Gas-phase Mass Research Articles

Gradient-constrained algorithm for simulating bubble growth in microchannel boiling flow using volume of fluid method

This study focuses on the numerical simulation of bubble growth in microchannels and addresses the interfacial deformations associated with phase transitions in the Volume of Fluid (VOF) method. In order to avoid the blurred deformation of the interface during bubble growth, a gradient-constrained algorithm is proposed to simulate bubble growth with sharp interface. The algorithm proposed in this paper is to compress the phase interface by selecting a suitable gradient range of the gas phase volume share change, and then adjust the position of the gas phase mass source to the compressed interface. It is recommended that the selected minimum value of the gas phase volume fraction gradient mode value falls between 20 % and 50 % of the maximum value. The proposed method is verified by three engineering problems: bubble growth in the microchannel, Taylor bubble movement in the microchannel and bubbles side-by-side rise and coalescing. The simulation results of these three engineering problems show good agreement with other researchers' simulation, theoretical model and experimental results. The algorithm proposed in this paper is more convenient in capturing the phase interface and describing the evaporation process.

Plasmon-Assisted Electrochemical CO2 Reduction on Copper Nanocubes

Optical excitation of plasmons on metal nanoparticles presents a promising opportunity to enable electrochemical CO2 conversion into hydrocarbons at low overpotentials on stable electrodes. Electrochemical CO2 conversion typically requires high overpotentials, resulting in low energy efficiency and catalyst reshaping. By using light to overcome reaction barriers, plasmon excitation has been shown to lower the required overpotential for electrochemical reactions. Plasmon excitation also facilitates C-C coupling on gold and silver, metals that usually produce no multicarbon products when used as electrocatalysts. While previous studies indicate clear potential that plasmon-based photo-electrocatalysts could enable new electrochemical pathways for CO2 reduction at low overpotentials and stable catalysts, yields and catalytic turnover remained low. To develop industrially viable photo-electrochemical CO2 reduction catalysts, the effect of plasmon excitation at high current density and high mass flux needs to be understood and optimized.Here we investigate the photo-electrochemical CO2 reduction on gold and copper nanoparticles on a gas diffusion electrode. We choose copper nanoparticles because they are the most promising electrocatalysts for C-C coupling and exhibit a strong plasmon resonance around 600 nm, yet have not been explored for plasmonic CO2 reduction. Gold nanoparticles are chosen due to their exceptional stability and because gold has been shown to perform C-C coupling under plasmon excitation, which does not happen electrochemically. Using a gas diffusion electrode allows efficient gas phase mass transport to and from the electrode. We synthesize 50 nm (100) faceted copper nanocubes using copper bromide and oleylamine, and gold nanorods using hexadecyltrimethylammonium bromide (CTAB) and sodium oleate (NaOL). In both cases, the nanoparticles have a plasmon resonance of 600 nm. We spray coat these nanoparticles onto a carbon paper gas diffusion membrane and incorporate them into our home-built gas reactor. First, we use real-time GC to investigate electrocatalysis in the dark and find high selectivity for CO on gold and high selectivity for ethylene and CH4 on copper. Then, we vary the optical illumination wavelength from 480 nm to 700 nm and the applied potential, investigating how these affect Faradaic efficiencies for the production of ethylene, CO, H2, and CH4 as well as photothermal contributions using an infrared camera. Finally, we use in-situ liquid cell transmission electron microscopy (TEM) to monitor nanoparticle stability and correlate morphological evolution with CO2 reaction rate. Our work provides the fundamental understanding necessary for building photo-electrocatalysts that can convert CO2 into value-added products under industrially relevant conditions.Figure caption: Schematic of our photo-electrochemical plasmonic gas diffusion electrode converting CO2 into hydrocarbons. Electrochemical CO2 conversion on gold typically leads to CO, under plasmon excitation gold can form hydrocarbons. Figure 1

Mathematical modeling of gas-phase mass transfer in hydrous materials for a total heat exchange ventilator

