Behavior Of Gas Bubbles Research Articles

(Invited) Elucidating the Hydrodynamic Behavior of Multi-Species Gas Bubbles in an Electrochemical Solvent Regenerator for Direct Air Capture

Direct Air Capture (DAC) is very significant to bolstering the global drive towards net negative emissions. DAC technologies/plants have emerged in recent years, with the regeneration of the capture solvent used in the process being the major bottleneck of most aqueous technologies. [1] Leveraging electrochemical principles has offered a potential opportunity to simplify the entire solvent regeneration process and potentially reduce its overall capture cost, compared to traditional approaches. The electrochemical approach also offers the benefit of direct integrating clean energy, and also eliminating the high thermal energy requirements of typical methods.[2] Despite these potentials, the complex three-phase (solid-liquid-gas) interaction on the electrode surface pose a significant impediment to this electrochemical approach for DAC. The evolution of gas bubbles in electrochemical cells are well-known to contribute to energy losses in such reactors, from previous studies. [3],[4],[5] Gas bubbles have been shown to influence ohmic overpotentials in electrochemical reactors and studies have shown that the energy demand for water electrolysis can be reduced by 10-25 percent if the formation of gas bubbles is suppressed. [6],[7] However, the evolution of gas bubbles in electrochemical systems remains a complicated issue requiring further investigation. This study advances previous work by investigating the simultaneous evolution of CO2 gas bubbles along with O2/H2 gas bubbles in an electrochemical reactor for DAC. Gas bubbles are infamous for their ability to cover the active area of electrodes, limiting the transport of reactive species to the electrode surface, thus, increasing cell resistance. In this work, we explore changes in the polarization and hydrodynamics behavior of gas bubbles in the electrolyzer used for DAC solvent regeneration owing to the evolution of CO2 bubbles from pH swing, and the implications of the additional CO2 bubble formation to electrode surface coverage. By using a high-speed camera, we observe that bubbles coverage appears to be larger at the edges of the electrodes, and that the orientation of the electrodes influence bubble coalescence and detachment rate. We also employ different cell designs to mitigate the impact of bubble surface coverage towards reducing cell resistance. References Sabatino, A. Grimm, F. Gallucci, M. Van Sint Annaland, G. J. Kramer, M. Gazzani, Joule, 5(8), 2047-2076 (2021).Gao, A. Omosebi, R. Perrone, K. Liu, Journal of The Electrochemical Society (2022).H. Li, Y. J. Chen, Scientific Reports, 11(1), 1-12 (2021).F. Swiegers, R. N. L.Terrett, G. Tsekouras, T. Tsuzuki, R. J. Pace, R. Stranger, Sustainable Energy & Fuels, 5(11), 3004–3004 (2021).Zhao, H. Ren, L. Luo, Langmuir, 35(16), 5392-5408 (2019).Mazloomi, N. B. Sulaiman, H. Moayedi, International Journal of Electrochemical Science, 7(4), 3314-3326 (2012).C. Wang, C. Y. Chen, Electrochimica Acta, 54(15), 3877-3883 (2009).

Operando Neutron Radiography Measurements of a Zero-Gap Alkaline Electrolysis Cell

