Bubble Stability Research Articles

Effect of sucrose ester S370 on interfacial layers and fat crystals network of whipped cream

The effect of sucrose ester S370 on the interfacial layers and fat crystals network of whipped cream has been studied in this work. The addition of S370 showed a little effect on the droplets size, interfacial protein concentration and viscosity of emulsion samples before whipping. However, the addition of S370, as a heterogeneous nucleating agent, could induce nucleation and lead to the formation of more small crystals in the bulk mixture and emulsions. These small crystals, which were not able to pierce the interface of fat droplets effectively, would retard fat coalescence during whipping process. The addition of S370 resulted in lower degree of fat coalescence, lower interfacial protein concentration, shorter optimum whipping time (top) and lower overrun of whipped cream. At lower S370 concentration (<0.05 wt%), large-size crystals and inhomogeneous fat crystals network led to lower firmness and less bubbles stability of whipped cream samples. At 0.05 wt% S370 concentration, homogeneous crystals network, resulted in whipped cream with high firmness and bubbles stability. However, lower interfacial protein concentration and small-size crystals were observed at higher concentration of S370 (>0.05 wt%). As a result, the aerated structure was not strong enough to stabilize whipped cream.

Influence of recycled concrete aggregate on the foam stability of aerated geopolymer concrete

The effect of recycled concrete aggregates (RCA) in enhancing the foam stability and hardened properties of aerated geopolymer concrete (GFC) produced by a mechanical foaming method is investigated. The RCA was used as a partial or full replacement to fine aggregates, and approximately the same amounts of foam were used in all mixes to achieve a targeted density of 800 kg/m3. Despite the same water/binder and activator/binder ratios in all mixes, the fresh and hardened properties of GFC significantly varied between mixes. The instability of fresh geopolymer mix, caused by the collapse of air bubbles and the settlement was identified as a major issue in the control GFC mix. The use of RCA in GFC has significantly improved the foam stability with a significant reduction in settlement. The foam stability criterion was correlated to the yield stress development of base mixes, where the addition of RCA increases the initial yield stress and yield stress development over time. This has significantly influenced the stability of bubbles in GFC. On the other hand, the setting time of the geopolymer has reduced with the increasing RCA content. Nevertheless, the foam instability and corresponding settlement were stabilized well ahead of the initial setting time, indicating the setting of geopolymer has less impact on the foam instability in GFCs. The XRD and TGA analyses detect the presence of Ca(OH)2 in RCA, which increases the yield stresses of fresh geopolymer pastes. The variation in foam stability was well reflected on the hardened properties of GFC, such as porosity, pore size distribution, and thermal properties.

Generation and Long‐Term Stability of Ultrafine Bubbles in Water

AbstractThis study investigated submicron‐sized bubbles, more precisely ultrafine bubbles (UFBs). The number concentration, size, and scattered light intensity of UFBs were measured by particle tracking analysis (PTA). The results showed that storage temperature had a significant effect, whereas the storage containers had little effect on the long‐term stability of UFBs. It was found that the second‐order aggregation rate equation could predict the stability of UFBs; however, there were some differences from the theory at high storage temperatures. The features of the PTA were also discussed in detail.

The role of non-frothing reagents on bubble size and bubble stability

Xanthates are widely used for the flotation of most sulphide minerals. As well as xanthates, various reagents (e.g. sodium hydrosulphide, NaHS) are used in sulphide mineral flotation to improve selectivity. Both xanthates and NaHS target the solid–liquid interface and modify the surface to achieve sufficient difference in wettability between the gangue and target mineral. This study examines the role of potassium amyl xanthate (PAX) and NaHS at the air–liquid interface in the presence of a frother, methyl isobutyl carbinol (MIBC). The separate and joint effects of these reagents on the stability of bubbles were studied by measuring bubble size in a batch flotation cell and the lifetime of bubble pairs using a bubble coalescence apparatus. The results of the bubble coalescence experiment with the PAX/MIBC mixture showed that the presence of PAX in a concentration as low as 1 ppm significantly increased the bubble lifetime compared to the MIBC only solution. The lifetime of the bubbles was longer in the NaHS/MIBC mixture, although this might be due to the gain in the liquid viscosity in the presence of high NaHS concentrations. Depending on the concentration of PAX in the solution, the bubbles showed unstable, metastable and ultra-stable behaviors. The influence of PAX and NaHS on the Sauter mean diameter of bubbles was studied and both had a notable effect on inhibiting bubble coalescence, reducing the bubble size by 26%, while in the PAX/MIBC mixture, the size of the bubbles was largely dominated by the concentration of MIBC. Overall, the results strongly suggested that the role of PAX and the synergistic effect of PAX, NaHS and MIBC in modifying the air–liquid interface should be considered when using these reagent combinations.

