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The computational study reported here is motivated by a desire to develop a computer model for predicting and analyzing experimental screen collection efficiency of wire-mesh filters for microparticles (up to 100 µm). The operational parameters include the particle size of 0.3 to 100 μm, screen opening size of 11 to 160 μm, fiber diameter of 33 to 60 μm and superficial velocity of 0.48 cm/s. We use a simplified 2-D model with the hybrid lattice-Boltzmann Lagrangian method to describe flow crossing a single fiber in a periodic cell of a wire screen. The newly proposed formula of the screen collection efficiency representing particle deposition on two crossed fibers in each screen cell effectively predicts the experimental data with good accuracy. The quality factor analysis that determines a filter performance is adopted to evaluate the interplay between the energy needed for gas transport and collection efficiency. In addition, the detailed analyses are given for particle deposition pattern and transport behavior in terms of particle fraction profiles and flow fields. Finally, the degree of individual forces acting on each particle traveling in the gas flow is revealed. Copyright © 2022 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

While previous experimental studies revealed the existence of optimal heat transfer performance in natural convection of magnetohydrodynamic (MHD) nanofluid flows, it is believed that this phenomenon is not unique in different levels of magnetic flux density. In order to prove this speculation, we numerically investigate the influence of the magnetic field on steady natural convection of aluminum-oxide (Al2O3) nanofluids inside an enclosure. The MHD flow model without the consideration of nanofluids is well validated against theoretical, numerical, and experimental results. The nanofluid in the present investigation has temperature-dependent physical properties and is modeled by a two-phase mixture considering thermophoresis and Brownian diffusion. While varying the volume fraction of nanoparticles from 0 to 6%, we methodically examine the effect of the Hartmann number on the heat transfer performance through the thermal behavior map in terms of the Hartmann–Rayleigh plane. Depending on the combination of magnetic intensity and buoyancy-induced flow, the nanofluid heat transfer with the addition of various concentrations of nanoparticles can be categorized into two patterns separated by a critical Hartmann number: the presence of a maximum Nusselt number (Type A) and continuously increased heat transfer rates (Type B) over a wide range of the Rayleigh number from 103 to 106 and the Hartmann number from 0 to 300. Described by a piecewise-defined function, the critical Hartmann number is exponentially proportional to the Rayleigh number from 104 to 106 and rises linearly in a logarithmic scale with elevating the Rayleigh number from 103 to 104. [ABSTRACT FROM AUTHOR]

Mechanism and kinetics of the thermal pyrolysis of ethyl 2‐furoate were studied in a wide range of conditions (ie, 500‐1500 K and 1‐7600 Torr) using the accurate dual‐level theory CCSD(T)&MP2(FC)//B3LYP/aug‐cc‐pVTZ and state‐of‐the‐art Rice‐Ramsperger‐Kassel‐Marcus based master equation rate model including hindered internal rotation and tunneling treatments. The predicted rate coefficients are found to be in accordance with the experimental data. The mechanism details are revealed as (i) the major decomposition channel occurs via a six‐center transition state with the barrier energy of 48.3 kcal/mol at 0 K, leading to the formation of C2H4 and 2‐furoic acid and (ii) pressure has a slightly positive effect on the rate constant, particularly at the high temperature. Also, the reactivity of ethyl 2‐furoate toward OH radicals was discussed in the first place. [ABSTRACT FROM AUTHOR]

Branched-chain fatty acid methyl esters (FAME), known for cold flow improvers for biodiesel, have received less attention to their chemical kinetics in flames. This study proposes a detailed mechanism reduced to be a compact form to predict the formation of non-fuel small hydrocarbons and light-weight polycyclic aromatic hydrocarbons (PAH) from the oxidation of methyl isobutanoate [MIB, (CH 3) 2 CHC(=O)OCH 3 ], a C5-branched methyl ester. Using the path flux analysis, the newly constructed MIB oxidation mechanism with 344 species and 2147 reactions is shrunk and refined to 63 species and 288 reactions, a minimum size for its application to computational fluid dynamics. The minimized MIB mechanism incorporated into a 2D axisymmetric coflow model is used to validate mass-spectrometric data obtained from a laminar coflow diffusion flame of methane doped with MIB. For the first time, ten experimentally measured centerline profiles in the flame are computationally interpreted by nine C3–C6 unsaturated hydrocarbons, three carbonyls and four aromatics. Furthermore, we analyze the spatial distribution of the investigated intermediates and reveal their corresponding reaction pathways linked to the MIB decomposition. • Compact kinetic mechanism for methyl isobutanote oxidation is proposed. • CFD coupled with the kinetic mechanism describes chemistry in a nonpremixed flame. • Non-fuel hydrocarbons measured by mass-spectrometry are modeled for the first time. • Reaction pathway analyses elucidate abundant formation of aromatics correlated with the fuel. [ABSTRACT FROM AUTHOR]