Total heat exchange ventilation systems are effective in achieving energy savings by reducing the ventilation load in buildings, while maintaining a certain amount of fresh outdoor air intake. As the system's elemental materials exchange both latent and sensible heat, hydrophilic chemical compounds may be exchanged simultaneously. Proper control of the exchange of hazardous chemicals and pollutants via these heat exchange elements is an important issue in the development of total heat exchange ventilation systems. In this respect, the development of a numerical model that facilitates repeated sensitivity analysis is important in the development of a new total heat exchanger that has high heat exchange efficiency and suppresses the exchange of polluting chemicals. This study proposes new hygrothermal and chemical compound transfer models for paper-based hydrous materials, which are the main components of total heat exchangers in indoor ventilation systems. Through a series of numerical analyses and experimental measurements, the prediction accuracy of the mathematical model was compared with experimental results for the gas transfer rate in hydrous materials and a building-sized total heat exchanger. The results demonstrated that an increase in water content in hydrous material has a significant impact on the permeability of water-soluble gases, with NH3 and HCHO permeability coefficients increasing by factors of 250 and 20 respectively. Conversely, for low-solubility gases such as CO2, the permeability coefficient only slightly increased at low humidity and remained largely unaffected thereafter. These findings contribute to the advancement of more efficient and safer total heat exchange ventilation systems.

Observation of Aromatic B13(CO)n+ (n = 1-7) as Boron Carbonyl Analogs of Benzene.

CO as a typical σ-donor is one of the most important ligands in chemistry, while planar B13+ is experimentally known as the most prominent magic-number boron cluster analogous to benzene. Joint gas-phase mass spectroscopy, collision-induced dissociation, and first-principles theory investigations performed herein indicate that B13+ reacts with CO successively under ambient conditions to form a series of boron carbonyl complexes B13(CO)n+ up to n = 7, presenting the largest boron carbonyl complexes observed to date with a quasi-planar B13+ core at the center coordinated by nCO ligands around it. Extensive theoretical analyses unveil both the chemisorption pathways and bonding patterns of these aromatic B13(CO)n+ monocations which, with three delocalized π bonds well-retained over the slightly wrinkled B13+ moiety, all prove to be boron carbonyl analogs of benzene tentatively named as boron carbonyl aromatics (BCAs). Their π-isovalent B12(CO)n (n = 1-6) complexes with a quasi-planar B12 coordination center are predicted to be stable neutral BCAs.

Characteristics of Gas–Liquid Two-Phase flow in rectangular narrow slits with varying cross sections driven by large pressure drop

Pressure pipelines and vessels inevitably contain some defects. Under the most unfavorable load combinations, these defects may gradually develop into through-wall cracks. High-pressure subcooled fluid leaks through these cracks, and two-phase gas–liquid flow often occurs within the cracks. In this study, natural through-wall cracks were replaced with narrow rectangular slits with varying cross sections. Experiments were conducted to investigate the variation patterns of gas–liquid two-phase leakage flow rates and pressure drops. The study focused on four types of rectangular narrow slits with varying cross sections, a width of 28 mm, a length of 80 mm, and a gap gradually ranging from 0.134 to 0.334 mm. The liquid-phase mass flow rate ranged from 150 to 700 kg/h, whereas the gas-phase mass flow rate varied from 0 to 20 kg/h. A one-dimensional homogeneous flow model was established by coupling two-phase velocity of speed calculations. This calibrated model was then used to predict pressure drops and flow parameters for gas–liquid two-phase flow in narrow rectangular slits with varying cross sections. The experimental data were analyzed to determine the two-phase leakage characteristics of different test pieces. The results show that the inlet–outlet pressure drop and flow quality are key factors affecting the two-phase leakage flow rate. The frictional pressure drop constitutes a major part of the total pressure drop along the flow path in different test pieces. Compared with the acceleration pressure drop in the expanding slit, that in the constricting slit is higher, with an increase of approximately 32 %. Among several commonly used empirical formulas for calculating two-phase viscosity, the McAdams and Dukler empirical correlations were found to be less suitable for high-velocity two-phase flows. In contrast, the Cicchitti empirical correlation provides better predictions, with a mean absolute deviation (MAD) and mean relative deviation (MRD) of no more than 8 %. The viscosity of the gas-phase medium affects the two-phase flow characteristics in narrow slits, which should be considered in practical engineering applications.

