Bubble Removal Research Articles

Theoretical and experimental study of PbO-SiO2-Sb2O3 glasses as gamma ray shielding materials

Investigation and application of high energy radiations require the availability of radiation shields. In this research, glasses with the composition of 0.65PbO.(0.35-x)SiO2.xSb2O3 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were fabricated and characterized using densitometry, XRD, UV-Vis spectrophotometry and gamma ray spectrometry. The theoretical attenuation coefficient of the samples was calculated using WinXCom software. It was observed that although PbO strongly increased the mass attenuation coefficient for Co-60 radiation of glass, its substitution by Sb2O3 initially increased the parameter from 0.0609 to 0.0621, due to the dominant effect of Sb2O3 on bubble removal. The results also showed that there was an inconsistency between the theoretical and empirical results, that is, with increasing Sb2O3 content of the samples, the attenuation coefficient initially increased and then decreased, while the theoretical calculations predicted a continuous decline. It appears that the disagreement is mainly due to the fining effect of Sb2O3 and its effects on the bubble content. The WinXCom software is designed to work solely based on the mixture law. The sample 0.65PbO.0.34SiO2.0.01Sb2O3 showed the highest mass attenuation. The coefficient was 0.0621 and 0.0609 in 1.250 MeV for the samples with x = 0 and 0.01.

Effects of downward-facing surface type and inclination on critical heat flux during pool boiling

The effectiveness of ex-vessel cooling systems in response to severe nuclear reactor accidents is attributable, in part, to the critical heat flux (CHF). As such, CHF enhancement has been the focus of significant research. Prior studies have demonstrated that porous and specifically, honeycomb surfaces can increase the CHF. In this study, we compared the CHF of bare- and various honeycomb downward-facing surfaces during pool boiling. In addition, we investigated the effects of surface inclination on the CHF. The results indicated that the honeycomb surfaces had higher CHF values than the bare surface. The honeycomb surfaces provided separate water supply and bubble removal paths, which decreased the liquid–vapor counterflow resistance and increased the water supply to the heating surface for cooling. The porous honeycomb surfaces (with 5-, 20-, and 100-μm pores) had higher CHF values than the honeycomb surface with no pores (with 0-μm pores). Among the different porous surfaces, the CHF values were equivalent. With respect to inclination, the results indicated that the CHF increased as surface inclination increased for both bare and honeycomb surfaces. The increased surface inclination facilitated bubble removal and again increased the water supply to the heating surface for cooling. Thus, the water supply and bubble removal capacities are two underlying factors affecting the CHF. The CHF (and ultimately ex-vessel cooling system effectiveness) is determined by the limiting water supply or bubble removal capacities. In this study, the bubble removal capacity was consistently the limiting factor for determining the CHF.

Application of low frequency vibration to degassing of highly viscous shear-thinning fluids

The removal of unwanted gas bubbles is an important operation in many processes. In this paper, the mechanism of the degassing of highly viscous fluids by low-frequency vibration is studied numerically using the computational fluid dynamics (CFD). The effects of vibration frequency and amplitude on the degassing rate are investigated. The results show that the superimposed mechanical vibration largely affects the degassing rate of shear-thinning fluids but exerts no effect on that of Newtonian fluids. The de-gassing rate of shear-thinning fluids depends on the vibration frequency and amplitude. What’s more, low-frequency and small-amplitude vibration is particularly useful in re-moving gas bubbles from viscous shear-thinning fluids, however, high-frequency or large-amplitude vibration may intensify air entrapment and brings new gas bubbles into fluids.

Energy distribution and melting efficiency in glass melting channel: Diagram of melt flow types and effect of melt input temperature

The synergy between glass melting and glass flow character was investigated by mathematical modelling of a Joule heated glass melting channel with a central longitudinal row of vertical heating electrodes. The glass melt containing sand particles and bubbles entered the channel where different types of the melt flow were set up. The sand particle dissolution and the bubble removal were monitored up to the achievement of phenomena completion. The increasing fraction of energy supplied to the input region of the channel proved to be crucial for setting up the beneficial character of the melt flow and consequent increase of the melting performance. When the temperature of the inputting melt decreased, the melting performance also decreased. The relations of the “energetic model” were derived and applied to predict the beneficial type and conditions of the melt flow. The best results have been obtained for the flow character near the uniform flow. The beneficial state was achieved when each region of the channel was supplied by the energy needed there for glass heating and heat losses. The impact of the temperature of the inputting melt on the detailed character of the melt flow was discussed with the help of the energetic model.

