Air Bubbles Research Articles

Mung bean protein colloid mixtures and their fractions - A novel and excellent foam stabiliser

Protein aggregates are known to enhance foam stability by either increasing the thin film viscosity or by blocking the lamellae of a foam. In this study, we produced a mung bean protein colloids mixture (MPCM) by heating protein coacervates that were formed by liquid-liquid phase separation. The functionality of MPCM was compared to a mildly purified mung bean protein extract (MIL). The MPCM showed extraordinary foaming properties, much better than MIL, with foamability of 324 % and a half-life time of 400 min. This work focused on elucidating the exact interface and foam stabilising mechanism of the MPCM by separating the colloids (COL) from the supernatant/continuous phase of the MPCM (SUP). Their interfacial properties were studied by performing surface dilatational rheology and microstructure analysis. Finally, foaming properties, such as foamability, foam stability, and air bubble size, were studied.It was found that the highest foam capacity was observed for the SUP fraction by generating stiffer interfaces. This fraction also contributed to the high foam stability of the MPCM. The COL fraction was found to form a viscoelastic thin film between air bubbles, thereby decreasing the drainage rate of the foam. In brief, SUP and COL fractions co-operate in the formation of highly stable MPCM foam, leading to a promising plant-derived candidate for producing stable foams in food products.

Microstructural investigation of hybrid CAD/CAM restorative dental materials by micro-CT and SEM

ObjectivesAn increasing number of CAD/CAM (computer-aided design/computer-aided manufacturing) hybrid materials have been introduced to the dental market in recent years. In addition, CAD/CAM hybrid materials for additive manufacturing (AM) are becoming more attractive in digital dentistry. Studies on material microstructures using micro-computed tomography (µ-CT) combined with scanning electron microscopy (SEM) have only been available to a limited extent so far. MethodsOne CAD/CAM three-dimensional- (3D-) printable hybrid material (VarseoSmile Crown plus) and two CAD/CAM millable hybrid materials (Vita Enamic; Voco Grandio), as well as one direct composite material (Ceram.x duo), were included in the present study. Cylindrical samples with a diameter of 2 mm were produced from each material and investigated by means of synchrotron radiation µ-CT at a voxel size of 0.65 µm. Different samples from the same materials, obtained by cutting and polishing, were investigated by SEM. ResultsThe 3D-printed hybrid material showed some agglomerations and a more irregular distribution of fillers, as well as a visible layered macrostructure and a few spherical pores due to the printing process. The CAD/CAM millable hybrid materials revealed a more homogenous distribution of ceramic particles. The direct composite material showed multiple air bubbles and microstructural irregularities based on manual processing. SignificanceThe µ-CT and SEM analysis of the materials revealed different microstructures even though they belong to the same class of materials. It could be shown that µ-CT and SEM imaging are valuable tools to understand microstructure and related mechanical properties of materials.

Global Ocean Cooling of 2.3°C During the Last Glacial Maximum

AbstractQuantitative constraints on past mean ocean temperature (MOT) critically inform our historical understanding of Earth's energy balance. A recently developed MOT proxy based on paleoatmospheric Xe, Kr, and N2 ratios in ice core air bubbles is a promising tool rooted in the temperature dependences of gas solubilities. However, these inert gases are systematically undersaturated in the modern ocean interior, and it remains unclear how air‐sea disequilibrium may have changed in the past. Here, we carry out 30 tracer‐enabled model simulations under varying circulation, sea ice cover, and wind stress regimes to evaluate air‐sea disequilibrium in the Last Glacial Maximum (LGM) ocean. We find that undersaturation of all three gases was likely reduced, primarily due to strengthened high‐latitude winds, biasing reconstructed MOT by −0.38 ± 0.37°C (1σ). Accounting for air‐sea disequilibrium, paleoatmospheric inert gases indicate that LGM MOT was 2.27 ± 0.46°C (1σ) colder than the pre‐industrial era.

