Arrhenius Pre-exponential Factor Research Articles

Mesoporous, high surface area and microrod-shaped cobalt (II) coordination polymer for assessment of molecular structure, thermolysis and non-isothermal kinetics parameters

This study is significant as it presents the assessment of molecular identification, thermal degradation, and non-isothermal kinetics of a cobalt (II) coordination polymer [Co (II) CPs] synthesized from suberoyl bis (2-ethoxybenzamide) (sbebz) and cobalt acetate through the condensation process. The condensation product sbebz was obtained from suberoyl chloride and 2-ethoxybenzamide. The XRD, FT-IR, Raman, and XPS investigated as aspects to identify its structure, purity, and chemical state. The morphological facet was confirmed by SEM and TEM. The morphology data revealed a microrod-shaped morphology of Co (II) CPs with an average particle size 0.7 µm to 1 µm. The pore size, and surface properties were examined by Brunauer-Emmett-Teller (BET) and atomic force microscopy (AFM), revealing a highly large surface area (1076 m2/g), mesoporous and monodisperse nature. The molecular interaction of ligand was estimated using protein molecule. The thermal-decomposition behavior and non-isothermal kinetics of Co (II) CPs were estimated at different heating rates (5 °C/min, 10 °C/min, 15 °C/min, and 20 °C/min) under nitrogen atmosphere by thermogravimetry/Derivative thermogravimetry (TG/DTG). As-synthesized Co (II) CPs show enhanced thermal stability compared to the ligand (sbebz). The multiple heating TG/DTG curve exhibits a more or less identical degradation profile/pattern. The kinetic parameters like order of reaction (n), pre-exponential Arrhenius factor (A), activation entropy (∆s), activation energy (Ea), activation free-energy (∆G), and activation enthalpy (∆H) were calculated using Coats-Redfern (CR) method.

Impact of Sn Lewis Acid Sites on the Dehydration of Cyclohexanol.

The impact of Sn on the concentration and strength of acid sites in Al containing zeolites with MFI topology and their catalytic activity for the dehydration of cyclohexanol in the aqueous phase has been investigated. The materials maintain constant Al concentrations and consequently Bro̷nsted acid site (BAS) concentrations, while exhibiting an increasing concentration of Sn Lewis acid sites (LAS). The presence of water alters LAS(Sn), leading to weak BAS(Sn) that increases the concentration of water in the zeolite micropore, while leaving the rate of dehydration of cyclohexanol unchanged. The TOF increases with the concentration of BAS(Al) in close contact with framework LAS(Sn), referred to as BAS(Pair). The increase in the Arrhenius pre-exponential factor, without affecting the activation barrier (E a), leads to the hypothesis that the proximity of both sites allows for a later transition state induced by the polarization of the C-O bond, leading in turn to a higher transition entropy.

Proton-Coupled Electron Transfer and Hydrogen Tunneling in Olive Oil Phenol Reactions.

Olive oil phenols are recognized as molecules with numerous positive health effects, many of which rely on their antioxidative activity, i.e., the ability to transfer hydrogen to radicals. Proton-coupled electron transfer reactions and hydrogen tunneling are ubiquitous in biological systems. Reactions of olive oil phenols, hydroxytyrosol, tyrosol, oleuropein, oleacein, oleocanthal, homovanillyl alcohol, vanillin, and a few phenolic acids with a DPPH• (2,2-diphenyl-1-picrylhydrazyl) radical in a 1,4-dioxane:water = 95:5 or 99:1 v/v solvent mixture were studied through an experimental kinetic analysis and computational chemistry calculations. The highest rate constants corresponding to the highest antioxidative activity are obtained for the ortho-diphenols hydroxytyrosol, oleuropein, and oleacein. The experimentally determined kinetic isotope effects (KIEs) for hydroxytyrosol, homovanillyl alcohol, and caffeic acid reactions are 16.0, 15.4, and 16.7, respectively. Based on these KIEs, thermodynamic activation parameters, and an intrinsic bond orbital (IBO) analysis along the IRC path calculations, we propose a proton-coupled electron transfer mechanism. The average local ionization energy and electron donor Fukui function obtained for the phenolic compounds show that the most reactive electron-donating sites are associated with π electrons above and below the aromatic ring, in support of the IBO analysis and proposed PCET reaction mechanism. Large KIEs and isotopic values of Arrhenius pre-exponential factor AH/AD determined for the hydroxytyrosol, homovanillyl alcohol, and caffeic acid reactions of 0.6, 1.3, and 0.3, respectively, reveal the involvement of hydrogen tunneling in the process.

