Reaction Rate Coefficients Research Articles

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.

Theoretical and experimental study of the OH radical with 3‐bromopropene gas phase reaction rate coefficients temperature dependence

AbstractIn this work, the rate‐determining steps of the OH radical + 3‐bromopropene gas phase reaction were studied, which could explain for the possible negative activation energy observed in experiments. To obtain new kinetic parameters and data for critical revisions, a reinvestigation of the rate coefficient (k) and its temperature dependence was carried out using the PLP‐LIF technique, in the 254‐ to 371‐K range. Moreover, quantum‐mechanical and canonical variational transition state theory calculations were performed, taking into consideration four OH addition and two β‐hydrogen atom abstraction reaction channels. The proposed kinetic model fits to the observed experimental Arrhenius behavior, and three not negligible reaction pathways are described for the first time.

Modelling the effect of bromide on chlorine decay in raw and coagulated surface waters

A novel and simple semi-mechanistic model describing the effect of bromide on chlorine decay was developed. A well validated two-reactant parallel second order (2R) chlorine decay model is available for planning and operation. Four parameters - reaction rate coefficients and initial concentrations of fast and slow reacting compounds - define the model. Bromide concentration varies in water bodies but considering the variability requires conducting individual tests and parameter estimation for each bromide concentration. The proposed model was developed and tested using data obtained from six water sources from the US and Australia. The samples included a mix of raw and coagulated waters with different pH (7.5–8.0), DOC (1.43–5.54 mg-C/L), SUVA (1.73–2.90), chlorine dose (2.32–8.29 mg/L), bromide (14–844 μg/L), chlorine to bromide ratios (4.7–230.4), and temperatures (20–23 °C). when it was assumed that the initial concentrations of fast and slow reacting compounds would not be affected by the addition of bromide, a linear relationship was established between fast and slow decay rate coefficients and the initial bromide concentration in each water source. The linearity coefficient (β) ranged from 1.73 ± 7.24E-04 to 3.56 ± 1.79E-03 L/μg-Br, but a common value of 3.00E-03 ± 5.79E-04 described the effect of bromide in all four tested sources (DOC 1.43–5.54 mg/L) from the US at pH 8 units and 20 °C. This model simplifies the consideration of the effect of bromide in chlorine decay and reduces the number of tests and parameters required to simulate water supply systems that incorporate the effect of bromide.

Reaction mechanism for atmospheric pressure plasma treatment of cysteine in solution

Mechanisms for the cold atmospheric plasma (CAP) treatment of cells in solution are needed for more optimum design of plasma devices for wound healing, cancer treatment, and bacterial inactivation. However, the complexity of organic molecules on cell membranes makes understanding mechanisms that result in modifications (i.e. oxidation) of such compounds difficult. As a surrogate to these systems, a reaction mechanism for the oxidation of cysteine in CAP activated water was developed and implemented in a 0-dimensional (plug-flow) global plasma chemistry model with the capability of addressing plasma-liquid interactions. Reaction rate coefficients for organic reactions in water were estimated based on available data in the literature or by analogy to gas-phase reactions. The mechanism was validated by comparison to experimental mass-spectrometry data for COST-jets sustained in He/O2, He/H2O and He/N2/O2 mixtures treating cysteine in water. Results from the model were used to determine the consequences of changing COST-jet operating parameters, such as distance from the substrate and inlet gas composition, on cysteine oxidation product formation. Results indicate that operating parameters can be adjusted to select for desired cysteine oxidation products, including nitrosylated products.

Diffusion combustion of NH3 in a single bubble of fluidized bed

Fluidized bed is a potential equipment for NH3 combustion due to its efficient gas–solid contact and high temperature particles as heat source for ignition. This paper studies the diffusion combustion of NH3 in a single bubble of fluidized bed, using an experimental approach and CFD-DEM simulation incorporated with a skeleton mechanism of 98 elementary reactions. The results show that the diffusion combustion of NH3 intermittently occurs in the bubble injection period and the oxygen is mainly consumed by H + O2 = OH + O. Slow oxidation, instead of combustion, takes place in the bubble rising period and the oxygen is mainly consumed by NNH + O2 = N2 + HO2. With the rupture of the bubble, unreacted NH3 re-burns, generating flames in the freeboard of the bed. The chemical reaction in the bubble is highly correlated to the mass transfer between the emulsion phase and bubble phase. Increasing the fluidization gas velocity promotes the accumulation of oxygen and enhances the reaction rate of slow oxidation of NH3 in the bubble due to the increasing inter-phase mass transfer. The increase of the bed temperature reduces the ignition delay time, and increases the chemical reaction rate and mass transfer coefficient. The changes in oxygen concentration of fluidizing gas not only changes the chemical reaction rate, but also affects the oxygen consumption path. The fraction of NH3 oxidized in the dense bed can be enhanced by increasing the fluidization gas velocity, bed temperature and oxygen concentration of the fluidizing gas, the latter exerting the greatest influence.

