Removal Of Gas Bubbles Research Articles

Features of water crystallization

Water is mainly composed of ice nanocrystals. The peculiarities of water crystallization can be explained on the basis of its nanostructural structure and nanostructural crystallization. Atmospheric air molecules dissolve well in water and are adsorbed by its nanocrystals. It is shown that the amount of expansion of ice, when water solidifies, is proportional to the concentration of air dissolved in it. The concentration of air dissolved in water decreases significantly with an increase in its temperature. Hot water solidifies faster than cold water because there is less air concentration in hot water. Its bubbles, released on ice crystals, reduce the rate of crystallization of water. A large supercooling of water occurs as a result of the blocking action of adsorbed air, which prevents the unification of ice nanocrystals into crystallization centers. Shaking a bottle of supercooled water leads to desorption of air and accelerated crystallization of water. Air bubbles released on dendritic ice crystals reduce the degree of branching of these crystals. It has been shown that music increases the intensity of removal of gas bubbles and is able to influence the shape of dendritic ice crystals during water crystallization. It has been shown that an increase in the volume of sound and (or) a decrease in its frequency increase the intensity of removal of air bubbles from dendritic ice crystals and increase the branching of these crystals.

Versatile, Stable, and Scalable Gel‐Like Aerophobic Surface System (GLASS) for Hydrogen Production

AbstractFacile removal of adsorbed gas bubbles from electrode surfaces is crucial to realize efficient and stable energy conversion devices based on electrochemical gas evolution reactions. Conventional studies on bubble removal have limited applicability and scalability due to their reliance on complex and energy/time‐intensive processes. In this study, a simple and versatile method is reported to fabricate large‐area superaerophobic electrodes (up to 100 cm2) for diverse gas evolution reactions using the gel‐like aerophobic surface system (GLASS). GLASS electrodes are readily and uniformly fabricated by simple spin‐coating and cross‐linking of polyallylamine on virtually any kinds of electrodes within 5 min under ambient conditions. Intrinsically hydrophilic gel overlayers with interconnected open pores allow the physical separation of bubble adhesion and catalytic active sites, reducing bubble adhesion strength, and promoting the removal of gas bubbles. As a result, GLASS electrodes exhibit greatly enhanced efficiency and stability for diverse gas evolution reactions, such as hydrogen evolution, hydrazine oxidation, and oxygen evolution reactions. This study provides deeper insights into understanding the effect of the hydrophilic microenvironment on gas evolution reactions and designing practical electrochemical devices.

Engineering Superaerophobic Electrodes Using Hydrophilic PEDOT and Colloidal Lithography for Enhanced Bubble Release and Efficient Hydrogen Evolution Reaction.

The efficient removal of gas bubbles is essential to reduce the reaction overpotential and improve the electrode stability in the hydrogen evolution reaction (HER). To address this challenge, the current study combines hydrophilic functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) with colloidal lithography to create superaerophobic electrode surfaces. The fabrication process involves the use of polystyrene (PS) beads with varying sizes (100, 200, and 500 nm) as hard templates and the electropolymerization of EDOTs with hydroxymethyl (EDOT-OH) and sulfonate (EDOT-SuNa) functional groups. The surface properties and HER performances of the electrodes are investigated. The electrode modified with poly(EDOT-SuNa) and 200 nm PS beads (SuNa/Ni/Au-200) exhibits the best hydrophilicity with a water contact angle of 37°. Moreover, the overpotential required at -10 mA cm-2 is substantially reduced from -388 mV (flat Ni/Au) to -273 mV (SuNa/Ni/Au-200). This approach is further applied to commercially available nickel foam electrodes, showing improved HER activity and electrode stability. These results highlight the potential for promoting catalytic efficiency by constructing a superaerophobic electrode surface.

