Bubble Escape Research Articles

A model for the interpretation of the bed collapse experiment

The bed collapse technique was first reported by Rietema in 1967. It is one of the standard techniques commonly used for the characterization of the fluidization quality of powders. It is particularly useful for fine fluidized particles or more generally for powders belonging to group A of the Geldart classification. The bed collapse experiment is used to measure the time required for the de-aeration of the particle suspension and, by extrapolating the linear portion of the collapse curve, the dense phase voidage. These should be dependent only on the particle and fluid properties, but it has long been recognised that the system configuration will affect these results. We present a new model that can be used to predict the bed collapse curve, the bubble escape time, and the de-aeration times taking into account the system configuration. This can be achieved from the knowledge of the initial conditions, the dense phase voidage, and the superficial velocity in the dense phase. The model can be used to predict under which conditions the 1-valve or 2-valve configuration will yield the correct extrapolation to obtain the dense phase voidage from the experimental curve. The model has been validated using experimental bed collapse curves for a set-up that can be operated in the 1-valve and 2-valve configuration. Excellent agreement between experiment and simulations was obtained.

A temperature‐dependent, structural‐optical model of first‐year sea ice

A model has been developed that relates the structural properties of first‐year sea ice to its inherent optical properties, quantities needed by detailed radiative transfer models. The structural‐optical model makes it possible to calculate absorption coefficients, scattering coefficients, and phase functions for the ice from information about its physical properties. The model takes into account scattering by brine inclusions in the ice, gas bubbles in both brine and ice, and precipitated salt crystals. The model was developed using concurrent laboratory measurements of the microstructure and apparent optical properties of first‐year, interior sea ice between temperatures of −33°C and −1°C. Results show that the structural‐optical properties of sea ice can be divided into three distinct thermal regimes: cold (T < −23°C), moderate (−23°C < T < −8°C), and warm (T > −8°C). Relationships between structural and optical properties in each regime involve different sets of physical processes, of which most are strongly tied to freezing equilibrium of the brine and ice. Volume scattering in cold ice is dominated by the size and number distribution of precipitated hydrohalite crystals. Scattering at intermediate temperatures is controlled by changes in the distribution of brine inclusions, gas bubbles, and mirabilite crystals. Total volume scattering in this regime is approximately independent of temperature because of a balance between increasing and decreasing scattering related to the thermal evolution of these inclusions and scattering by drained inclusions. In warm ice, scattering is controlled principally by temperature‐dependent changes in the real refractive index of brine and by the escape of gas bubbles from the ice. Model predictions indicate that scattering coefficients can exceed 3000 m−1 for cold ice, averaging ∼450 m−1 for moderate and warm ice and reaching a minimum of ∼340 m−1 at −8°C. Scattering in all three regimes is very strongly forward peaked, with values of the asymmetry parameter g generally falling between 0.975 (T = −8°C) and 0.995 (T = −33°C).

An experimental study on the temperature distribution in IRWST

The In-Containment Refueling Water Storage Tank (IRWST), one of the design improve-ments applied to the APR-1400, has a function to condense the high enthalpy fluid discharged from the Reactor Coolant System (RCS). The condensation of discharged fluid by the tank water drives the tank temperature high and causes oscillatory condensation. Also if the tank cooling water temperature approaches the saturated state, the steam bubble may escape from the water uncondensed. These oscillatory condensation and bubble escape would burden the undue load to the tank structure, pressurize the tank, and degrade its intended function. For these reasons simple analytical modeling and experimental works were performed in order to predict exact tank temperature distribution and to find the effective cooling method to keep the tank temperature below the bubble escape limit (93.3°C), which was experimentally proven by other researchers. Both the analytical model and experimental results show that the temperature distributions are horizontally stratified. Particularly, the hot liquid produced by the condensation around the sparger holes goes up straight like a thermal plume. Also, the momentum of the discharged fluid is not so strong to interrupt this horizontal thermal stratification significantly. Therefore the layout and shape of sparger is not so important as long as the location of the sparger hole is sufficiently close to the bottom of the tank. Finally, for the effective tank cooling it is recommended that the locations of the discharge and intake lines of the cooling system be cautiously selected considering the temperature distribution, the water level change, and the cooling effectiveness.