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.

Direct methanol fuel cell bubble removal mechanism using magnetic actuation

ABSTRACTThis article develops a direct methanol fuel cell (DMFC) with a magnet-actuated bubble removal mechanism. A micro-DC motor is used to control the bubble removal mechanism. The lower magnetic device is operated to extrude a Polydimethylsiloxane (PDMS) runner to compress the liquid fuel in the anode flow channel, forcing the CO2 bubbles in the runner to flow toward the outlet end. The bubble retention in the anode flow channel is thereby improved, enhancing the cell performance. The proposed mechanism stability and performance and Polymethylmethacrylate (PMMA) runner are also discussed.

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.

Intensification of photocatalytic decomposition of water by ultrasound

Photocatalysis of water with and without ultrasound was studied using rGO supported CdS catalyst utilizing visible light. A higher hydrogen production was observed when ultrasound was used. This is attributed to a faster removal of bubbles of hydrogen from the surface of photocatalyst due to the mechanical energy associated with ultrasound overcoming surface tension. It has been further reported that the rate of hydrogen production decreased with time due to reversible deactivation of catalyst. This has been attributed to decrease in rate of hydrogen desorption with time.

P15 超音波および他の方法によるウルトラファインバブル脱泡(ポスターセッション)

P15 超音波および他の方法によるウルトラファインバブル脱泡(ポスターセッション)

Bubble removal with the use of a vacuum pressure generated by a converging-diverging nozzle.

Bubbles are an intrinsic problem in microfluidic devices and they can appear during the initial filling of the device or during operation. This report presents a generalizable technique to extract bubbles from microfluidic networks using an adjacent microfluidic negative pressure network over the entire microfluidic channel network design. We implement this technique by superimposing a network of parallel microchannels with a vacuum microfluidic channel and characterize the bubble extraction rates as a function of negative pressure applied. In addition, we generate negative pressure via a converging-diverging (CD) nozzle, which only requires inlet gas pressure to operate. Air bubbles generated during the initial liquid filling of the microfluidic network are removed within seconds and their volume extraction rate is calculated. This miniaturized vacuum source can achieve a vacuum pressure of 7.23psi which corresponds to a bubble extraction rate of 9.84 pL/s, in the microfluidic channels we characterized. Finally, as proof of concept it is shown that the bubble removal system enables bubble removal on difficult to fill microfluidic channels such as circular or triangular shaped channels. This method can be easily integrated into many microfluidic experimental protocols.

Electrochemical Size Measurement and Characterization of Electrodeposited Platinum Nanoparticles at Nanometer Resolution with Scanning Electrochemical Microscopy.

The properties of nanoparticles (NPs) are determined by their size and geometric structures. A reliable determination of NP dimension is critical for understanding their physical and chemical properties, but sizing ultrasmall particles on the order of nanometer (nm) scale in the solution is still challenging. Here, we report the size measurement of PtNP at nanometer resolution by in situ scanning electrochemical microscopy (SECM), performed with the electrochemical generation and removal of H2 bubble at a reasonably small distance between tip and substrate electrodes in 200 or 500 mM HClO4 solution. A series of different PtNPs or nanoclusters were electrodeposited and in situ measured in the solution, proving the concept of sizing ultrasmall particles using tip generation/substrate collection mode of SECM. This technique could be also used for investigations of other supported ultrasmall metal nanocluster systems.

Effect of air removal with extracorporeal balloon inflation on incidence of asymptomatic cerebral embolism during cryoballoon ablation of atrial fibrillation