Digital Image Correlation Technique to Aid Monotonic and Cyclic Testing in a Noisy Environment during In Situ Electrochemical Hydrogen Charging

Hydrogen is receiving growing interest as an energy carrier to facilitate the shift to a green economy. However, hydrogen may cause the significant degradation of mechanical properties of structural materials, premature strain localisation, crack nucleation, and catastrophic fracture. Therefore, mechanical testing in hydrogenating conditions plays a vital role in material integrity assessment. Digital image correlation (DIC) is a versatile optical technique that is ideally suited for studying local deformation distribution under external stimuli. However, during mechanical testing with in situ electrochemical hydrogen charging, gas bubbles inherent to hydrogen recombination are created at the sample surface, causing significant errors in the DIC measurements, and posing significant challenges to researchers and practitioners utilising this technique for testing in harsh environments. A postprocessing technique for the digital removal of gas bubbles is presented and validated for severe charging conditions (−1400 mV vs. Ag/AgCl) under monotonic and cyclic loading conditions. Displacement fields and strain measurements are produced from the filtered images. An example application for measuring the crack tip opening displacement during a slow strain rate tensile test is presented. The limitations of the technique and a comparison to other bubble mitigation techniques are briefly discussed. It was concluded that the proposed filtering technique is highly effective in the digital removal of gas bubbles during in situ electrochemical hydrogen charging, enabling the use of DIC when the sample surface is almost completely obscured by gas bubbles.

(Invited) Designing Microscale Structures for Enhanced Function of Electrocatalysts for Alkaline Water Electrolysis

Water electrolysis has already been implemented for many decades on an industrial scale. It does, however, remain an active area of research and development for the pursuit of materials that have enhanced electrocatalytic performance and prolonged durability. For example, the accumulation of gas bubbles on the surfaces of electrodes during water electrolysis remains a challenge. Persistent bubbles on the surfaces of electrocatalysts can block electrolyte access to the electrode and reduce the electrochemically active surface area. At current densities that are relevant to industrial applications an extensive portion of the electrode can become covered with bubbles. There are a range of solutions that are being utilized in industrial settings, but also additional solutions being sought to optimize the efficiency of these systems. These solutions include applied shear flows across the surfaces of the electrodes, the implementation of ultrasonic induced cavitation, and an increase in electrolyte temperature. These solutions require further expenditures of energy and decrease the overall energy efficiency of the system. Alternative approaches may yield a lower energy demand for maintaining accessibility of the electrolyte to the electrochemically active surface area. One approach is through the design of electrode surface architectures that can assist with the removal of gas bubbles during water electrolysis. This work includes a review of the progress made in preparing structured electrodes for the alkaline based water electrolysis and specifically for the oxygen evolution reaction. These structures can influence the dynamics that occur at the electrode-electrolyte interface, such as the growth, coalescence, and release of oxygen gas bubbles. Understanding the correlations between the structures on the electrodes and their influence on the function of these materials towards the gas evolution are sought to guide the future development of optimal surface structures that are self-cleaning. Designs of electrode surface architectures are sought that can improve the efficiency of electrodes toward this and other gas evolution reactions.

High-gravity intensified electrodeposition for efficient removal of Cd2+ from heavy metal wastewater

Efficiently treating heavy metal wastewater are the goal that industries pursuit. A novel Multi-concentric Cylindrical Electrodes-Rotating Bed (MCCE-RB) which could provide high-gravity fields was proposed to enhance electrodeposition for efficient treatment of Cd-containing wastewater in this paper. Under the optimal operating conditions covering current density of 53.1 A m−2, wastewater circulation flowrate of 64 L h−1, high-gravity factor of 15, NaCl concentration of 0.2 mol L−1, initial pH value of 2, and initial Cd2+ concentration of 800 mg L−1, the removal efficiency of Cd2+ reached 99.4% after 120 min electrodeposition. Compared with the results of electrodeposition in normal gravity field, the removal efficiency of Cd2+, current efficiency and the mass of deposits were increased by 18.4%, 15.7% and 35.4%, respectively. The cell voltage, electrodeposition time and total energy consumption (ETotal) were decreased by 21.7%, 42% and 21.2%, respectively. SEM, EDS, XRD and XPS analyses showed that the deposits were flaky and layered structure in high-gravity fields, avoiding the formation of dendrite in normal gravity field. The deposits were comprised of the mixture of Cd and Cd(OH)2, and the percent weight of elemental Cd was 91.29% in the high-gravity field which was 19.17% higher than that in normal gravity field. The purity of Cd was improved in the high-gravity field. These was ascribed to the depressed hydrogen evolution reaction, the removal of gas bubbles from the electrodes and the improvement in mass transport in the optimal high-gravity field. High-gravity intensified electrodeposition could serve as a clean, high efficient and low energy consumption method for treating heavy metal wastewater.