Improving the air bubble stability of air-entrained mortar in low air pressure environments via adopted rheology and surface tension methods

Air bubble stability in cementitious materials in low air pressure (AP) environments is influenced by the Ostwald ripening process, which causes coarsening behavior of air bubbles. This research reports the enhancement of air bubble stability in low AP via the adoption of rheology and surface tension methods. Besides, the evolution of air bubbles during the cement early hydration process is proposed. It was found that incorporating viscosity-modifying agents (VMAs) and shrinkage-reducing admixtures (SRAs) resulted in improving air bubble stability by 37.7 % and 23.4 %, upon undergoing AP change from 100 to 60 kPa. Calculation of air bubbles via ripening equations under low AP revealed that VMA induced a notable decrease in the effective diffusion flux within fresh cement mortar, leading to a reduction of 9.8 % in air bubble ripening within 120 min. Conversely, SRAs were primarily aimed at reducing the initial dimensions of air bubbles.

On the short-term response of entrained air bubbles in the upper ocean: a case study in the north Adriatic Sea

Abstract. Air bubbles in the upper ocean are generated mainly by waves breaking at the air–sea interface. As such, after the waves break, entrained air bubbles evolve in the form of plumes in the turbulent flow, exchange gas with the surrounding water, and may eventually rise to the surface. To shed light on the short-term response of entrained bubbles in different stormy conditions and to assess the link between bubble plume penetration depth, mechanical and thermal forcings, and the air–sea transfer velocity of CO2, a field experiment was conducted from an oceanographic research tower in the north Adriatic Sea. Air bubble plumes were observed using high-resolution echosounder data from an upward-looking 1000 kHz sonar. The backscatter signal strength was sampled at a high resolution, 0.5 s in time and 2.5 cm along the vertical direction. Time series profiles of the bubble plume depth were established using a variable threshold procedure applied to the backscatter strength. The data show the occurrence of bubbles organized into vertical plume-like structures, drawn downwards by wave-generated turbulence and other near-surface circulations, and reaching the seabed at 17 m depth under strong forcing. We verify that bubble plumes adapt rapidly to wind and wave conditions and have depths that scale approximately linearly with wind speed. Scaling with the wind–wave Reynolds number is also proposed to account for the sea-state severity in the plume depth prediction. Results show a correlation between measured bubble depths and theoretical air–sea CO2 transfer velocity parametrized with wind-only and wind/wave formulations. Further, our measurements corroborate previous results suggesting that the sinking of newly formed cold-water masses helps bring bubbles to greater depths than those reached in stable conditions for the water column. The temperature difference between air and sea seems sufficient for describing this intensification at the leading order of magnitude. The results presented in this study are relevant for air–sea interaction studies and pave the way for progress in CO2 gas exchange formulations.

The underground performance analysis of compressed air energy storage in aquifers through field testing

Compressed air energy storage in aquifers (CAESA) has been considered a potential large-scale energy storage technology. However, due to the lack of actual field tests, research on the underground processes is still in the stage of theoretical analysis and requires further understanding. In this study, the first kilometer depth compressed air injection-production field test with multiple flat aquifers is controlled. For all three production rates considered, the minimum pressure drop rate can reach 0.9 MPa/h. An actual wellbore-aquifer-coupled numerical model simulated by T2Well/EOS3 is verified using monitoring data. Due to the limitation imposed by the injection rate, air only flows into the top three sandstone aquifers to build air bubbles. During the production stage, air is first produced from the aquifers and then the air stored in the wellbore is gradually extracted due to the weakened air bubble support effect. Finally, an air-water two-phase occurs and the water level rises in the wellbore. Considering a hypothetical long-term cycle, the designed single aquifer scheme has a better underground performance. A concentrated and larger high air saturation domain can support a stable cycle pressure and above 95% underground efficiency. However, the wellhead pressure drops once water coning happens in the wellbore. With an air bubble replenishment scheme in each cycle, it becomes feasible to maintain stable pressure, ensuring a production pressure difference below 0.94 MPa without water production, over a 100-day cycle in the field. The results provide support for future practical engineering applications.