Low temperature alkaline water electrolysis is a well-known technology for hydrogen production and advantageous because less noble metals are needed compared to Proton Exchange Membrane (PEM) electrolysis. However, the two-phase flow behavior and especially the gas bubble distribution and flow during the operation in a zero-gap alkaline electrolysis cell have not been investigated in sufficient detail. Previous studies used e.g. transparent model electrolysis cells or focused on single flow phenomena e.g. gas bubble nucleation, growth or detachment.Recent publications show evidence that the ohmic resistance of zero-gap alkaline electrolysis cells is greater than the ohmic resistance of the used diaphragm, which has been believed the only term contributing to the ohmic resistance in zero-gap cells [1]. This suggests that the evolving gas bubbles might have a relation to the total ohmic resistance of the cell. As possible reasons nano bubbles in the pores of the diaphragm and a possible finite gap between electrodes and diaphragm is mentioned [2]. Haverkort et al. assume that the frontal area of the electrodes might be inactive [3].To prove the hypothesis and to deepen the general understanding of the two-phase flow inside an alkaline electrolysis cell we conducted operando cell measurements and visualized the electrolyte-gas bubble flow in an alkaline electrolysis cell by using neutron radiography. Thanks to the powerful neutron source at Institute Laue-Langevin in Grenoble, it was possible to observe the whole flow field with all flow channels at once with a sufficient temporal resolution to observe the movement of single gas bubbles, from nucleation to the moment of exiting the channel. The temporal resolution was 50 fps, which makes these measurement, to the best authors’ knowledge, the first to show the transient effects inside of a zero gap alkaline electrolysis cell. For the measurements, the NeXT (Neutron and X-Ray Tomograph) instrument was used which is the imaging station with one of the highest neutron fluxes of the world (1.4 E10 n/cm²/s at the end of the guide) [4]. The neutron beam was used to carry out through-plane measurements of the electrolysis cell.The measurements were conducted at a variety of operation conditions, varying the current density, the electrolyte volume flow and the operation temperature. At different operation conditions Electrical Impedance Spectroscopy (EIS) measurements have been conducted to measure the ohmic resistance of the cell. The used cell is an alkaline single cell out of a Nickel alloy with vertical parallel flow channel and a pocket milled to the backside of the cell in order to increase the transmission through the cell material.From the results of the measurements we observe a relation between current density (forming gas amount) and the ohmic resistance and thus establish a relation to the gas bubble behavior inside the electrolysis cell. Furthermore, we analyzed the velocity of the gas bubbles inside the channel depending on the different operation conditions, as well as the agglomeration behavior of the bubbles and their flow regime.[1] Phillips et al.,Minimising the ohmic resistance of an alkaline electrolysis cell through effective cell design, 2017[2] de Groot et al., Ohmic resistance in zero gap alkaline electrolysis with a Zirfon diaphragm,2021[3] Haverkort et al., Voltage losses in zero-gap alkaline water electrolysis,2021[4] Tengattini et al., NeXT-Grenoble, the Neutron and X-ray tomograph in Grenoble, 2020 Figure 1

In situ exploring the dynamic behaviors of gas bubbles in liquid by using a tapered dual-hole hollow fiber

Multiphase systems are often accompanied by highly complex gas-liquid-solid interactions and interface behaviors, which are difficult to be captured directly. This work reports theoretically and experimentally the studies on monitoring the dynamic behaviors of the gas bubbles in liquid by using a tapered dual-hole optical fiber-based interferometer. As demonstrated by regulating their size, quantity, and arrangement, gas bubbles touching the waist region of the tapered fiber lead to a spectral response of the interferometer, and the total area of the gas-solid interface between them directly determines the wavelength shift of the output spectrum. Beyond that, the sensor with the uniform tapered waist region (length: 1.5 cm, diameter: Ф 5 μm) is fabricated to explore the gas bubbles’ coalescence. In this case, the gas bubbles contact each other until the waist region of tapered fiber is radially enclosed entirely. When the enclosed gas-solid interface area varies between 16,000 - 24,000 µm2, the wavelength shift responds exponentially to the area, and the sensitivity at the area of 16,000 µm2 is calculated to be 2.42 pm/μm2. The proposed sensing platform could be adapted to in situ and online explore the multiphase dynamics for applications such as cell analysis, energy production, and environmental monitoring.

