Bubble Surface Research Articles

Commercial‐scale removal of short‐chain PFAS in a batch‐wise adsorptive bubble separation process by dosing with cationic co‐surfactant

AbstractStudies performed by Burns et al. in 2021 and 2022 demonstrated that a three‐stage batch‐wise adsorptive bubble separation process, surface active foam fractionation (SAFF), is effective at removing most per‐ and polyfluoroalkyl substances (PFASs) from contaminated groundwaters and landfill leachates. However, PFAS species with very low adsorption coefficients to bubble surfaces are difficult to remove, which is parallel to the difficulties in removing short‐chain PFAS in granulated activated carbon beds and other solid media. It is well known that the adsorption coefficient to bubble surfaces improves in the presence of electrolytes in solution and it has previously been shown that this improves the removal of PFAS. By developing a correlation for the removal percentage of one species or another of PFAS due to SAFF in commercial‐scale processes as a function of the adsorption coefficient, it is possible to generally estimate the removal percentage of any PFAS. The addition of a cationic co‐surfactant, cetrimonium bromide, to the feed can significantly further improve the adsorption coefficient and, as a consequence, materially improve the removal of short‐chain PFAS due to SAFF. A method for estimating this improved performance is in qualitative agreement with plant trials of SAFF at a North American site with a history of groundwater contamination due to the use of aqueous film forming foams firefighting foams, but the precise improvements appear to be dependent upon the concentration of the added co‐surfactant. The required concentration of co‐surfactant is significantly larger than might be expected on charge equivalence considerations, and this may be due to its consumption by other species in the feed, including PFAS that have not been accounted for. It is noted that the SAFF process may not be true foam fractionation and may, instead, be a bubble fractionator, both of which can be collectively described by the term “adsorptive bubble separation processes.”

Formation processes of paper-thin raft and coated bubble: Calcium carbonate deposition at gas–water interface

Travertines are hot spring carbonate deposits that exhibit characteristic fabrics, including a paper-thin raft and a coated bubble formed by the calcification of water and bubble surfaces, respectively. A previous study interpreted that compared with the water surface, the bubble surface displays more active CO2 degassing and resultant active CaCO3 precipitation. However, considering the CO2 partial pressure and the volumes of atmosphere and bubbles, it is possible that more active CO2 degassing occurs on the water surface. In addition, the surfaces of water and bubbles at the travertine-depositing sites are negatively charged, but it is still unclear whether the CaCO3 nucleation on these surfaces occurs via amorphous precursors, like the CaCO3 nucleation on negatively charged organic matter. This study provides a solution to these uncertainties by examining the aragonitic travertines formed in the Nagayu area of Japan. Through field observations, two types of paper-thin rafts were recognized: one with a smooth surface and formed in approximately 1 h, and the other with a rough surface and formed in approximately 3 h. In addition, the bubbles generated on the microbial mat during the daytime were covered with white minerals within an hour, and with ivory-colored minerals over 8 h after sunset, forming firm coated bubbles. Microelectrode measurements revealed that the active CO2 degassing on the water surface significantly increased the CaCO3 saturation state to cause active CaCO3 precipitation. In contrast, less active CO2 degassing on the bubble surface did not increase the saturation state, and moderate CaCO3 precipitation occurred due to the moderately high saturation state of the hot spring water. Various microscopic observations revealed that the smooth-surfaced paper-thin raft comprises a micritic layer of approximately 10–20 μm, which represents tightly arranged submicron-sized granular aragonite. At the lower surface of this layer, hemispherical aragonite partially grew toward the hot spring water. In addition, the rough-surfaced paper-thin raft and coated bubble comprise bundled and acicular aragonites arranged along the surfaces of water and bubble, from which hemispherical aragonite grew toward the hot spring water. Neither the paper-thin raft nor the coated bubble contains primary amorphous CaCO3. These results suggest that the smooth-surfaced paper-thin raft is formed by active CaCO3 nucleation on the water surface and subsequent crystal growth, and that the water surface is unfavorable for preserving the amorphous precursors potentially involved in the nucleation. The rough-surfaced paper-thin raft and the coated bubble could have been formed by the attachment of externally formed acicular aragonite to the water/bubble surface and subsequent crystal growth. The revealed formation processes of the paper-thin raft and coated bubble provide valuable information for interpreting their formation mechanism in other travertine deposits, including those in the geological past.