Numerical simulation of droplet impact onto heated surfaces below the boiling point

Droplet impact onto heated surfaces is a widespread process in industrial applications, particularly in the context of spray cooling techniques. Therefore, it is essential to study the complex phenomenon of droplet spreading, heat removal and flow distributions during this process. The primary focus of this research centers on the wetting dynamics at a surface temperature below the saturation temperature of the liquid. This study employs a Computational fluid dynamics (CFD) framework to simulate the impact dynamics of a water droplet onto a heated surface. The impact dynamics, spreading, air entrapment and heat transfer in the process are discussed using simulation results. The Direct Numerical Simulation (DNS) tool Free Surface 3D (FS3D), an in-house code at the Institute of Aerospace Thermodynamics, University of Stuttgart, is utilized. The Finite-Volume method is used to solve the incompressible Navier-Stokes equations, and the interface is defined by the Volume of fluid (VOF) method. In this study, the temperature change above the entrapped air bubble formed due to droplet inertia is shown, which can influence the heat removal rate in the process. Therefore, conducting a comprehensive study on the temperature shift caused by the air bubble is crucial.

Intentional Insertion of Air to Predict the Diagnostic Accuracy of Stereotactic Biopsy and a Uniform Grading System for Reporting

Background and Objectives: Stereotactic biopsies are a relatively safe and reliable way of tissue diagnosis and characterization of eloquent area lesions/neoplasm. However, predicting the accuracy of the site of biopsy with the desired/planned site is not always possible. We describe a technique to identify the precise location of the biopsy site in the post-operative computed tomography (CT) scan using the injection of a low volume of air into the biopsy cannula. Methods: Hundred consecutive biopsies were performed in 80 adults/20 children (59 males/41 females, median age 51 years) over 3 years, consisting of 75 frameless and 25 frame-based stereotactic biopsies. After the biopsy specimens had been collected, a small volume of air (median 1 cc) was injected into the site. Post-operative CT was done within 4 hours of the biopsy to see the site of the air bubble, and the same was correlated with the histopathological accuracy. Results: Intra-cranial air in the selected target was present in 95 patients (Grade 1 and 2), while the air was seen in the track (Grade 3) in 3% and at an unrelated site (Grade 4) in 2% of cases. Both Grade 4 biopsies were negative on histopathology (diagnostic yield = 98%). Two negative biopsies were reported, which were both predicted with the Grade 4 biopsy. The grading allowed uniform reporting across series and eliminated the chance of upgrading/downgrading the report due to wrong site sampling within the lesion/neoplasm. Conclusion: The air-injection manoeuvre proposed for use in stereotactic biopsies of intra-cranial mass lesions is a safe and reliable technique that allows the exact biopsy site to be located without any related complications.

Facile compliance-based pump for blood physiometer

The biomechanical properties of blood are considered promising label-free biomarkers for early disease detection. Disposable pumps have been suggested as replacements for bulky and expensive syringe pumps. However, they have limitations, including initial air bubble removal, simple stop-and-run flow control, and quantification of many rheological properties. In this study, a compliance-based pump (CP) is developed by fitting a blood-loaded syringe, an air-compliance unit, and a needle into each port of a three-way valve. When blood is loaded into the microfluidic channel from the CP, the initial air bubbles are removed from the channels. By manipulating the three-way valve, blood flow is stopped immediately. Red blood cell (RBC) aggregation index (AI) is obtained by analyzing microscopic blood images. The air-compliance unit induces a transient blood flow. The time-resolved micro-particle image velocimetry technique is employed to obtain the blood velocity. The flow rate and time constant are obtained by assuming the flow rate as Q (t) = Q1 exp(−t/λ1) + Q2 exp(t/λ2) and conducting nonlinear regression analysis. The proposed method is employed to obtain the properties (AI, Q1, Q2, λ1, and λ2) of suspended bloods (hematocrit = 30%–70%, 5–30 mg/ml dextran solution, and heat-shocked RBCs). It is also used to detect four different types of suspended blood prepared by adding two types of RBCs (normal or hardened RBCs) to two types of diluents (1 × phosphate-buffered saline or dextran). In conclusion, the proposed method can be used to detect differences in suspended blood by manipulating the CP and consistently analyzing microscopic blood images.

