Survey of Data and Models for Refrigerant Mixtures Containing Halogenated Olefins
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Chemistry↗
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On using a multiphase combustion configuration to evaluate detailed kinetic mechanisms of gasoline/biofuel blends
The atmospheric pressure results presented show that n-heptane and iso-butanol mixtures had droplet diameter squares that decreased nearly linearly with time during burning while the flame standoff ratio increased throughout burning. Increasing the iso-butanol fraction decreased the burning-rate because of the accompanying increase in the density of the iso-butanol compared to heptane. At the same time, increasing iso-butanol mixture fraction appreciably reduced the maximum acetylene mole fraction and the sooting tendency. The mechanism is consistent with carbon atoms in iso-butanol binding to oxygen atoms that cannot then be transformed into soot. Computational and experimental results exhibited generally very good agreement. The simulated flame diameters bounded the measurements using definitions of flame diameter based on the maximum temperature and maximum OH mole fraction. With the simulations validated by the experiments, predictions of the peak acetylene concentrations as a soot precursor were made and found to occur very near the 1350 K isotherm as a soot inception temperature. Moreover, simulated greenhouse gas concentrations (CO2) were not appreciably changed with increasing iso-butanol concentration. As such, the results show a tradeoff with iso-butanol addition, namely that mixture droplets burn slower but produce less particulates and with little influence on formation of CO2 as a representative greenhouse gas.
Avedisian, Thomas↗
Combustion of petroleum-based transportation fuels and their blends with biofuels
The atmospheric pressure results presented show that n-heptane and iso-butanol mixtures had droplet diameter squares that decreased nearly linearly with time during burning while the flame standoff ratio increased throughout burning. Increasing the iso-butanol fraction decreased the burning-rate because of the accompanying increase in the density of the iso-butanol compared to heptane. At the same time, increasing iso-butanol mixture fraction appreciably reduced the maximum acetylene mole fraction and the sooting tendency. The mechanism is consistent with carbon atoms in iso-butanol binding to oxygen atoms that cannot then be transformed into soot. Computational and experimental results exhibited generally very good agreement. The simulated flame diameters bounded the measurements using definitions of flame diameter based on the maximum temperature and maximum OH mole fraction. With the simulations validated by the experiments, predictions of the peak acetylene concentrations as a soot precursor were made and found to occur very near the 1350 K isotherm as a soot inception temperature. Moreover, simulated greenhouse gas concentrations (CO2) were not appreciably changed with increasing iso-butanol concentration. As such, the results show a tradeoff with iso-butanol addition, namely that mixture droplets burn slower but produce less particulates and with little influence on formation of CO2 as a representative greenhouse gas.
Avedisian, Thomas↗
Influence of Equation-of-States on Supercritical CO2 Combustion Mixtures
Abstract Fossil fuel based direct-fired supercritical CO2 (sCO2) cycles are gaining the attention of industry, academia, and government due to their remarkable efficiency and carbon capture at high-source temperatures. Modeling plays an important role in the development of sCO2 combustors because experiments are very expensive at the designed operating conditions of these direct-fired cycles. Inaccurate density estimates are detrimental to the simulation output. Hence, this work focuses on comprehensive evaluation of the influence and applicability of various equation-of-states (EOS) which are being used in the supercritical combustion modeling literature. A state-of-the-art supercritical combustion modeling methodology is used to simulate counter-flow supercritical CO2 flames by using various equation-of-states. The results show that using the corresponding state principle to evaluate compressibility factor is not accurate. Also, van der Waal type EOSs predictions can be as accurate as complex Benedict–Webb–Rubin EOSs; hence van der Waal EOSs are more suitable to simulate sCO2 combustor simulations. Non-ideal effects are significant under the operating conditions considered in this work. The choice of EOS significantly influences the flame structure and heat release rate. Also, assuming the binary interaction parameter as zero is reasonable in sCO2 combustion simulations.