Analysis of Dynamic Behavior of Gas Bubbles and Solid Particles in an Oscillatory Baffled Reactor and Its Application to Design of Hydrogenation Proces

Analysis of Dynamic Behavior of Gas Bubbles and Solid Particles in an Oscillatory Baffled Reactor and Its Application to Design of Hydrogenation Proces

Numerical study of gas bubble rising in liquid sodium using advanced MPS method

In Sodium cooled Fast Reactor (SFR), study on the behavior of gas bubble is very crucial to the safety of SFR. In this study, an advanced Moving Particle Semi-implicit (MPS) method, the least square MPS (LSMPS), is used to study the rising behavior of gas bubble in liquid sodium. To improve the calculation, modified multiphase model is developed for the purpose of clear interface capture. The accuracy of LSMPS with modified multiphase model in simulate single rising bubble behavior is verified by several benchmarks with available experiment results. Then LSMPS is used to study single gas bubble rising in liquid sodium pool with different diameters. Velocity and shape of gas bubble is predicted using the LSMPS method. Side wall effects is also investigated.

Real‐Time Monitoring of Hydrogen Production by Water Electrolysis Using a Tapered Polarization‐Maintaining Optical Fiber Mach–Zehnder Interferometer

Gas microbubbles easily cover surface active sites of the solid electrodes in most gas evolution reactions, hindering the transfer of mass and energy and declining the reaction efficiency. However, online monitoring of gas bubbles’ behaviors on the surface of solid electrodes accurately in real time remains challenging. Herein, a tapered polarization‐maintaining fiber Mach–Zehnder interferometer for in situ monitoring of H2 bubbles detachment in water electrolysis is reported. In the experiment, the H2 bubble released from the platinum microelectrode can be detected by recording the variation of transmitted optical power in the optical fiber. By comparing it with the electrochemical measurement and the charge‐coupled device imaging, the measurement accuracy can be regarded as near 100%, and the time resolution is determined to be ≈ms. It is found that the size of the detached bubbles on the microelectrode surface is positively correlated with the electrolysis voltage. The increasing electrolysis time causes a long detachment time. Three different charged surfactants are all proved to accelerate the H2 detachment. This method is adapted to study gas bubble behaviors in various complex gas‐involving reaction systems, even for the invisible gas bubbles in a dark environment.

A Study of Bubble Behavior and Anode Effect on the Graphite and Industrial Carbon Anode in a See-Through Furnace During Aluminium Electrolysis

Anode gas bubble behavior and anode effect on graphite and industrial carbon rod-shaped anode in a cryolite melt have been studied using a see-through furnace. The different carbon materials have different properties which can affect bubble behavior and electrochemical properties. Industrial carbon is more inhomogeneous with respect to structure, pore, aggregates and impurities in comparison to the graphite. More bubbles were nucleated on the industrial carbon than on the graphite for the same current density. The time related to the coalescence process for both anodes was found to be in interval 16 to 24 ms and independent of the current densities. Bubbles detached from the horizontal surface of the anode have similar average diameter value for both anodes for current densities < 1.0 A cm−2, while for current densities > 1.0 A cm−2, the average diameter is lower for the industrial carbon anode. The onset of the anode effect occurred faster on the graphite than on the industrial anode. The PFC-containing gas layer appeared to be thicker and more stable on the graphite anode than on the industrial carbon anode.

Microbubble-enhanced water activation by cold plasma

Plasma activated water (PAW) is water treated by ionized gas. As a clean and sustainable technology, PAW attracts intensive attention from various fields of wastewater treatment, disinfectant, food processing and smart agriculture. However, the current challenge is high processing efficiency in production of PAW. In this work, we investigate bubble-enhanced plasma technology to activate a flow of water. Gaseous plasma is supplied through self-suction to water flowing in a Venturi tube. A large amount of microbubbles transfer reactive species in the gas phase into the water flow. The degradation of a model compound shows that with the same energy input, our approach can achieve more than 5 times higher activation efficiency, compared to the configuration in absence of microbubbles. Meanwhile, computational fluid dynamic simulations are performed to model the gas volume fraction, pressure, velocity distributions and bubble behaviors during cold plasma activation. To the best of our knowledge, this is the first time integrating bubbles in plasma activation to transfer active species from the gas phase into the flow of water. The design reported in this work may lead to efficient activation of water on a large scale as a green and sustainable technology for disinfection, food industry and agriculture.