Kinetic and thermodynamic study of composite with jute fiber as reinforcement

In the present work, engineered by compression molding process via a hydraulic press, the A and B composite samples were carried out with 5% and 10% ratio respectively of Ricinodendron heudelotii oil-based alkyd resin in bio-based matrix made of unsaturated polyester using jute fibers as reinforcement material. The samples’ thermal decomposition was performed through thermogravimetry (TG) and derivative thermogravimetry (DTG) analyses. Both composite samples exhibit two stages of decomposition, where the main occurs at 200 - 550°C. Aiming to study and being able to model the thermal degradation of the elaborated composites, finding the kinetic triplets appears the best option to describe the kinetic process undergo by the composites in order to evaluate the performance application of the composites. Two non-isothermal techniques, Flynn-Wall-Ozawa (FWO) and Kissinger have been used to assess the activation energy Ea, and it is found that the apparent activation energy varies with the degree of conversion indicating that both composites decompose with a multiple step mechanism process. The appropriate reaction model for the second stage of decomposition was best suited with Johnson-Mel-Avrami (n<1) model and has been established, allowing us to model thermal degradation behavior of our elaborated composite material and set predictions. The estimated Arrhenius factor values were respectively about A and B composites, 4.12.1015 min-1 and 10.42.1015 min-1, allowing us to set the final equation characterizing the degradation process for the second and main decomposition stage. Finally, as a result of comparison between A and B composites, A appears to be the more thermally stable due to its lower values of Arrhenius pre-exponential factor over the main stage of decomposition and higher calculated the activation energy values.

Morphology-dependent Li+ ion dynamics in X-ray amorphous and crystalline Li3PS4 prepared by solvent-assisted synthesis.

Solid-state electrolytes with high ionic conductivity will be crucial for future energy storage systems. Among many possible materials, thiophosphates offer both favourable mechanical properties and fast ionic transport. β-Li3PS4, as a member of the thiophosphate family, has gained recent attention, due to its remarkable increase in Li+ ionic conductivity when prepared via solvent-assisted synthesis. Despite earlier studies, the lithium ion migration processes causing the increased conductivity remain, however, still uncertain. Here, we study both long-range cation transport and local Li+ jump processes by broadband impedance spectroscopy and nuclear magnetic resonance (NMR), respectively. In particular, we focus on the comparison between mechanochemical and solvent-assisted synthesis to determine the origin of the increased ionic conductivity observed in the latter. Our measurements reproduce the previously reported high ionic conductivity and reveal that synthesis conditions significantly affect the Arrhenius pre-exponential factor governing ionic conductivity. Diffusion-controlled 7Li (and 31P) NMR spin relaxation rates confirm rapid, anisotropic lithium ion hopping that is characterized by timescale-dependent activation energies Ea ranging from 0.40 eV (long-range transport, as also seen by conductivity spectroscopy) to values down to 0.09 eV (local barriers).