Estimation of gas diffusion coefficient for gas/oil-saturated porous media systems by use of early-time pressure-decay data: An experimental/numerical approach

This paper presented a novel numerical method for estimating the gas diffusion coefficient based on the early-time pressure-decay data. Experimentally, “flooding–soaking” procedures were developed to perform the gas diffusion in an oil-saturated tight core under different gas phase volume conditions. After flooding, the capillary bundle model was used to calculate the oil–gas contact area. The early-time pressure-decay data of the gas phase were monitored and recorded during the soaking process. Theoretically, a non-equilibrium inner boundary condition coupled with the characteristics of experimental early-time pressure had been incorporated to develop a diffusion model for a gas/oil-saturated tight core system. Based on gas-phase mass balance equations and gas equation of state, the diffusion coefficients were optimized once the discrepancy between experimental data and numerical solutions was minimized. According to the estimated results in this study, the CH4 diffusion coefficients were 3.74 × 10−11 and 3.86 × 10−11 m2/s in tight core saturated with crude oil, respectively. Moreover, the oil–gas contact area significantly impacts the diffusion flux in oil-saturated porous media. Specifically, an additional 10% contact area results in a 75% increase in CH4 diffusion mass. In addition, with the application of our proposed model to CH4/bitumen and CO2/bitumen systems, the diffusion coefficients were in close agreement with the results reported in previous literature, indicating that the proposed model was applicable to both gas/liquid and gas/liquid-saturated porous media systems.

Migration patterns of organophosphate esters from plastic food packaging simulants to foods: Donors, behaviours, and influencing factors

In recent years, organophosphate esters (OPEs) have been widely produced and used as flame retardants and plasticizer additives, posing significant ecological and health risks. Dietary intake is considered to be the primary route of human exposure to OPEs. Plastic food packaging materials are considered a crucial source for contamination of OPEs in food. However, the migration behaviour of OPEs from plastic food packaging materials into foods has received limited attention. In this study, we employed a novel method to prepare migration donors containing 13 kinds of OPEs. The migration behaviours of OPEs from food packaging simulants (polypropylene) to foods (full-fat milk powder) were simulated, and factors influencing the migration of OPEs were examined, including the properties of the target compounds, migration temperature, fat content of the migration receptors, and mass transfer mode. The results indicated that OPEs exhibited a significant migration tendency. Low molecular weight OPEs (< 300 Da) had faster migration efficiency compared to high molecular weight OPEs. The mean migration efficiencies of various OPEs showed a significant negative correlation with their molecular weights (p < 0.01) and a significant positive correlation with temperature (p < 0.01). Except for resorcinol bis(diphenyl phosphate) (RDP), which showed almost no migration, the mean migration efficiencies of other OPEs at 25 °C, 40 °C, and 60 °C were 3.1–37.5 %, 9.0–60.0 %, and 23.9–80.4 %, respectively. Most of the OPEs demonstrated higher migration efficiency in high-fat content food than low-fat content food. The migration of OPEs from food packaging simulants to foods primarily occurred through contact rather than gas-phase mass transfer. Overall, this study uncovers the migration behaviours of OPEs from food packaging simulants to foods and scrutinized the relevant factors influencing the migration. It is expected that the research in terms of the contamination control of OPEs in food will benefit from this work.

Analysis of effective area and mass transfer in a structure packing column using machine learning and response surface methodology

The study examined mass transfer coefficients in a structured CO2 absorption column using machine learning (ML) and response surface methodology (RSM). Three correlations for the fractional effective area (af), gas phase mass transfer coefficient (kG), and liquid phase mass transfer coefficient (kL) were derived with coefficient of determination (R2) values of 0.9717, 0.9907 and 0.9323, respectively. To develop these correlations, four characteristics of structured packings, including packing surface area (ap), packing corrugation angle (θ), packing channel base (B), and packing crimp height (h), were used. ML used five models, represented as random forest (RF), radial basis function neural network (RBF), multilayer perceptron (MLP), XGB Regressor, and Extra Trees Regressor (ETR), with the best models being radial basis function neural network (RBF) for af (R2 = 0.9813, MSE = 0.00088), RBF for kG (R2 = 0.9933, MSE = 0.00056), and multilayer perceptron (MLP) for kL (R2 = 0.9871, MSE = 0.00089). The channel base had the most impact on af and kL, while crimp height affected kG the most. Although the RSM method produced adequate equations for each output variable with good predictability, the ML method provides superior modeling capabilities.