CFD simulation and experimental comparison of bubble-induced convection during electrochemical water splitting

The behavior of gas bubbles produced during electrochemical processes is of large interest because of the increase in cell overpotential induced by their production, the electrode surface covering by them and, finally, the detachment of these bubbles and their direct impact on the energy consumption during the reaction. In this work, we used coupled experimental and computational approaches to investigate bubble formation under those conditions where there are important convective effects. We have measured both normal and parallel velocity of the solution and built up a computational fluid dynamics (CFD) model. The results were compared to experimental data. Then, having the computational model validated by experimental data, we have simulated different conditions following bubble displacement. An important change of the surface covering is observed during the electrochemical reaction. Considering just the covering change, for example, there is up to 23 % increase comparing to the electrode edge and center. • Finite element method is suitable to evaluate the bubble-induced convection. • The bubbles create a vortex in the electrolyte. • The induced convection create a non-homogeneous gas covering over electrode surface. • The bubble size has an important effect in the covering variance.

Stimuli-Responsive Liquid-Crystal-Infused Porous Surfaces for Manipulation of Underwater Gas Bubble Transport and Adhesion.

Biomimetic artificial surfaces that enable the manipulation of gas bubble mobility have been explored in a wide range of applications in nanomaterial synthesis, surface defouling, biomedical diagnostics, and therapeutics. Although many superhydrophobic surfaces and isotropic-lubricant-infused porous surfaces have been developed to manipulate gas bubbles, the simultaneous control over the adhesion and transport of gas bubbles underwater remains a challenge. Thermotropic liquid crystals (LCs), a class of structured fluids, provide an opportunity to tune the behavior of gas bubbles through LC mesophase transitions using a variety of external stimuli. Using this central idea, the design and synthesis of LC-infused porous surfaces (LCIPS) is reported and the effects of the LC mesophase on the transport and adhesion of gas bubbles on LCIPS immersed in water elucidated. LCIPS are demonstrated to be a promising class of surfaces with an unprecedented level of responsiveness and functionality, which enables the design of cyanobacteria-inspired object movement, smart catalysts, and bubble gating devices to sense and sort volatile organic compounds and control oxygen levels in biomimetic cell cultures.

Acoustic cavitation model based on a novel reduced order gas pressure law

The thermal behavior of a spherical gas bubble in a liquid excited by an acoustic pressure signal is investigated by constructing an iterative solution of the energy balance equations between the gas bubble and the surrounding liquid in the uniform pressure approximation. This iterative solution leads to hierarchy equations for the radial partial derivatives of the temperature at the bubble wall, which control the temporal rate of change of the gas pressure and gas temperature within the bubble. In particular, a closure relation for the hierarchy equations is introduced based on the ansatz that approximates the rapid change of state during the collapse of the bubble from almost isothermal to almost adiabatic behavior by time averaging the complex dynamics of change of state over a relatively short characteristic time. This, in turn, leads to the desired reduced order gas pressure law exhibiting power law dependence on the bubble wall temperature and on the bubble radius, with the polytropic index depending on the isentropic exponent of the gas and on a parameter that is a function of the Péclet number and a characteristic time scale. Results of the linear theory for gas bubbles are recovered by identifying this parameter as a function of the Péclet number based on the Minnaert frequency. The novel gas pressure law is then validated against the near-isothermal solution and against the results of the numerical simulations of the original energy balance equations for large amplitude oscillations using spectral methods. Consequently, an acoustic cavitation model that accounts for phase change but that neglects mass diffusion is constructed by employing the reduced order gas pressure law together with the Plesset–Zwick solution for the bubble wall temperature and the Keller–Miksis equation for spherical bubble dynamics. Results obtained using variable interface properties for acoustically driven cavitation bubbles in water show that the time variations of the bubble radius and the bubble wall temperature lie between those obtained by the isothermal and adiabatic laws depending on the value of the Péclet number and the characteristic time scale.