Theoretical Insights into the Dynamics of Gas-Phase Bimolecular Reactions with Submerged Barriers.

Much attention has been paid to the dynamics of both activated gas-phase bimolecular reactions, which feature monotonically increasing integral cross sections and Arrhenius kinetics, and their barrierless capture counterparts, which manifest monotonically decreasing integral cross sections and negative temperature dependence of the rate coefficients. In this Perspective, we focus on the dynamics of gas-phase bimolecular reactions with submerged barriers, which often involve radicals or ions and are prevalent in combustion, atmospheric chemistry, astrochemistry, and plasma chemistry. The temperature dependence of the rate coefficients for such reactions is often non-Arrhenius and complex, and the corresponding dynamics may also be quite different from those with significant barriers or those completely dominated by capture. Recent experimental and theoretical studies of such reactions, particularly at relatively low temperatures or collision energies, have revealed interesting dynamical behaviors, which are discussed here. The new knowledge enriches our understanding of the dynamics of these unusual reactions.

Measurements of rate coefficients of CN+, HCN+, and HNC+ collisions with H2 at cryogenic temperatures.

The experimental determination of the reaction rate coefficients for production and destruction of HCN+ and HNC+ in collision with H2 is presented. A variable-temperature, 22-pole radio frequency ion trap was used to study the reactions in the temperature range 17-250K. The obtained rate coefficients for the reaction of CN+ and HCN+ with H2 are close to the collisional (Langevin) value, whereas that for the reaction of HNC+ with H2 is quickly decreasing with increasing temperature. The product branching ratios for the reaction of CN+ with H2 are also reported and show a notable decrease of the HNC+ product with respect to the HCN+ product with increasing temperature. These measurements have consequences for current astrochemical models of cyanide chemistry, in particular, for the HCNH+ cation.

Numerical approaches in simulating Trichel pulse characteristics in point-plane configuration

In this work, a detailed comparison is made of a few different approaches to numerical modeling of non-equilibrium gas discharge plasmas in dry ambient air at atmospheric conditions, leading to Trichel pulse discharge. Simulation models are based on a two-dimensional axisymmetric finite element discretization of point-plane geometry. The negative corona discharge and the hydrodynamic approximation for generic ionic species (electrons, positive and negative ions) are used. The models account for the drift, diffusion, and reactions of the species. They comprise continuity equations coupled to Poisson’s equation for the electric field. Three different formulations were used to specify the ionic reaction rate coefficients. In the first one, the reaction coefficients are approximated by the analytical expressions as a function of the electric field intensity. Two others extract the reaction coefficients from the solution of the Boltzmann equation as a function of the reduced electric field or the electron energy. The effect of gas flow and heating on the pulse characteristics is also investigated. The accuracy of the models has been validated by comparing them with the experimental data.

Identifying the essential roles of light and sonication in dual‐stimuli regulated bulk atom transfer radical polymerization by multiscale simulation

AbstractMore and more attention has been paid to the important roles of external fields in controlled radical polymerization (CRP). However, their essential roles have not been studied thoroughly yet, which hinders the in‐depth understanding of the mechanism and kinetics. Herein, a strategy combining quantum chemical calculations (QCC) and kinetic modeling was adopted to identify the essential roles of light and ultrasonication in the dual‐stimuli regulated bulk atom transfer radical polymerization (ATRP). At the molecular level, the impact of light on Cu‐catalyzed ATRP was investigated. The CuIIBr/Me6TREN has high absorbance at an experimental wavelength of 365 nm (main excitation S0 → D7 accounts for 84.93%). Electron transfer reactions involving Me6TREN are more favorable paths for photochemical reactions, and the mechanism of the copper activation/deactivation pathway is inner sphere electron transfer. At the micro‐scale, a kinetic model based on the method of moment was established with a “series” encounter pair model to consider the influence of ultrasound on diffusional limitation. Simulation results show that the changes of the reaction rate coefficients ka, kda, and kt at high conversion reflect the degree of diffusional limitation by ultrasound. The multiscale modeling strategy applied in this study identifies the essential roles of photo and ultrasonication in dual‐stimuli regulated model systems, which can be extended to other external‐field regulated CRP to improve the mechanistic understanding.