Reusing biofloc-culture water and microbubble aeration for culturing the white-leg shrimp Litopenaeus vannamei

This study investigated the effects of reusing biofloc-culture water for culturing the white-leg shrimp Litopenaeus vannamei. Experiments were conducted for two continuous cycles without water exchange for 30 days during the nursery stage. The studies were performed with two different aeration systems, namely microbubbles (MB) and large air bubbles (LB). Water quality parameters such as dissolved oxygen (DO), temperature, pH, salinity, alkalinity, total ammonia nitrogen (TAN), nitrite, nitrate, settleable solids (SS), and total suspended solids (TSS) were recorded throughout the culture days. Also, comparisons were performed on parameters of the shrimp growth, i.e., body weight and length, feed conversion ratio (FCR), and specific growth rates (SGR) for the 30-day culture for Cycles 1 and 2. Cycle 2 showed no deterioration in water quality and no significant difference in growth performance compared to Cycle 1 for either aeration method (MB and LB). However, when comparing between aeration methods, MB aeration significantly improved the DO of the water and accelerated the conversion of TAN to nitrate. Shrimps in the MB aeration system were significantly larger (by 39%) with a lower FCR value (reduced by 30%) than in the LB aeration system. Harmful bacteria from the Vibro group were detected. However, they occurred at a minimum level in both cycles and aeration types. Overall, the biofloc-culture water might be reused for the subsequent cycle, while the MB aeration might promote the growth of biofloc and L. vannamei.

Imaging of foam concrete air bubbles with an alternative method of combined digital holographic microscopy

Five different foam concretes were synthesized and examined. A new hybrid optical sensor, called combined digital holographic microscopy (CDHM), was proposed by combining microscopic fringe projection profilometry and lateral shearing digital holographic microscopy to detect the pore radii of produced foamed concretes. It was applied in addition to SEM and has not been applied to foam concretes before. Thanks to the proposed method, it was revealed that the measured CDHM radii contained a relative error of less than 6% compared to the SEM radii. The pore radii increased as the % of foaming agent used in the samples increased. Accordingly, the sample densities decreased and thermal insulation properties enhanced. Two-layer quantum chemical calculations performed at the ONIOM (M06-2X/6-31+G(d,p):UFF) theoretical level showed that thermodynamic stability of foam concretes increased as the % of foaming agent used, or more precisely, the pore radius, increased. The CDHM method provides results close to SEM and has superior features such as being more cost-effective, cleaner and faster. For this reason, it is thought that the proposed method will lead to future studies in terms of measuring pore radii as an alternative to SEM.Graphical The combined digital holographic microscopy (CDHM) method is proposed as an alternative to SEM with a relative error of less than 6% in determining the pore radius of foam concretes.

Analysis on degassing at microgravity condition

For the future diversity and sustainability of the International Space Station, the manned flight time will be greatly increased, and the water required will be greatly increased as well. It is particularly important to deal with resources in more detail. In the process of treating drinking water, tiny air bubbles may be created. Bubbles can form in the Water Recovery and Management System (WRMS) on the ISS due to gas dissolution, microgravity environment, chemical reactions, and microbial metabolism. Water under pressure can dissolve gases. In the ISS, if water comes from a high-pressure environment to a lower one, gas may come out of solution, forming bubbles. Also, in the microgravity environment of the ISS, bubbles can remain suspended in the water, interfering with the systems sensors and pumps. Some processes in the water recovery system can produce gases as byproducts, such as electrolysis used in the Oxygen Generation System of the ISS. Finally, some microbial metabolic processes generate gases which can form bubbles in the water. According to four reasons given above, the passage will first introduce the current situation about dealing with bubbles in ISS, then providing some future directions of the development of the bubble-remove techniques.

Passion fruit by-products (Passiflora edulis f. flavicarpa) as a potential fat replacer in ice cream.