Kinetics of vanadium reduction from slags by solid carbon

The laboratory investigation results of the vanadium reduction are presented. Experiments were performed with CaO–SiO2–Al2O3–MgO–V2O3 slags in an air atmosphere. The solid carbon was used as a reducing agent. The reduction kinetics was studied by sampling. It has been shown that reduction proceeds to VC carbide. The process rate is inversely proportional to the slag viscosity. The formation of a carbide film on the carbon surface leads to a sudden, by an order of magnitude, reduction in the rate. The process of vanadium reduction from oxide melts by solid carbon is electrochemical in nature and is limited by the stage of carbon anodic oxidation. The influence of slag viscosity on the process kinetics is explained by the fact that it is controlled by the growth rate and removal of gas bubbles. The appearance of the carbide film, apparently, transfers the reduction process into the intra diffusion mode, when the transfer of carbon and vanadium through the carbide film is limiting.

Removal of Gas Bubbles on an Electrode Using a Magnet

Oxygen evolution reaction is an enabling process of energy storage, metal extraction and nature photosynthesis. Bubble growth on the electrode surface can block the following reaction. Here we pres...

The self-supported Zn-doped CoNiP microsphere/thorn hierarchical structures as efficient bifunctional catalysts for water splitting

The hierarchical electrocatalysts with the superaerophobic property are in favor of removal of gas bubbles and supply of numerous active sites to improve the electrochemical catalytic activity for water splitting. In this work, the self-supported Zn-doped CoNiP (Zn–CoNiP/NF) hierarchical structure that consisted of nanothorns and radial microspheres were prepared with via a facile precursor phosphorization method. Zn-doping could tailor the initial electronic state of CoNiP to improve the hydrogen or oxygen atom binding, which effectively promoted the catalytic kinetics of water splitting. The hierarchical structure not only offered more catalytic active sites for water splitting, but also facilitated gas releasing due to the superaerophobic interface. The hierarchical Zn–CoNiP structure showed a high hydrogen evolution reaction (HER) efficiency in electrolytes with pH 0–14, which yielded low overpotentials of 73 mV in acidic solution and 34 mV in alkaline media at current density of 10 mA cm−2. Furthermore, it also had evidenced by an overpotential of 310 mV for oxygen evolution reaction (OER) at the current density of 50 mA cm−2. Note that the required cell initial voltage was 1.51 V for overall water splitting. These results were comparable or even better than many non-noble catalysts.

Numerical modeling of effect of slot on bubble motion in aluminum electrolytic process

Abstract A transient three-dimensional (3D) model was established to understand the bubble motion in an industrial electrolytic process. An anode with a new design was tested. It incorporates two slots that allow an efficient removal of gas bubbles. The electromagnetic fields were described by solving Maxwell's equations. The bubble movement was studied with two-way coupling Euler–Lagrange approach. The interplay of current density and bubble nucleation rate was included. The collision and coalescence of bubbles were considered. Random walk module was invoked for involving the chaotic effect of the turbulence. The numerical results were validated by experimental measurements. The results indicate that the current distribution and the bubble nucleation periodically change. Due to the slot, the bubble elimination heavily increases. The contribution of the slot to the bubble removal exceeds 50% in the case of three currents, and the promotion of the slot decays with increasing the current.