A novel method of fabricating porous silicon material: ultrasonically enhanced anodic electrochemical etching

Ultrasonically enhanced anodic electrochemical etching is developed to fabricate luminescent porous silicon (PS) material. The samples prepared by the new etching method exhibit superior characteristics to those prepared by conventional direct current etching. By applying ultrasonically enhanced etching, PS microcavities with much higher quality factors can be fabricated. The improved quality induced by ultrasonic etching can be ascribed to increased rates of escape of hydrogen bubbles and other etched chemical species from the porous silicon pillars' surface. This process will cause the reaction between the etchant and the silicon wafer to proceed more rapidly along the vertical direction in the silicon pores than laterally.

CFD Simulations of bubbling/collapsing fluidized beds for three Geldart Groups

AbstractA multiphase computational fluid dynamics (CFD) model was applied to a commonly used industrial experiment known as the collapsing fluidized‐bed experiment. The experiment involves several hydrodynamic regimes including the bed expansion, bubbling, sedimentation, and consolidation of the fluidized bed. The CFD model is capable of predicting all four of these regimes. The three Geldart Groups, C, A, and B were simulated in a bubbling and subsequently collapsing fluidized bed. Results show that hydrodynamic Models A and B, the use of the modified Ergun equation or the MFIX code drag models, and solids rheology have limited impact on the bubbling‐ and collapsing‐bed simulations. The major finding of this study is that the solids modulus, G, is the controlling parameter during the consolidation regime. The simulated bubble sizes and bed collapse rates for all three Geldart groups were found to be within reported experimental error. The computed high turbulent intensity of Geldart Group A particles also agrees with data in the literature measured using an acoustic shot noise probe. It is also demonstrated that the traditional interpretation of the collapsing bed as consisting of separate bubble escape and sedimentation regimes is incorrect and that, in fact, they occur simultaneously.

Modeling of the Trajectories of the Hydrogen Bubbles in a Fluorine Production Cell

The fluid velocity and temperature fields in a fluorine production cell were studied using the finite element method. The trajectories of the hydrogen bubbles evolving from the cathode within the cell were investigated based on the concept of hydrodynamic diffusion. To reduce the ohmic voltage loss between the electrodes, a quantitative examination was made of the effect of changing the configuration of the slits formed on the cathode, such as the locations, inclination, size, and number of the slits, on the escape of the hydrogen bubbles toward the rear of the cathode. This quantitative examination was performed by calculating the normalized distribution function of the bubbles. The results showed that the cathode configuration has a profound effect on both the flow pattern near the cathode and the bubble trajectories. © 2003 The Electrochemical Society. All rights reserved.

Hot spots in superconducting tantalum

We discuss experimental results on nonequilibrium superconductivity in Ag-Ta point contacts. From a hysteretic dc characteristics we conclude a normal bubble suddenly to form in the superconductor below the contact at a critical bias, its radius $R(U)$ monotonically increasing with bias voltage U. The observed radii are unexpectedly large compared with what is expected from existing models. The investigation is intended to describe this behavior in physical terms and theoretically to calculate the function $R(U)$ for varying values of contact resistance. We calculate mean values over the bubble volume of the electron and phonon distribution functions using simplified Boltzmann equations which describe the effects of electron injection into the bubble, electron-phonon scattering, and electron and phonon escape from the bubble to the surrounding superconductor. Downscattering of high-energy injected quasiparticles into subgap states $0lEl\ensuremath{\Delta}$ leads to strong occupation of subgap states because escape is prevented for these energies by Andreev reflection from the N-S interface. This explains the large bubble size. In contrast with this, occupation of states $Eg\ensuremath{\Delta}$ is typically two orders of magnitude smaller. The function $R(U)$ is determined by a self-consistency condition postulating that the calculated nonequilibrium distribution function $f(E)$ satisfies the BCS gap equation in the limit of vanishing gap parameter. Agreement of the calculated and the experimentally determined $R(U)$ functions is satisfactory.

Modeling of the trajectories of the hydrogen bubbles evolving from the cathode in a fluorine production cell

The fluid velocity and temperature fields and the trajectories of the hydrogen bubbles evolving from the cathode in a fluorine production cell were studied by using the finite element method. It was examined the effect of the configuration of the slits formed on the cathode on the escape of the hydrogen bubbles toward the backside of the cathode to reduce the ohmic voltage loss between the electrodes. The results showed that the cathode configuration has a profound effect on both of the flow pattern near the cathode and the bubble trajectories. It was found that the cathode with the slits only on the upper half of the electrode is more effective in removing the bubbles to the backside of the cathode than the one with the slits over the entire electrode.

