Concentration Profiles Of Species Research Articles

Photo-reductive decomposition of perfluorooctane sulfonate (PFOS) and its common alternatives by UV/VUV/sulfite process: Mechanism, kinetic modeling, and water matrix effects

The present study investigated the photo-reduction of perfluorooctane sulfonate (PFOS) and its alternatives, focusing on decomposition mechanisms, active species involvement, the influence of background water constituents, and kinetic model development. The decomposition and defluorination rates followed the order of PFOS > PFHxS > 6:2 FTSA > PFBS, with shorter chains and CH2 linkers enhancing the resistance of PFOS alternatives against the attack of hydrated electrons (eaq−). Two primary pathways were identified during the photodegradation of PFAS: (i) H/F exchange at CF bonds with the lowest bond dissociation energies (BDEs) and (ii) functional group cleavage followed by short-chain PFCAs formation, with OH playing a crucial role in transforming intermediates. Adding iodide and elevated temperatures demonstrated a synergistic effect on PFBS decomposition and defluorination, with high temperatures promoting functional group cleavage as the preferred defluorination pathway. The study examined the impact of background water constituents in different aqueous environments, from surface waters to wastewater streams and ion-exchange brine concentrates. Chloride exhibited a concentration-based dual impact on the UV/VUV/sulfite process: promotive effects at low dosages (1–10 mM) by acting as a secondary eaq− mediator, and adverse effects at high dosages (20–500 mM) due to the scavenging effect of generated chlorine radicals (Cl). High ionic strength adversely affected eaq− quantum efficiency. Additionally, bicarbonate and natural organic matter (NOM) had opposing effects on PFOS photo-reduction, primarily through eaq− scavenging and pH alteration. Kinetic modeling revealed reaction rate constants of the studied PFAS with eaq− ranging from 1.8 × 106 to 1.3 × 109 M−1 s−1, corroborating the concentration profiles of active species and highlighting the reductive nature of sulfite-mediated processes.

Influence of activation energy and multidiffusive quadratic convective nanoliquid flow past a cone and wedge

The present problem aims to examine the impact of quadratic buoyancy-driven flow nanofluid flow on two specific geometries such as cone and wedge in the presence of binary chemical reactions with activation energy, using liquid hydrogen species. This analysis is relevant for various industrial applications and are widely used in thermal energy storage devices for cooling or heating processes. The fluid flow model's governing equations are numerically solved using a fifth-order boundary value approach in matrix laboratory (MATLAB). In order to obtain the numerical solution, we initially transformed the coupled equations of the flow model and the partial differential equations into ordinary differential equations using similarity variables. The graphs and tables illustrate the importance of different physical factors that impact fluid flow and heat transfer. The quadratic combined convection parameter leads to an augmentation in fluid velocity while also inducing an elevation in frictional forces between the object's surface and the fluid. The increased in values of Schmidt number cause a decrease in mass diffusivity, which in turn leads to lower concentration profiles and improved mass transport efficiency. The activation energy is directly proportional to the decreased amplitude of the concentration profiles of liquid hydrogen species.

Designing optimal sensor arrays: leveraging hard modeling for improved performance.

In a sensor array system with the ability to design multiple sensor elements, selecting the optimal sensor elements can maximize the efficiency of the sensor array in responding to various analytes. This paper proposes the application of hard chemical modeling as a means to identify the optimal subset of indicator displacement assay (IDA)-based sensors in the array, aiming to achieve maximum performance for detection or quantification. The model governing all reactions in the IDA sensor and the model of the pure spectrum of active species are first determined. Next, by applying the model of the pure spectrum of active species (including the indicator and indicator-receptor complex) to each sensor element and taking into account the system's nonlinearity, corrected concentration profiles of active species are derived using the generalized classical least square (G-CLS) method. These corrected concentration profiles are utilized as the output signal for each sensor element. Finally, the dynamic ranges (DR) of each sensor element and subsequently the DR for all possible sensor arrays are determined.To assess the effectiveness of the sensor array through dynamic range analysis, an IDA-based sensor system comprising five different elements was designed. It was observed that sensors with a larger dynamic range, when arranged together in an array, are more efficient for the quantitative identification of analytes. However, simply increasing the number of elements in the sensor array may not necessarily enhance its effectiveness; instead, it could amplify the noise within the system. Additionally, multivariate fitting regression with Gaussian function (MFRG), a nonlinear calibration method, was applied to assess the prediction ability of all possible designed sensor arrays.

