within the skull except at the focus(es) and becomes higher at the focus(es) than in the surrounding regions. The ultrasonic waves are strongly scattered by air bubbles in the water-like medium, so we attempted to install a crossbar switch in the medium covering the head and constructed an acoustic lens by producing an instantaneously adaptive air bubble array. This lens can focus an incident plane wave to the diffraction limit in the direction perpendicular to the incident direction, while the peak width in the propagation direction is more than five times higher. In this work, in order to practically improve it, we propose to arrange a point-like scatterer so as to partially cover the head and further increase the number of layers. The shape of the skull is modeled based on CT data, and more realistic parameters are employed than in a previous paper [T. Ueta, J. Appl. Phys. 132, 144504 (2022)].

Turbulent free-surface in self-aerated flows: superposition of entrapped and entrained air

The characterisation and the modelling of air concentration distributions in self-aerated free-surface flows has been subject to sustained research interest since the 1970s. Recently, a novel two-state formulation of the structure of a self-aerated flow was proposed by Kramer &amp; Valero (J. Fluid Mech., vol. 966, 2023, A37), which physically explains the air concentration through the weak interaction of two canonical flow momentum layers, comprising a turbulent boundary layer and a turbulent wavy layer (TWL). The TWL was modelled using a Gaussian error function, assuming that the most dominant contribution are wave troughs. Here, it is shown that air bubbles form an integral part of the TWL, and its formulation is expanded by adopting a superposition principle of entrapped air (waves) and entrained air (bubbles). Combining the superposition principle with the two-state formulation, an expression for the depth-averaged (mean) air concentration is derived, which allows us to quantify the contribution of different physical mechanisms to the mean air concentration. Overall, the presented concepts help to uncover new flow physics, thereby contributing fundamentally to our understanding of self-aerated flows.

Re-descemet membrane endothelial keratoplasty (DMEK) with preservation of the original graft after free roll in anterior chamber: A case report

IntroductionLamellar keratoplasties have had a great impact in the management of corneal edema due to endothelial dysfunction. Minimally invasive transplant techniques such as Descemet Membrane Endothelial Keratoplasty (DMEK) have helped to reduce the morbidity involved in performing penetrating keratoplasty in this type of patient. Even so, these are complex techniques that are not free of complications and require a long line of surgical learning and an even more demanding experience in postoperative management. Clinical caseAn 89-year-old woman suffering from Fuchs endothelial dystrophy and undergoing combined cataract and DMEK surgery presented stromal edema predominantly inferior and sectoral detachment of the graft 24 h after the intervention. After re-bubbling in consultations and 4 days later, the graft was observed rolled and free in the anterior chamber.She underwent re-DMEK with preservation of the original graft after 24 h, with de-epithelialization to optimize visualization. The graft was stained with trypan blue and the posterior stroma was protected with air. The graft was reimplanted under intraocular maneuvers and with an air bubble.24 h after surgery, the adhered graft was observed, with a great decrease in stromal edema. One month later, the patient had a clear cornea, persistent complete graft adhesion, and visual acuity of 0.9. ConclusionThe discovery of free roll in the anterior chamber after DMEK surgery constitutes the most complex form of graft detachment. Corneal edema as well as the arrangement of the different intraocular structures are conditions to be considered for the surgical resolution of this complication. In many cases, surgical repositioning of the graft is feasible, which means saving costs without the need to use new donor corneal tissues.

Effects of Intraoperative Cochlear Implant Electrode Conditioning on Impedances and Electrically Evoked Compound Action Potentials.

The current study investigates whether, during a Cochlear Implant (CI) surgery, conditioning (i.e. applying short bursts of electrical stimulation) within a saline solution can have positive effects on subsequent intra-operative measurements. We hypothesize that, based on previous research, the impedance values will be reduced, and that the reproducibility of Electrically Evoked Compound Action Potentials (ECAPs) is improved as a result of conditioning. We conditioned half of the electrode contacts, within a saline solution, before CI insertion, using 23 MED-EL implants. Impedance was measured for both the conditioned and non-conditioned groups at five time points. Repeated ECAP recordings were measured and compared between the conditioned and non-conditioned groups. Impedance of the electrode contacts were reduced by 31% after conditioning in saline solution; however, there were no clinically relevant differences after the implantation of the electrode array. The hypothesis that measurement reproducibility would be increased after conditioning could not be confirmed with our data. Within the saline solution, we observed that 44% of the electrode contacts were covered with air bubbles, which most disappeared after implantation. However, these air bubbles limited the effectiveness of the conditioning within the saline solution. Lastly, the effect of conditioning on the reference electrode stimulation was approximately 16% of the total reduction in impedance. Our data does not suggest that intraoperative conditioning is clinically required for cochlear implantation with MED-EL implants. Additionally, an in-vivo ECAP recording can be considered as a method of conditioning the electrode contacts. We confirm that the common clinical practice does not need to be changed.