Non-spherical collapse of a cavitation bubble induced by a rigid filament

A combination of high-speed shadowgraph imaging and numerical simulations was used to study the collapse of a bubble near a rigid filament. The dynamic behavior of the collapsing bubble was investigated concerning two non-dimensional parameters: the filament radius (r*) and the initial near-wall distance (γ0). The critical distance (1 < γc < 3) between spherical and non-spherical collapse was positively correlated with r*. The collapsing bubbles were found to exhibit three different morphologies with different γ0 values: flat two-dimensional necking with a strong jet, teardrop-shaped collapse with an weak jet, and spherical collapse with no jet. The first collapse time (T1st) hardly varies with γ0, and the second collapse time (T2nd) shows an increasing and then decreasing trend as γ0 increases, reaching a maximum at γ0 = 1 and stabilizing after γ0 > γc. In addition, when γ0 = 0.76, the pressure difference between the upper and lower surfaces of the bubble is high, the jet is strong, and the maximum pressure and maximum fluid velocity are found in the jet, producing a stronger impact on the rigid wall. When γ0 > 1, as γ0 increases, the jet weakens, the pressure on the wall is far less than the pressure on the bubble surface when it collapses. Our results would deepen the understanding of the kinetics of the bubble collapsing near a slender cylindrical wall and provide an important reference for the improvement of pulp pumps and interpreting the degradation of microfiber-reinforced plastics.

Hydrodynamic modifications in vertical bubble plumes by a grid-screen

Air injection through a single circular nozzle has been used for aeration enhancement, oxygen transfer, and mixing in natural lakes and reservoirs. A series of laboratory experiments with different hydrodynamic conditions was carried out to improve mixing capacity and entrainment in vertically discharged bubble plumes. Hydrodynamic modifications were performed by inserting a grid-screen with different openings and distances from the nozzle and hydrodynamic modifications were examined for different air discharges. Bubble plume characteristics such as bubble concentration and velocity were measured along the vertical axis of the plume using an accurate Refractive Bubble Index (RBI) probe. Utilizing bubble concentration and bubble velocity data, the hydrodynamic forces such as buoyancy, drag, added mass, and surface tension were calculated before and after the grid-screen to evaluate modification by a grid-screen. The bubble induced force acting on the grid-screen was then calculated by implementing the momentum transfer at the vicinity of the grid-screen. The effects of grid-screen openings, the location of grid-screen respect to the nozzle, and air discharge on the contributed forces were examined to design the optimum operation condition. The results indicated that the grid-screen size and its distance from the nozzle decreased the buoyancy and drag forces after the grid-screen by 49% and 42%, respectively. Non-linear correlations between the hydrodynamic forces and bubble Reynolds number were proposed indicating that all contributing forces increased with increasing bubble Reynolds number. Empirical models were also developed for prediction of surface tension and bubble induced forces on the grid-screen.

Enhancing medical ultrasound imaging through fractional mathematical modeling of ultrasound bubble dynamics

The classical mathematical modeling of ultrasound acoustic bubble is so far using to improve the medical imaging quality. A clear and visible medical ultrasound image relies on bubble’s diameter, wavelength and intensity of the scattered sound. A bubble with diameter much smaller than the sound wavelength is regarded as highly efficient source of sound scattering. The dynamical equation for a medical ultrasound bubble is primarily modeled in classical integer-order differential equation. Then a reduction of order technique is used to convert the modeled dynamic equation for the bubble surface into a system of incommensurate fractional-orders. The incommensurate fractional-order values are calculated directly, by using Riemann stability region. On the basis of stability the convergence and accuracy of the numerical scheme is also discussed in detail. It has been found that the system will remain stable and chaotic for the incommensurate values α1<0.737 and α2<2.80, respectively.