Deuterium and helium desorption behavior and microstructure evolution in beryllium during annealing

Beryllium was chosen as a plasma-facing material (PFM) for the first wall in an international thermonuclear experimental reactor (ITER). In this study, the deuterium and helium retention behavior in Be and the associated microstructure evolution were investigated using thermal desorption spectroscopy (TDS) and transmission electron microscopy (TEM). Since the disappearance of bubbles was observed at desorption peak temperatures of about 773 K for deuterium and 973 K for helium, these desorption peaks could be attributed to the release from each bubble. The existence of deuterium or helium within each bubble was also clearly confirmed using electron energy-loss spectroscopy (EELS) combined with scanning transmission electron microscopy (STEM). There was a clear difference between the disappearance process of the deuterium and helium bubbles. While the deuterium bubble gradually shrunk and disappeared, the helium bubble instantly vanishes. The results showed that the stability of helium bubbles was higher than that of deuterium bubbles.

Auto-Aspirated DAF Sparger Study on Flow Hydrodynamics, Bubble Generation and Aeration Efficiency

A novel auto-aspirated sparger is examined experimentally in a closed-loop reactor (CLR) at lab scale using particle image velocimetry, high-speed camera and oxygen mass transfer rate measurements. State-of-the-art 3D printing technology was utilized to develop the sparger design in stainless steel. An insignificant change in the bubble size distribution was observed along the aerated flow, proving the existence of a low coalescence rate in the constraint domain of the CLR pipeline. The studied sparger created macrobubbles evenly dispersed in space. In pure water, the produced bubble size distribution from 190 to 2500 μm is controlled by liquid flow rate. The bubble size dynamics exhibited a power-law function of water flow rate approaching a stable minimum bubble size, which was attributed to the ratio of the fast-growing energy of the bubble surface tension over the kinetic energy of the stream. Potentially, the stream energy can efficiently disperse higher gas flow rates. The oxygen transfer rate was rapid and depended on the water flow rate. The aeration efficiency below 0.4 kW/m3 was superior to the commonly used aerating apparatuses tested at lab scale. The efficient gas dissolution technology has potential in water treatment and carbon capture processes applications.

Whole Field Measurements to Understand the Role of Varying Depths of Nucleation Site on Vapor Bubble Dynamics and Heat Transfer Rates

Abstract This work studies the possible effects of varying depths of cavity on bubbling features and the associated heat transfer rates in nucleate pool boiling regime. A single vapor bubble has been generated on a substrate with a cylindrical cavity at its center that acts as the nucleation site. Experiments have been conducted for three cavity depths (250, 500, and 1000 μm), while keeping its throat diameter constant at 200 μm. With the bulk fluid maintained under saturated conditions, for each cavity depth, surface superheat level has been varied in the range of ΔTsuperheat = 8, 10 and 12 °C. A gradient-based visualization technique, coupled with a high speed camera, has been employed to simultaneously map the changes in thermal gradients during the formation of the vapor bubble as well as bubble dynamic parameters. The image sequence obtained has been qualitatively and quantitatively analyzed to elucidate the dependence of bubbling features and various heat transfer processes on cavity depth. With an increase in the depth of cavity, the net effect of reduction in the available thermal energy due to the increased convection effects and significant depletion of superheated layer are identified as the dominant heat transfer processes that influence the bubbling features. Furthermore, based on the statistics of bubble departure characteristics, the cavity with higher depth (1000 μm) showed a much stable bubble formation with minimal variation in the bubble departure frequency as compared to the bubbling features from a cavity with smaller depth (250 μm). Evaporative heat transfer process has been identified as the primary cause for increased inconsistency of bubbling features at high superheat conditions for experiments performed for low cavity depths.