SERS Substrate Based on Ag Nanoparticles@Layered Double Hydroxide@graphene Oxide and Au@Ag Core–Shell Nanoparticles for Detection of Two Taste and Odor Compounds

Sulfide organics and phenols are ubiquitous in freshwater lakes all over the world. As two taste and odor (T and O) compounds, they are harmful to the environment and human body. The existing detection methods for T and O compounds mainly include sensory analysis and gas-phase mass spectrometry, which are cumbersome and time-consuming. Herein, a method for the simultaneous and rapid detection of two T and O compounds (methyl sulfide and 2,4-di-tert-butylphenol) based on surface-enhanced Raman spectroscopy (SERS) is firstly developed. The SERS substrate was prepared by coating Ag nanoparticles (Ag NPs), layered double hydroxide (LDH), and graphene oxide (GO) on the surface of an Ag-coated Au nanoparticle (Au@Ag NP) substrate. Under optimal conditions, this SERS substrate possessed low detection limits of 1.53 ppm for methyl sulfide and 0.39 ppm for 2,4-di-tert-butylphenol. In addition, it took only 20 min to complete the detection using this method, without complex sample pretreatment. Furthermore, it was successfully applied to simultaneously detect methyl sulfide and 2,4-di-tert-butylphenol in actual water samples and had good application prospects for the rapid detection of T and O compounds in water.

The High-Redshift Gas-Phase Mass–Metallicity Relation in FIRE-2

The unprecedented infrared spectroscopic capabilities of JWST have provided high-quality interstellar medium metallicity measurements and enabled characterization of the gas-phase mass–metallicity relation (MZR) for galaxies at z ≳ 5 for the first time. We analyze the gas-phase MZR and its evolution in a high-redshift suite of FIRE-2 cosmological zoom-in simulations at z = 5–12 and for stellar masses M * ∼ 106–1010 M ⊙. These simulations implement a multichannel stellar feedback model and produce broadly realistic galaxy properties, including when evolved to z = 0. The simulations predict very weak redshift evolution of the MZR over the redshift range studied, with the normalization of the MZR increasing by less than 0.01 dex as redshift decreases from z = 12 to z = 5. The median MZR in the simulations is well approximated as a constant power-law relation across this redshift range given by log(Z/Z⊙)=0.37log(M*/M⊙)−4.3 . We find good agreement between our best-fit model and recent observations made by JWST at high redshift. The weak evolution of the MZR at z > 5 contrasts with the evolution at z ≲ 3, where increasing normalization of the MZR with decreasing redshift is observed and predicted by most models. The FIRE-2 simulations predict increasing scatter in the gas-phase MZR with decreasing stellar mass, in qualitative agreement with some observations.

A Broadened Class of Donor-Acceptor Stacked Macrometallacyclic Adducts of Different Coinage Metals.

A yet-outstanding supramolecular chemistry challenge is isolation of novel varieties of stacked complexes with finely-tuned donor-acceptor bonding and optoelectronic properties, as herein reported for binary adducts comprising two different cyclic trinuclear complexes (CTC@CTC'). Most previous attempts focused only on 1-2 factors among metal/ligand/substituent combinations, resulting in heterobimetallic complexes. Instead, here we show that, when all 3 factors are carefully considered, a broadened variety of CTC@CTC' stacked pairs with intuitively-enhanced intertrimer coordinate-covalent bonding strength and ligand-ligand/metal-ligand dispersion are attained (dM-M' 2.868(2) Å; ΔE>50 kcal/mol, an order of magnitude higher than aurophilic/metallophilic interactions). Significantly, CTC@CTC' pairs remain intact/strongly-bound even in solution (Keq 4.67×105 L/mol via NMR/UV-vis titrations), and the gas phase (mass spectrometry revealing molecular peaks for the entire CTC@CTC' units in sublimed samples), rather than simple co-crystal formation. Photo-/electro-luminescence studies unravel metal-centered phosphorescence useful for novel all metal-organic light-emitting diodes (MOLEDs) optoelectronic device concepts. This work manifests systematic design of supramolecular bonding and multi-faceted spectral properties of pure metal-organic macrometallacyclic donor/acceptor (inorganic/inorganic) stacks with remarkably-rich optoelectronic properties akin to well-established organic/organic and organic/inorganic analogues.

