Air Bubble System Research Articles

Rheology, bubble-particle interaction and air bubble system: A study of the influence of inorganic salts on air entrainment by bubble rising measurement

Rheological properties and the interaction between air bubbles and solid particles are important factors influencing the air bubble system in air-entrained concrete. The former may affect the bubble motion and the latter may influence the strength of bubbles. However, none of them were properly discussed by direct observation. In this study, we observe the rising behavior of various-sized bubbles in air-entrained cement paste. By a modified drag equation, the bubble-particle interaction is determined and represented by the interaction coefficient Ki. By Ki the bubble-particle interaction can be quantified and correlated with air entrainment properties. In combination with rheological properties and surface tension, the influence of inorganic salts on air entrainment is systematically studied. It is found that the content of bubbles <200 μm and the specific surface area of bubbles in the fresh mortar decrease with the increase of Ki, and the content of bubbles >1000 μm and the spacing factor increase with increasing Ki.

Numerical Simulation of an Air-Bubble System for Ice Resistance Reduction

Ships sailing through cold regions frequently encounter floe ice fields. An air-bubble system that reduces friction between the hull and ice floes is thus considered useful for the reduction of ice-induced resistance. In this study, a numerical analysis procedure based on coupled finite volume method (FVM) and discrete element method (DEM) is proposed to simulate complicated hull-water-gas-ice interactions for ice-going ships installed with air-bubble systems. The simulations reveal that after turning on the air-bubble system ice floes in contact with the hull side wall are pushed away from the hull by the gas-water mixture, resulting in an ice-free zone close to the side hull. It is found that the drag reduction rate increases with the increase of ventilation, while the bow ventilation plays a deciding role in the overall ice-resistance reduction. The proposed procedure is expected to facilitate design of new generations of ice-going ships.

Accelerated iron cycle inducing molecular oxygen activation for deep oxidation of aromatic VOCs in MoS2 co-catalytic Fe3+/PMS system

In this work, MoS2 is utilized as a cocatalyst to enhance Fe3+/PMS reaction for the deep oxidation of aromatic VOCs in a continuous air-bubbling system. The exposed Mo4+ active sites achieve high-speed electron transfer from MoS2 (001) surface to Fe3+ and accelerate Fe2+ regeneration (∼60%), which greatly promotes O2 and PMS activation for the formation of radicals like O2•-, HO• and SO4•-. Consequently, the Fe3+/PMS/MoS2 system exhibits strong catalytic ability for various VOCs degradation including styrene, toluene and chlorobenzene (with removal efficiency of 97%, 84% and 83%, respectively) at a wide pH range (3−9). MoS2 cocatalyst in Fe3+/PMS reaction greatly promotes the activation of O2 into radicals and inhibits the formation of toxic aromatic byproducts via the deep oxidation of styrene into CO2. Our study provides a green strategy to activate O2 for pollutants degradation and has great potential to be widely applied in actual environment remediation.

An insightful analysis of dimethyl phthalate degradation by the collaborative process of DBD plasma and Graphene-WO3 nanocomposites

In this paper, the prepared graphene-WO3 nanocomposites (rGO-WO3) were added into a dielectric barrier discharge (DBD) plasma system with spiral discharge electrode to set up a collaborative process to treat the dimethyl phthalate (DMP) in water. Degradation of the DMP under different experimental conditions were studied to illustrate the catalysis of the rGO-WO3 in the DBD plasma system. The obtained results proved that there was the catalysis of the rGO-WO3 for the DMP degradation within the studied DMP concentration, solution initial pH values and conductivities. From the results of the energy utilization efficiency (G50) analysis, the catalysis was more apparent in the case of the oxygen bubbling system than that in the nitrogen or the air bubbling system, which was due to the higher oxygen constitution in the oxygen bubbling system. The reduction of the measured liquid phase ozone concentrations in the DBD/rGO-WO3 system bubbled with air as well as oxygen than those measured in the sole DBD system, which verified the consumption of the ozone by the catalysis of the rGO-WO3. Furthermore, the UV–Vis and the three-dimensional fluorescence spectra analysis were also carried out to state the catalytic effect of the rGO-WO3 for the DMP degradation. Toxicity analysis for the degradation byproducts confirmed the collaborative process could reduce the negative effect of the original DMP on the environment.