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ ВЗАЄМОДІЇ СІТЧАСТИХ РОЗДІЛЮВАЧІВ ФАЗ С ГАЗОВИМИ ПУЗИРЯМИ В УМОВАХ ЗМІННОГО ПОЛЯ МАСОВИХ СИЛ

Modern multi-purpose spacecraft for several years must perform complex and diverse tasks in outer space. At the same time, it is necessary to turn on jet engines dozens of times in conditions of practical weightlessness. At the time of starting the engine, the liquid fuel is mixed randomly with the boost gas. In this case, it is impossible to guarantee the contact of the drainage hole with the gas phase, and the drain hole with the fuel. To solve this problem, it is proposed to use various, so-called means of ensuring the continuity of fuel (MECF). The effectiveness of monitoring the position of the liquid in the flight conditions of the aircraft in the passive section of the trajectory is determined by the ability of the MECF to ensure the discharge of fuel from the tank without gas inclusions at any required time with a given flow rate and in the required amount with a minimum volume of unselected residues.&#x0D; The article deals with the features of the functioning of the SOST of the inertial type, which includes mesh phase separators (MPS). The need to use the MPS is due to the possibility of the gas phase entering the drain line, both in the passive section of the trajectory and at the stage of switching on the main engines, which can lead to a disruption of their launch. When fuel moves into the drain line, bubbles remain on the mesh surface and prevent the passage of liquid. &#x0D; The article builds a mathematical model of the behavior of gas bubbles on the surface of the MPS in the flow of a viscous liquid. On the basis of the constructed mathematical model, the corresponding numerical calculations were carried out. The proposed method of engineering calculation makes it possible to determine such a MECF design that excludes the possibility of "contamination" of the surface of the MPS by gas bubbles and the disruption as a result of this normal functioning of the fuel supply system to the engines of spacecraft.

Bubble-trap layer for effective removing gas bubbles and stabilizing power generation in direct liquid fuel cell

The power generation property of direct liquid fuel cells at high current densities is plagued by gas bubbles generation. Herein, we propose a bubble-trap layer to help mitigate the problem and improve the power generation stability performance. A novel chip-based liquid fuel cell with the bubble-trap layer is fabricated as a facile visualization and fast test platform, validating that most of CO2 bubble releases from the bubble-trap layer in situ rather than at the microchannel outlet. The dynamic behaviors of gas bubbles are visualized and their impact on the power generation performance is discussed. It suggests the fuel cell equipped with the bubble-trap layer has superior power generation stability, power density (29 mW cm−2) and current density (163 mA cm−2), which are 10% and 27% higher than that without the bubble-trap layer. And a maximum power density of 35 mW cm−2 is achieved. The bubble growth and gas emission mechanisms are analyzed according to the mechanical model, providing a guidance for the channel design and operation condition determination of cells. These results demonstrate the viability of applying the bubble-trap layer for stabilizing power generation and cast new light on the structure design of direct liquid fuel cells.

Electrochemical Visualization of Gas Bubbles on Superaerophobic Electrodes Using Scanning Electrochemical Cell Microscopy.

Electrocatalytic gas evolution reactions, where gaseous molecules are electrogenerated by reduction or oxidation of a species, play a central role in many energy conversion systems. Superaerophobic electrodes, usually constructed by their surface microstructures, have demonstrated excellent performance for electrochemical gas evolution reactions due to their bubble-repellent properties. Understanding and quantification of the gas bubble behavior including nucleation and dynamics on such microstructured electrodes is an important but underexplored issue. In this study, we reported a scanning electrochemical cell microscopy (SECCM) investigation of individual gas bubble nucleation and dynamics on nanoscale electrodes. A classic Pt film and a nonconventional transition-metal dichalcogenide MoS2 film with different surface topologies were employed as model substrates for both H2 and N2 bubble electrochemical studies. Interestingly, the nanostructured catalyst surface exhibit significantly less supersaturation for gas bubble nucleation and a notable increase of bubble detachment compared to its flat counterpart. Electrochemical mapping results reveal that there is no clear correlation between bubble nucleation and hydrogen evolution reaction (HER) activity, regardless of local electrode surface microstructures. Our results also indicate that while the hydrophobicity of the nanostructured MoS2 surface promotes bubble nucleation, it has little effect on bubble dynamics. This work introduces a new method for nanobubble electrochemistry on broadly interesting catalysts and suggests that the deliberate microstructure on a catalyst surface is a promising strategy for improving electrocatalytic gas evolution both in terms of bubble nucleation and elimination.