Microrotating chemically reactive hybrid nanomaterial in a high porous medium influenced by Cattaneo-Christov double diffusion and non-linear slip

ABSTRACT A simultaneous heat and mass transfer due to microrotating Darcy-Forchheimer flow of hybrid nanofluid over a moving thin needle is investigated. Darcy-Forchheimer medium accommodating hybrid nanofluid flow yields greater heat transfer rate, thereby leading to greater mass transfer rate over thin needle in industrial applications such as blood flow problems, aerodynamics, transportation, coating of wires, lubrication, and geothermal power generation. The thermophoresis and Brownian motion phenomena are introduced to enrich thermal treatment. Heat and mass transfer are accompanied by Cattaneo-Christov heat and mass flux. The hybrid nanofluid is radiative and dissipative in nature. Arrhenius pre-exponential factor law is introduced. Entropy generation analysis is carried out. The 4th order Runge-Kutta method along with shooting technique is devised to get requisite numerical solution of the transformed non-dimensional system of equations. Darcy-Forchheimer effect to simultaneous heat and mass transfer of microrotating hybrid nanofluid flow over thin needle subject to non-linear slip is the novelty of present study which is beyond of previous investigations. Rise in Forchheimer number (strengthening Darcy Forchheimer medium) leads to surface viscous drag decreases by 11.11% for hybrid nanofluid and 10.78% for pure nanofluid indicating the control of momentum transfer, thereby regulating heat transfer rate effectively.

Local and Large-Scale Conformational Dynamics in Unfolded Proteins and IDPs. II. Effect of Temperature and Internal Friction.

Internal dynamics of proteins are essential for protein folding and function. Dynamics in unfolded proteins are of particular interest since they are the basis for many cellular processes like folding, misfolding, aggregation, and amyloid formation and also determine the properties of intrinsically disordered proteins (IDPs). It is still an open question of what governs motions in unfolded proteins and whether they encounter major energy barriers. Here we use triplet-triplet energy transfer (TTET) in unfolded homopolypeptide chains and IDPs to characterize the barriers for local and long-range loop formation. The results show that the formation of short loops encounters major energy barriers with activation energies (Ea) up to 18 kJ/mol (corrected for effects of temperature on water viscosity) with very little dependence on amino acid sequence. For poly(Gly-Ser) and polySer chains the barrier decreases with increasing loop size and reaches a limiting value of 4.6 ± 0.4 kJ/mol for long and flexible chains. This observation is in accordance with the concept of internal friction encountered by chain motions due to steric effects, which is high for local motions and decreases with increasing loop size. Comparison with the results from the viscosity dependence of loop formation shows a negative correlation between Ea and the sensitivity of the reaction to solvent viscosity (α) in accordance with the Grote-Hynes theory of memory friction. The Arrhenius pre-exponential factor (A) also decreases with increasing loop size, indicating increased entropic costs for loop formation. Long-range loop formation in the investigated sequences derived from IDPs shows increased Ea and A compared with poly(Gly-Ser) and polySer chains. This increase is exclusively due to steric effects that cause additional internal friction, whereas intramolecular hydrogen bonds, dispersion forces, and charge interactions do not affect the activation parameters.

Kinetic Study on Alkaline Hydrolysis of an Ester to Correlate the Solvent Effect with Some Thermodynamic Functions

In the present research paper, second-order rate constants for the alkaline hydrolysis of ethyl benzoate and of ethyl p-nitrobenzoate in ethanol–water mixtures in the ethanol mol fraction range 0.16–0.72 and at 278.15– 318.15 K measured by a specially developed titrimetric technique. The results show interesting variations in the rate constants with ethanol content at the various temperatures, especially over the mol fraction ranges 0.16–0.25 and 0.4–0.5. The rate constant (k2) data, the Arrhenius activation energy (EA) and preexponential factor (A) for ethyl benzoate and the parameters of the fitted polynomials from which other derived thermodynamic functions may be calculated are provided as supplementary material.