Development of a reduced primary reference fuel – oxymethylene dimethyl ether (PRF-OMEx) mechanism for diesel engine applications

Oxymethylene dimethyl ethers (OMEx), having a chemical formula of CH3O-(CH2O)x-CH3 where x varies from 1 to 5, have been widely considered as a promising fuel to partially replace diesel in CI engines in terms of reducing soot emissions. This work is focused on developing a reduced primary reference fuel (PRF)-OMEx chemical mechanism to better describe the combustion and emission characteristics of gasoline/diesel blends with OMEx. The novelty of this work lies in the fact that the OMEx part of the mechanism is represented not only by OME3 as done in most studies found in literature, but also with other OME chain lengths that is, OME2-4 which are considered to be optimum and better represent the commercial OMEx blends. For this purpose, a detailed OMEx mechanism is reduced by applying different reduction techniques considering a wide range of operating conditions including pressure, temperatures, equivalence ratios and fuel compositions. The result is merged with an already validated PRF mechanism to form a reduced PRF-OMEx mechanism consisting of 213 species and 840 reactions. The newly formed mechanism is validated against a wide set of experimental data including ignition delay times, laminar flame speeds and species concentration profiles. Furthermore, a rigorous set of numerical simulations for various diesel-OMEx blends in a compression ignition engine are carried out at two different operating points to validate the developed mechanism. Simulation results highlight that the developed mechanism not only replicates the experimental behavior in terms of in-cylinder pressure and heat release rate but exhibits a better combustion phasing closer to experimental data when compared with other mechanisms where only OME3 is utilized to represent OMEx. Overall, the developed PRF-OMEx mechanism proves to be realistic and suitable for application in engine combustion simulations involving gasoline/diesel and OMEx blends.

Development of an Elementary Reaction-Based Kinetic Model to Predict the Aqueous-Phase Fate of Organic Compounds Induced by Reactive Free Radicals.

ConspectusAqueous-phase free radicals such as reactive oxygen, halogen, and nitrogen species play important roles in the fate of organic compounds in the aqueous-phase advanced water treatment processes and natural aquatic environments under sunlight irradiation. Predicting the fate of organic compounds in aqueous-phase advanced water treatment processes and natural aquatic environments necessitates understanding the kinetics and reaction mechanisms of initial reactions of free radicals with structurally diverse organic compounds and other reactions. Researchers developed conventional predictive models based on experimentally measured transformation products and determined reaction rate constants by fitting with the time-dependent concentration profiles of species due to difficulties in their measurements of unstable intermediates. However, the empirical treatment of lumped reaction mechanisms had a model prediction limitation with respect to the specific parent compound's fate. We use ab initio and density functional theory quantum chemical computations, numerical solutions of ordinary differential equations, and validation of the outcomes of the model with experiments. Sensitivity analysis of reaction rate constants and concentration profiles enables us to identify an important elementary reaction in formating the transformation product. Such predictive elementary reaction-based kinetics models can be used to screen organic compounds in water and predict their potentially toxic transformation products for a specific experimental investigation.Over the past decade, we determined linear free energy relationships (LFERs) that bridge the kinetic and thermochemical properties of reactive oxygen species such as hydroxyl radicals (HO•), peroxyl radicals (ROO•), and singlet oxygen (1O2); reactive halogen species such as chlorine radicals (Cl•) and bromine radicals (Br•); reactive nitrogen species (NO2•); and carbonate radicals (CO3•-). We used literature-reported experimental rate constants as kinetic information. We considered the theoretically calculated aqueous-phase free energy of activation or reaction to be a kinetic or a thermochemical property, and obtained via validated ab initio or density functional theory-based quantum chemical computations using explicit and implicit solvation models. We determined rate-determining reaction mechanisms involved in reactions by observing robust LFERs. The general accuracy of LFERs to predict aqueous-phase rate constants was within a difference of a factor of 2-5 from experimental values.We developed elementary reaction-based kinetic models and predicted the fate of acetone induced by HO• in an advanced water treatment process and methionine by photochemically produced reactive intermediates in sunlit fresh waters. We provided mechanistic insight into peroxyl radical reaction mechanisms and critical roles in the degradation of acetone and the formation of transformation products. We highlighted different roles of triplet excited states of two surrogate CDOMs, 1O2, and HO•, in methionine degradation. Predicted transformation products were compared to those obtained via benchtop experiments to validate our elementary reaction-based kinetic models. Predicting the reactivities of reactive halogen and nitrogen species implicates our understanding of the formation of potentially toxic halogen- and nitrogen-containing transformation products during water treatment processes and in natural aquatic environments.