Experimental Study of Bubble Behavior in a Two-Dimensional Gas–Solid Tapered Fluidized Bed

Experimental Study of Bubble Behavior in a Two-Dimensional Gas–Solid Tapered Fluidized Bed

Bubble Phenomena and Bubble Properties for Horizontal and Vertical Carbon Anode Surfaces in Cryolite Melt Applying a See-Through Cell

Gas bubble behavior on a carbon anode in a cryolite melt has been studied using a see-through cell. The phenomena studied have been growth, coalescence, detachment, and wetting during electrolysis. The surface orientation affects bubble behavior. Therefore, two different anode designs were tested, an anode with a horizontal downward-facing surface and an anode with a vertical surface. At the horizontal anode, it was found that one large bubble was formed by the growth and coalescence of smaller bubbles, and finally, the large bubble detached periodically. For the vertical anode surface, the detaching bubbles were smaller, and most of them had been going through a coalescence process prior to detachment. The bubbles detached randomly. The coalescence process from the initiation to the final bubble shape at the vertical surface took about 0.016–0.024 s. The current density did not affect the duration of the coalescence. The bubble diameter was decreasing with increasing current density for both anodes. The values were in the range 7.2 to 5.7 mm for the horizontal anode in the current density interval 0.2–1.0 A cm−2 and in the range 3.7 mm to 1.5 mm for the vertical anode in the current density interval 0.1–2.0 A cm−2. The wetting contact angle for the vertical anode stayed more or less constant with an increase in current density, which likely can be attributed to the decreasing bubble size rather than an increase in polarization. In addition to the bubble phenomena described and bubble properties found, the impact of the results for better design of laboratory-scale studies is discussed.

Capabilities and Limitations of 3D-CFD Simulation of Anode Flow Fields of High-Pressure PEM Water Electrolysis

In this work, single-phase (liquid water) and two-phase (liquid water and gaseous oxygen) 3D-CFD flow analysis of the anode of a high pressure PEM electrolysis cell was conducted. 3D-CFD simulation models of the anode side porous transport layer of a PEM electrolyzer cell were created for the flow analysis. For the geometrical modelling of the PTL, two approaches were used: (a) modelling the exact geometry and (b) modelling a simplified geometry using a porosity model. Before conducting two-phase simulations, the model was validated using a single-phase approach. The Eulerian multiphase and the volume-of-fluid approaches were used for the two-phase modelling and the results were compared. Furthermore, a small section of the PTL was isolated to focus on the gas bubble flow and behaviour in more detail. The results showed plausible tendencies regarding pressure drop, velocity distribution and gas volume fraction distribution. The simplified geometry using the porous model could adequately replicate the results of the exact geometry model with a significant reduction in simulation time. The developed simulation model can be used for further investigations and gives insight into two-phase flow phenomena in the PTL. Additionally, the information obtained from simulation can aid the design and evaluation of new PTL structures.

Circular motion of submillimeter-sized acoustic bubbles attached to a boundary by high-speed image analysis

The circular motion of submillimeter-sized bubbles attached to a boundary in an 18.5 kHz ultrasonic field are investigated experimentally by high-speed photography and image analysis. It is found that the vibration of gas bubbles with diameters of 0.2–0.4 mm is between spherical radial vibration and regular surface fluctuation. Different from the circular motion of suspended bubbles in water, the circular motion of gas bubbles attached to a boundary presents some new characteristics. These bubbles attached to a boundary (wandering bubbles) will rotate around a fixed bubble array (holding bubbles). Both the wondering bubbles and holding bubbles are “degas” bubbles. The primary Bjerknes force acting on wandering bubbles in the acoustic wave field and the secondary Bjerknes force between the wandering bubbles and the holding bubbles strongly affects the circular motion. The circling and residence behavior of gas bubbles is described and analyzed in detail, which is helpful to understand and improve industrial applications such as ultrasonic cleaning, sonochemical treatment, aeration and cavitation reduction.