Impact of Cattaneo–Christov double diffusion theory and Arrhenius pre-exponential factor law on flow of radiative Reiner–Rivlin nanofluid over rotating disk

Reiner–Rivlin nanofluid flow due to rotating disk has significance in manufacturing of computer disks, pumping of liquid metals, spin coating, centrifugal machinery, turbo-machinery, crystal growth and rotational viscometer. In light of such real and relevant industrial applications, this study deals with the numerical investigation of unsteady rotationally symmetric flow of Reiner–Rivlin nanofluid over a stretchable rotating disk. The purpose of this investigation is to explore heat transfer characteristics of Reiner–Rivlin nanofluid subject to radial stretched surface implementable in several thermal systems. For facilitation of heat transport in complex thermal systems, mathematical models, such as Cattaneo–Christov, Buongiorno and nonlinear thermal radiation models, are assumed to be introduced. Runge–Kutta–Fehlberg technique along with shooting method is used for numerical computation of the transformed equations. It is captivating that radial and circumferential velocities decelerate with rise in Reiner–Rivlin and stretching strength parameters, respectively. Amplified thermal relaxation and Reiner–Rivlin parameters led to diminution of wall temperature gradient. Nanoparticle concentration profiles exhibit opposite behavior in response to escalation of activation energy and reaction rate parameters.

Detailed Understanding of Solvent Effects for the Cationic Ring-Opening Polymerization of 2-Ethyl-2-oxazoline

Polymerization of 2-ethyl-2-oxazoline (EtOx) has often been in the spotlight for fundamental studies of poly(2-alkyl/aryl-2-oxazoline)s (PAOx) polymerization, especially initiator screening, solvent screening, and copolymerization trends. In this work, we build on previous observations of solvent effects on the cationic ring-opening polymerization (CROP) of EtOx, with additional experimental observations of previously unreported solvents to expand the explored parameter space. Our objective is to find solvents with the lowest activation energy (Ea) and higher Arrhenius preexponential factor (A), which will allow us to produce narrow molar mass distributions at higher molecular weights, in the least time. To achieve this, we examined the various single factors like Dimroth ET(30) values, the Kamlet–Abraham–Taft (KAT) linear free-energy relationship (LFER) equation(s), and the Catalan LFER equations. Only one of Catalan’s equations sufficiently disentangled dipolarity and polarizability to give a good fit due to contradictory effects. It was found that solvent nucleophilicity, electrophilicity, and polarizability affected the Ea, but not dipolarity. All four factors affected the A. This indicates that the Ea is minimized in solvents that do not solvate ions well (i.e. force ion-pairing), and A was minimized in more dipolar solvents that solvate the polymer chains well. A strongly negative activation entropy (ΔS‡) shows that the propagation reaction is associative. The Catalan LFER allows for the prediction of Ea, A, ΔH‡, and ΔS‡, and the derived kp, across a broad range of solvents.

Evaluation of Oxidative Stability and Kinetic Parameters of the Cottonseed and Soybean Biodiesels by Rancimat and Differential Scanning Calorimetry Techniques

In this study, the oxidative stability of the cottonseed oil biodiesel (CB) and soybean oil biodiesel (SB) was investigated by two methodologies, Rancimat and Differential Scanning Calorimetry (DSC), using samples fresh and aged (mid-term storage condition (100 days)). The biodiesel samples were synthesized by transesterification and characterized by specific mass, kinematic viscosity, acidity value, ester content, viscosity index, and peroxide value. The activation energy (<em>E<sub>a</sub></em>), Arrhenius pre-exponential factor (<em>Z</em>), reaction order (<em>n</em>), and reaction rate at constant temperature (<em>k</em>(T)) were calculated by Borchardt and Daniels method. The results showed that oxidation affected the physicochemical properties of the biodiesel samples, especially, acidity (mg KOH/g), peroxide value (meq/1000 g), and induction period, with a decrease of around 55% for CB and 29% for SB. For kinetic parameters, the k(T) of both aged samples presented the highest values, with an increase of around 314% for SB. It was also observed that the rate constants increased with decreasing values of the induction period, in agreement with the current literature. According to the evaluation, the Borchardt and Daniels method can be recommended for a quick assessment of the biodiesel oxidation kinetic parameters.