On the increasing competitiveness of UV/Cl to UV/H2O2 advanced oxidation as the organic carbon concentration increases

UV/Cl and UV/H2O2 are advanced oxidation processes (AOPs) used for drinking water treatment and water reuse. This work explored the hypothesis that UV/Cl becomes more competitive to UV/H2O2 at neutral-to-high pH as the concentration of total organic carbon (TOC) increases. Lab experiments and kinetic modelling were used to compare initial pseudo first-order contaminant decay rate coefficients between the AOPs at various pH and TOC conditions. The relative effect of increasing TOC concentrations on UV/Cl vs. UV/H2O2 depended on the pH, contaminant, and organic matter reactivity towards radicals. For example, while the reaction rate coefficients during both AOPs generally decreased with increasing TOC, the UV/Cl reaction rate coefficients for the solely •OH-reactive sucralose decreased 41–138% less than the UV/H2O2 coefficients as the TOC concentration was increased from 0 to 5 mg-C L−1. However, UV/Cl was more affected than UV/H2O2 when targeting caffeine (a contaminant reactive to chlorine radicals). The data were used to define TOC-pH conditions for which either AOP would be more energy-efficient, under a set of standard conditions. The results suggest that UV/Cl may be competitive to UV/H2O2 under a wider range of treatment scenarios than has been conventionally thought based on tests in pure water.

Quantitative structure-activity relationship models for the reaction rate coefficients between dissolved organic matter and PPCPs

To predict PPCPs’ photolysis rate in natural aquatic environment, it is essential to grasp the reaction rates between DOM and PPCPs, yet there are few measured data and no prediction models for this important photochemical parameter. To address this, a reaction rate coefficient (αDOM) was defined to describe the apparent rate of DOM-involved photoreaction for PPCPs. The measured αDOM values for 40 PPCPs in 9 DOM samples varied dramatically, ranging from (−2.1 ± 0.1)× 1010 to (2.2 ± 0.1)× 1011 M−1 s−1. Then the quantitative structure-activity relationship (QSAR) models were developed using chemical and water quality descriptors via the random forest method. We initially separated positive and negative values by a classifier with an AUC value of 0.965, followed by the construction of regression models for positive and negative values, respectively, using a regressor. Positive models achieved satisfactory goodness-of-fit and predictive ability (R2adj=0.92 and Q2ext=0.86), while negative models demonstrated acceptable performance (R2adj=0.71 and Q2ext=0.70). Finally, a comprehensive photolysis model that incorporates the QSAR models for αDOM was established and the significance of water quality parameters was emphasized through sensitive analysis. This model enables more elaborate predictions of PPCPs’ photolysis rates in various water samples, providing valuable assistance for forecasting PPCPs’ environmental fate.

Role of methyldioxy radical chemistry in high‐pressure methane combustion in CO2

AbstractThe combustion chambers of direct‐fired supercritical CO2 power plants operate at pressures of approximately 300 bar and CO2 dilutions of up to 96%. The rate coefficients used in existing chemical kinetic mechanisms are validated for much lower pressures and much smaller concentrations of CO2. Recently, the UoS sCO2 1.0 and UoS sCO2 2.0 mechanisms have been developed to better predict ignition delay time (IDT) data from shock tube studies at pressures from 1 to 260 bar in various CO2‐containing bath gas compositions. The chemistry of the methyldioxy radical (CH3O2) has been identified as an essential combustion intermediate for methane combustion above 100 bar, where mechanisms missing this species begin to vastly overpredict the IDT. The current literature available on CH3O2 is very limited and often concerned with atmospheric chemistry and low‐pressure, low‐temperature combustion. This means that the rate coefficients used in UoS sCO2 2.0 are commonly determined at sub‐atmospheric pressures and temperatures below 1000 K with some rate coefficients being over 30 years old. In this work, the rate coefficients of new potential CH3O2 reactions are added to the current mechanism to create UoS sCO2 2.1 It is shown that the influence of CH3O2 on the IDT is greatest at high pressures and low temperatures. It has also been demonstrated that CO2 has very little effect on the chemistry of CH3O2 at 300 bar meaning that CH3O2 rate coefficients can be determined in other bath gases, reducing the impact of non‐ideal effects such as bifurcation when studying in a CO2 bath gas. The updated UoS sCO2 2.1 mechanism is then compared to high‐pressure IDT data and the most important reactions which require reinvestigation have been identified as the essential next steps in understanding high‐pressure methane combustion.