Development of cost effective ultra-lightweight cellulose-based sound absorbing material over silica sol/natural fiber blended substrate

An Ultra-lightweight cellulose-based foam material (ULW-CFM) reinforced with silicasol was prepared by foam forming technology. The sodium dodecylbenzene sulfonate (SDBS) was a suitable foaming agent, creating stable bubbles for ULW-CFM with silicasol. The modulus of elasticity of ULW-CFM modified by silicasol was enhanced from 14.8 kPa to 83.32 kPa, and the yield strength was improved from 1.6 kPa to 4.36 kPa, respectively. The FTIR analysis indicated that the silicasol was deposited inside the material by SiOSi bonds and might has dehydration condensation reaction with cellulose. The thermostability of this material was also enhanced by silicasol. The weight loss of ULW-CFM with silicasol was less pronounced (60.36 %) than the one without (81.12 %). Owing to three dimensionally dispersed fiber structure, ultralightweight, high porosity, the sound absorption coefficient of ULW-CFM with silicasol reached 0.65 above 5000 Hz. Results show that ULW-CFM modified by silicasol has a promising application as a degradable sound absorbing material for dealing with noise.

Effects of polycarboxylate superplasticisers with various functional groups on the pore structure of cement mortar

The air-entraining capabilities of polycarboxylate superplasticisers (PCEs) with different functional groups were systematically analysed. Using different molecular PCEs, the evolution process from bubbles in fresh cement mortar to pores in hardened cement mortar was investigated, considering their effects on mortar workability and mechanical performance. The results showed that PCEs with various functional groups have different air-entraining capabilities. PCEs with ester groups decreased the surface tension and significantly promoted the air-entraining capability, resulting in a notable increase of air content in fresh cement mortar. PCEs with sulfonic acid groups increased the surface tension and remarkably decreased the air content in the fresh cement mortar. A higher air-entraining capability benefits the dispersing properties of PCEs and therefore the PCEs with ester groups performed better in dispersibility in comparison with the PCEs with sulfonic acid groups. The stability of bubbles entrained in fresh cement mortar leads to differences in the pore structure of hardened cement mortar. The PCEs with ester groups diminished the size of large bubbles, leading to significantly decreased porosity of the hardened mortar. PCEs with sulfonic acid groups in the backbone barely optimised the pore structure, with a large amount of large pores remaining in the hardened mortar. Decreased porosity and pore size hence led to higher compressive strength of the hardened cement mortar.

Film Blowing of PHB-Based Systems for Home Compostable Food Packaging

Abstract One of the routes to minimize the environmental impact of plastics waste is the use of bio-sourced and biodegradable alternatives, particularly for packaging applications. Although Polyhydroxyalkanoates (PHA) are attractive candidates for food packaging, they have poor processability, particularly for extrusion film blowing. Thus, one relatively successful alternative has been blending PHA with a biodegradable polymer. This work proposes film blowing of a co-extruded Poly (hydroxybutyrate) (PHB) layer with a poly butylene adipateco- terephtalate (PBAT) layer to enhance bubble stability, mechanical and barrier properties. Co-extrusion is detailed, together with the different strategies followed to improve adhesion between film layers and the PHB content in the films. Films with thicknesses below 50 micron and elongation at break beyond 500% were consistently produced.

Ultrasonic Regeneration Studies on Activated Carbon Loaded with Isopropyl Alcohol

Ultrasonic regeneration of activated carbon loaded with isopropyl alcohol (IPA) was studied. IPA adsorption was performed batchwise at varying solution pH. Adsorption was optimal at solution pH 7, which was closest to the point of zero charge of the activated carbon (6.7). Ultrasonic regeneration was performed on IPA-loaded activated carbon with three factors being tested: ultrasonic intensity, solution temperature and ethanol addition. Regeneration efficiency increased with ultrasonic intensity up to 32.4 W/cm2. A higher intensity led to a higher desorption but damaged the activated carbon, shown by a decrease in the particle size of activated carbon. The regeneration efficiency increased with solution temperature primarily because desorption is endothermic and because the surface tension and viscosity of a solution are reduced with increasing temperature, promoting cavitation bubble production. Ethanol addition increased regeneration efficiency up to 10%, as ethanol reduces tensile stress, facilitating cavitation bubble generation. At 15% and above, regeneration decreases, possibly due to coalescence of bubbles into larger, more stable bubbles. Under optimal parameters, the regeneration efficiency was 83%, which dropped to 64% after four regeneration cycles.