Thermal and reactive effects in nanofluid flow around a contracting cylinder under magnetic field influence

This study investigates the dynamic behavior of natural ester-based ferrous oxide (Fe3O4) nanofluid flow around an unsteady contracting cylinder under the influence of a magnetic field, heat generation, and homogeneous-heterogeneous reactions. The governing equations for the flow, heat transfer, and chemical reactions are solved numerically using appropriate mathematical models. The bvp4c built-in MATLAB package is applied to address the complexity of the problem. The effects of magnetic field, heat generation, and reactive chemistry on the flow field, temperature distribution, and species concentration profiles are analysed comprehensively. As part of the validation process, we validate the reliability of our findings by comparing them to established benchmarks. Motivated by the increasing interest in environmentally friendly and sustainable fluid mediums, natural esters are chosen as the base fluid due to their biodegradability, low toxicity, and excellent insulating properties. This research aims to provide valuable insights into optimizing processes involving nanofluid flow in magnetohydrodynamic systems with reactive heat generation, utilizing natural esters as a promising alternative to conventional fluids. Insights gained from this study offer potential applications in various engineering and industrial contexts, contributing to the advancement of eco-friendly technologies.

FEM study of blood gold electrically conducting micropolar nanofluid flow within a permeable channel

In this work, Hermite interpolation polynomials are utilized to develop a numerical model to analyze the influence of transport phenomena on blood gold electrically conducting micropolar nanofluid within a permeable channel with chemical reaction and thermal radiation. By considering blood as a micropolar fluid and applying Berman’s similarity transformation the resulting governing equations are transmuted to fourth-order nonlinear ODE which are solved utilizing FEM. The validity of the FEM code is established by comparing the present computations with existing work. Further, the influence of driving parameters are studied and graphically depicted. When utilizing a blood-gold micropolar nanofluid with a 1% volume fraction, it is observed that varying the Hartmann number from 0 to 15 leads to a decline in temperature profiles, resulting in a 2.51% reduction in heat transfer rate. Similarly, an increase in the chemical reaction parameter up to 10 causes species concentration profiles to decrease, leading to an 18.25% reduction in mass transfer rate compared to base fluid. Moreover, an increase in the volume fraction up to 5% results in an increase in coefficient of skin friction under the influence of the Hartmann number. These findings signify the critical role of Hartmann number in controlling blood velocity and chemical reaction parameter assists in lowering the species concentration levels. The results of the present investigation may help analyze flow models related to drug-delivery systems as gold nanoparticles are proficient drug-delivery and drug-carrying medium.