Energy & Fuels↗
Charge regulation effects on colloidal mixture nanoparticles
Changes in pH within a system containing dissociable sites affect the protonation and deprotonation of these groups, thereby influencing their physical properties. In response, the system modifies their surface charge, affecting electrostatic interactions, aggregation, stability, and structural behavior. Although the pH can be tuned in experiments, it is difficult to model this phenomenon using simulations or theoretical approaches. Here, we perform hybrid Monte Carlo-molecular dynamics simulations to model charge regulation effects in an equimolar colloidal charged system. We compare charge regulation effects with those of a system in which the charges of colloidal nanoparticles are not dissociable. The comparison between the two cases modifies the phase diagram, and it changes the volume fraction where a percolation network of nanoparticles is found. Charge regulation is found to destroy network formation, as the charge in the nanoparticles is modified because of the cooperativity dependency of the degree of charge dissociation sites among the nanoparticles favoring cluster formation. Furthermore, our work suggests that the ionic and/or electronic conductivity in functionalized nanoparticles can be modified by changing pH values. It also guides the experimental design of oppositely charged nanoparticles as inks for 3D printing processes.
Classical statistical mechanics↗
Effects of spatiotemporal plasma power distribution on the modeling of ignition kernel evolution in quiescent and turbulent methane/air mixtures
Abstract The present work improves a phenomenological plasma-assisted combustion model by integrating the spatiotemporal distribution of plasma power density, thereby considering the evolution of plasma streamers in the modeling, and subsequently, better predicting the ignition kernel evolution. The improved phenomenological model is validated against experiments representing the plasma discharge and post-discharge ignition kernel evolution. Specifically, the new model demonstrates a more accurate prediction of ultrafast gas heating and O 2 dissociation during the plasma discharge, compared to the original model. In addition, the new model is found to closely match the experimental pressure wave and heated channel profiles post-discharge without the need for tuning the energy deposition (unlike the original model), highlighting its accuracy of post-discharge ignition kernel dynamics. The improved phenomenological model is then employed to investigate ignition kernel evolution for a stoichiometric methane-air discharge across various discharge gap configurations. Simulations reveal a non-uniform temperature and streamer distribution progressing from the electrode tips toward the center, contrasting uniform cylindrical discharges previously described in the original model. Streamer propagation is observed to be faster for larger gaps when maintained at the same average electric field for different discharge gaps. The tendency of smaller gaps to produce detached toroidal ignition kernels is observed, while larger gaps promote cylindrical and attached ignition kernels. Interactions between successive ignition kernels from consecutive discharges varied significantly, with the smallest gap (1 mm) promoting the quenching of the preceding ignition kernel due to the initial kernel–kernel separation. The intermediate gap (2 mm) promotes detached kernel growth. In contrast, in the largest gap (4 mm), kernels consistently combine and expand attached to electrodes. The impact of homogeneous isotropic turbulence is also explored, showing the persistence of ignition kernels early on but eventually quenching due to enhanced radical and heat losses with pronounced turbulence intensity.
Johnson, Praise Noah↗
Stability study of aqueous foams under high-temperature and high-pressure conditions relevant to Enhanced Geothermal Systems (EGS)
In Enhanced Geothermal System (EGS) hydraulic fracturing is carried out by injecting cold water into deep Hot Dry Rocks (HDR) under carefully controlled conditions to create new or reopen existing fractures. Water-based fracturing fluids demonstrate some challenges including immense quantity of water usage, water sensitivity of the formations, water blocking, and lack of proppant carrying capacity and transportation. Thus, an alternative is to use foam-based fracturing fluid which offers potential advantage over conventional water-based fracturing fluid such as minimum water usage, reduced wellbore damage, high proppant carrying capacity, and less environmental damage. However, foams are complex mixture of gaseous phase and liquid phase which are thermodynamically unstable at