Stability of nanobubbles in different salts solutions

The stability of nanobubbles in electrolyte solutions under different ion valence values was studied using deionized water, NaCl, Na2SO4, Na3PO4, CaCl2, and FeCl3. Nanobubbles were generated using hydrodynamic cavitation, and bubbles were tested for size and zeta potential. All the samples were stable for one week with no significant deviation in either bubble size or zeta potential values. The variation of size and zeta potential among six samples can be attributed to the solution properties and was mainly dependent on solution pH and the cation valency. The ion profiles revealed that the cation concentration at the bubble surface was higher than that of bulk, confirming that the bubbles were negatively charged for neutral and high pH values (≥4) under low valency cation adsorption. The high valency cations have the potential to neutralize or completely reverse the bubble charge. Anions or co-ions have minimal effect on the surface potential or the surface charge. The calculated internal pressures of bubble were unrealistically high, suggesting that the surface tension should be lower than that of water for nanobubble solutions. The interaction energy profile shows no significant energy barrier that overcomes the attractive van der Waals forces for all the solutions, except NaCl which had a 1.87 × 10−20 J barrier at a 5 nm separation distance. However, with the recorded stable bubbles, the calculation of the attractive van der Waals forces produced unrealistic values indicating that the Hamaker constant used for the calculation may not be valid at the nanobubble gas-liquid interface. This revealed that nanobubbles should contain exceptional interfacial properties that need to be carefully investigated and evaluated.

Atomic-scale mechanisms of He/V ratio effect on helium bubble hardening in iron for neutron irradiated F/M steels

The helium-to-vacancy (He/V) ratio is a key factor related to the helium bubble hardening mechanisms induced by neutron irradiation in ferritic/martensitic (F/M) steels as advanced nuclear structural materials. According to the helium bubble hardening results in F/M steel irradiated in the spallation neutron source, the interactions between a 1/2<111>{110} edge dislocation and helium bubbles with various sizes of 0.7–3.0 nm in bcc-Fe under irradiation temperatures and room temperature was investigated by using molecular dynamics simulation. The effect of various He/V ratios in the ranges of zero to the highest He/V ratios, 1.85–4.0 of stable helium bubbles with no dislocation loop emission, on the interaction mechanisms was analyzed. The results indicated that the critical resolved shear stress (CRSS) drops rapidly to a very low stress level, and immediately bottoms out and rebounds to a very high stress level, when the He/V ratio increases from 1.0 to the highest He/V ratio. The significant change of CRSS values is not only related to the climbing degree of dislocation after releasing, but also related to the moment when the climb appears. A new repulsion mechanism of interaction between dislocation and bubble was proposed to elucidate the abnormal phenomena of the bottoming rebound of CRSS with a great climbing degree, according to the repelling interaction between helium bubble and superjog of dislocation with both strong compressive stress field.

Effect of Low Atmospheric Pressure on Air Entrainment in Cement-Based Materials: An On-Site Experimental Study at Different Elevations.

The efficiency and stability of air entrainment in concrete are sometimes found to be weaker at higher elevation. This phenomenon was attributed to the low atmospheric pressure by many researchers, however, the level of influence of atmospheric pressure on concrete air content dramatically varied among different studies. In order to clarify the effect of low atmospheric pressure on air entrainment in cement-based materials, an on-site experimental study was conducted with a rigorous control of irrelevant variables. The study focused on the air-entraining efficiency in cement paste, mortar, and concrete prepared in both low and standard atmospheric pressures. The air bubble stability in fresh mortar and air void characteristics of hardened mortar in different atmospheric pressures were also included. In the study, little effect of low atmospheric pressure on the air-entraining efficiency and air bubble stability in mortar with studied air-entraining agents (AEAs) was found. The air void characteristics were found to be similar between mortar with SJ-2 or 303R type AEAs prepared in different atmospheric pressures. Concrete with either SJ-2 or 303R type AEA prepared in low atmospheric pressure presented a satisfactory air content. These conclusions indicate that it is not necessary to worry excessively about the potentially adverse effect of atmospheric pressure on the frost resistance of concrete if a suitable AEA is applied. Additionally, a supplementary mortar study found that the low temperature of raw materials stored at high elevation would significantly weaken the air entrainment, reminding that potential causes in addition to low atmospheric pressure should also be taken seriously.