Vacuum evaporation and condensation thermodynamics and evaporation kinetics of pure silver

A comprehensive analysis of the characteristics of vacuum evaporation and condensation of pure silver is crucial for advancing vacuum separation and purification technology for crude silver. This study analyzes the vacuum evaporation and condensation thermodynamics and evaporation kinetics of pure silver. The results reveal a substantial increase in the saturated vapor pressure and theoretical maximum evaporation rate of pure silver with increasing temperature. When the temperature is in the range of 1373 ∼ 1773 K and the pressure is in the range of 0.1 ∼ 10 Pa, the average molecular free path is between 0.514 ∼ 66.415 cm. Moreover, the mean molecular free path of silver increases with increasing temperature and decreasing pressure. Besides, the silver triple point occurs at a temperature of 1234.78 K and a pressure of 0.343 Pa. The average evaporation rate of pure silver demonstrates a linear relationship with temperature, and the relationship with pressure conforms to the Logistic model. Notably, the vacuum evaporation of pure silver is a first-order reaction. Furthermore, in this study, the kinetic equation of vacuum evaporation of pure silver is established. In the temperature range of 1473–1673 K, the gas phase mass transfer is the rate-controlling step rather than the mass transfer in the gas phase boundary layer. As the temperature increases, the rate-controlling step gradually changes into gas relative flow mass transfer and gas-liquid interface evaporation mass transfer.

Performance and reaction kinetics of NO absorption by Fe(II)EDTA in a multistage zeolite absorption column-H2-MBfR system

Efficient NOX complexation absorption is a key to biological flue gas denitrification. In this study, the influencing factors, efficiency, and kinetic parameters of Fe(II)EDTA absorption of NO in a multistage zeolite absorption column were evaluated. The response surface methodology (RSM) was used to determine the ideal absorption conditions. Based on these results, a combined process of a multistage zeolite absorption column and a hydrogen-based membrane biofilm reactor (H2-MBfR) was built to verify the efficiency of denitrification. The optimal conditions for achieving maximum efficiency in the absorption of NO by Fe(II)EDTA were obtained as pH of 6.5, Fe(II)/EDTA molar ratio of 1:1.1, and temperature of 30 ℃. The kinetic parameters, including liquid phase mass transfer coefficient (KNO,L) and gas phase mass transfer coefficient (KNO,G), all increased with temperature, while the NO interfacial-area concentration (aNO) exhibited the opposite trend. The reaction for Fe(II)EDTA absorption of NO was a conjugation reaction, and its activation energy was 50.38 kJ·mol-1. More than 90 % of NO in flue gas on 14 days was removed in the combined multistage zeolite absorption column-H2-MBfR process, which provided a sustainable NO treatment solution without secondary pollutants or CO2 emissions and demonstrated its potential for NO removal in industrial applications.

The MUSE Ultra Deep Field (MUDF). V. Characterizing the Mass–Metallicity Relation for Low-mass Galaxies at z ∼ 1–2

Using more than 100 galaxies in the MUSE Ultra Deep Field with spectroscopy from the Hubble Space Telescope’s (HST) Wide Field Camera 3 and the Very Large Telescope’s Multi Unit Spectroscopic Explorer, we extend the gas-phase mass–metallicity relation (MZR) at z ≈ 1–2 down to stellar masses of M ⋆ ≈ 107.5 M ⊙. The sample reaches 6 times lower in stellar mass and star formation rate (SFR) than previous HST studies at these redshifts, and we find that galaxy metallicities decrease to log(O/H) + 12 ≈ 7.8 ± 0.1 (15% solar) at log(M ⋆/M ⊙) ≈ 7.5, without evidence of a turnover in the shape of the MZR at low masses. We validate our strong-line metallicities using the direct method for sources with [O iii] λ4363 and [O iii] λ1666 detections, and find excellent agreement between the techniques. The [O iii] λ1666-based metallicities double existing measurements with a signal-to-noise ratio ≥ 5 for unlensed sources at z > 1, validating the strong-line calibrations up to z ∼ 2.5. We confirm that the MZR resides ∼0.3 dex lower in metallicity than local galaxies and is consistent with the fundamental metallicity relation if the low-mass slope varies with SFR. At lower redshifts (z ∼ 0.5) our sample reaches ∼0.5 dex lower in SFR than current calibrations and we find enhanced metallicities that are consistent with extrapolating the MZR to lower SFRs. Finally, we detect only an ∼0.1 dex difference in the metallicities of galaxies in groups versus isolated environments. These results are based on robust calibrations and reach the lowest masses and SFRs that are accessible with HST, providing a critical foundation for studies with the Webb and Roman Space Telescopes.