Formation and dispersal of pyroclasts on the Moon: Indicators of lunar magma volatile contents

We use new estimates of the total content and speciation of volatiles released during the ascent and eruption of lunar mare basalt magma to model the generation and behavior of gas bubbles, the disruption of magma at shallow depth by bubble expansion, and the acceleration and dispersal of the resulting pyroclasts. Lunar eruptions in near-vacuum differ significantly from those on bodies with an atmosphere: 1) exposure to near-zero external pressure maximizes volatile release to form gas bubbles; 2) the infinite potential expansion of the gas bubbles both ensures and maximizes magma fragmentation into pyroclastic liquid droplets with sizes linked to the bubble size distribution; 3) the speeds to which gas and entrained pyroclasts can be accelerated by gas expansion are also maximized. Generation of CO gas bubbles at much greater depths and pressures than bubbles of other volatiles produces bimodal (~120 and 650 μm) total pyroclast size distributions. In the near-vacuum, gas expands to pressures so low that gas-particle interactions enter the Knudsen regime, resulting counter-intuitively in the median grainsize in pyroclastic deposits first increasing, then decreasing, and finally increasing again with increasing distance from the vent, instead of decreasing monotonically as when an atmosphere is present. These complex gas-particle interactions cause clast size distributions to vary in a complex way with distance from the vent and the maximum thickness of the deposit to occur at about 75% of the maximum pyroclast range. Lunar eruptions typically evolve through four stages, which significantly influence gas release patterns. Most volatiles are released during the second, hawaiian-style eruption stage. However, elevated gas concentration can occur both in the short first stage (due to gas accumulation in the dike tip during ascent from the mantle) and in the third and fourth stages (due to reduced volume flux, increased time for gas bubble formation, growth, rise and coalescence, and strombolian activity replacing the hawaiian eruption style). Such gas concentration mechanisms can increase pyroclast ranges by a factor of ~5, but result in very much thinner deposits than if no concentration occurs. Maximum pyroclast range scales essentially linearly with total mass fraction of released volatiles; thus determination of the deposit radius around specific vents can provide data on lunar magma volatile contents. If the volatile inventory of the Apollo 17 orange glass bead picritic magma (~3400 ppm maximum) is typical, maximum ranges of the majority of pyroclasts would have been ~20 km. Such eruptions could explain 79% of the currently recognized pyroclastic deposits on the Moon. A few larger deposits and vents, such as the Aristarchus Plateau Dark Mantle and Cobra Head, suggest higher magma volatile contents. Numerous lunar vents show little evidence of associated pyroclastic deposits. Together, these observations suggest a wide range of volatile contents in lunar basaltic magma mantle source regions.

Investigation of Bubble Behavior in Gas‐Solid Fluidized Beds with Different Gas Distributors

AbstractThe behavior of gas bubbles in a gas‐solid fluidized bed was investigated by computational fluid dynamics simulation. A two‐phase flow model incorporating the kinetic theory of granular flow was used to study the effect of gas distributor design on the size distribution and the rise velocity of gas bubbles in the bed column. The experiments were conducted on four gas distributors with different orifice sizes and pitches. The geometry of the gas distributor had a significant influence on the bubble behavior in the gas‐solid fluidized bed. The effects of static bed height and superficial gas velocity were also considered. Bubble diameter and bubble rise velocity increased with gas velocity. However, at low bed height, the deviation in bubble size was indistinct because at higher gas velocity the rising tendency of the bubble formed just above the gas distributor increased and the probability of bubble coalescence decreased.