Spontaneous Directional Transportation Surface of Water Droplet and Gas Bubble: A Review

The spontaneous directional transportation (SDT) of water and gas has functions such as efficient water collection, enhanced heat transfer, underwater drag reduction, and so on, having great application prospects in aerospace and navigation fields. Therefore, it is important to efficiently prepare spontaneous directional water droplet transportation (SDWT) surfaces and spontaneous directional gas bubble transportation (SDBT) surfaces and apply them in different fields. In recent years, researchers have used biological structures as the basis for their studies and have continued to analyze the SDT transport mechanism in depth, aiming to find more efficient transportation methods. In this review, we first summarize the important basic theories related to fluid transportation. Then, the related methods and the limitations corresponding to SDWT and SDBT are introduced and discussed. In addition, we review the applications of SDWT and SDBT. Finally, we highlight the challenges and future perspectives of SDWT and SDBT.

INITIATION OF A STREAMER IN A LIQUID FROM THE SURFACE OF A BUBBLE IN WHICH A PARTIAL DISCHARGE OCCURRED

The analysis of experimental data on the initiation of streamers in a liquid di- electric from the surface of a free-floating up gas bubble after partial discharge is performed. Calculations of electric fields in a dielectric after partial discharge in bubbles corresponding to experimental conditions, with different degrees of deformation of the bubbles and their dif- ferent position relative to flat electrodes, have been carried out. The effect of image charges on the value of the maximum electric field on the surface of a spherical bubble is estimated. The probability of initiation of branching streamers from the bubble surface into the liquid is analyzed.

Generation and Release Mechanism and Abatement Measures for Gas Supersaturation Downstream of Hydropower Dams: A Review

AbstractDespite the considerable social and economic benefits of hydropower dams, they can cause total dissolved gas (TDG) supersaturation downstream of hydropower dams, which can harm fish through gas bubble trauma (GBT) and cause issues with aquatic ecology. This paper systematically reviewed the generation and release mechanism of TDG supersaturation, including three stages of TDG generation and release, to broaden the research ideas of TDG supersaturation and encourage the construction of environmentally friendly dams and other hydropower projects. The factors affecting the generation and release were summarized from the three stages of TDG generation and release, including temperature, momentum difference at the water‐air interface, and effective depth of bubble arrival. The research methods were introduced from four aspects: theoretical methods, field observations, experiments, and numerical simulations. The advantages, disadvantages, and application scopes of different research methods were outlined. Finally, the abatement measures in the three stages of TDG generation and release were introduced from the engineering and non‐engineering perspectives, and the future research directions were pointed out from the four aspects of TDG supersaturation generation and release mechanism, research methods, abatement measures, and management methods, including in‐depth study of whether gas‐liquid transfer through bubble surfaces or free surfaces dominates, consideration of bubble coalescence and rupture to improve the accuracy of numerical methods in TDG supersaturation prediction, the combination of engineering and non‐engineering measures to optimize TDG supersaturation abatement measures and consideration of artificial intelligence technology to improve hydropower project management methods.

Preparation of high-purity nickel by floating zone refining under a hydrogen atmosphere

This study focuses on preparing high-purity nickel using floating zone refining under hydrogen atmosphere to overcome challenges related to impurity removal. The utilized high-vacuum floating zone refining device minimizes contamination and external impurities. The purification process's effectiveness is particularly notable for gaseous impurities, such as carbon and oxygen, with removal rates reaching 94.5% and 96.3%, respectively. The purification mechanism of the melt is considered as involving the nucleation and growth of hydrogen bubbles in the molten zone, and the adsorption of impurities on the bubble surface, followed by the ascent and overflow of bubbles, which effectively carry impurities out of the molten zone.