Computing the Differences between Asn-X and Gln-X Deamidation and Their Impact on Pharmaceutical and Physiological Proteins: A Theoretical Investigation Using Model Dipeptides

Protein deamidation is a degradation mechanism that significantly impacts both pharmaceutical and physiological proteins. Deamidation impacts two amino acids, Asn and Gln, where the net neutral residues are converted into their acidic forms. While there are multiple similarities between the reaction mechanisms of the two residues, the impact of Gln deamidation has been noted to be most significant on physiological proteins while Asn deamidation has been linked to both pharmaceutical and physiological proteins. For this purpose, we sought to analyze the thermochemical and kinetic properties of the different reactions of Gln deamidation relative to Asn deamidation. In this study, we mapped the deamidation of Gln-X dipeptides into Glu-X dipeptides using density functional theory (DFT). Full network mapping facilitated the prediction of reaction selectivity between the two primary pathways, as well as between the two products of Gln-X deamidation as a function of solvent dielectric. To achieve this analysis, we studied a total of 77 dipeptide reactions per solvent dielectric (308 total reactions). Modeled at a neutral pH and using quantum chemical and statistical thermodynamic methods, we computed the following values: enthalpy of reaction (ΔHRXN), entropy (ΔSRXN), Gibbs free energy of reaction (ΔGRXN), activation energy (EA), and the Arrhenius preexponential factor (log(A)) for each dipeptide. Additionally, using chemical reaction principles, we generated a database of computed rate coefficients for all possible N-terminus Gln-X deamidation reactions at a neutral pH, predicted the most likely deamidation reaction mechanism for each dipeptide reaction, analyzed our results against our prior study on Asn-X deamidation, and matched our results against qualitative trends previously noted by experimental literature.

Benchmarking higher energy collision dissociation (HCD) by investigation of binding energies of gas-phase host-guest complexes of hemicryptophane cages.

Synthesis of host molecules that feature well-defined characteristics for molecular recognition of guest molecules is often a major aim of synthetic host-guest (H-G) chemistry. A key consideration in evaluating the selectivity of hosts and the affinities of guests is the measurement of binding energies of obtained H-G complexes. In contrast to nuclear magnetic resonance (NMR) or fluorescence measurements that are capable of measuring binding strengths in solution, mass spectrometry offers the opportunity to measure gas-phase binding energies. Presented in this article is a higher energy collision dissociation (HCD) approach for determining critical energies of dissociation of H-G complexes. Experiments were performed on electrospray ionization (ESI)-generated H-G pairs in an LTQ-XL/Orbitrap hybrid instrument. The presented HCD approach requires preliminary calibration of the internal energy distribution of generated ions that was achieved by the use of activation parameters that were known from previous low-energy collision-induced dissociation (low-energy CID) experiments. Internal energy deposition was modeled based on a truncated Maxwell-Boltzmann distribution and characteristic temperature (Tchar ). Using this method, critical energies of dissociation were determined for 10 H-G biologically relevant complexes of the heteroditopic hemicryptophane cage host (Host). Obtained results are compared with those found previously by low-energy CID. The use of this HCD technique is relatively straightforward, although its implementation does require knowledge (or a presumption) about the Arrhenius pre-exponential factor of the complexes to obtain their critical energies of dissociation.

Kinetic synergistic effect in co-pyrolysis of Eucalyptus globulus with high and low density polyethylene