downhole conditions, and their stability can decrease over time due to liquid drainage, bubble coarsening, and coalescence. This paper shows laboratory experiments executed to study foam stability at high temperature (200°C) and high pressure (6.9MPa) conditions which simulates the geothermal environment. Foam stability was characterized by half-life of foam, which is defined as the time taken by the foam to decreases by 50% of its original height due to drainage. In this paper, two types of gaseous phases, nitrogen (N 2 ) and carbon dioxide (CO 2 ) were investigated. Also, based on successful practice of foam-based fracturing fluid in oil and gas industries, four surfactants, including Alpha olefin sulfonate (AOS), Sodium dodecyl sulfonate (SDS), Tergitol™ (NP – 40), and Cetyltrimethylammonium chloride (CTAC) at optimum concentration of 1wt.% were tested for best stability performance. In addition, different stabilizing agents including guar gum, bentonite clay, crosslinker, silicon dioxide nanoparticles (SiO 2 ), graphene oxide (GO) were also studied. Experimental results showed that N 2 foams were more stable than CO 2 foams. It was observed that foam half-life decreased with the increase in temperature. Among all the surfactants, AOS foams showed the most promising thermal stability at high temperatures. Moreover, with the addition of stabilizing agents, foam's half-life was enhanced. Stabilizing agents such as crosslinker and GO dispersion showed the most stable foams with half-life recorded at 20min and 17min, respectively, at 200°C and 6.9MPa. Finally, pressure also showed a positive effect on foam stability; with increased pressure, foam half-life was increased. Based on the experimental data, analytical models for the effect of temperature and pressure were developed, considering foam degradation is a first-order kinetic reaction that linearly depends on the foam drainage mechanism. The effect of temperature on foam half-life was studied as an exponential decay model. In this model, foam half-life is a function of drainage rate constant (D A ) and activation energy (E a ) of the foam system. The effect of pressure on foam half-life was found to obey a power-law model where an increase in pressure showed an increase in foam half-life. Furthermore, a linear relation was studied for the effect of pressure on foam activation energy and drainage rate. Then the combined effects of temperature and pressure were studied, which yielded an analytical model to predict the foam stabilities in terms of half-life for different foam compositions. In conclusion, this research indicates that with an appropriate selection of surfactants and stabilizing agents, it is possible to obtain stable foams, which could replace conventional water fracturing fluid under EGS conditions.
15 GEOTHERMAL ENERGY↗
Controlled synthesis and optical properties of BaFBr:Eu{sup 2+} crystals via ethanol/water solutions
Graphical abstract: A facile and cost-effective approach for the controlled synthesis of BaFBr:Eu{sup 2+} crystals is introduced. The structures and morphologies of the obtained products are affected by the amount of water and ethanol in the solvent mixtures. Highlights: ► Precipitation route for preparing BaFBr nano and micro crystals in water/ethanol solvent mixtures. ► Controlled growth of BaFBr nano crystals by tuning the volume ratio of Ethanol/water. ► Luminescence properties after annealing at 200 °C are investigated. ► Short lifetimes of photoluminescence and photostimulated luminescence in BaFBr:Eu{sup 2+} nano crystals are presented. ► Shortened lifetimes in BaFBr:Eu{sup 2+} nano crystals demonstrate that they are promising materials for use in X-ray imaging systems. -- Abstract: BaFBr:Eu{sup 2+} crystals with different structures were successfully fabricated via a simple precipitation method using ethanol/water mixtures as solvents. The amount of ethanol in the solvent mixtures played a significant role in the formation of final products, enabling the well-controlled growth of the BaFBr crystals. A possible formation mechanism was proposed based on the results of controlled experiments. The phases and morphologies of the resulting samples were systematically investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED) and elementary analysis. The optical properties of the annealed BaFBr:Eu{sup 2+} nano-cuboids were investigated using photoluminescence (PL), photo-stimulated luminescence spectroscopy (PSL) and kinetic decays. Faster decay behaviors demonstrate that these BaFBr:Eu{sup 2+} phosphors are promising materials for applications in optical storage fields. Furthermore, it is envisaged that this environmentally benign method can be extended to prepare other fluoride halides.