Mercury Mobility in Epibenthic Waters of a Deltaic Environment

AbstractMercury (Hg) cycling at the sediment‐water interfaces (SWI) encompasses multiple homogeneous and heterogeneous biogeochemical reactions whose result is not yet elucidated. Estuarine SWIs, where the organic matter mineralization is active, constitute experimental sites particularly suitable for scrutinizing Hg speciation and mobilization. Here, we present high‐resolution vertical concentration profiles of Hg species, including inorganic divalent Hg () and monomethyl Hg (MMHg) in solid and dissolved (<0.22 μm) phases, on both sides of the SWI of the proximal part of the Rhône prodelta (northwestern Mediterranean Sea) using sediment cores and dialyzers implemented for a 67‐day‐long period. Concentrations of the dissolved species were <0.10 nM in the sediment pore waters but reached up to 0.58 nM in the epibenthic water zone, a concentration level that is ∼200 times higher than that of the water column. Conversely, MMHg concentrations were low (<0.5 pM) above the SWI and increased to up to 4.6 pM in the sulfate‐reducing zones of the sediment. The dynamic of the Hg species interconversions was explored using one‐dimensional transport‐reaction equations. This model allowed us to constrain the depth intervals where various species are produced or consumed and to approximate the reaction rates. We conclude that the epibenthic zone of the Rhône prodelta is a location of intense mobilization of inorganic HgII associated with organic matter mineralization and MMHg distribution in pore water is controlled by microbiological in situ reactions, but sedimentary MMHg does not diffuse in the overlying water column.

Effects of syngas and methanol fuel substitution on ammonia counterflow diffusion flames

Ammonia (NH3) is increasingly recognized as a promising alternative fuel. Various blending options have been proposed that are aimed at improving its flammability and applicability across diverse energy systems. This study conducts a comprehensive investigation, employing both experimental and numerical approaches, to understand the impact of blending ammonia with CH3OH or syngas, at various H2:CO ratios, on flame extinction limits, structure, and NOx emissions in counterflow laminar diffusion flames. Concentration profiles of ammonia and intermediate species (O2, CO, CO2, H2, NO, and N2O) were measured using Fourier-transformed infrared (FTIR) and gas chromatographic (GC) techniques. The findings indicate that increasing the H2:CO ratio in syngas-blended flames increases the extinction limits and reduces NO and N2O emissions. Compared with ammonia/methanol flames the ammonia/syngas flames exhibit higher extinction limits, flame temperatures, and lower NO and N2O emissions. Multiple kinetic models were found to underestimate the extinction strain limits, with Wang et al.’s 2021 model offering the closest predictions. Notably, discrepancies in ammonia dissociation and oxygen leakage to the rich side of stoichiometry impact reaction zone characteristics, extinction limits, and NOx predictions. Further kinetic analyses reveal that reactivity in syngas-blended flames is dominated by heat and radicals-producing reactions, while methanol-blended flames are sensitive to reactions involving ammonia fragments, resulting in decreased reactivity compared to syngas-blended flames. The results and findings from this study yield valuable insights into optimizing ammonia blends for enhanced flame stability and reduced emissions across various energy applications. It also provides data for chemical kinetics model validation in non-premixed diffusion environment where both species chemistry and transport are encountered.

Application of static integrated skeletal reduction and tabulation of dynamic adaptive chemistry in the combustion simulation of ethylene-fueled scramjet combustor.

The high-fidelity reduced mechanism is one of the key elements in the combustion simulation of scramjet combustors to reveal their combustion and flow phenomena. In the present work, the hierarchically constructed NUIGMech1.2 (2857 species and 11 814 reactions) is applied to the combustion simulation of an ethylene-fueled scramjet combustor using the method of static integrated skeletal reduction and tabulation of dynamic adaptive chemistry (TDAC). The integrated skeletal reduction strategy successively consists of species elimination using the revised directed relation graph with error propagation method of fixed species scheme and improved sensitivity analysis method, and reactions elimination based on computational singular perturbation importance index. A preferred ethylene skeletal mechanism (26 species and 117 reactions) is obtained through the integrated skeletal reduction strategy under target working conditions of temperature range of 900-1800 K, pressure range of 1-4 atm, and equivalence ratio range of 0.25-5.0. The compact skeletal mechanism is comprehensively validated against the experimental results of ignition delay times, laminar flame speeds, and key species concentration profiles. Meanwhile, it shows consistent results with the detailed mechanism on the adiabatic flame temperature profiles and "S"-curves. When applying this skeletal mechanism to combustion simulations of ethylene-fueled scramjet combustor with double parallel cavities, the path flux analysis method and in situ adaptive tabulation algorithm of TDAC is further utilized to speed up the chemical reaction solution process at run-time. Under the scramjet and ramjet modes, the corresponding simulation results in terms of flame luminosity images, schlieren images, and static pressure distributions, coincide well with those of experimental measurements. The combustion and flow characteristics of the two modes are investigated and analyzed comparatively based on above results and combustion performance parameters. Present work contributes to the application of fuel kinetic mechanisms in scramjet combustor combustion simulation.