Mechanism of hydrogen desorption during palladium brush-plating

Continuous Pd deposits were fabricated by brush-plating. The morphologies of the Pd deposits were characterized by atom force microscopy (AFM). No micro-cracks were found in the deposits. The deposits were made up of spherical nano-clusters. Analyses of the morphology of Pd deposits brush-plated with different anode sliding speeds indicated that the H 2 bubbles desorbed from the deposits by two modes, passive and active, respectively. For the first mode, H 2 bubbles are removed by the anode movement. For the second mode, H 2 bubbles escape from the deposits actively. As a result, pores were avoided in the Pd deposit by brush-plating. A deposit self-repairing mechanism in Pd brush-plating is proposed.

Characterizing bubble penetration from a falling stream

The depth that bubbles will penetrate a receiving pool before rising due to buoyancy forces is an important phenomena in designing Low Head Oxygenator (LHO) devices, particularly in an indoor application where the available elevation between the top of the fish tank water column and the inside ceiling height is limited. The relationship between bubble loss and LHO geometry is unclear. If the submergence of the LHO is less than the bubble penetration depth, excessive escape of bubbles can increase operating costs substantially. A series of physical experiments were conducted using an elevated bucket with a single orifice to create a falling stream into a receiving pool. The primary variables of hydraulic head, hole diameter and fall height were varied over a practical range for such applications. Videotaping was used to analyze bubble penetration. Regression equations were developed to predict both bubble penetration and standard deviation associated with a specific set of operating conditions. The standard deviation regression equation can be used to predict the statistical variation in bubble penetration depth. Bubble penetration depth decreased as fall height was increased and became stable at a fall height of 50 cm. Bubble penetration increased as hole diameter was increased at all fall heights and hydraulic heads. An example is provided of how to predict bubble penetration depth to meet some user defined statistical confidence for maximum bubble penetration.

Dynamics of the egress of gas microbubbles from a melt under laser irradiation of a metal surface

The results of a theoretical investigation of the efficiency of degassing of the near-surface region of a material exposed to laser radiation are presented. The case of a low volume concentration of the monodispersed gas phase representing microbubbles of size no greater than 10 μm is considered. The principal parameters are revealed which determine the regimes of the egress of gas bubbles from a laser-produced melt, and analytical formulas are obtained for estimating the process rate. The analytical results are compared with the results of two-dimensional numerical simulations which include the laser heating of a solid sample, its melting, the development of thermocapillary melt convection, and the escape of gas bubbles from the melt. The analytical and numerical results are found to be in good agreement.

Fusion zone microstructure and porosity in electron beam welds of an α+β titanium alloy

The effect of electron beam welding parameters on fusion zone (FZ) microstructure and porosity in a Ti - 6.8 Al - 3.42 Mo - 1.9 Zr - 0.21 Si alloy (Russian designation VT 9) has been investigated. It has been observed that the FZ grain width increased continuously with increase in heat input when the base metal was in the β heat-treated condition, while in the α + β heat-treated base metal welds, the FZ grain width increased only after a threshold energy input. The difference is attributed to both the weld thermal cycle and the pinning effect of equiaxed primary alpha on grain growth in the heat-affected zone (HAZ) of α + β heat-treated base metal. Postweld heat treatment (PWHT) in the subtransus and supertransus regions did not alter the columnar grain morphology in the FZ, possibly due to the lack of enough driving force for the formation of new grains by the breaking up of the columnar grains and grain boundary movement for grain growth. As the PWHTs were conducted in a furnace, the role of thermal gradients can be ruled out. Intragranular microstructure in the aswelded condition consisted of hexagonal martensite. The scale of the martensite laths depended on welding speed. The highest porosity was observed at intermediate welding speeds. At low speeds, a majority of pores formed at the fusion boundary, while at high speeds, occurrence of porosity was maximum at the weld center. The trends on porosity can be explained on the basis of solubility of hydrogen in titanium as a function of temperature and the influence of weld thermal cycle on nucleation, growth, and escape of hydrogen gas bubbles. The porosity at slow welding speeds is low because sufficient time exists for the nucleation, growth, and escape of hydrogen gas bubbles, while insufficient time exists for the nucleation of gas bubbles at high welding speeds. The effect of pickling of joint surface, vacuum annealing of the base metal, and successive remelting of the weld metal has also been investigated.