Stochastic optimization of a uranium oxide reaction mechanism using plasma flow reactor measurements

In this work, a coupled Monte Carlo Genetic Algorithm (MCGA) approach is used to optimize a gas phase uranium oxide reaction mechanism based on plasma flow reactor (PFR) measurements. The PFR produces a steady Ar plasma containing U, O, H, and N species with high temperature regions (3000–5000 K) relevant to observing UO formation via optical emission spectroscopy. A global kinetic treatment is used to model the chemical evolution in the PFR and to produce synthetic emission signals for direct comparison with experiments. The parameter space of a uranium oxide reaction mechanism is then explored via Monte Carlo sampling using objective functions to quantify the model-experiment agreement. The Monte Carlo results are subsequently refined using a genetic algorithm to obtain an experimentally corroborated set of reaction pathways and rate coefficients. Out of 12 reaction channels targeted for optimization, four channels are found to be well constrained across all optimization runs while another three channels are constrained in select cases. The optimized channels highlight the importance of the OH radical in oxidizing uranium in the PFR. This study comprises a first step toward producing a comprehensive experimentally validated reaction mechanism for gas phase uranium molecular species formation.

New Measurements and Calculations on the Kinetics of an Old Reaction: OH + HO2 → H2O + O2.

Literature rate coefficients for the prototypical radical-radical reaction at 298 K vary by close to an order of magnitude; such variations challenge our understanding of fundamental reaction kinetics. We have studied the title reaction at room temperature via the use of laser flash photolysis to generate OH and HO2 radicals, monitoring OH by laser-induced fluorescence using two different approaches, looking at the direct reaction and also the perturbation of the slow OH + H2O2 reaction with radical concentration, and over a wide range of pressures. Both approaches give a consistent measurement of k1,298K ∼1 × 10-11 cm3 molecule-1 s-1, at the lowest limit of previous determinations. We observe, experimentally, for the first time, a significant enhancement in the rate coefficient in the presence of water, k1,H2O,298K = (2.17 ± 0.09) × 10-28 cm6 molecule-2 s-1, where the error is statistical at the 1σ level. This result is consistent with previous theoretical calculations, and the effect goes some way to explaining some, but not all, of the variation in previous determinations of k1,298K. Supporting master equation calculations, using calculated potential energy surfaces at the RCCSD(T)-F12b/CBS//RCCSD/aug-cc-pVTZ and UCCSD(T)/CBS//UCCSD/aug-cc-pVTZ levels, are in agreement with our experimental observations. However, realistic variations in barrier heights and transition state frequencies give a wide range of calculated rate coefficients showing that the current precision and accuracy of calculations are insufficient to resolve the experimental discrepancies. The lower value of k1,298K is consistent with experimental observations of the rate coefficient of the related reaction, Cl + HO2 → HCl + O2. The implications of these results in atmospheric models are discussed.

Elastic and electron capture processes in slow He+–He collision

Aims. The elastic and electron-capture processes of He+ ions with ground helium atoms are very important for studies in astrophysics. It is essential to have reliable state-selective charge transfer, elastic, and transport cross-sections, along with the corresponding reaction rate coefficient data, especially for low collision energies. Methods. We investigated the elastic and non-radiative electron-capture processes in He+(1s)–He(1s2) collisions are investigated employing the full quantum-mechanical molecular orbital close-coupling method. The adopted ab initio adiabatic potentials and coupling matrix elements were obtained by a multi-reference single- and double-excitation configuration interaction approach. Results. We computed the elastic, charge-transfer, and transport cross-sections in the energy range of 0.01–2500eVamu−1 and the reaction rate coefficient in the temperature range of 10–109 K. Good agreement was achieved when compared to the available experimental and theoretical results. Shape resonance, Regge, and Glory oscillations were also found in the elastic and charge transfer cross-sections in the energy region considered here.