Asymptomatic cerebral embolism (ACE) is sometimes detected after cryoballoon ablation of atrial fibrillation. The removal of air bubbles from the cryoballoon before utilization may reduce the rate of ACE. This study aims to compare the incidence of ACE between a conventional and a novel balloon massaging method during cryoballoon ablation. Of 175 consecutive patients undergoing initial cryoballoon ablation of paroxysmal atrial fibrillation, 60 (34.3%) patients underwent novel balloon massaging with extracorporeal balloon inflation in saline water (group N) before the cryoballoon was inserted into the body. The remaining 115 (65.7%) patients underwent conventional balloon massaging in saline water while the balloon remained folded (group C). Of those, 86 propensity score-matched patients were included. The baseline characteristics were similar between the 2groups. In group N, even after balloon massaging in saline water was carefully performed, multiple air bubbles remained on the balloon surface when the cryoballoon was inflated in all cases. Postprocedural cerebral magnetic resonance imaging detected ACE in 14.0% of all patients. The incidence of ACE was significantly lower in group N than in group C (4.7% vs 23.3%; P = .01). According to multivariable analysis, the novel method was the sole factor associated with the presence of ACE (odds ratio 0.161; 95% confidence interval 0.033-0.736; P = .02). Preliminary removal of air bubbles in heparinized saline water with extracorporeal balloon inflation reduced the incidence of ACE. Since conventional balloon massaging failed to remove air bubbles completely, this novel balloon massaging method should be recommended before cryoballoon utilization.

Hydrodynamics and Oxygen Bubble Characterization of Catalytic Cells Used in Artificial Photosynthesis by Means of CFD

Miniaturized cells can be used in photo-electrochemistry to perform water splitting. The geometry, process variables and removal of oxygen bubbles in these cells need to be optimized. Bubbles tend to remain attached to the catalytic surface, thus blocking the reaction, and they therefore need to be dragged out of the cell. Computational Fluid Dynamics simulations have been carried out to assess the design of miniaturized cells and their results have been compared with experimental results. It has been found that low liquid inlet velocities (~0.1 m/s) favor the homogeneous distribution of the flow. Moderate velocities (0.5–1 m/s) favor preferred paths. High velocities (~2 m/s) lead to turbulent behavior of the flow, but avoid bubble coalescence and help to drag the bubbles. Gravity has a limited effect at this velocity. Finally, channeled cells have also been analyzed and they allow a good flow distribution, but part of the catalytic area could be lost. The here presented results can be used as guidelines for the optimum design of photocatalytic cells for the water splitting reaction for the production of solar fuels, such as H2 or other CO2 reduction products (i.e., CO, CH4, among others).

Application effect of three methods of bubble-removal in preflush of combined artificial kidney hemoperfusion apparatus

Objective To investigate the application effect of three methods of bubble-removal in preflush of combined artificial kidney hemoperfusion apparatus. Methods Twenty patients, treated by combined artificial kidney HP+HD, were selected and divided into three groups: hand beating group, hammer beating group and shaking group, each with twenty cases every time, according to the method they adopted for bubble removal in the preflush process of hemoperfusion for three times. Under the three methods of bubble removal in preflush process, times of nurses' intervention, their satisfaction, and crack or damage of the perfusion apparatus were compared. Results Among the three methods of bubble removal, differences in average intervention frequency and average intervention time were statistically significant (P<0.01) . Differences in nurses' satisfaction were statistically significant (P<0.01) . In all the three groups, there was no crack or damage in the perfusion apparatus. Conclusions The shaking method is more effective in preflush of hemoperfusion apparatus, which can enhance nurses' satisfaction and work efficiency. Key words: Hemodialysis; Hemoperfusion; Pre-flush

Swing-like pool boiling on nano-textured surfaces for microgravity applications related to cooling of high-power microelectronics

Here, we demonstrate that heat removed in pool boiling from a heater mimicking high-power microelectronics could be used to facilitate a swing-like motion of the heater before being finally dissipated. This swing-like motion could be beneficial for shedding a large vapor bubble that encapsulates high-power heaters in microgravity where buoyancy force is unavailable for vapor bubble removal. The swing-like motion is propelled by vapor bubble recoil, the force which exists irrespective of gravity and buoyancy. We also demonstrate that this force could be significantly enhanced by depositing on the heater surface supersonically blown polymer nanofibers with cross-sectional diameters below 100 nm. These nanofibers provide additional nucleation sites, resulting in much more frequent bubble nucleation and departure, and thus a higher overall vapor recoil force propelling the heater motion. Such nanofibers strongly adhere to the heater surface and withstand prolonged harsh pool boiling. The measured velocity of the model swing-like heater in Novec 7300 fluid is about 1 cm/s.