Experimental investigation of the effect of droplet size on the vaporization of butanol in turbulent environments at elevated pressure

This paper presents an experimental study of the effect of droplet size on the vaporization rate of butanol fuel under turbulent flow conditions at elevated pressure and room temperature. The butanol droplet is suspended at the intersection of two micro-fibers in the center of a spherical vessel. The initial size of the butanol droplet is varied in the range between 300 and 700 μm. A controlled turbulent flow field, characterized by quasi-zero mean velocity and turbulence intensity of up to 1.5 m/s, was generated by eight axial fans. The findings reveal an improvement in the vaporization rate of butanol droplet as the droplet size increases. This improvement is more pronounced under conditions of elevated pressure and turbulence intensity. The results show that turbulence begins to influence the vaporization process when the droplet diameter exceeds the Kolmogorov length scale. Butanol droplet vaporization rate is found to lie between heptane and decane, leaning towards decane under all explored test conditions. The results reveal that the vaporization rate of hydrocarbon fuels is more sensitive to the droplet size variations than butanol. Turbulence is found to exert greater impact on the vaporization of fuels that have lower gas-phase mass diffusivity and higher thermal diffusivity. Finally, the previously proposed correlations, expressed in terms of Damköhler and turbulent Reynolds numbers, are assessed and found capable of predicting the vaporization of butanol droplet over a wide range size.

Ammonia absorption by water droplet in a small controlled atmosphere wind tunnel

The mass transfer characteristics during ammonia absorption into a sessile water droplet in a small controlled-atmosphere wind tunnel were investigated using particle tracking velocimetry (PTV) with polystyrene microspheres. The results showed that the flow field inside the droplet transformed from Marangoni convection to Rayleigh convection in the absence of gas flow. As the gas velocity increased, the drag force-induced circulation inhibited the Marangoni convection in the initial stage of the mass transfer process and Rayleigh convection in the advanced stage. However, the suppressed Marangoni convection cells recurred at high initial ammonia concentrations. Compared with the initial ammonia concentration in the wind tunnel and droplet size, the gas velocity significantly increased the gas-phase mass transfer coefficient. Furthermore, a calculation model for ammonia absorption by a moving droplet was derived based on the Colburn analogy and the two-film theory. The gas-phase mass transfer coefficients calculated using the model coincided with the experimental results. These results will help the design of water curtains.

The Gas-phase Mass–Metallicity Relation for Massive Galaxies at z ∼ 0.7 with the LEGA-C Survey

The massive end of the gas-phase mass–metallicity relation (MZR) is a sensitive probe of active galactic nuclei (AGN) feedback that is a crucial but highly uncertain component of galaxy evolution models. In this paper, we extend the z ∼ 0.7 MZR by ∼0.5 dex up to log (M ⋆/M ⊙) ∼ 11.1. We use extremely deep VLT VIMOS spectra from the Large Early Galaxy Astrophysics Census (LEGA-C) survey to measure metallicities for 145 galaxies. The LEGA-C MZR matches the normalization of the z ∼ 0.8 DEEP2 MZR where they overlap, so we combine the two to create an MZR spanning from 9.3 to 11.1 log (M ⋆/M ⊙). The LEGA-C+DEEP2 MZR at z ∼ 0.7 is offset to slightly lower metallicities (0.05–0.13 dex) than the z ∼ 0 MZR, but it otherwise mirrors the established power-law rise at low/intermediate stellar masses and asymptotic flattening at high stellar masses. We compare the LEGA-C+DEEP2 MZR to the MZR from two cosmological simulations (IllustrisTNG and SIMBA), which predict qualitatively different metallicity trends for high-mass galaxies. This comparison highlights that our extended MZR provides a crucial observational constraint for galaxy evolution models in a mass regime where the MZR is very sensitive to choices about the implementation of AGN feedback.

Migration behavior of fugitive methane in porous media: Multi-phase numerical modelling of bench-scale gas injection experiments