Pool-boiling critical heat flux of water on small plates: Effects of surface orientation and size

A series of experiments have been performed to understand the pool-boiling critical heat flux (CHF) behavior on small plates, varying the inclination angle and size of the heated surface under near atmospheric pressure: the first-phase experiment to clarify the CHF behavior at near the horizontal downward-facing position and the second-phase experiment to find out the general CHF behavior for overall inclination angles. The first- and second-phase experiment were performed for the inclination angles from −90° (horizontally downward position) to −40° using two plate-type test sections (20×200 mm and 25×200 mm) submerged in a pool of saturated water and for overall inclination angles from −90° to 90° using two plate-type test sections (30×150 mm and 40×150 mm) submerged in a slightly subcooled water pool, respectively. The CHF generally decreases as its inclination approaches to −90°, but there is a transition angle, at which the rate of decrease in the CHF suddenly changes. The measured CHF is lower for the wider test section due to the increased difficulty of bubble escape and this size effect increases as the inclination angle approaches to −90°.

Submarine eruption near Socorro Island, Mexico: Geochemistry and scanning electron microscopy studies of floating scoria and reticulite

Products of an underwater eruption near Socorro Island in the NE Pacific were observed directly on January 29, 1993, ten days after precursors were first recorded by SOFAR (Sound Fixing and Ranging) hydrophones located in Hawaii and Tahiti. Eruptive activity was noticed from boats and ships as small steam plumes rising from the sea at an area centered at 18 °48′N, 111 °05′W, 2.4 km NW of Punta Tosca and 4.6 km SSW of Cape Henslow on Socorro Island. The observed steam was produced by 1–3-m-large blocks of hot, dark-grey, highly vesiculated basalt rising buoyantly to the surface from two submarine shallow vents at 210 and 30 m depth. Tens of blocks accompanied by bubbles could be observed rising to the surface in irregular pulses. These scoriaceous blocks remained floating at the surface until they would crack into smaller pieces by thermal contraction, emitting hissing noises from vapourizing seawater in contact with the hot interior of the blocks. Steam jets several metres in height were produced and occasionally blocks were propelled laterally by the steam jet. Depending on vesicularity and permeability, blocks remained floating and drifting with the surface current for 1–15 minutes before sinking back. Floating rocks covered an area of about 6000 m2. This intermittent activity has been observed ever since and has not stopped as of April 1994. Buoyant scoria and reticulite are indicative of volatile (mostly CO2) supersaturation and exsolution in the magma prior to rapid quenching, which inhibits loss of volatiles by bubble escape. A high-velocity ascent of low-viscosity magma in a relatively narrow conduit is also required to prevent substantial gas escape and allow formation of reticulite. The buoyant scoria is most probably ejected by intermittent lava fountaining at fixed vents as a result of changes in eruption velocities due to changes in the exsolved gas content of the lava. Between January and July 1993 floating blocks of scoria and reticulite were collected on several occasions from the surface of the sea for chemical and mineralogical analyses. Major- and minor-element analyses (including REE), as well as electron microprobe analyses of different phases revealed that the composition of the emitted lava has not changed through time. Blocks of basalt (SiO2 = 45–47%) are highly vitric and vesicular with tabular anorthite phenocrysts up to 3 mm in length and minor grains of forsteritic olivine. REE and trace-element composition of these rocks suggest an anomalous mantle source for the erupted alkali basalt lava. The ongoing eruption will either continue in a similar fashion as described and eventually cease or built up a mound that reaches the surface and forms an island with accompanying change in eruptive style.

Oxygen evolution on PTFE-modified ruthenium oxide electrodes investigated by CV techniques

Abstract A method of analyzing the process of oxygen evolution on both RuO 2 and PTFE-modified RuO 2 electrodes has been developed. The method is based on the use of oxygen reduction to analyze the removal of oxygen from the electrode surface. Oxygen evolution on the electrodes is determined by a kinetic process on the electrode surface. This process depends on the rates of oxygen bubble collection, oxygen bubble escape and oxygen dissolution, which are related to the hydrophobicity of the electrode surface. The role of PTFE in oxygen evolution is also discussed.

Surface degassing and modifications to vesicle size distributions in active basalt flows