36 MATERIALS SCIENCE↗
Reductive Functionalization of a Rhodium(III)-Methyl Bond in Acidic Media: Key Step in the Electrophilic Oxidation of Methane
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catalysis (homogeneous), catalysis (heterogeneous)↗
Ab Initio Density Functional Calculations and Infra-Red Study of CO Interaction with Pd Atoms on θ-Al 2 O 3 (010) Surface
The ab initio density functional theoretical studies show that energetics favor CO oxidation on single Pd atoms supported on θ-alumina. The diffuse reflectance infra-red spectroscopy (DRIFTS) results show that carbonates are formed as intermediates when single supported Pd atoms are exposed to a gaseous mixture of CO + O 2 . The rapid agglomeration of Pd atoms under CO oxidation conditions even at 6°C leads to the presence of Pd particles along with single atoms during CO oxidation experiments. Thus, the observed CO oxidation has contributions from both single Pd atoms and Pd particles.
36 MATERIALS SCIENCE↗
Controlling saturation to improve per- and polyfluoroalkyl substance (PFAS) removal in biochar-amended stormwater bioretention systems
Black carbon-amended bioretention systems are an increasingly popular strategy for the removal of organic contaminants, including poly- and perfluoroalkyl substances (PFASs) and other trace organic contaminants (TOrCs), from urban stormwater. Many PFASs preferentially accumulate at the air–water interface, but detention time requirements for stormwater bioretention systems typically result in full saturation of the bioretention systems, effectively removing their air–water interfaces. This study assessed the effect of bioretention system saturation on removal of PFASs, metals, and hydrophilic TOrCs. A field-aged mixture of 40% v/v sand, 30% v/v zeolite, and 30% v/v biochar was packed into columns which were operated with hydraulic controls to remain unsaturated or fully saturated throughout the duration of the experiment. Twenty-four storm events sized to a 95th percentile storm at a California, United States military site were simulated using synthetic stormwater fortified with aqueous film forming foam-derived PFASs, TOrCs, and metals to mimic real-world conditions. Unsaturated conditions outperformed saturated conditions for removal of all PFASs analyzed. A simulated inadvertent system perturbation (i.e. flooding event) in the unsaturated columns did not result in significantly greater mobilization of PFAS mass, suggesting that more sorption to the biochar occurred as a result of the transient retention of PFASs at the air–water interface reducing kinetic sorption limitations. Overall, maintaining unsaturated conditions in a biofilter may extend the sorptive filter lifetime for PFASs by up to 83%. The results have implications for bioretention system application and design for PFAS removal in contaminated catchment areas.
13 HYDRO ENERGY↗
Expansion dynamics of femtosecond laser-induced plasmas: Influence of thermophysical plasma properties
This study investigates the expansion dynamics of femtosecond laser-induced plasmas, emphasizing the impact of plasma thermophysical properties and ambient gas composition. Through shadowgraphy experiments and multiphase computational fluid dynamics (CFD) simulations, the influence of parameters such as heat capacity, molecular weight, and thermal conductivity on plume morphology, shockwave evolution, and energy dissipation mechanisms is examined. A mixture multiphase model is implemented to capture the interaction between the plasma and the surrounding gas. Simulation results reveal that plasma expansion is strongly inertia-driven. Results show that differences in plasma properties and ambient conditions affect the shape and temperature distribution of the expanding plume. The early-stage dynamics are primarily dictated by pressure forces, whereas thermal and viscous effects play a growing role in the plume's behavior during later stages of expansion. The CFD findings show the necessity of accurate initial condition characterization, including crater geometry and plasma pressure and temperature, for reliable modeling of plasma evolution in laser ablation processes.