The pyrolysis of Eucalyptus globulus (EG) with different blends of high density polyethylene (HDPE) and low density polyethylene (LDPE) by thermogravimetry has been studied. ASTM-E1641-16 standard method has been used to evaluate the kinetics during the pyrolysis of the studied blends. For all feedstocks (EG, HDPE and LDPE) and blends studied, the relative content (%) of the volatile organic compound has been determined by GC–MS analysis. Different synergistic effects on the activation energy of EG blends with HDPE and LDPE have been found. EG-HDPE blends showed a minimum activation energy (Ea) (125 kJ mol−1) at the 80% EG–20% HDPE ratio, while the minimum Ea value for EG-LDPE blends was found at the 60% EG–40% LDPE ratio (135 kJ mol−1) has been identified. To test which components exert a greater synergistic effect, mixtures of HDPE and LDPE with the main components of eucalyptus (cellulose, hemicellulose and lignin) have also been studied. However, no synergistic effects on the pyrolysis of cellulose have been detected. Moreover, in hemicellulose and lignin with both types of polyethylene mixtures, a significant decrease in Ea has been appreciated. The lowest Ea values for 60% cellulose–40% HDPE (167 kJ mol−1) and 60% lignin–40% HDPE (140 kJ mol−1) has been calculated. On the other hand, minimum values for 40% cellulose–60% LDPE (166 kJ mol−1) mixture and for 40% lignin–60% LDPE (168 kJ mol−1) mixture have been detected. Thus, the decrease in both Ea and the Arrhenius pre-exponential factor on the eucalyptus-polyethylene blends to the presence of hemicellulose and lignin can be attributed. Moreover, during the co-pyrolysis of HDPE-EG mixtures, n-paraffins, ketones, phenols and sugars are the main VOCs identified. In contrast, in LDPE-EG mixtures, only n-paraffins (55%) and olefins (44%) have been identified.

Hydrogen Tunneling in Catalytic Hydrolysis and Alcoholysis of Silanes

AbstractAn unprecedented quantum tunneling effect has been observed in catalytic Si−H bond activations at room temperature. The cationic hydrido‐silyl‐iridium(III) complex, {Ir[SiMe(o‐C6H4SMe)2](H)(PPh3)(THF)}[BArF4], has proven to be a highly efficient catalyst for the hydrolysis and the alcoholysis of organosilanes. When triethylsilane was used as a substrate, the system revealed the largest kinetic isotopic effect (KIESi−H/Si−D=346±4) ever reported for this type of reaction. This unexpectedly high KIE, measured at room temperature, together with the calculated Arrhenius preexponential factor ratio (AH/AD=0.0004) and difference in the observed activation energy [(E −E )=34.07 kJ mol−1] are consistent with the participation of quantum tunneling in the catalytic process. DFT calculations have been used to unravel the reaction pathway and identify the rate‐determining step. Aditionally, isotopic effects were considered by different methods, and tunneling effects have been calculated to be crucial in the process.

Hydrogen Tunneling in Catalytic Hydrolysis and Alcoholysis of Silanes.

An unprecedented quantum tunneling effect has been observed in catalytic Si−H bond activations at room temperature. The cationic hydrido‐silyl‐iridium(III) complex, {Ir[SiMe(o‐C6H4SMe)2](H)(PPh3)(THF)}[BArF 4], has proven to be a highly efficient catalyst for the hydrolysis and the alcoholysis of organosilanes. When triethylsilane was used as a substrate, the system revealed the largest kinetic isotopic effect (KIESi−H/Si−D=346±4) ever reported for this type of reaction. This unexpectedly high KIE, measured at room temperature, together with the calculated Arrhenius preexponential factor ratio (AH/AD=0.0004) and difference in the observed activation energy [(E aD −E aH )=34.07 kJ mol−1] are consistent with the participation of quantum tunneling in the catalytic process. DFT calculations have been used to unravel the reaction pathway and identify the rate‐determining step. Aditionally, isotopic effects were considered by different methods, and tunneling effects have been calculated to be crucial in the process.