Transport of aerosol particles is a fundamental phenomenon in many environmental and industrial applications. Among the several computational fluid dynamical schemes used to study this problem, the lattice Boltzmann methods (LBMs) have shown great promise. Using a 2-D LBM model coupled with a Lagrangian formalism, this study investigates an early stage of particle–surface collisions in a free-stream flow over a semi-infinite array of staggered obstructions at operating conditions of woven-wire screens. After an initial validation of the model, the particle–surface collision efficiency with different diameters is then examined as functions of the number of staggered obstructions, obstruction morphology, and separation distance between two center points of obstructions. Particle motion mechanisms include drag, lift, and Brownian forces. Enhanced collision efficiency of particles to obstructions due to the presence of multiple staggered cylindrical obstructions is identified and highlighted. Based on these insights, our work also explores the possibility that collision efficiency of particles to obstructions can be enhanced by a change of obstruction morphology. Finally, the results highlight the range where particle–surface collision efficiency is sensitive to the longitudinal spacing between two cylindrical obstructions. Copyright 2014 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

A chemical kinetic submechanism proposed here is an essential prerequisite to model autoignition of methyl esters at low temperature region (less than ∼900 K), where reactions of methyl-ester peroxy radicals (ROO∙) and hydroperoxy methyl-ester radicals (Q∙OOH) are crucial and relatively unexplored. The potential energy surfaces of the methyl butanoate peroxy radicals + O2 systems are computed by the G3MP2B3 composite approach. 114 pathways are identified leading to the formation of key radicals in the ignition kernel such as OH and HO2. Particular attention is focused on: (1) intramolecular H-migration of ROO∙, (2) unimolecular dissociations of ROO∙ and Q∙OOH and (3) reactions of ROO∙ + HO2. Using the canonical transition state theory, the high-pressure limit rate constants for reactions in the kinetic submechanism are calculated. Standard enthalpy of formation, entropy and heat capacities are evaluated for intermediates and products formed during combustion by means of the standard statistical mechanics formulae. The agreement and disagreement between our calculated kinetic parameters and previous estimates offer further insight into the uncertainty associated with theoretical estimation. We perform the branching ratio analysis for the competing channels between the reverse dissociation of ROO∙ (ROO∙ → R∙ + O2) and explored unimolecular reactions decomposing ROO∙. Additionally, we also quantify the similarity and dissimilarity between the rate constants determined here and those previously calculated for normal alkanes. Finally, the effect of transition state size on the rate constants for the isomerizations of methyl-ester peroxy radicals is systematically analyzed. [ABSTRACT FROM AUTHOR]

In an attempt to construct detailed kinetic mechanisms for biodiesel fuels on the fly, high-pressure rate rules for the concerted HO 2 elimination reaction class were derived using a comprehensive training reaction set of more than 60 reactions involving different alkyl methyl/ethyl ester peroxy radicals (RCOOR')-OO • . Using the composite electronic structure method CBS-QB3 in combination with classical statistical mechanics and the transition state theory (TST) rate model, high-pressure rate constants for the reactions in the training set as well as thermodynamic properties for the species involved were calculated. The corrections from Eckart tunneling and hindered internal rotation (HIR) treatments were also included in the calculations. The results reveal that the ester group (-COO-) selectively promotes the reaction when compared with the traditional hydrocarbon fuels; thus it is recommended that the seven derived rate rules for the title reaction class (including the thermodynamic data of the species involved in the NASA format) should be used for construction of detailed kinetic mechanisms for real biodiesel molecules.