CFD modeling↗
Spectral and photochemical diversity of tandem cysteine cyanobacterial phytochromes
The atypical trichromatic cyanobacterial phytochrome NpTP1 from Nostoc punctiforme ATCC 29133 is a linear tetrapyrrole (bilin)-binding photoreceptor protein that possesses tandem-cysteine residues responsible for shifting its light-sensing maximum to the violet spectral region. Using bioinformatics and phylogenetic analyses, in this study we established that tandem-cysteine cyanobacterial phytochromes (TCCPs) compose a well-supported monophyletic phytochrome lineage distinct from prototypical red/far-red cyanobacterial phytochromes. To investigate the light-sensing diversity of this family, we compared the spectroscopic properties of NpTP1 (here renamed NpTCCP) with those of three phylogenetically diverged TCCPs identified in the draft genomes of Tolypothrix sp. PCC7910, Scytonema sp. PCC10023, and Gloeocapsa sp. PCC7513. Recombinant photosensory core modules of ToTCCP, ScTCCP, and GlTCCP exhibited violet-blue–absorbing dark-states consistent with dual thioether-linked phycocyanobilin (PCB) chromophores. Photoexcitation generated singly-linked photoproduct mixtures with variable ratios of yellow-orange and red-absorbing species. The photoproduct ratio was strongly influenced by pH and by mutagenesis of TCCP- and phytochrome-specific signature residues. Our experiments support the conclusion that both photoproduct species possess protonated 15E bilin chromophores, but differ in the ionization state of the noncanonical “second” cysteine sulfhydryl group. We found that the ionization state of this and other residues influences subsequent conformational change and downstream signal transmission. We also show that tandem-cysteine phytochromes present in eukaryotes possess similar amino acid substitutions within their chromophore-binding pocket, which tune their spectral properties in an analogous fashion. Taken together, our findings provide a roadmap for tailoring the wavelength specificity of plant phytochromes to optimize plant performance in diverse natural and artificial light environments.
59 BASIC BIOLOGICAL SCIENCES↗
Data from: Nitrous oxide emissions during establishment of eight alternative cellulosic bioenergy cropping systems in the North Central United States
Greenhouse gas (GHG) emissions from soils are a key sustainability metric of cropping systems. During crop establishment, disruptive land-use change is known to be a critical, but under reported period, for determining GHG emissions. We measured soil N2O emissions and potential environmental drivers of these fluxes from a three-year establishment-phase bioenergy cropping systems experiment replicated in southcentral Wisconsin (ARL) and southwestern Michigan (KBS). Cropping systems treatments were annual monocultures (continuous corn, corn–soybean–canola rotation), perennial monocultures (switchgrass, miscanthus, and poplar), and perennial polycultures (native grass mixture, early successional community, and restored prairie) all grown using best management practices specific to the system. Cumulative three-year N2O emissions from annuals were 142% higher than from perennials, with fertilized perennials 190% higher than unfertilized perennials. Emissions ranged from 3.1 to 19.1 kg N2O-N ha−1 yr−1 for the annuals with continuous corn > corn–soybean–canola rotation and 1.1 to 6.3 kg N2O-N ha−1 yr−1 for perennials. Nitrous oxide peak fluxes typically were associated with precipitation events that closely followed fertilization. Bayesian modeling of N2O fluxes based on measured environmental factors explained 33% of variability across all systems. Models trained on single systems performed well in most monocultures (e.g., R2 = 0.52 for poplar) but notably worse in polycultures (e.g., R2 = 0.17 for early successional, R2 = 0.06 for restored prairie), indicating that simulation models that include N2O emissions should be parameterized specific to particular plant communities. Our results indicate that perennial bioenergy crops in their establishment phase emit less N2O than annual crops, especially when not fertilized. These findings should be considered further alongside yield and other metrics contributing to important ecosystem services.
09 BIOMASS FUELS↗
On the Inversion of Light Scattering Data into Information on Aerosol Properties
The Backus-Gilbert inversion technique was applied to scattering data and calculated examples were given to ascertain its ability to recover the aerosol properties with no a-priori assumptions. In order to cheque this inversion procedure as well as other techniques (such as Daves' and Herman's et al.), a controlled experiment was performed. The experiment dealt with spherical particles the Mie scattering curves of which was measured by use of a dye-laser. These curves were used to accurately determine the refractive index of the particles. Mixtures of three different known sizes were then prepared and the scattering intensity vs. wavelength was measured at 90 deg scattering angle. The mixtures contained also various known relative concentrations of the three sizes. The analysis of the measured results will be shown and discussed.