Comparative analysis of energy efficiency of ballast tank anti-freezing systems

Choosing the best way to deal with the internal icing of ballast tanks is the important task of the designing Arctic vessels. To prevent excessive ice formation in the ballast tank, various methods are used, the main of which are: heating the water and increasing of the water circulation intensity inside the tank (air and steam bubbling, forced water circulation). The report presents qualitative assessment of the heating method and air bubbling system and investigation of energy efficiency of anti-freezing systems.

Standing Air Bubble-Based Micro-Hydraulic Capacitors for Flow Stabilization in Syringe Pump-Driven Systems.

Unstable liquid flow in syringe pump-driven systems due to the low-speed vibration of the step motor is commonly observed as an unfavorable phenomenon, especially when the flow rate is relatively small. Upon the design of a convenient and cost-efficient microfluidic standing air bubble system, this paper studies the physical principles behind the flow stabilization phenomenon of the bubble-based hydraulic capacitors. A bubble-based hydraulic capacitor consists of three parts: tunable microfluidic standing air bubbles in specially designed crevices on the fluidic channel wall, a proximal pneumatic channel, and porous barriers between them. Micro-bubbles formed in the crevices during liquid flow and the volume of the bubble can be actively controlled by the pneumatic pressure changing in the proximal channel. When there is a flowrate fluctuation from the upstream, the flexible air-liquid interface would deform under the pressure variation, which is analogous to the capacitive charging/discharging process. The theoretical model based on Euler law and the microfluidic equivalent circuit was developed to understand the multiphysical phenomenon. Experimental data characterize the liquid flow stabilization performance of the flow stabilizer with multiple key parameters, such as the number and the size of microbubbles. The developed bubble-based hydraulic capacitor could minimize the flow pulses from syringe pumping by 75.3%. Furthermore, a portable system is demonstrated and compared with a commercial pressure-driven flow system. This study can enhance the understanding of the bubble-based hydraulic capacitors that would be beneficial in microfluidic systems where the precise and stable liquid flow is required.

Effect of morphology on interactions between nanoparticle-stabilised air bubbles and oil droplets.

High-speed video analysis has enabled the interaction between a pair of millimetre-sized air bubbles to be studied in aqueous solution. The bubbles were grown in the presence of either poly(glycerol monomethacrylate)-poly(benzyl methacrylate) (PGMA-PBzMA) diblock copolymer spheres or poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate)-poly(benzyl methacrylate) (PGMA-PHPMA-PBzMA) triblock copolymer worms prepared by polymerisation-induced self-assembly (PISA). A reduction in interfacial tension relative to air bubbles grown in the absence of nanoparticles indicated the adsorption of nanoparticles at the air-water interface. A concentration of 0.01% w/v PGMA-PBzMA spheres conferred air bubble stability after just 30 s interfacial ageing with stirring, whereas 300 s ageing was required for worms to prevent coalescence at the same copolymer concentration. However, longer coalescence times with interfacial age suggested greater worm adsorption on the air bubbles during this period. In striking contrast, although stable millimetre-sized n-dodecane droplets were obtained in the presence of 0.01% w/v copolymer worms, the copolymer spheres did not prevent coalescence at this low concentration. Finally, the multiphase interaction and stability of immiscible fluids in the presence of either spheres or worms was assessed. More specifically, an n-dodecane oil droplet and an air bubble were grown separately in the presence of either the spheres or worms and then brought into contact. In the absence of any nanoparticles, aqueous film drainage resulted in the formation of a compound droplet consisting of an air lens on the oil droplet. In the presence of 0.01% w/v nanoparticles, ageing times of either 30 s or 120 s were required to prevent formation of compound droplets when using spheres and worms, respectively. Moreover, this asymmetric system required much shorter ageing times in the presence of adsorbed nanoparticles to gain stability compared to either the symmetric air bubble or oil droplet systems. This stability is attributed to a bridging nanoparticle monolayer between the oil droplet and the air bubble.

A study on novel reactive oily bubble technology enhanced collophane flotation

Collophane is an important phosphate mineral, which has proven to be difficult to float from gangue. In this work, the novel application of reactive oily bubbles to enhance collophane flotation is reported. Three different types of bubbles, conventional air bubble, oily bubbles (kerosene only) and reactive oily bubbles (kerosene containing fatty acids) approaching collophane particles were studied by measurements of zeta potential, induction time and contact angle. The reactive oily bubble shows negligible effects on the zeta potential of collophane particles. A shorter induction time of reactive oily bubble was found at pH6.0 and/or at pH9.0 relative to the conventional air bubbles and the oily bubbles. This suggests a strong collection power of reactive oily bubble. Advancing contact angles of the reactive oily bubble on collophane increased dramatically with pH. At pH9.0, a contact angle of 120 degrees was observed where the reactive oily bubble flotation is anticipated. Micro-flotation results demonstrate the superiority of reactive oily bubbles over air bubbles for collophane flotation. A concentrate containing 35.67% of P2O5 and 0.39% of MgO was obtained using reactive oily bubble flotation at pH9.0. Micro-flotation results also show that Ca2+ and Mg2+ ions have a negative effect on the collophane flotation, but the effect of reactive oily bubble system is smaller than that of air bubble system.