In recent years, people have become interested in consuming low-fat foods as this reduces the risk of obesity and cardiovascular disease. For this reason, this study optimized the incorporation of passion fruit epicarp (PFE) as a partial fat substitute in dairy ice cream. For this purpose, a central composite rotational design 22 was performed and 5 response variables were optimized, of which 4 variables were maximized (percentage overrun, hardness, adhesiveness, and color coordinates L*, a*, b*), while the melting rate was minimized as a function of two factors (% PFE and % fat). The stability of three types of ice cream was then evaluated: experimental ice cream (3% milk fat and 0.97% PFE), commercial ice cream (4% milk fat and 2% vegetable fat) and control ice cream (3% milk fat without PFE added), according to their physicochemical and sensory properties during 57 days of storage (-22 °C, 85% relative humidity). The results showed that it was possible to reduce the milk fat by up to 25% by adding PFE (0.97%), which significantly reduced the melting rate and resulted in higher hardness (N), adhesiveness and increased yellowness compared to the commercial samples. The optical microscopy analysis also showed that PFE keeps the air bubbles immobile due to the increased viscosity in the serum phase during the 57-day storage.

Numerical modeling of turbulent air-water mixture flows in spilling breaking waves

This paper presents a numerical study of turbulent air-water mixture flows under spilling breaking waves by using a mixture-flow model. The model is extended from the earlier 2D numerical framework NEWFLUME, which solves the Reynolds-averaged Navier-Stokes (RANS) equations for mean flow motions. The turbulence closure is accomplished by a modified k−ε two-equations model, in which the effect of entrained bubbles on turbulence production and dissipation is considered by incorporating additional buoyancy terms. A transient equation based on two-fluid formulation is solved for air bubble transport. The present model is validated by comparing the simulated free surface displacement, void fraction, mean velocity and turbulence kinetic energy against existing experimental data and the previous numerical results. The effects of the additional convective term in transient equation of void fraction and the bubble-induced turbulence term in turbulence transport equation are further explored. The results reveal that the additional convective term in the transient equation of void fraction plays an essential role of suppressing unphysical turbulence growth and bringing correct amount of air entrainment into water during wave breaking processes. The additional bubble-induced turbulence production and dissipation terms become effective after wave breaks when the void fraction has been appropriately modeled, and they can further reduce the simulated turbulence intensities in spilling breaking wave, rendering a better agreement with the experimental measurements.

Modelling and application of dissolved air flotation for efficient separation of microplastics from sludges and sediments

The pervasive presence of microplastics in our environment necessitates urgent measures to prevent further release and address existing contamination hotspots. This work focuses on the removal of microplastics from sludges and sediments through the application of dissolved air flotation (DAF). In addition to experimental investigations, the study presents the development of a predictive model for the formation of aggregates comprising air bubbles and microplastics in the DAF contact zone. First an empirical model was established to predict the attachment efficiency between air bubbles and particles (αdb). To this end, the experimental attachment efficiency was determined for various plastics, with varying particle sizes and shape factors, and system conditions. The obtained data set was utilized to establish an empirical model by PLS regression describing αdb based on particle size, bubble size, density, Hamaker constant, contact angle, solid load, aspect ratio, circularity, and sphericity, resulting in an MSPE of 0.011 and adjusted-R² of 0.64. Secondly, a semi-deterministic model based on the XDLVO theory was developed using MLR, where αdb was described by the natural logarithm of the Van der Waals, electrostatic and hydrophobic forces acting between the particle and air bubble, and the solid load, with an RSE of 0.067 and adjusted-R² of 0.63. Finally, the applicability of these models was demonstrated in a case study on industrial sludge consisting of sediment and PVC microplastics. Validation of the attachment efficiency and the dimensioning of a DAF unit for processing this sludge at a capacity of 20 m³.h−1 emphasize the practical implications of the developed models.

Can Arbuscular Mycorrhizal Fungi Enhance Crop Productivity and Quality in Hydroponics? A Meta-Analysis