The character of the vesicle population in lava flows includes several measurable parameters that may provide important constraints on lava flow dynamics and rheology. Interpretation of vesicle size distributions (VSDs), however, requires an understanding of vesiculation processes in feeder conduits, and of post-eruption modifications to VSDs during transport and emplacement. To this end we collected samples from active basalt flows at Kilauea Volcano: (1) near the effusive Kupaianaha vent; (2) through skylights in the approximately isothermal Wahaula and Kamoamoa tube systems transporting lava to the coast; (3) from surface breakouts at different locations along the lava tubes; and (4) from different locations in a single breakout from a lava tube 1 km from the 51 vent at Pu'u ‘O’o. Near-vent samples are characterized by VSDs that show exponentially decreasing numbers of vesicles with increasing vesicle size. These size distributions suggest that nucleation and growth of bubbles were continuous during ascent in the conduit, with minor associated bubble coalescence resulting from differential bubble rise. The entire vesicle population can be attributed to shallow exsolution of H 2O-dominated gases at rates consistent with those predicted by simple diffusion models. Measurements of H 2O, CO 2 and S in the matrix glass show that the melt equilibrated rapidly at atmospheric pressure. Down-tube samples maintain similar VSD forms but show a progressive decrease in both overall vesicularity and mean vesicle size. We attribute this change to open system, “passive” rise and escape of larger bubbles to the surface. Such gas loss from the tube system results in the output of 1.2 × 10 6 g/day SO 2, an output representing an addition of approximately 1% to overall volatile budget calculations. A steady increase in bubble number density with downstream distance is best explained by continued bubble nucleation at rates of 7–8/cm 3s. Rates are ∼25% of those estimated from the vent samples, and thus represent volatile supersaturations considerably less than those of the conduit. We note also that the small total volume represented by this new bubble population does not: (1) measurably deplete the melt in volatiles; or (2) make up for the overall vesicularity decrease resulting from the loss of larger bubbles. Surface breakout samples have distinctive VSDs characterized by an extreme depletion in the small vesicle population. This results in samples with much lower number densities and larger mean vesicle sizes than corresponding tube samples. Similar VSD patterns have been observed in solidified lava flows and are interpreted to result from either static (wall rupture) or dynamic (bubble rise and capture) coalescence. Through comparison with vent and tube vesicle populations, we suggest that, in addition to coalescence, the observed vesicle populations in the breakout samples have experienced a rapid loss of small vesicles consistent with ‘ripening’ of the VSD resulting from interbubble diffusion of volatiles. Confinement of ripening features to surface flows suggests that the thin skin that forms on surface breakouts may play a role in the observed VSD modification.

History and Sociological Imagining

Sociology without history resembles a Hollywood set: great scenes, sometimes brilliantly painted, with nothing and nobody behind them. Seen only as the science of the present or, worse yet, of the timeless, sociology misses its vocation to fix causation in time. It thereby vitiates its vital influence on historical thinking, its influence as the study of social mechanisms operating continuously in specific times and places. Although after years of living in the borderland of the two disciplines little lectures on the complementarity of sociology and history burst from me as easily as bubbles escape from champagne, that pleasant cohabitation will not be my subject here.

Behaviour of electrogenerated hydrogen and oxygen bubbles in narrow gap cells—part II. Application in chlorine production

A comparison is made between H 2 and O 2 evolution inside a thin channel cell and Cl 2 evolution inside an industrial membrane cell. Since the appearance of bridging bubbles is linked to the behaviour of free bubbles and that similar conditions of gas evolution exist (gas flow rate and free bubble escape behaviour), it is concluded that bridging bubbles are expected to form on the anode side inside industrial chlor/alkali cells. This phenomenon may also occur on the cathode side of the cell depending on the distance between the membrane and the electrode. Solutions to the problems caused by these particular bubbles are discussed which include correct selection of the electrode geometry, membrane positioning and cell design.

Vesiculation of basaltic magma during eruption

Vesicle size distributions in vent lavas from the Pu9u9O9o-Kupaianaha eruption of Kilauea volcano are used to estimate nucleation and growth rates of H 2 O-rich gas bubbles in basaltic magma nearing the earth9s surface (≤120 m depth). By using well-constrained estimates for the depth of volatile exsolution and magma ascent rate, nucleation rates of 35.9 events ⋅ cm -3 ⋅ s -1 and growth rates of 3.2 x 10 -4 cm/s are determined directly from size-distribution data. The results are consistent with diffusion-controlled growth as predicted by a parabolic growth law. This empirical approach is not subject to the limitations inherent in classical nucleation and growth theory and provides the first direct measurement of vesiculation kinetics in natural settings. In addition, perturbations in the measured size distributions are used to examine bubble escape, accumulation, and coalescence prior to the eruption of magma.

Air bubble holdup in quiescent wood pulp suspensions

AbstractAir bubbles were injected into the bottom of a column filled with an aqueous suspension of wood pulp fibers to permit measurement of the probability that the bubbles escape the fiber network to reach the surface. Escape probabilities were measured as functions of bubble volume, pulp consistency (weight fraction of fibers), and pulp type. For a given consistency, larger bubbles rose through the column whereas smaller bubbles were held up in the fiber network. The higher the consistency, the greater the bubble diameter required for escape. The minimum buoyancy forces required for bubble escape were correlated with estimates of the yield stress of the fiber network.