Effects of surfactants on bubble-induced turbulence

We use experiments to explore the effect of surfactants on bubble-induced turbulence (BIT) at different scales, considering how the bubbles affect the flow kinetic energy, anisotropy and extreme events. To this end, high-resolution particle shadow velocimetry measurements are carried out in a bubble column in which the flow is generated by bubble swarms rising in water for two different bubble diameters (3 and 4 mm) and moderate gas volume fractions (0.5 %–1.3 %). We use tap water as the base liquid and add 1-Pentanol as an additional surfactant with varying bulk concentration, leading to different bubble shapes and surface boundary conditions. The results reveal that with increasing surfactant concentration, the BIT generated increases in strength, even though bubbles of a given size rise more slowly with surfactants. We also find that the level of anisotropy in the flow is enhanced with increasing surfactant concentration for bubbles of the same size, and that for the same surfactant concentration, smaller bubbles generate stronger anisotropy in the flow. Concerning the intermittency quantified by the normalized probability density functions of the fluid velocity increments, our results indicate that extreme values in the velocity increments become more probable with decreasing surfactant concentration for cases with smaller bubbles and low gas void fraction, while the effect of the surfactant is much weaker for cases with larger bubble and higher void fractions.

Nanoscale Investigation of Bubble Nucleation and Boiling on Random Rough Surfaces.

Surface roughness is one of the significant factors affecting liquid-vapor phase change heat transfer. This paper explores the effect of surface roughness on bubble nucleation and boiling heat transfer, as well as the microscopic mechanism, by constructing random rough surfaces using molecular dynamics (MD) simulation. Bubbles randomly nucleate on a flat surface and tend to nucleate in pits on rough surfaces. The pits on the random rough surface gather more argon atoms than the protrusions, forming low potential energy regions on the surface, thus providing stable nucleation sites for bubbles. As the surface roughness increases, bubble generation, merging, and growth are advanced. In addition, rough surfaces offer a larger effective heat transfer area for the heat transfer process, increase the strength of solid-liquid coupling, and obtain smaller solid-liquid interaction energy. The critical heat flux (CHF) value positively correlates with surface roughness. As the roughness increases, the surface superheat at the onset of CHF decreases accordingly. This paper provides new insights into the mechanism of heat transfer enhancement on rough surfaces and surface design in thermal management.

Foaming Properties of Lignosulfonates in the Flotation Process.

The widely used technology for the selective flotation of copper and molybdenite using sodium hydrosulfide (NaSH) to depress copper sulfides creates environmental issues related to the potential emissions of toxic hydrosulfide gas (H2S) and bad odors. Previous studies showed that molybdenite flotation can be depressed by the action of lignosulfonates, but no significant progress has been made in studying the effect that these reagents have on the foaming/frothing phenomena in flotation. The objective of this work was to investigate the foaming properties of three samples of lignosulfonates through measurements of surface tension, foamability, bubble size distributions, and water recovery. A sugared sodium lignosulfonate (NaLS), a calcium lignosulfonate (CaLS), and a sample prepared by sulphomethylation of kraft lignin (KLS) were tested. It was found that all lignosulfonates displayed surface activity that decreased with pH and was related to the degree of anionicity and molecular weight. The NaLS lignosulfonate showed the highest dynamic foamability index (DFI) value, compared to that of the CaLS and KLS samples. The lignosulfonates tested in this study strongly affected bubble size. Water recovery tests performed using flotation experiments in a two-phase system showed that the KLS and NaLS samples had the strongest effect, which correlated with the surface tension, foamability, and bubble size results.

Liquid-solid contact electrification through the lens of surface and interface science

Triboelectric nanogenerators (TENGs) are cutting-edge technology that converts mechanical energy into electrical energy through contact electrification (CE). The CE process involves the chemical, physical, and mechanical properties of material surfaces and interfaces. Studying CE from the perspective of interfacial science can provide a comprehensive understanding of the charging mechanism and improve the performance of TENGs through structural design and technical optimization. Therefore, this paper reviews the research progress in CE from the perspective of surface and interface science. Specifically, we introduce the static and dynamic behavior of the liquid-solid (L-S) interaction during CE separately. Then, the interface phenomenon involved in gas-liquid-solid CE, such as surface wettability and ionic effect on liquid film drainage between the bubble and solid surface in water is discussed. This new interdisciplinary area of surface science of TENGs provides many research opportunities, while it is essential to explain critical phenomena in the CE process.