Room temperature rate coefficients for the reaction of chlorine atoms with a series of volatile methylsiloxanes (L2‐L5, D3‐D6)

AbstractThe kinetics of chlorine (Cl) atom reactions with a series of volatile methylsiloxanes (VMS) including hexamethyldisiloxane (L2), octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), dodecamethylpentasiloxane (L5), hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) were investigated in relative rate experiments at room temperature and atmospheric pressure. The experiments were carried out in a 0.2 m3 PFA Teflon chamber, employing proton‐transfer‐reaction time‐of‐flight mass spectrometry (PTR‐ToF‐MS) as the chemical‐analytical tool. The following relative and absolute reaction rate coefficients were obtained using isoprene as reference compound (kVMS/kisoprene; kVMS × 1010 cm3 molec−1 s −1): L2 (0.32 ± 0.02; 1.31 ± 0.21), L3 (0.38 ± 0.00; 1.56 ± 0.23), L4 (0.48 ± 0.01; 1.98 ± 0.29), L5 (0.54 ± 0.03; 2.22 ± 0.34), D3 (0.14 ± 0.02; 0.56 ± 0.13), D4 (0.26 ± 0.01; 1.05 ± 0.16), D5 (0.36 ± 0.02; 1.46 ± 0.22), D6 (0.39 ± 0.02; 1.61 ± 0.25). The following relative and absolute reaction rate coefficients were obtained using toluene as reference compound (kVMS/ktoluene; kVMS × 1010 cm3 molec−1 s −1): L2 (1.59 ± 0.18; 0.95 ± 0.14), L3 (2.25 ± 0.14; 1.35 ± 0.16), L4 (2.38 ± 0.01; 1.43 ± 0.14), L5 (3.57 ± 0.11; 2.14 ± 0.22), D3 (0.87 ± 0.01; 0.52 ± 0.05), D4 (1.48 ± 0.12; 0.89 ± 0.11), D5 (2.02 ± 0.15; 1.21 ± 0.15), D6 (2.54 ± 0.11; 1.52 ± 0.17). Our data confirm that reactions with Cl atoms need to be taken into account when assessing the decomposition of VMS in Cl‐rich tropospheric environments.

The weakening effect of the inhibition of CO2 on the explosion of HCNG with the increase of hydrogen: Experimental and chemical kinetic research

To explore the inhibitory effect of CO2 on HCNG (Hydrogen enriched compressed natural gas) explosion and its chemical kinetic mechanism, the explosion pressure and flame of CO2/HCNG/Air (hydrogen ratio: 0–0.6, CO2 addition: 3 vol%, 6 vol%, and 9 vol%) were tested in a 20 L spherical explosion tank at normal temperature and normal pressure. The experiment results shown that: as the addition of CO2 increases, the inhibition effect on HCNG explosion flame and pressure becomes more obvious. The larger the H2 ratio, the more difficult it is to inhibit HCNG explosion flame and pressure. To explore the chemical kinetics reasons for the above laws, the chemical kinetic parameters (such as free radical formation rate and temperature sensitivity coefficient) of the explosion reaction under the above conditions were calculated by CHEMKIN-PRO. The results indicate that CO2 mainly acts as a stable third body in the reaction system, thereby slowing down the growth of explosion chain reactions. In addition, as the main product of the CH4 oxidation reaction, CO2 has a certain weakening effect on the CH4 oxidation reaction. As the proportion of H2 increases, the elementary reactions such as 3# and 84# that generate ·H radicals are promoted, increasing the concentration of ·H radicals in the reaction system. Therefore, the dominant role of 38# on the temperature rise of the reaction system is enhanced, and the contribution of the CH4 oxidation reaction to the temperature rise of the reaction system is weakened. This is the chemical kinetic reason that CO2 has a weak inhibitory effect on the energy release of the HCNG explosion reaction when the proportion of H2 is large. The research results can provide a theoretical basis for the development of HCNG explosion prevention and control technology.

Comprehensive Theoretical Study on Four Typical Intramolecular Hydrogen Shift Reactions of Peroxy Radicals: Multireference Character, Recommended Model Chemistry, and Kinetics.