Energy harvesting using air bubbles on hydrophobic surfaces containing embedded charges

Technology to harvest electrical power from waste micro-mechanical energy is increasingly in demand. A promising approach lies in manipulating the electrical double layer on hydrophobic surfaces; however, the underlying mechanism is still unclear. Here, we demonstrate that ascending air bubbles in water can produce electrical power in a mode similar to other systems that use descending water droplets. Although the two systems, which are analogous to electrons and holes in semiconductors, are similar in fundamental principle, their detailed electrification mechanisms are significantly different. In the air bubble system, only the pre-existing charges on the surface are involved. However, electrification in the water droplet system is dominated by triboelectric charges accumulated on the surface over time. An air bubble can produce a maximum of nine times more energy than a water droplet due to its advantages in terms of its geometry, hydrodynamics, and electro-circuitry. We also suggest an innovative approach to improve energy-harvesting efficiency using artificially embedded charges.

Arsenic removal by nanoiron coupled with gas bubbling system

Arsenic removal was investigated by nanoscale zero valent iron (NZVI) under CO2–air bubbling system. The measure of gas bubbling was to acidify the solution and oxygenate NZVI adsorbent. Effects of carbonation and aeration periods were studied in four different scenarios. The most favorable condition was as follows; pretreatment step: CO2 bubbling (300mL/min for 5min) and air bubbling (300mL/min for 10min), and treatment step: Continuous air bubbling (300mL/min). In the condition of having an initial concentration of 1000μg/L, As(III) and As(V) could be removed by 78 and 99%, respectively. When we applied this conditions to the field groundwater spiked with arsenic, the removal efficiency was a little higher than the system both without gas- and acidic chemical-pretreatment. The X-ray absorption near edge spectroscopy (XANES) suggested the apparent valence states of the activated NZVI to be 2+ and 3+.

Numerical Analysis on Freezing in the Ship Voyaging in Polar Regions

For vessels operating in the cold climate regions, the ballast water inside or hopper tanks above the waterline may be frozen, starting at the top of the tank and at the side walls. Therefore, countermeasures against freeze-up of the ballast tank such as air-bubbling system, hot steam injecting system, heating coil system and water circulating system are taken to prevent freeze-up phenomenon; however, there are no rigorous investigations of anti-freezing to examine the effectiveness and validity of systems against freeze-up of the ballast tank, in which the temperatures are about -25℃ (ambient air temperature) and 0℃ (sea water), respectively. In this paper, to ensure reasonable specifications for cold regions if the measures from the above-mentioned systems against freeze-up are effective, the phenomenon of ballast tank freeze-up is simulated and discussed in low temperature conditions. With the results using the commercial CFD code, CFX 14, the most cost-effective solution is conducted to prevent being frozen along the outer surface.

Numerical Investigation on Freezing in Ballast Tank of Ship Navigating in Ice-bound Sea

For vessels operating in the cold climate regions, the ballast water inside or hopper tanks above the waterline may be frozen, starting at the top of the tank and at the side walls. Therefore, countermeasures against freeze-up of the ballast tank such as air-bubbling system, hot steam injecting system, heating coil system and water circulating system are taken to prevent freeze-up phenomenon; however, there are no rigorous investigations of anti-freezing to examine the effectiveness and validity of systems against freeze-up of the ballast tank, in which the temperatures are about <TEX>$-25^{\circ}C$</TEX> (ambient air temperature) and <TEX>$0^{\circ}C$</TEX> (sea water), respectively. In this paper, to ensure reasonable specifications for cold regions if the measures from the above-mentioned systems against freeze-up are effective, the phenomenon of ballast tank freeze-up is simulated and discussed in low temperature conditions. With the results using the commercial CFD code, CFX 14, the most cost-effective solution is conducted to prevent being frozen along the outer surface.