Bubble Formation and Motion in Liquids—A Review

In flotation, a bubble acts as a carrier for attached particles. The properties of the gas–liquid interface of the bubble are one of the main factors determining the bubble motion and flotation efficiency. Monitoring of the bubble motion may deliver interesting information about the state of the gas–liquid interface. In the case of pure liquids, a bubble surface is fully mobile, while the presence of surface-active substances (e.g., surfactants) causes diminishing bubble velocity due to the retardation of the interface fluidity. The theoretical prediction of the terminal velocity value for the bubble has been investigated for over a century, delivering a number of various models describing bubble motion in a liquid. This narrative review is devoted to the motion of the bubble in stagnant liquids and is divided into three main sections describing: (i) experimental techniques for tracking bubble motion, (ii) bubble motion and shape deformation in clean water, and (iii) bubble motion in solutions of surface-active substances.

Quantitative estimation of phospholipid molecules desorbed from a microbubble surface under ultrasound irradiation

Microbubbles have potential applications as drug and gene carriers, and drug release can be triggered by externally applied ultrasound irradiation while inside blood vessels. Desorption of molecules forming the microbubble shell can be observed under ultrasound irradiation of a single isolated microbubble, and the volume of desorbed molecules can be quantitatively estimated from the contact angle between the bubble and a glass plate. Microbubbles composed of a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) shell and a poorly-soluble gas are created. When the microbubbles are exposed to a pulsed ultrasound, the contact angles increase dramatically; the percentage of DMPC molecules desorbed from the bubble surface reaches 70%. Vibration of a single bubble in the radial direction is measured using a laser Doppler vibrometer. The relationship between the vibrational characteristics and the amount of molecular desorption reveals that a larger vibrational amplitude of the bubble around the resonance size induces a larger amount of molecular desorption. These results support the possibility of controlling molecular desorption with pulsed ultrasound.

Isothermal and non-isothermal growth of a vapor bubble in pool boiling – Effect of translational velocity of bubble

In the present work, we have numerically simulated the effect of bubble translation on the growth of a vapor bubble in a pool of superheated liquid based on the isothermal and non-isothermal model. The isothermal growth uses the ODE solver and the non-isothermal growth the PDE-ODE solver. The overall model at present considers the forces acting on the bubble to compute the bubble motion and the energy balance at the bubble surface to include the effect of bubble size on its motion. Thus, it computes equivalent bubble radius and bubble velocity simultaneously. The numerical simulation shows a remarkable improvement by our method over the previous numerical model while validating with the experimental and numerical results on bubble growth with the phase motion. The improved model has significantly reduced the deviation from the experiments reported in literature on the growth of a moving bubble. The aspect ratio of the bubble is computed to see the shape change of the bubble and is used to model the drag force accurately. It has been shown that the model of the isothermal growth can better explain the bubble growth at the initial stage, and the model of the non-isothermal growth at the final stage. The non-isothermal growth of bubble is accompanied by the slowdown of the bubble translation in the superheated liquid.

Study on the effect of flocculation morphology on the floatability of talc flocs and the adhesion mechanism with air bubbles

This study investigates the impact of floc morphology on flotation by preparing two types of flocs with similar apparent particle sizes but different aggregation degrees through varying the stirring speed. Flotation tests were conducted on the two flocs, revealing that flocs with higher aggregation degrees demonstrated superior floatability and higher flotation rate constants. Fractal dimension and AFM analysis indicated that flocs with higher aggregation degrees exhibited higher fractal dimensions, displaying a more circular and compact overall morphology, as well as a more regular and uniform surface morphology. XPS and contact angle tests showed that, for flocs with comparable particle sizes, an increase in fractal dimension led to increased adsorption of flocculant (PEO) on the surface, accompanied by enhanced hydrophobicity. Further analysis of the induction time for particle-bubble attachment and coverage angle demonstrated that flocs with higher fractal dimensions had shorter induction times and larger coverage angles, indicating faster attachment between flocs and bubbles. These findings suggest that flocs with higher fractal dimensions can acquire greater kinetic energy in a flow field, enabling them to more effectively disrupt the hydration film on the bubble surface and adhere to the bubble surface, thereby enhancing floatability.