Intramolecular hydrogen shift reactions in peroxy radicals (RO2• → •QOOH) play key roles in the low-temperature combustion and in the atmospheric chemistry. In the present study, we found that a mild-to-moderate multireference character of a potential energy surface (PES) is widely present in four typical hydrogen shift reactions of peroxy radicals (RO2•, R = ethyl, vinyl, formyl methyl, and acetyl) by a systematic assessment based on the T1 diagnostic, %TAE diagnostic, M diagnostic, and contribution of the dominant configuration of the reference CASSCF wavefunction (C02). To assess the effects of these inherent multireference characters on electronic structure calculations, we compared the PESs of the four reactions calculated by the multireference method CASPT2 in the complete basis set (CBS) limit, single-reference method CCSD(T)-F12, and single-reference-based composite method WMS. The results showed that ignoring the multireference character will introduce a mean unsigned deviation (MUD) of 0.46-1.72 kcal/mol from CASPT2/CBS results by using the CCSD(T)-F12 method or a MUD of 0.49-1.37 kcal/mol by WMS for three RO2• reactions (R = vinyl, formyl methyl, and acetyl) with a stronger multireference character. Further tests by single-reference Kohn-Sham (KS) density functional theory methods showed even larger deviations. Therefore, we specifically developed a new hybrid meta-generalized gradient approximation (GGA) functional M06-HS for the four typical H-shift reactions of peroxy radicals based on the WMS results for the ethyl peroxy radical reaction and on the CASPT2/CBS results for the others. The M06-HS method has an averaged MUD of 0.34 kcal/mol over five tested basis sets against the benchmark PESs, performing best in the tested 38 KS functionals. Last, in a temperature range of 200-3000 K, with the new functional, we calculated the high-pressure-limit rate coefficients of these H-shift reactions by the multi-structural variational transition-state theory with the small-curvature tunneling approximation (MS-CVT/SCT) and the thermochemical properties of all of the involved key radicals by the multi-structural torsional (MS-T) anharmonicity approximation method.

Imaging concentration fields in microfluidic fuel cells as a mass transfer characterization platform

Microfluidic fuel cells (MFCs) are microfluidic electrochemical conversion devices that are used to power electrical equipment. Their performance relies on improving reactant mass transfer at the electrode interface. In this work, a MFC is developed to implement a novel imaging technique that allows the measurement of reactant concentration fields, featuring formic acid as the fuel and potassium permanganate as the oxidant. The concentration fields were imaged based on transmitted visible spectroscopy, which links the light intensity passing through the MFC to its local reactant concentration. An analytical model was developed to estimate the mass diffusivity and kinetic reaction rate coefficient. For the first time, mass transport and transfer coefficient were simultaneously measured during operation. These parameters estimated using the proposed technique can be implemented in a numerical model to predict the MFC performance and concentration distribution. This work paves the way towards advanced imaging tools for operando mass transfer characterizations in microfluidics and Tafel kinetic characterization in many electrochemical devices.

Radiative magnetodydrodynamic cross fluid thermophysical model passing on parabola surface with activation energy

The proposed work is significantly important due to its applications in manufacturing process of submarine, bullets and aircrafts, and many more engineering and industrial works such as cooling and heating processes and chemical works. The purpose of this article is to scrutinize the flow, heat and mass transferal rate for the boundary layer flow of non-Newtonian fluid with variable fluid characteristics on the radiative paraboloid surface. The non-Newtonian fluid which is under consideration is Cross fluid model which is generalized Newtonian fluid and it acts as a shear thickening and thinning. For the sake of heat and mass transport, we have considered the activation energy and thermal radiation effects. The governing equations of considered fluid model occurred in the PDEs form and then transmuted into ODEs form by using similarity variables. The graphical behavior in terms of velocity field is noted due to viscosity parameter and Hartmann number which shows drops behavior in velocity profile. The impact of thermal radiation and thermal conductivity coefficients is noted here and concluded that both quantities creates enhancement in temperature field. The concentration transfer rate is observing for activation energy, reaction rate coefficient and mass diffusion parameters. Activation energy and mass diffusion coefficient improves the concentration rate while reaction rate diminishes the concentration layer thickness. The result of varying the Weissenberg number upon the skin friction is also analyzed. Also the comparison analyses with published articles are presented.