PICNIK: A python package with isoconversional computations for non-isothermal kinetics

Isoconversional computations are widely-used methods to determine activation energies for thermally stimulated processes. pICNIK (python Isoconversional Computations for Non-Isothermal Kinetics) is an open-source module designed with the purpose of being a seed to a complete Python package to facilitate kinetic computations. It is object oriented with two classes: DataExtraction and ActivationEnergy. Five isoconversional methods were implemented: Friedmann's method, the Kissinger-Akahira-Sunose method, Ozawa-Flynn-Wall method, Vyazovkin and advanced Vyazovkin. This module allows to compute the activation energy from thermogravimetric data in minutes and the results can be exported as spreadsheet format or comma separated values files instead of traditional tedious and time consuming data processing. The module was validated with simulated data and two study cases: vaporization of n-decane and the thermal degradation of polypropylene. Program summaryProgram Title: pICNIKCPC Library link to program files:https://doi.org/10.17632/dpwtnmjpj5.1Developer's repository link:https://github.com/ErickErock/pICNIKCode Ocean capsule:https://codeocean.com/capsule/0740039Licensing provisions: MITProgramming language: PythonNature of problem: Numerical determination of the parameters of the Arrhenius function and the reaction model under the isoconversion hypothesis.Solution method: A Python module with implemented isoconversional methods. The algorithms implemented include several computations such as linear regressions, numerical integration and differentiation, and minimizing functions, all over several data sets.Additional comments including restrictions and unusual features: The initial data processing is focused on thermogravimetry and may not work for calculating conversion to other properties. However, the object-oriented implementation allows to overcome this limitation easily. Methods for calculating the Arrhenius pre-exponential factor and the reaction model remain to be implemented. It is a small module conceived to be further developed by the community. Another limitation of the code is that it does not include a graphical interface.

Significance of Buongiorno Model and Arrhenius Pre-exponential Factor Law to Entropy Optimized Darcy Forchheimer Hybrid Nanoparticle (Al₂O₃, Cu) Flow Over Thin Needle

In the fields of engineering, industry, and biology, thin needles serve a critical role. The thermocouple hot wire anemometer for wind speed monitoring, microscale heat extraction cooling systems, and electronic microstructure outfitting are only a few of the needle

Physical impact of double stratification in Darcy–Forchheimer hybrid nanofluid (Al2O3–Cu–H2O) subject to Arrhenius pre-exponential factor law and entropy generation

This thermal research communicates the thermal aspect of hybrid Casson nanofluid in the presence of entropy generation and double stratification. The contributions of Buoyancy force are studied through mixed convection. Darcy Forchheimer condition is also applied in momentum equation along with the effects of thermal radiation, viscous dissipation and convective condition. The flow is generated by stretching a thin needle. Double stratification effect is implemented in boundary conditions of the thermal and concentration equation. Transformations are implemented to form ordinary differential equations from partial differential equations. The shooting numerical method is used to find the solution of local similar expressions. The motion of the fluid slows down for higher Casson fluid parameter and Forchheimer number. The temperature shows the contrast behavior for Brinkman number and thermal relaxation parameter. Solutal relaxation parameter and thermophoresis parameter have opposite behavior for concentration parameter. The entropy generation enhances for Forchheimer number and Casson fluid.

Reduction and optimization for combustion mechanism of dimethyl ether–air mixtures

AbstractAs an alternative fuel, dimethyl ether (DME) has attracted much attention due to its high efficiency and low emission. In this study, first, a skeletal mechanism of DME is obtained using a directed relation graph with error propagation (DRGEP) and sensitivity analysis (SA). Then the Arrhenius preexponential factors of the selected reactions in the skeletal mechanism are adjusted by the particle swarm optimization (PSO) algorithm to improve the prediction accuracy. Finally, an optimized mechanism with 30 species and 65 elementary reactions is proposed to describe the combustion of DME–air mixtures. This reaction mechanism is validated against the experimental data of ignition delay time, species concentration, and laminar flame speed, covering a wide range of initial temperatures (298–1600 K), pressures (1.0–60 bar), and equivalence ratios (0.5–2.0). Comparing the previous skeletal mechanisms, the optimized mechanism can excellently reproduce the experiment results, especially in the prediction of the ignition delay time of low‐temperature zone and laminar flame speed of high‐pressure conditions. It means that this mechanism corresponds to higher precision and more extensive applicability.