Effects of bubbling operations on a thermally stratified reservoir: implications for water quality amelioration

Artificial thermal mixing of the water column is a common method of addressing water quality problems with the most popular method of destratification being the bubble curtain. The air or oxygen distribution along submerged multiport diffusers is based on similar basic principles as those of outfall disposal systems. Moreover, the disposal of sequestered greenhouse gases into the ocean, as recently proposed by several researchers to mitigate the global warming problem, requires analogous design criteria. In this paper, the influence of a bubble-plume is evaluated using full-scale temperature and water quality data collected in San Roque Reservoir, Argentina. A composite system consisting of seven separated diffusers connected to four 500 kPa compressors was installed at this reservoir by the end of 2008. The original purpose of this air bubble system was to reduce the stratification, so that the water body may completely mix under natural phenomena and remain well oxygenated throughout the year. By using a combination of the field measurements and modelling, this work demonstrates that thermal mixing by means of compressed air may improve water quality; however, if improperly sized or operated, such mixing can also cause deterioration. Any disruption in aeration during the destratification process, for example, may result in a reduction of oxygen levels due to the higher hypolimnetic temperatures. Further, the use of artificial destratification appears to have insignificant influence on reducing evaporation rates in relatively shallow impoundments such as San Roque reservoir.

Numerical Simulation of Vitrification Processes: Glass Homogeneity by Gas Bubbling Study

A direct induction process using the cold crucible technology has been developed by the French Atomic Commission and AREVA-NC for 25 years. In this process, walls of the crucible are cooled by internal water circulation which protect them from the corrosion and allow higher temperature of the molten glass. Moreover, a mechanical stirrer and air bubbling system promote a good homogeneity of the melt. This study describes how the air bubbling in the glass is modelled in our simulation and enlightens his important role in the homogenisation of the glass during his elaboration. Air bubbling in liquids as viscous as the glass (viscosity up to 10Pa.s) is not common and specific models have to be built. Two different models are used, first one is a semi-empirical based model, and the second is a two phase model (VOF).

극지운항용 빙해선박의 밸러스트 수 결빙방지 기법 연구

When freezing is present on ballast water, it can impose additional loads on the hull and effect on stabilization of ship. The anti-icing techniques of ballast water, therefore, are key criteria for ship safety. The existing anti-icing techniques of ballast tank are hull heating, water circulation and air bubble system etc. In this research, anti-icing performance tests for the ballast water using micro-bubble system and sea water circulation system have been carried out at two temperature conditions(-10℃ and -25℃). Ambient temperature, sea water temperature and temperature of the inner parts of the ballast tank are measured and also ballast water conditions are checked during the model test. The applied anti-icing techniques of ballast water, such as micro-bubble system and sea water circulation system show good performance in the low temperature conditions.

Effective removal of antibiotic metronidazole from water by nanoscale zero-valent iron particles

The removal of antibiotic metronidazole (MNZ) in aqueous solution by nanoscale zero-valent iron (NZVI) particles was investigated. The experimental results showed that MNZ was completely removed by NZVI, MNZ solution at 80 mg L − 1 was rapidly removed by NZVI within 5 min, at initial solution pH 5.60, NZVI dose of 0.1 g L − 1 . Influencing factors such as NZVI dosage, initial MNZ concentration and initial solution pH were systematically studied, and the removal process of MNZ followed a pseudo-first order kinetics model. The removal efficiency was enhanced with increasing NZVI dosage while it was decreased with the increase of initial MNZ concentration and initial solution pH. The removal of MNZ in a nitrogen bubbling system (NZVI/N 2 process) and in an air bubbling system (NZVI/air process) was compared, and the results showed that the removal rate in the NZVI/air process was slightly higher than that in the NZVI/N 2 process. The removal efficiencies of MNZ by using NZVI and commercial iron powder were investigated as well, indicating that MNZ removal efficiency by NZVI was about 49 times higher than that by commercial iron powder under the same dosages. This study demonstrates that the NZVI technology could be a promising approach for antibiotic wastewater treatment.