Removal of gas bubbles from highly viscous non-Newtonian fluids using controlled vibration

Formation of gas bubbles is normal and practically inevitable when fluids are agitated or flow in open containers. The unwanted gas bubbles will damage the product quality, and they are very difficult to be removed from highly viscous fluids. In this paper, the effectiveness of vibration degassing for highly viscous non-Newtonian fluids is investigated using volume of fluid (VOF) model coupled with continuous surface force (CSF) model. The motions of gas bubbles in liquid under vibration are simulated and the effects of various rheological parameters as well as vibration parameters on the degassing rate are studied. The results show that the shear thinning (or thickening) induced by vibration is responsible for the enhancement (or retardation) of degassing rate for non-Newtonian fluids. The more pronounced the non-Newtonian behaviors of fluids are, the greater the effects of vibration on the degassing rate are. The degassing rate is governed by the vibration amplitude and frequency of vibration. However, high frequency or large amplitude vibration may intensify air entrapment and bring new gas bubbles into fluids. Thus, the feasible region of vibration degassing in which the vibration frequency and amplitude don’t cause new gas bubbles are further studied. The vibration degassing technology has the added advantage that it does not use intrusive devices to container, nor does it limit the container structure or shape, and thus will find wide applications in laboratory and industrial fields.

Bioreactors with hydrostatic pressures imitating physiological environments in intervertebral discs.

Intervertebral discs are normally exposed to a variety of loads and stresses but hydrostatic pressure (HP) could be the main biosignal for chondrogenic cell differentiation and maintenance of this tissue. Although there are simple approaches to intermittently expose cell cultures to HP in separate material testing devices, utilization of biomimetic bioreactors aiming to provide in vitro conditions mimicking those found in vivo, attracts special attention. However, design of such bioreactors is complex due to the requirement of high HP magnitudes (up to 3MPa) applied in different regimes mimicking pressures arising in intervertebral disc during normal daily activities. Furthermore, efficient mass transfer has to be facilitated to cells within 3D scaffolds, and the engineering challenges include avoidance or removal of gas bubbles in the culture medium before pressurization as well as selection of appropriate, biocompatible construction materials and maintenance of sterility during cultivation. Here, we review approaches to induce HP in 2D and 3D cell cultures categorized into 5 groups: (I) discontinuous systems with direct pressurization of the cultivation medium by a piston, (II) discontinuous systems with indirect pressurization by a compression fluid, (III) continuous systems with direct pressurization of the cultivation medium, static culture, (IV) continuous systems with culture perfusion, and (V) systems applying HP in conjunction with other physical signals. Although the complexity is increasing as additional features are added to the systems, the need to understand HP effects on cells and tissues in a physiologically relevant, yet precisely controlled, environment together with current technological advancements are leading towards innovative bioreactor solutions.

Increasing Gas Bubble Escape Rate for Water Splitting with Nonwoven Stainless Steel Fabrics.

Water electrolysis has been considered as one of the most efficient approaches to produce renewable energy, although efficient removal of gas bubbles during the process is still challenging, which has been proved to be critical and can further promote electrocatalytic water splitting. Herein, a novel strategy is developed to increase gas bubble escape rate for water splitting by using nonwoven stainless steel fabrics (NWSSFs) as the conductive substrate decorated with flakelike iron nickel-layered double hydroxide (FeNi LDH) nanostructures. The as-prepared FeNi LDH@NWSSF electrode shows a much faster escape rate of gas bubbles as compared to that of other commonly used three-dimensional porous catalytic electrodes, and the maximum dragging force for a bubble releasing between NWSSF channels is only one-seventh of the dragging force within nickel foam channels. As a result, it exhibits excellent electrocatalytic performance for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), with low overpotentials of 210 and 110 mV at the current density of 10 mA cm-2 in 1 M KOH for OER and HER, respectively. There is almost no current drop after a long-time durability test. In addition, its performance for full water splitting is superior to that of the previously reported catalysts, with a voltage of 1.56 V at current density of 10 mA cm-2.