Finding environmentally friendly solutions for crop growth and productivity has been gaining more attention recently. This meta-analysis aims to understand the combined application of arbuscular mycorrhizal fungi (AMF) and hydroponic systems compared to AMF in conventional (soil) systems. The analysis of up-to-date studies revealed that the root colonization, calculated as the proportion of colonized root segments relative to the total root length, by AMF in conventional (soil-based) culture exceeded hydroponic (or soilless) culture systems by 16.8%. The mean root colonization by AMF was determined to be 52.3% in hydroponic systems and 61.1% in conventional systems. Within hydroponic systems, the root colonization ranged from 2% to 20% after 10 days of inoculation, and notably, it exceeded 50% after 30 to 65 days, depending on the growing substrate and species. Under hydroponics, AMF application had a higher (compared to none-inoculated) positive effect on crop biomass and yield than fruit and leaf quality (antioxidants, phenols, and sugars) as well as leaf nutrients. However, AMF do not always have the potential to improve crop growth, quality and productivity in hydroponics. Among the studies analyzed in this review, approximately 34% (no effect: 29%; negative: 5%) reported no discernible positive effect on biomass or yield, 37% (no effect: 16%; negative: 21%) on fruit or leaf quality, and 60% (no effect: 47%; negative: 13%) on nutrient levels within plant tissues. To improve the performance of AMF in hydroponic systems, the meta-analysis recommended maintaining phosphorus levels in the nutrient solution within the range of 0.15 to 15.5 mg L−1 as elevated levels (40–75 mg L−1) were found to significantly reduce AMF colonization. Additionally, it was observed that certain hydroponic techniques, such as the presence of air bubbles generated by air pumps in floating hydroponic systems (Deep Flow technique) and continuous circulation of the nutrient solution (Ebb and Flow systems), may create dynamic conditions that could potentially hinder the introduction of AMF spores into hydroponic systems and potentially compromise the integrity of the spores and hyphae.

Analyzing Leak Detection Methods for Aluminum Cast Components in Automotive Manufacturing Processes

Evaluation of the effectiveness of the 'Cosmo Air Leak Tester' machine and the 'Waterleak' method in detecting leaks in aluminum casting transmission components in the manufacturing process in the automotive industry. Although the 'Cosmo Air Leak Tester' successfully detects large leaks, it has limitations in detecting small leaks such as air bubbles. The research proposed a combination of both methods to improve early leak detection and ensure higher product quality. The research findings highlight the importance of considering cost, cycle time, and safety aspects in the manufacturing process.

Turning Non-Sticking Surface into Sticky Surface: Correlation between Surface Topography and Contact Angle Hysteresis.

We present a surface modification technique that turns CuNi foam films with a high contact angle and non-sticking property into a sticky surface. By decorating with mesh-like biaxially oriented polypropylene (BOPP) and adjusting the surface parameters, the surface exhibits water-retaining capability even when being held upside down. The wetting transition process of droplets falling on its surface were systematically studied using the finite element simulation method. It is found that the liquid filled the surface microstructure and curvy three-phase contact line. Moreover, we experimentally demonstrated that this surface can be further applied to capture underwater air bubbles.

Mitigation Strategies to Reduce Detrimental Effects of Air Bubbles in Shaft Spillways: A Literature Review

Mitigation Strategies to Reduce Detrimental Effects of Air Bubbles in Shaft Spillways: A Literature Review

Foaming Properties and Foam Structure of Milk Determined by Its Protein Content and Protein to Fat Ratio

AbstractMilk proteins, integral to stable foam production, exhibit seasonal and type-dependent variations. Understanding the impact of protein levels with and without fat on foaming properties is essential for selecting suitable milk types and controlling the foaming process. In this study, we employed steam injection and mechanical mixing to assess foamability, foam stability, and foam structure of (1) reconstituted skim milk powder dispersions (1.5–15% solids concentration, corresponding to 0.5–5.0% protein), (2) reconstituted whole milk powder and commercial whole milk dispersions (0.5% protein), and (3) whole milk with added skim milk powder and milk protein concentrate (3.5 and 4% protein) and butter milk powder (0.5 and 1% total solid content). Results reveal that increasing solids concentration from 1.5 to 15% significantly increased lactose content, viscosity, and surface tension. However, these changes did not impact foamability or foam stability, while slightly decreasing air bubble size. At 0.5% protein, skim milk powder dispersions demonstrated higher foam volume (16 times greater) and more stable foam compared to reconstituted whole milk powder and whole milk dispersions, despite similar foam structure and appearance. These findings emphasize the substantial influence of the protein/fat ratio on milk’s foaming properties. Additionally, the addition of skim milk powder, milk protein concentrate, or butter milk powder at the investigated content did not affect the foaming properties of whole milk.