Structure and nitric oxide formation in laminar diffusion flames of ammonia–hydrogen and air

In this work, we present an investigation of the structure and formation of nitrogen oxides (NOx) in an axisymmetric laminar diffusion flame in which an ammonia–hydrogen fuel stream is surrounded by co-flowing air. Green ammonia, produced using renewable energy, is a promising carbon-free fuel for replacing hydrocarbon fuels over a diverse range of combustion applications. A key challenge for ammonia combustion is to understand the kinetics of nitrogen oxide formation for designing low-NOx combustion systems. In this experimental study, ammonia fuel is blended with hydrogen to increase fuel reactivity, with a fuel composition range of 15%–100% hydrogen. NOx emissions and fuel slip are measured by downstream sampling of NO, NO2, N2O and NH3 with a Fourier Transform Infrared (FTIR) gas analyzer. Flame structure is visualized by planar laser-induced fluorescence (LIF) for NO, NH, and OH radicals, as well as OH* by filtered chemiluminescence. Species concentration profiles are compared to predictions from 2-dimensional axisymmetric numerical models of the laminar flame using recent kinetic mechanisms developed for ammonia combustion. No measurable ammonia slip was recorded for any fuel composition, in agreement with model predictions. Good agreement between predictions and measurements was obtained for exhaust nitrogen oxide concentrations and for in-flame radical profiles, although larger variation and deviations are observed for predictions of NO2 and N2O than for NO. Numerical predictions for spatial distribution of flame radicals and flame liftoff height also showed good agreement with LIF and chemiluminescence measurements. For high fuel hydrogen content, the measured NH and NO profiles are shifted inward toward the fuel outlet, away from the peak temperature contour. Reaction path analysis is used to illustrate the important contributions to NO creation and destruction, including the differing role of key reaction pathways with varying fuel hydrogen content.

Coupled Simulation of Chemical Membrane Degradation and Oxygen Crossover in PEM Water Electrolysis

The membrane of polymer electrolyte membrane water electrolysis (PEMWE), as one of the lifetime limiting components, does not only have an impact on performance, but also plays an important role for safety issues over time. Membrane thinning is a key phenomenon caused by chemical membrane degradation and directly affects the conductivity and gas crossover. Therefore, a chemical membrane degradation model based on Fenton equations [1,2] coupled with a gas crossover model [3] is presented in this work. The presence of Oxygen at cathode side is considered by oxygen crossover, which is strongly enforced by supersaturation effects. Specifically, this cathode-side oxygen is conducive to hydrogen peroxide formation. In interaction with metal ions, e.g. iron, from the feed water, which partially migrate through the membrane, hydroxyl radicals can be formed. These attack the polyfluorinated sulfonicacid (PFSA) membrane at different points, releasing sulfon acid head groups (SO3H-) and fluride ions (F-), which can be measured as sulfur release rates (SRR) and fluride release rates (FRR) in the effluent water, respectively. The degradation model provides concentration profiles for the relevant species involved in the process, which, e.g., influence the thickness and conductivity of the membrane via structure-function relations. In particular, the changed thickness again influences the crossover effect, which itself represents an input for the degradation model. Through this coupling, both models can be updated at specific times. Implications of the model-based analysis on the mechanistic understanding of chemical membrane degradation by radical attack in PEMWE are discussed. Furthermore, the model results can be verified and calibrated by experimental data in combination with adapted accelerated stress tests (AST) and also encourage their enhancement.