Numerical simulation of droplet impacting on a microstructured surface: Geometry, wettability, and control of jump-off force

Droplet impacting on the solid substrate, which typically is a simple planar surface, has been extensively studied for various technological applications. Here, through numerical calculation, we explore the droplet impacting on a single hemispherical bead and double bead structures. Several key physical parameters have been taken into account, including the Weber number, wettability, and geometry of microstructures. We reveal the spatiotemporal evolution of the droplet pattern, the correlated physical parameters, and the underlying physical mechanisms (air cushion or bubble). These results provide theoretical guidance to control jump-off forces via the structure design and suitable wettability for the relevant applications such as erosion protection.

CFD evaluation of hydrophobic feedstock bench-scale fermenters for efficient high agitation volumetric mass transfer.

A new biomanufacturing platform combining intracellular metabolic engineering of the oleaginous yeast Yarrowia lipolytica and extracellular bioreaction engineering provides efficient bioconversion of plant oils/animal fats into high-value products. However, predicting the hydrodynamics and mass transfer parameters is difficult due to the high agitation and sparging required to create dispersed oil droplets in an aqueous medium for efficient yeast fermentation. In the current study, commercial computational fluid dynamic (CFD) solver Ansys CFX coupled with the MUSIG model first predicts two-phase system (oil/water and air/water) mixing dynamics and their particle size distributions. Then, a three-phase model (oil, air, and water) utilizing dispersed air bubbles and a polydispersed oil phase was implemented to explore fermenter mixing, gas dispersion efficiency, and volumetric mass transfer coefficient estimations (kL a). The study analyzed the effect of the impeller type, agitation speed, and power input on the tank's flow field and revealed that upward-pumping pitched blade impellers (PBI) in the top two positions (compared to Rushton-type) provided advantageous oil phase homogeneity and similar estimated kL a values with reduced power. These results show good agreement with the experimental mixing and kL a data.

The effects of NaCl addition on the particle-bubble interactions of galena in the presence of xanthate

This work investigated the effects of NaCl addition on galena flotation in the presence of xanthate. The micro-flotation experiments were performed using NaCl solutions which also included xanthate, at pH 9 (±0.1). Our results indicated that galena recovery improved for higher NaCl as well as higher xanthate concentrations.A pH-dependent chemisorption model for the galena surface, with the addition of xanthate adsorption was calibrated using measured zeta potential values. We propose that xanthate adsorption on galena can take place via two separate mechanisms. The first mechanism involves direct xanthate chemisorption to specific surface sites. The second mechanism involves lead/xanthate complexes formed in the bulk solution. These lead/xanthate complexes attach on the galena surface as hydrophobic lead xanthate salts.The galena-air bubble interactions are repulsive in 1 mM NaCl, with or without xanthate, consistent with the lower galena recovery measured experimentally. An increase to 100 mM NaCl, irrespective of the xanthate addition, resulted in attractive galena-air bubble total interaction energies. The agreement with the experimental results shows the effectiveness of the charge regulated model for estimating the galena and air bubble behaviours during flotation in NaCl solutions.

Design of Dodol Mixer on Based on Microcontroller Arduino Nano

In the process of cooking dodol dough requires the power of several people to continuously stir until the dough releases air bubbles. the process of making dodol generally takes time depending on how much dough you want to cook. If you want to cook 10 kg of dodol dough, then the time needed to cook it is approximately 8-10 hours with normal or medium heat. Currently, the household-scale dodol industry still uses the manual method for the dodol mixing process, which will require energy. more than one person to stir for a long time so that it will take time for one repetitive job and the production costs will be higher. With this tool, it is hoped that the household-scale dodol industry will become more efficient, because there is no need to manually stir and can do another work while the dodol dough is being stirred.