Two-dimensional multi-phase numerical simulations based on detailed laboratory experiments are used to provide insight into the key processes of methane migration in porous media and to analyze the suitability of a continuum approach for modelling gas migration at the intermediate bench-scale. The simulations were conducted using the multi-phase numerical model DuMux, including groundwater flow, transport of free-phase methane subject to capillary and buoyancy forces, kinetic-controlled dissolution of methane into the flowing groundwater, and advective-diffusive transport of dissolved-phase methane. Mass transfer kinetics are controlled by the water-gas interfacial area, avoiding the assumption of thermodynamic equilibrium which was shown not applicable under these conditions of high aqueous velocity in sandy materials.The model is applied to a series of 2D laboratory experiments in which gas-phase methane was injected near the bottom of a 1.5 m square vertical flow cell under a background flow gradient and with homogeneous and heterogeneous configurations. Simulations are compared to the observed behavior with respect to gas-phase mass distribution over time, gas-phase saturations, and to breakthrough of the dissolved-phase methane at selected monitoring points. In this first comparative study (simulations vs real data), insights are provided into the role of spatial property distributions on methane migration, in particular gas-phase pooling below low-permeability layers. Similar to the laboratory results, the simulations confirmed that the concentrations of dissolved-phase methane are strongly dependent on the structure of the gas-phase plume which in turn is influenced by the geology. We show that at the local metre-scale, kinetic-controlled mass transfer is needed to reproduce the dissolved-phase methane concentrations. Nevertheless, an assessment of capillary parameter values typically encountered in sandy aquifer materials suggests that an equilibrium approach could still be suitable for field-scale simulations.

Overpotential Behavior of Electrolysis and Fuel Cell Modes of Molten Carbonate Cells

Molten carbonate is an high operating temperature electrolyte for the fuel cell (MCFC) and electrolysis cells (MCEC). In particular, the liquid molten carbonates allow the reversible operation between fuel cell and electrolysis cells. The electrode kinetics and mass transfer characteristics of MCFC have been rather extensively investigated compared with those of MCEC. In this work, the mass transfer behaviors between MCFC and MCEC have been focused by experimental way with 100 cm2 class bench cells.The electrodes and matrix in the cell were supplied by KIST in Korea. The cells were operated at 923K under atmospheric pressure. The hydrogen electrode was supplied by a mixture of H2:CO2=1:1, 2:1, 1:2 ratios at 20% or 40% H2O. The oxygen electrode was fed by Air:CO2=0.7:0.3 atm. The steady state polarization (SSP) from 0 to 150 mA cm-2, inert gas step addition (ISA), and reactant gas addition (RA) methods were employed. The ISA adds inert gas to the hydrogen or oxygen electrodes, then the addition varies reactants flow rate and partial pressures. Consequently, the variations are reflected to the cell voltage at open circuit and polarization states. The voltage shift by the flow and partial pressure change represents overpotential behaviors at the electrodes [1]. The RA method uses a reactant gas instead of inert gas in the ISA. Therefore, the RA provides the overpotential information of the added reactant species [2].From the experimental investigations, the total voltage loss at the FC is larger than that of EC mode. In addition, the hydrogen electrode has significant gas phase mass transfer resistance due to the H2, CO2, and H2O species at the FC and EC modes. A similar overpotential was observed at the hydrogen electrode. On the other hand, the oxygen electrode has much less overpotential at the EC mode than the FC mode. Since the oxygen reduction at the FC mode contains O2 dissolution and mass transfer through the carbonate electrolytes, liquid phase mass transfer resistance is dominant. However, the oxidation of carbonate ions to oxygen does not contain liquid phase mass transfer process at the EC mode. Therefore, much less overpotential was observed at the oxygen electrode at the EC mode than the FC mode. This can be a reason of smaller total voltage loss at the MCEC than the MCFC.[1] Samuel Koomson, Choong-Gon Lee, J. Electroanalytical Chemistry, 925, 116896 (2022).[2] C.-G. Lee, H.-C. Lim, J. Electrochem. Soc., 152, A219-A228 (2005).

Effect of temperature on the electrode overpotential of molten carbonate electrolysis and fuel cells with inert-gas step addition method

This study explores molten carbonate electrolysis and fuel cell behaviour across temperatures from 823 to 973 K using steady-state polarization (SSP), electrochemical impedance spectroscopy (EIS), and inert-gas step addition (ISA) techniques. The findings reveal that total voltage loss decreases with rising temperature in fuel cell (FC) and electrolysis (EC) modes. The ohmic loss similarly declines as temperature increases. The ISA method determines the gas-phase mass transfer-induced overpotential, which increases as temperature increases in both modes at the hydrogen electrode (HE). This indicates that pore diffusion resistance strongly affects the HE in both modes. The liquid-phase mass transfer-induced overpotential at the oxygen electrode (OE) exhibits a much smaller value in EC mode than in FC mode at all temperatures. The increased O2 and CO2 partial pressures and decomposition of sufficient amounts of carbonate electrolytes to generate O2 in EC mode would reduce the liquid-phase resistance and its induced overpotential at the OE in the temperature range.