Degradation of azo and anthraquinone dyes by a low-cost Fe 0/air process

Degradation of two different kinds of dyes, anthraquinone Reactive Blue 4 (RB4) and azo Reactive Black 5 (RB5), by low-cost zero valent iron (Fe 0) in a N 2 bubbling system (Fe 0/N 2 process) and air bubbling system (Fe 0/air process) was investigated. The operating parameters, including initial solution pH, dye concentration and Fe 0 dose, were also evaluated. The Fe 0/air process shows a higher decolorization rate compared to the Fe 0/N 2 process. Both RB4 and RB5 solutions at 100 mg L −1 were rapidly decolorized by Fe 0/air process within 9 and 3 min, respectively, at initial solution pH 3, Fe dose of 50 g L −1 and air flow rate of 5 L min −1. The optimal initial solution pH was 3. The Fe 0/N 2 process removed only <17% of COD. However, significant COD removals were achieved for RB 4 (87%) and RB5 (43%) by the Fe 0/air process after 9 min of treatment. Spectra analysis results indicated that the Fe 0/N 2 process destroyed only the anthraquinone group (A 594) for the RB4 solution and decreased the azo (A 596) and naphthalene group (A 310) for the RB5 solution. However, the Fe 0/air process rapidly removed A 594, A 370, A 296 (anthraquinone group) and A 256 (aromatic and dichlorotriazine group) for RB4, and A 597 and A 310 (naphthalene group) for RB5. The results indicated that the low-cost Fe 0/air process is a potential technique for rapid degradation of RB4 and RB5 solutions.

프리징 현상을 고려한 발라스트 탱크 내 유동 및 열전달 해석

Several anti-freezing systems, such as heating coil system, hot air spray system, ballast water circulation system and air bubbling system, have been applied to the water ballast tanks for the vessels, operating in cold sea. In this study, numerical simulations were performed to investigate effectiveness of the air bubbling system used for winterization design concept for water ballast tank. Through the results of this study, it became clear that the air bubbling system equipped in each frame of water ballast tanks was effective to prevent freezing along the outer surface by promoting convective heat transfer.

Photon- and carbon-use efficiency in Ulva rigida at different CO2 and N levels.

The seaweed Ulva rigida C. Agardh (Chlorophyta) was cultured under two CO(2) conditions supplied through the air bubbling system: non-manipulated air and 1% CO(2)-enriched aeration. These were also combined with N sufficiency and N limitation, using nitrate as the only N source. High CO(2) in U. rigida led to higher growth rates without increasing the C fixed through photosynthesis under N sufficiency. Quantum yields for charge separation at photosystem II (PSII) reaction centres (phi(PSII)) and for oxygen evolution (phi(O2)) decreased at high CO(2) even in N-sufficient thalli. Cyclic electron flow around PSII as part of a photoprotection strategy accompanied by decreased antennae size was suspected. The new re-arrangement of the photosynthetic energy at high CO(2) included reduced investment in processes other than C fixation, as well as in carbon diverted to respiration. As a result, quantum yield for new biomass-C production (phi(growth)) increased. The calculation of the individual quantum yields for the different processes involved allowed the completion of the energy flow scheme through the cell from incident light to biomass production for each of the CO(2) and N-supply conditions studied.

Freezing of air-entrained cement-based materials and specific actions of air-entraining agents

The freeze–thaw resistance of all cement-based materials is improved by incorporating a fine air bubble system in them. For acceptable life expectancy, incorporated air bubble volume should be about 25% of the cement paste. The specific surface of the air bubble system need to be above 25 mm2/mm3 and a spacing factor below about 0.16 mm. Powers explained these on the basis of his saturated flow hydraulic pressure mechanism. According to Powers’ mechanism, the chemical nature of the air-entraining agent has no part in this improvement in performance. Helmuth, one of the principal co-workers of Powers, has questioned a number of assumptions of Powers’ mechanism. Most importantly, Helmuth showed that ice penetrates concrete as dendritic crystals. Furthermore, a number of workers have shown that the chemical nature of the air-entraining agent affects the freeze–thaw resistance of cement-based materials. Some air-entraining agents do not improve the freeze–thaw resistance even though they entrain air of the required characteristics. In this paper, a modified and expanded version of Helmuth’s model of ice penetration in concrete is utilised to explain the action of air bubbles. All air bubbles contain a layer of water on their inner surfaces. Surface tension spreads out water in the air bubbles as annular layers. Air-entraining agents may form or precipitate hydrophobic layers on air bubble surfaces. When an ice dendrite reaches an air bubble, the annular water layer freezes to an annular layer of ice. The hydrophobic layer on the air bubble surface reduces the ice–paste bond. Under this circumstance, the ice layer within the air bubble grows. During this growth, water is withdrawn from the surrounding by suction. A water movement under suction does not produce any expansive pressure. Withdrawal of water to the air bubbles explains the beneficial action of air entrainment. The specific efficiency of air-entraining agents is explained by the different degree of hydrophobicity produced by air-entraining agents.