The combustion chemistry of ammonia and ammonia/hydrogen mixtures: A comprehensive chemical kinetic modeling study

Ammonia (NH3) is relatively less reactive compared to hydrocarbon fuels. Therefore, ammonia mixtures blended with hydrogen (H2) have been shown to be a promising fuel for internal combustion engines. In this study, a detailed NH3/H2 chemical kinetic model is developed over a wide range of engine-relevant conditions and comprehensively validated to describe the combustion of NH3/H2 mixtures using available experimental literature data, including ignition delay times, laminar flame speeds and species concentration profiles. The new model captures very well the combustion properties of pure NH3 and NH3/H2 mixtures at most conditions. By performing sensitivity and reaction path flux analyses the key reactions controlling fuel reactivity at high-temperature (≥ 1500 K) and low-to-intermediate temperature (1000 ≤ T ≤ 1500 K) regimes are identified. Moreover, the formation and consumption pathways of nitrogen oxides (NOx) in NH3/H2 combustion at different conditions have also been investigated, which are found to be highly coupled to the underlying chemical reactions that dictate fuel reactivity. The kinetic data for the important reactions and species thermochemistry data used in our model are rigorously evaluated and are discussed in detail.

3D study of a chemically reacting fixed-bed under gasification conditions for non-porous char: Laminar flow

This paper reports a computational investigation of the combustion of char particles in a fixed-bed using a three-dimensional model. Numerical simulations were carried out using the commercial software AnsysⓇ Fluent, implementing a six semi-global kinetic scheme, where carbon monoxide combustion, forward and backward water-gas-shift reaction (WGS), Boudouard reaction, and two other heterogeneous reactions take place inside the reactor composed of 85 spherical particles. The diameter of the particles is 5.6 mm. Laminar flow regime (Rein = 50, 75 and 100), inflow gas temperature in the range of 900–1500 K, and mass fraction of oxygen at the inlet (YO2,in) of 0.05, 0.11, and 0.233 are the parameters of interest to study the heterogeneous combustion of carbon char particles inside the unit. The Boudouard reaction and oxidation of carbon monoxide are dominant among heterogeneous and homogeneous chemical reactions, respectively, being the inflow gas temperature a critical parameter to assess, since the kinetic scheme is dramatically activated at higher temperatures. A linear dependency has been found for species concentration and temperature profile in most of the simulations using YO2,in=0.05. Further studies are necessary to extend this research to intrinsic chemical reactions (tracking of porosity and particle radius), and the hybridization of the bed zone by incorporating inert solid particles into the system.

Process flowsheet test of the i-SANEX process with CHON-compliant ligands in aqueous and organic phases

We report the results of a “CHON-compliant” i-SANEX flowsheet test using a surrogate feed with process concentrations of 241Am (>1 g/L) and major lanthanide and fission product species in a 32-stage counter-current centrifugal contactor (CC) rig. By combining flowsheet modelling with experience from the European GENIORS project, a flowsheet was designed that included the lanthanide/actinide extraction, fission product scrubbing, actinide stripping and finally, lanthanide stripping; therefore, covering the entire flowsheet except solvent treatment. The extraction system was 0.2 M N,N,N′,N′-tetraoctyldiglycolamide (TODGA) in Isane-185 with 5 v/v.% 1-octanol as a phase modifier. Actinide stripping was afforded by the aqueous soluble pyridine-2,6-bis(1H-1,2,3-triazol-4-yl) (PTD), whilst the lanthanide stripping was performed by N,N,N′,N′-tetraethyldiglycolamide (TEDGA). This represents the first test of PTD and TEDGA across the full flowsheet using counter-current CC and with process concentrations of americium. This CHON-compliant i-SANEX flowsheet offers clear improvements to the reference process. The use of a full PUREX raffinate simulant as the feed for the process has also permitted the measurement of concentration profiles of many species that are not normally followed in such detail. This has highlighted that under the conditions used – 8 stages of extraction, 8 stages of scrubbing (0.7 M HNO3) – some of the lanthanides recycle and do not reach steady-state in the timeframe of the experiment. Overall, the flowsheet demonstrated good control of 241Am with 98.6 % being routed to the actinide product although further work is needed to fully control some lanthanides and fission products, including; La, Ce, Pr, Gd, Tc, Ru and Sr.