Experimental Research on the Influence of Different Curved Rigid Boundaries on Electric Spark Bubbles.

It is well known that the bubble dynamics and load characteristics of cavitation bubbles depend to a great extent on their proximity to the boundary. The purpose of this study is to explore the relationship between the boundary curvature and bubble dynamics, as well as the load characteristics, and summarize the relevant change laws. This study takes three hemispheres of different curvatures and one flat board as its main research boundaries. The hemisphere was chosen as the curved surface boundary because the hemisphere represents the simplest type of curved surface boundary. This method allowed us to easily observe the experimental results and summarize the change laws of bubble dynamics and load characteristics. A high voltage electricity of 400 V was used to produce stable and repeatable electric spark bubbles in this experiment. Since the pulsation time of the bubbles is very short, we used a high-speed camera to acquire the necessary photographs. We also used a Hopkinson bar (HPB) to measure the bubble collapse load. Suppose that the dimensionless parameter of curvature is ζ and the dimensionless parameter of the explosion distance is γ. By summarizing the 44 groups of the experimental results under different combinations of ζ and γ, we found that the cavitation bubble dynamics and loading characteristics are affected by ζ. With an increase of ζ, the shockwave load and bubble collapse load will decrease. In addition, in terms of load characteristics, this study further verified the change trend of the shockwave load and bubble collapse load with γ. For the bubble shrink shape, this paper illustrates the relationship between the bubble’s shrink shape and its shrinkage speed. Four typical bubble shrink shapes are summarized. The effects of different ζ and γ values on the jet are preliminarily explored using the experimental results, and, by considering the experimental results, the developmental trends of the time of the bubble’s first pulsation period are discussed.

Laccase-zein interactions at the air-water interface: Reactors on an air bubble and naphthalene removal from water

Zein and laccase were used to remove naphthalene from water using two approaches. The first approach sorbed naphthalene onto laccase-containing solid zein sorbents coagulated with either CaCl2 at pH = 13 or with Fe2Cl3 at pH = 10. These sorbents were never used before for this purpose. Fluorescence spectroscopy showed that laccase degraded naphthalene in water at neutral pH. Laccase activity was pH-dependent: laccase retained its activity after exposure to pH values as high as 10, and had maximum activity at pH = 5.5. Laccase immobilized in zein sorbents coagulated with Fe2Cl3 at pH = 10 had a relative activity of approximately 8%, whereas activity significantly decreased in zein sorbents coagulated with CaCl2 at pH = 13. Attenuated total reflection Fourier-Transform Infra-Red (ATR-FTIR) spectroscopy showed naphtalene sorption onto zein sorbents through hydrophobic interactions and CH/π bonding between naphthalene (the π base) and the aliphatic groups (hydrogen donors) of non-polar residues of zein. Gas Chromatography Mass Spectroscopy (GCMS) demonstrated naphthalene removal from water. The sorption capacity of zein sorbents was ≈ 14 mg/g at 21⁰C, and followed first-order kinetics with a rate constant of 0.0066 min−1. The second approach used zein and laccase to stabilize air bubbles in water, for air sparging applications. Air sparging injects air in contaminated aquifers to strip volatile contaminants from groundwater. Small, stable air bubbles with large surface area enhance contaminant removal. Previous studies used surfactants to stabilize air bubbles. However, they did not use foaming agents that were also able to adsorb and degrade contaminants. In this study, we produce “reactors on an air bubble” able to strip and degrade naphthalene in groundwater. Interfacial tension measurements showed that laccase and zein adsorbed at the air-water interface at either acidic or alkaline pH. At acidic pH, the compression isotherms of zein-laccase films at the air-water interface differed from those of the individual components, suggesting zein-laccase co-adsorption. At alkaline pH, iron promoted co-adsorption of zein-laccase at the air-water interface, likely by modulating their electrostatic interactions. Foams were stable at alkaline, with either zein alone or zein-laccase complexes, and iron enhanced foam stability. These results indicate that zein and laccase can facilitate the remediation of naphthalene by promoting air bubble stability and naphthalene sorption at the air-water interface, as well as its enzymatic degradation.