Bubble-assisted matte transportation into slag phase: A numerical investigation

Copper loss into the slag phase during the smelting process can be minimized by controlling gas bubble size and hydrodynamics. Here, bubble rising characteristics from copper matte to slag phase were investigated using the volume-of-fluid modelling approach, in which the continuous surface force model was adopted to define the surface tension parameters. The simulated results for bubble terminal velocities in bulk water and the literature data showed relative errors up to 4.51 %. The obtained qualitative and quantitative data from simulation at the liquid–liquid interface agreed well with the literature experimental results. The simulation setup was applied to investigate three different sizes of bubble rising dynamics from matte to slag phase with the bubble Reynolds number (Re) up to 1734 and the Eotvos number (Eo) up to 3.2. For low Re and Eo, the bubble rising velocity decreased before the matte film rupture and the bubble required a long time to complete that film drainage due to the balance of interfacial tension force and bubble buoyancy. No matte residue associated with the bubble rise in the slag phase was obtained because of restoring initial, non-deformed shape of bubbles. For the higher Re and Eo, quicker matte film drainage was obtained around the upper bubble surface while the entrained matte contribution to the slag phase was strongly dependent on the bubble-shape deformation, which was discussed with the well-known Grace diagram. The decreasing viscosity and increasing surface tension of the slag phase significantly affected the matte film height more than the film rupture time. The film height and rupture time increased and decreased with increasing Eo, respectively. The outcomes of our studies are useful for the design and operation of smetling furnaces in pyrometallurgical purification of metal concentrates.

Synergistic promotion of particulate matter reduction and production performance via adjusting electrochemical reactions in the zinc electrolysis industry

Heavy particulate matter (PM) pollution and high energy consumption are the bottlenecks of hydrometallurgy, especially in the electrolysis process. Therefore, an urgent need is to explore PM reduction methods with production performance co-benefits. This study presents three PM reduction methods based on controlling operating parameters, i.e., lowering electrolyte temperature, H2SO4 concentration, and current density of the cathode. The optimized conditions were also investigated using the response surface methodology to balance the PM reduction effect and Zn production. The results showed that lowering electrolyte temperature is the most efficient, with an 89.0% reduction in the PM generation flux (GFPM). Reducing H2SO4 concentration led to the minimum side effects on the current efficiency of Zn deposition (CEZn) or power consumption (PC). With the premise of non-deteriorating CEZn and PC, GFPM can be reduced by 86.3% at the optimal condition (electrolyte temperature = 295 K, H2SO4 = 110 g/L, current density = 373 A/m2). In addition, the reduction mechanism was elucidated by comprehensively analyzing bubble characteristics, electrochemical reactions, and surface tension. Results showed that lower electrolyte temperature inhibited the oxygen evolution reaction (OER) and compressed gas volume. Lower H2SO4 concentration inhibited the hydrogen evolution reaction (HER) and reduced electrolyte surface tension. Lower current density inhibited both OER and HER by decreasing the reaction current. The inhibited gas evolutions reduced the microbubbles’ number and size, thereby reducing GFPM. These results may provide energy-efficient PM reduction methods and theoretical hints of exploring cleaner PM reduction approaches for industrial electrolysis.

Investigation and application of microscopic mechanism of multiple bubble movement on directional frozen crystallization of seawater

In this study, we simulated the crystallization of seawater under multi bubble motion using the lattice Boltzmann method – phase field method (LBM - PFM) coupling method [1]. In addition, the crystallization mechanism with multiple bubbles movement is investigated, and the results indicate that the decisive factor for crystallization rate is boundary heat flux [1]. The change in bubble radius does not affect the formation of brine pockets (BP), while reducing bubble surface tension, increasing crystallization angle and bubble motion speed can effectively reduce BP area. Furthermore, we also propose an extremely low-cost, zero pollution application technology to improve desalination rate based on the influence of bubble velocity on crystallization.