Experimental and theoretical insights into advanced removal of the refractory cibacron green H3G dye by UV/chlorine innovative oxidation process

The discharge of highly persistent Cibacron Green H3G (CG-H3G) dye by textile factories poses a significant threat to both environmental and human health. In this study, the UV/chlorine advanced oxidation process was successfully used to degrade and mineralize this dye. The synergism resulted from coupling 254 nm irradiation UV and low chlorine dosage was assessed at various solution pH (5–10) and liquid temperature (up to 50 °C) for a range of chlorine dosage (50–200 µM). In only 5 min, 85 and 100 % of CG-H3G (20 mg/L) were eliminated with high synergy indexes of 4.34 and 6.3 for 100 and 200 µM of dissolved chlorine, respectively. Besides, 45 and 72 % of the initial TOC were mineralized after 30 and 60 min of photoirradiation with 100 µM chlorine. The synergistic treatment was more efficient as chlorine dosage increased (in the range 10–200 µM), and solution pH and temperature decreased (pH range: 5–10, temperature range: 20–50 °C). Cl2− and OH/Cl radicals were identified as the key oxidants degrading CG-H3G with contributions of 35 % for {OH + Cl}, 65 % for Cl2− at 100 µM of chlorine, and 25 % for {OH + Cl}, 75 % for Cl2− at 200 µM of chlorine. The contribution of Cl2− increased by 10 % chlorine dosage increase from 100 to 200 µM, whereas the contribution of {OH + Cl} decreased by 10 %. Finally, the different project’s results were analyzed by adopting a simulation approach, where the concentration profiles of the different reactive species generated during chlorine photo-activation (specifically at steady state) was related to the degradation outcomes. This analysis provides an easier understanding of the degradation mechanism that occurs in the UV/chlorine process when applied to treat refractory textile effluents in deionized water.

A numerical study on MHD Cu-Al2O3/H2O hybrid nanofluid with Hall current and cross-diffusion effect

A numerical investigation has been performed to analyze an unsteady magnetohydrodynamic gravity-driven flow of a Newtonian hybrid nanofluid (Cu-Al2O3/H2O) along an impermeable vertical plate with linearly accelerated temperature and concentration. The Hall current, nanoparticle volume fraction, inclined magnetic field, and Soret effect on water-based Cu-Al2O3 hybrid nanofluid are incorporated into the flow model. The model's governing nonlinear partial differential equations are formulated and transformed into a non-dimensional form by introducing suitable variables and parameters. The finite difference method is implemented via the MATLAB solver fsolve to resolve the model equations numerically. The evolution of the primary and secondary velocities, temperature, and species concentration profiles is discussed via graphical illustration. Furthermore, a comparative analysis is performed on the coefficient of skin friction, rate of heat, and mass transport for hybrid nanofluid and nanofluid through tabular values. The novelty of the investigation reveals that a deceleration in the primary velocity and acceleration in the secondary velocity with the increasing magnetic field inclination parameter exists. The rising value of Cu nanoparticle volume fraction augments the primary, secondary skin friction coefficients, and the heat and mass transport rates at the plate. The Dufour number stimulates a reduction in the heat transport rate, while an enhancement occurs with the Soret number. The present investigation demonstrates that the heat transfer rate for water-based Cu-Al2O3 hybrid nanofluid is higher than that for water-based Cu nanofluid. The current research can be implemented to augment the efficiency of the cooling mechanism of heat exchangers, solar collectors, nuclear reactors, and many more.

Development of Physical-Chemical Surrogate Models and Skeletal Mechanisms for the Combustion Simulation of Several Jet Fuels

Abstract The physical–chemical surrogate models for S-8, Jet-A, and RP-3 fuels to capture their physical and kinetics properties have been developed in this study. n-dodecane (nC12H26), 2,5-dimethylhexane (C8H18-25), and toluene (C6H5CH3) were chosen as candidate surrogate components and formulated by the function group based surrogate fuel methodology. Some important physical properties and spray characteristics for S-8, Jet-A, and RP-3 surrogate models were validated. The results indicate that present surrogate models can well emulate various physical properties to accurately reproduce the spray characteristics. Then, a minimal and high-precision surrogate skeletal mechanism that can be suitable for computational fluid dynamics (CFD) simulations was developed and validated against some fundamental combustion experiments for each surrogate component. Furthermore, the performances of surrogate models that contain the surrogate formulation and associated skeletal mechanisms were validated against the experimental data on ignition delay times (IDTs), species concentration profiles, and laminar flame speeds (Su0) in a wide range of conditions. Finally, the surrogate fuels were used to combustion CFD simulations to model the spray combustion process in a constant volume combustion chamber. It can be seen that the agreements between the simulation and experiment in fundamental and spray combustion characteristics are reasonably good, which proves that present surrogate models are accurate and robust to be applied in CFD simulations.