Effect of Slotted Anode on Gas Bubble Behaviors in Aluminum Reduction Cell

In the aluminum reduction cells, gas bubbles are generated at the bottom of the anode which eventually reduces the effective current contact area and the system efficiency. To encourage the removal of gas bubbles, slotted anode has been proposed and increasingly adopted by some industrial aluminum reduction cells. Nonetheless, the exact gas bubble removal mechanisms are yet to be fully understood. A three-dimensional (3D) transient, multiphase flow mathematical model coupled with magnetohydrodynamics has been developed to investigate the effect of slotted anode on the gas bubble movement. The Eulerian volume of fluid approach is applied to track the electrolyte (bath)–molten aluminum (metal) interface. Meanwhile, the Lagrangian discrete particle model is employed to handle the dynamics of gas bubbles with considerations of the buoyancy force, drag force, virtual mass force, and pressure gradient force. The gas bubble coalescence process is also taken into account based on the O’Rourke’s algorithm. The two-way coupling between discrete bubbles and fluids is achieved by the inter-phase momentum exchange. Numerical predictions are validated against the anode current variation in an industrial test. Comparing the results using slotted anode with the traditional one, the time-averaged gas bubble removal rate increases from 36 to 63 pct; confirming that the slotted anode provides more escaping ways and shortens the trajectories for gas bubbles. Furthermore, the slotted anode also reduces gas bubble’s residence time and the probability of coalescence. Moreover, the bubble layer thickness in aluminum cell with slotted anode is reduced about 3.5 mm (17.4 pct), so the resistance can be cut down for the sake of energy saving and the metal surface fluctuation amplitude is significantly reduced for the stable operation due to the slighter perturbation with smaller bubbles.

Glass frit bonding with controlled width and height using a two-step wet silicon etching procedure

A simple and versatile two-step silicon wet etching technique for the control of the width and height of the glass frit bonding layer has been developed to improve bonding strength and reliability in wafer-level microelectromechanical systems (MEMS) packaging processes. The height of the glass frit bonding layer is set by the design of a vertical reference wall which regulates the distance between the silicon wafer and the encapsulation capping substrate. On the other hand, the width of the bonding layer is constrained between two micro grooves which are used to accommodate the spillages of extra glass frit during the bonding process. An optimized thermal bonding process, including the formation of glass liquid, removal of gas bubbles under vacuum and the filling of voids under normal atmospheric condition has been developed to suppress the formation of the bubbles/voids. The stencil printing and pre-sintering processes for the glass frit have been characterized before the thermal bonding process under different magnitudes of bonding pressure. The bonding gap thickness is found to be equal to the height of the reference wall of 10 μm in the prototype design. The bubbles/voids are found to be suppressed effectively and the bonding strength increases from 10.2 to 19.1 MPa as compared with a conventional thermal annealing process in air. Experimentally, prototype samples are measured to have passed the high hermetic sealing leakage tests of 5 × 10−8 atm cc s−1.

Effects of Electrode Modification on the Air Electrode for Water Electrolysis

The oxygen evolution reaction (OER) is taking place on the air electrode during charging period of rechargeable metal air battery. Removal of gas bubbles from the electrode is one of the key issues for better performance. This study investigated the effects of surface modified on the polarization curve of air electrode. Stainless steel mesh coated with needle-like deposit had better performance than those without coating. Electrode with needle-like surface had substantially lower OER over-potential. This electrode was combined with electrode for oxygen reduction reaction for acharge-discharge cycling test. A stable charging potential over 428 cycles was achieved.