Transparent and Freestanding Single-Walled Carbon Nanotube Films Synthesized Directly and Continuously via a Blown Aerosol Technique.

Single-walled carbon nanotube (SWCNT) films are promising materials as flexible transparent conductive films (TCFs). Here, inspired by the extrusion blown plastic film technique and the SWCNT synthesis approach by floating catalyst chemical vapor deposition (FCCVD), a novel blown aerosol chemical vapor deposition (BACVD) method is reported to directly and continuously produce freestanding SWCNT TCFs at several hundred meters per hour. The synthesis mechanism, involving blowing a stable aerosol bubble and transforming the bubble into an aerogel, is investigated, and a general phase diagram is established for this method. For the SWCNT TCFs via BACVD, both carbon conversion efficiency and SWCNT TCF yield can reach three orders of magnitude higher than those with the conventional FCCVD. The film displays a sheet resistance of 40ohmsq-1 at 90% transmittance after being doped, representing the record performance based on large-scale SWCNT films. Transparent, flexible, and stretchable electrodes based on BACVD films are demonstrated. Moreover, this high-throughput method of producing SWCNT TCFs can be compatible with the roll-to-roll process for mass production of flexible displays, touch screens, solar cells, and solid-state lighting, and is expected to have a broad and long-term impact on many fields from consumer electronics to energy conversion and generation.

The dynamics of gas-bubble formation at saturated conditions in porous media flow

We investigate the stability of gas bubbles formed at saturated (bubble-point) conditions during two-component (hbox {CO}_2, hbox {H}_2O), two-phase (gas, liquid) flow by developing and analyzing a 2times 2 dynamical system describing flow through a single pore to study the dynamics of gas bubble formation and evolution. Our analysis indicates that three regimes occur at conditions pertinent to petroleum reservoirs. These regimes correspond to a critical point changing type from an unstable node to an unstable spiral and then to a stable spiral as flow rates increase. In the stable spiral case gas bubbles will achieve a steady-state finite size only if they form within the attractor region of the stable spiral. Otherwise, all gas bubbles that form undergo, possibly oscillatory, growth and then dissolve completely. Under steady flow conditions, this formation and dissolution repeats cyclically.

Skyrmion bubbles stabilization in confined hole and trench materials

We report the direct evidence of the stabilization of magnetic skyrmion bubbles (SkBs) in confined trench and hole structures. By using a high-resolution atomic force microscope, we demonstrated that SkBs exhibit smaller sizes in nanoscale holes and trenches compared with that in uniform films. Our micromagnetic simulations indicate that emergence of the magnetic anisotropic gradient in these confined geometries has an additional contribution to the decrease in SkBs' sizes.

Understanding bubble and void nucleation in dual ion irradiated T91 steel using single parameter experiments

Ferritic-martensitic steels are attractive candidates for structural materials in next generation nuclear reactor systems due to their resistance to radiation induced swelling. Cavity and dislocation loop evolution was characterized in dual ion irradiated T91 steel in three separate irradiation campaigns examining single parameter dependencies of temperature, helium co-injection rate, and damage rate. Irradiations resulted in bimodal cavity size distributions across nearly all ranges of experimental parameters. It was determined that irradiation temperature and helium co-injection rate are stronger influences on bubble stability and the transition from bubbles to voids than is the irradiation damage rate. At low helium injection rates all helium is in vacancy clusters that evolve into bubbles or voids. At high helium injection rates, bubbles become saturated with helium resulting in accumulation of helium at other traps such as dislocation loops. At intermediate levels of He that should aid in the nucleation of bubbles and enhance swelling, the high density of sinks in the F-M microstructure suppresses bubble nucleation and therefore, the onset of swelling. At high enough temperatures, helium is only in bubbles as other strong helium traps, such as dislocation loops, did not form. The mechanism of bubble to void transition was found to shift from being driven by the accumulation of helium to the critical bubble at low damage rates to being driven by spontaneous formation by stochastic vacancy fluctuation at high damage rates.