Experimental and kinetic modeling studies on oxidation of methanol and di-tert-butyl peroxide in a jet-stirred reactor

Methanol is a potential carbon neutral fuel, but it faces the challenge of ignition difficulties in engines. Di-tert-butyl peroxide (DTBP), a cetane number improver, is considered to be added into methanol to improve ignition. However, there is currently no research of experiments and simulations on the kinetic model of methanol and DTBP. Therefore, the oxidation characteristics of methanol and DTBP were experimentally studied in a jet-stirred reactor under temperatures of 400–1000 K and pressures of 1.03 atm, with equivalence ratios of 0.5, 1 and 2 for pure methanol, pure DTBP, blended fuel (97 % CH3OH + 3 % DTBP; 94 % CH3OH + 6 % DTBP). Then, a new reduced CH3OH-DTBP mechanism containing 75 species and 443 reactions was proposed, which was widely validated by experimental data of ignition delay times, laminar flame speeds and species concentration profiles. Next, the simulations were conducted with CHEMKIN PRO to analyze the effect of DTBP on methanol. The major findings are as follows. After adding DTBP, methanol can react at a lower temperature (550 K), which is due to CH3 generated by decomposition of DTBP promotes the enrichment of OH, thereby promoting the oxidation of methanol. The source of OH at 650 K is CH3 → CH3O2 → CH3O2H → CH3O. At 850 K, the early OH comes from R27 (CH3 + HO2=CH3O + OH), while the later OH comes from the decomposition of H2O2. When the temperature is above 850 K, the addition of DTBP has only a slight effect on the oxidation of methanol. As the temperature increases, the effect of DTBP on shortening the ignition delay time weakens. As DTBP concentration increases, the effect also shows a weakening trend. At low temperatures, the contribution of thermal effects caused by DTBP is greater. As DTBP concentration increases, the proportion of thermal effect contribution increases.

New insight into the oxidation of propene at elevated pressure

Comprehensive experimental and kinetic studies of propene (C3H6) oxidation were conducted by using a jet-stirred reactor at 12.0 atm within 725–1020 K under both fuel-lean (Φ = 0.5) and fuel-rich (Φ = 3.0) conditions. Molecular species concentration profiles were obtained by using online gas chromatography and gas chromatography-mass spectrometry, including CO, CO2, CH4, C2H4, C2H6, A-C3H4, C3H8, 1,3-C4H6, 1-C4H8, nC4H10, CH3CHO, C2H3CHO, CH3COCH3, C3H6O1-2 CH3CH2CHO, and C6H6. Sixteen products and intermediates including light hydrocarbons, oxygenated and aromatic species were identified and quantified. Based on Aramco Mech 3.0 and previous works, the rate coefficients of some key elementary reactions were updated, and a detailed kinetic reaction model was developed with reasonable predictions involving 587 and 3037 reactions. Rate-of-production analysis indicates the four main pathways for high-pressure oxidation of C3H6, namely hydrogen atom abstraction reactions, OH addition reactions, H atom addition reactions, and the formation of C3H6O1-2. Sensitivity analysis reveals that H2O2(+M) <=> 2OH(+M) and the H-abstraction of C3H6 by OH radicals are the most promoting and inhibiting reactions for C3H6 consumption, respectively. The benzene formation during C3H6 oxidation was analyzed, mainly generated by the C1 + C5 channel and consumed by OH addition. It was found that increasing pressure can decrease the initial reaction temperature and increase the conversion of C3H6. The importance of addition and hydrogen abstraction reactions in the oxidation of C3H6 was identified by analyzing the pressure effect. To confirm its validity, the proposed kinetic model could be used to the previous literature data, including JSR oxidation at around 1 atm and ignition delay times for C3H6. These experimental and modeling efforts provide a basis for gaining a more comprehensive insight into the oxidation of propene.