Study on wire electrochemical machining assisted with large-amplitude vibrations of ribbed wire electrodes

A large-amplitude vibration of wire electrode tool is introduced to enhance electrolyte renewal and bubble removal in wire electrochemical machining. It is verified via simulation and high-speed video that hydrogen bubbles generated in electrochemical reactions can be expelled effectively from the machining gap by means of large-amplitude vibrations and a better effect was obtained in the upward duration. A ribbed wire electrode is employed to intensify electrolyte renewal process due to its specific structure. The experimental results demonstrated that the proposed large-amplitude vibration and ribbed electrode significantly accelerate electrolyte renewal, thereby hastening material removal rate and improving machining efficiency.

Bubble removal and sand dissolution in an electrically heated glass melting channel with defined melt flow examined by mathematical modelling

The electrically heated glass melting channel as a part of the segmented melting furnace was examined by mathematical modelling. Different melt flow characters were set up by proper configurations of the heating electrodes in the channel with either level or close-to-bottom melt input. The sand particle dissolution and bubble removal of defined sizes were followed up to the achievement of the critical state. This was characterized by the termination of the less effective melting phenomenon just before the output from the channel. The utilization of the melting space, the melting performance, and the specific heat losses in the critical state were evaluated. The effect of the melt input character and melt input temperature, electrode length, and energy distribution were investigated. The results have shown that the best results were attained when the energy distribution in the channel was balanced or when it was near the balanced state. Hence, no or only weak longitudinal circulations of the melt arose in the space and the helical-like melt flow could be set. This state was achieved when the melt input temperature was equivalent or not far from the average temperature of the melt in the space. Such as state can be set up by an energy shift to the regions with lower temperature and by enhancement of the transversal melt circulations.

Entrapment and venting of bubbles during vacuum bag prepreg processing

During composites manufacturing with partially pre-impregnated fibers (i.e. “prepregs”) in Out-of-Autoclave processes, non-impregnated fabric cross-sections serve as air pathways to evacuate entrapped bubbles of air, moisture, or volatiles. The bubbles trapped within a laminate during processing lead to decreased structural performance. In this work, the motion of resin and bubbles during the processing of a characteristic prepreg is directly visualized in situ. This is performed utilizing a previously developed flow visualization technique under known pressure and temperature conditions. This study investigates the processing conditions under which a bubble succeeds or fails to meet and coalesce with available air pathways in order to escape the laminate. A key finding of this study is that tunable process parameters, such as pressure and temperature, are less important for successful bubble removal as compared to the initial state of resin impregnation in the prepreg. Prepregs with initially high states of resin impregnation will often fail to draw bubbles into air pathways through the center of fiber tow cross sections, whereas prepregs with initially low states of resin impregnation have clear pathways for bubbles to meet local resin flow fronts, coalesce, and escape. The relevant literature on the motion of bubbles in confined spaces is discussed. It is observed that small Capillary number theory (i.e. Ca &lt; 0.01) under predicts the relative velocity of bubbles, and the faster than expected bubble transport is likely due to effects given by the bubble aspect ratio via the fibrous micro-channel geometry.

In vivo dynamic analysis of water refilling in embolized xylem vessels of intact Zea mays leaves.

Background and Aims The refilling of embolized xylem vessels under tension is a major issue in water transport among vascular plants. However, xylem embolism and refilling remain poorly understood because of technical limitations. Direct observation of embolism repair in intact plants is essential to understand the biophysical aspects of water refilling in embolized xylem vessels. This paper reports on details of the water refilling process in leaves of the intact herbaceous monocot plant Zea mays and its refilling kinetics obtained by a direct visualization technique. Methods A synchrotron X-ray micro-imaging technique was used to monitor water refilling in embolized xylem vessels of intact maize leaves. Xylem embolism was artificially induced by using a glass capillary; real-time images of water refilling dynamics were consecutively captured at a frame rate of 50 f.p.s. Key Results Water supply in the radial direction initiates droplet formation on the wall of embolized xylem vessels. Each droplet grows into a water column; this phenomenon shows translation motion or continuous increase in water column volume. In some instances, water columns merge and form one large water column. Water refilling in the radial direction causes rapid recovery from embolism in several minutes. The average water refilling velocity is approx. 1 μm s-1. Conclusions Non-destructive visualization of embolized xylem vessels demonstrates rapid water refilling and gas bubble removal as key elements of embolism repair in a herbaceous monocot species. The refilling kinetics provides new insights into the dynamic mechanism of water refilling phenomena.