Cohen, A.↗
Experimental Evaluation of an Oxidizing Hazard in the Presence of Sorbents
Oxidizing chemicals are commonly found in waste generated from actinide separations and other chemical processes. Because they can create and/or increase the combustion of combustible materials, they need to be experimentally evaluated, in order to provide a highly reliable assessment of their potential hazards. Two sets of experiments were performed using a modified approach to the Environmental Protection Agency (EPA) SW-846 Method 1040. In the first set of experiments (scoping studies), the purpose was to determine the relative strength of some selected oxidizers. In the second set of experiments, the potential of the strongest tested oxidizer to increase the burning rate or burning intensity of some selected sorbents was investigated. The overall goal of this work was to conservatively identify oxidizer/sorbent mixtures producing non-oxidizer results. A few results from this experimental study are presented herein. More exhaustive information on this work can be found in supporting documentation.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Unraveling the CO Oxidation Mechanism over Highly Dispersed Pt Single Atom on Anatase TiO 2 (101)
Catalysts with noble metals deposited as single atoms on metal oxide supports have recently been studied extensively due to their maximized metal utilization and potential for performing difficult chemical conversions owing to their unique electronic properties. Understanding of the reaction mechanisms on supported single-metal atoms is still limited but is highly important for designing more efficient catalysts. In this study, we report the complexity of the CO oxidation reaction mechanism on Pt single atoms supported on anatase TiO 2 (Pt SA /a-TiO 2 ) by coupling density functional theory (DFT) calculations and microkinetic analysis with kinetic measurements, in situ/operando infrared, and X-ray absorption spectroscopies. Starting from the adsorbed Pt SA occupying an O vacancy induced by reductive pretreatment, we show that CO oxidation follows a complex mechanism consisting of initiation steps to reorganize the active site and multibranch reactive cycles, with the Pt SA /a-TiO 2 catalyst not returning to its initial configuration. The initiation step consists of CO and O 2 adsorption healing the O vacancy, followed by CO oxidation using gas-phase CO to form Pt(CO). The reactive cycle alternates O 2 adsorption and dissociation to oxidize the catalyst to Pt(O)(O)(CO) and branching pathways of competing Langmuir–Hinshelwood (LH)- or Eley–Rideal (ER)-type CO oxidation steps to reduce it again to Pt(CO). In situ/operando infrared experiments, including cryogenic CO adsorption and isotopic CO exchange, confirm the combined involvement of strongly adsorbed CO and gas-phase CO in an Eley–Rideal step along the reaction cycle. Microkinetic modeling shows that Pt single atoms are present in a mixture of Pt(CO), Pt(CO)(O 2 ), Pt(O)(CO)(O 2 ), and Pt(CO)(CO 3 ) structures as the main intermediates during steady-state CO oxidation, all having the C–O vibrational stretch close to the experimentally observed value of 2115 cm –1 . Microkinetic modeling also shows that the fractional orders of CO and O 2 measured experimentally originate from multiple steps with a high degree of rate control and not from a simple competitive adsorption. The results demonstrate the complex reaction pathways that even CO oxidation on a simple single-atom system can follow, providing mechanistic insights for designing efficient Pt-based single-atom catalysts. Here, we further show that microkinetic modeling results are sensitive to changes in energies of intermediate and transition states within errors of density functional theory, which can ultimately lead to incorrect conclusions regarding the reaction pathways and most abundant reaction intermediates if not accounted for by experiments.
36 MATERIALS SCIENCE↗
Explosion-induced ignition and combustion of acetylene clouds
We investigate the explosion-induced ignition and combustion of an acetylene cloud in a rectangular chamber (10 cm × 10 cm × 39 cm). In the experiments, a 0.2-g PETN charge was located at $x = 9.7\,\hbox {cm}$ and a soap bubble (d=5cm) filled with pure acetylene was located at $x = 27\,\hbox {cm}$ as measured relative to the end wall. Detonation of the charge created a blast wave that crushed the soap bubble—inducing mixing with the air. After 0.55 ms, the mixture ignited, forming at turbulent combustion cloud. The flow was modeled using the compressible Navier–Stokes equations assuming unity Lewis number. Arrhenius-based kinetics were used to model ignition. Adaptive mesh refinement was used to capture turbulent mixing on the grid (the MILES approach of J. Boris). Computed pressures were found to be in agreement with measured pressure histories. Finite-rate kinetics were required to capture the ignition processes over the duration of the experiment.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