Bubbles no more: in-plane trapping and removal of bubbles in microfluidic devices

Gas bubbles present a frequent challenge to the on-chip investigation and culture of biological cells and small organs. The presence of a single bubble can adversely impair biological function and often viability as it increases the wall shear stress in a liquid-perfused microchannel by at least one order of magnitude. We present a microfluidic strategy for in-plane trapping and removal of gas bubbles with volumes of 0.1-500 nL. The presented bubble trap is compatible with single-layer soft lithography and requires a footprint of less than ten square millimetres. Nitrogen bubbles were consistently removed at a rate of 0.14 μL min(-1). Experiments were complemented with analytical and numerical models to comprehensively characterize bubble removal for liquids with different wetting behaviour. Consistent long-term operation of the bubble trap was demonstrated by removing approximately 4000 bubbles during one day. In a case study, we successfully applied the bubble trap to the on-chip investigation of intact small blood vessels. Scalability of the design was demonstrated by realizing eight parallel traps at a total removal rate of 0.9 μL min(-1) (measured for nitrogen).

Fast fabrication of glass ceramics by high gravity combustion synthesis

Three systems of glass ceramics with different chemical compositions were prepared by high gravity combustion synthesis. Most samples were dense with a low porosity, which can be attributed to accelerated separation and removal of gas bubbles from ceramic melts in a high gravity field. The hardness of the as prepared glass ceramics varied in the range of 8·2–12·8 GPa and could be improved by a fine eutectic structure. Compared with conventional techniques, high gravity combustion synthesis can offer a fast and efficient way to prepare glass ceramic materials.

A degassing plate with hydrophobic bubble capture and distributed venting for microfluidic devices

This paper introduces a microfluidic wall plate that allows the removal of gas bubbles from a gas/liquid mixture in a distributed fashion, i.e., throughout the flow path, eliminating the need for discrete separators common in macroscopic practice. Integrated into a microfluidic system at critical locations, such a degassing plate prevents the build up of gas bubbles in microchannels so as to maximize the effective reaction area, decrease the flow resistance and keep the chamber pressure under check. Furthermore, the plate surface is designed to capture the gas bubbles preferentially on designated venting sites, so that the rest of the surface can be dedicated to other functions, such as the catalyst or electrodes. The mechanism of bubble capture is explained by surface energy minimization, and two types of bubble sinks are proposed and verified. Once captured, the bubbles can be vented out through hydrophobic venting holes small enough (e.g. sub-micron) to block the liquid by surface tension. By chemically generating CO2 inside a small chamber (30 mm × 50 mm × 1.5 mm) sealed by the degassing plate, the process of bubble capture and removal is visually demonstrated. A porous polypropylene membrane with ∼0.2 µm diameter holes shows that gas can be removed with only several kPa of internal pressure while water stays free of leakage even under 2.4 × 105 Pa (35 psi). Venting is effective in any gravitational orientation, paving the way for portable microfluidic devices.

Chemistry, physics and time: the computer modelling of glassmaking.

A decade or so ago the remains of an early flat glass furnace were discovered in St Helens. Continuous glass production only became feasible after the Siemens Brothers demonstrated their continuous tank furnace at Dresden in 1870. One manufacturer of flat glass enthusiastically adopted the new technology and secretly explored many variations on this theme during the next fifteen years. Study of the surviving furnace remains using today's computer simulation techniques showed how, in 1887, that technology was adapted to the special demands of window glass making. Heterogeneous chemical reactions at high temperatures are required to convert the mixture of granular raw materials into the homogeneous glass needed for windows. Kinetics (and therefore the economics) of glassmaking is dominated by heat transfer and chemical diffusion as refractory grains are converted to highly viscous molten glass. Removal of gas bubbles in a sufficiently short period of time is vital for profitability, but the glassmaker must achieve this in a reaction vessel which is itself being dissolved by the molten glass. Design and operational studies of today's continuous tank furnaces need to take account of these factors, and good use is made of computer simulation techniques to shed light on the way furnaces behave and how improvements may be made. This paper seeks to show how those same techniques can be used to understand how the early Siemens continuous tank furnaces were designed and operated, and how the Victorian entrepreneurs succeeded in managing the thorny problems of what was, in effect, a vulnerable high temperature continuous chemical reactor.