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Homogeneous and heterogeneous reactions play a decisive role in biological procedures such as burning, polymer creation, ceramic construction, distillation, and catalysis. The magnetic properties of hemoglobin molecules are organic. Magnetic resonance imaging (MRI) and electronic components with an electromagnetic field are now readily available, allowing for the explanation of fundamental biological processes. These ideas form the foundation of an ongoing study that attempts to look into the impact of both homogeneous and heterogeneous reactivity on the peristaltic transport of magnetohydrodynamics Oldroyd-B fluid. When convective and partial sliding conditions are present, the configuration changes to a non-uniform vertical channel. The fundamental partial differential equations are resolved utilizing the Homotopy Analysis Method. Entropy optimization has been carried out. The primary limits entering the problem are investigated, and then a graph is used to show the influences of temperature, velocity, skin fraction, Nusselt number, and pressure increase against mean circulation, trapping phenomena, homogeneous reactions, and heterogeneous way to respond. When magnetic parameter rises, the velocity of Oldroyd-B fluid and Bejan number decrease, while temperature, entropy generation, and pressure gradient increase. The tables show that the skin friction coefficient rises for accumulative values of the Grashof number and magnetic parameter, while the skin friction coefficient drops for rising values of the velocity slip parameter and Reynolds number. The Nusselt number increases for large values of Eckert, Grashof numbers, and magnetic parameters.

In this paper, we establish a thermochemical ablation model of C/C composite based on the lattice Boltzmann method, in which the flow, diffusion, chemical reaction, heat transfer, and the evolution of solid phase are comprehensively considered. In the model, the flow, mass transport and heat transfer, chemical reaction, and the evolution of solid phase are addressed by the multiple relaxation time model, the single relaxation time model, boundary condition, and the volume of pixel method, respectively. Then, we research the ablation process of carbon fibers based on the pore-scale using this model, and we discuss the effects of temperature field, inlet temperature, inlet velocity, and inlet concentration. Numerical results indicate that H 2 O contributes more ablation than CO 2 . Without temperature source term, increasing inlet temperature, inlet velocity, and inlet concentration can accelerate ablation. [ABSTRACT FROM AUTHOR]

Experimental data are presented on the taper of silicon whiskers grown in an open chloride system. The whisker taper is shown to depend on the crystal growth rate, whisker radius and length, and process parameters. The experimental data are analyzed under the assumption that the size of the liquid droplet on the whisker tip decreases because of the heterogeneous chemical reaction responsible for the etching of the metallic component of the alloy. The influence of the crystal radius and vapor phase composition on the flux that leads to a decrease in the size of the liquid droplet. A model is proposed for whisker tapering as a result of the heterogeneous chemical reaction responsible for the etching of the metal on the surface of the liquid phase, and conditions for the growth of zero-taper whiskers are discussed. [ABSTRACT FROM AUTHOR]

The present paper aims at an upscaled description of coupled heat and mass processes during solid–fluid combustion in porous media using volume-averaging theory (VAT). The fluid flows through the pores in a porous medium where a heterogeneous chemical reaction occurs at the fluid–solid interface. The chemical model is simplified into a single reaction step with Arrhenius kinetic law, but no assumption of local thermal equilibrium is made. An array of horizontal channels is chosen for the microstructure. The corresponding effective properties are obtained by solving analytically the closure problems over a representative unit cell. For a range of Péclet and Δ numbers, the results of the upscaled model are compared with microscale computations found in the literature. The results show that, under the same circumstances, the upscaled model is capable of predicting the combustion front velocity within an acceptable discrepancy, smaller than 1% when compared to the analytical solution. Furthermore, it has been found that for the Péclet and Δ numbers considered in this study, the fluid concentration and temperature profiles that stem from the present upscaled model are in accordance with those obtained using a microscale model. [ABSTRACT FROM AUTHOR]

Supercritical CO2 (sCO2) Brayton cycles have gained interest in the frame of Sodium-cooled nuclear Fast Reactors (SFRs), as an alternative to the conventional water Rankine cycles. If CO2 leaks inside the CO2-Na heat exchanger, an underexpanded CO2-into-liquid-sodium jet is formed. CO2 chemically reacts with sodium, following an exothermic reaction which forms mainly solid products. In order to develop a model to numerically reproduce the jet development, a detailed description of the CO2-Na chemical reaction mechanism must be investigated. In this paper, a chemical reaction model at the dispersed phase scale between CO2-sodium, inside an underexpanded CO2-into-sodium jet, is presented. The model considers the reaction between a sodium droplet with the surrounding CO2 environment for the region close to the leakage, where mist flow is supposed to exist, and between a CO2 bubble with the surrounding liquid sodium environment for the region further downstream the leakage, where bubbly flow takes place. The depletion rate for a single particle (droplet or bubble) is determined, as a function of the main influencing parameters, such as temperature, droplet slip velocity, bulk mass fractions, and the chemical kinetics. [ABSTRACT FROM AUTHOR]

When the solid phase of a porous medium is a hydrate, bound water is chemically linked to the anhydrous solid molecule instead of being physically adsorbed. Consequently, its elimination does not consist of a continuous desorption but of a discontinuous succession of chemical heterogeneous dehydration reactions. It results in the appearance of successive plateaus in desorption isotherm curves but also in water content and temperature-drying kinetics and profiles of a hydrate. The writing of boundary conditions between the porous medium and its surroundings explains the origin of the dehydration plateau observed in convective-drying-temperature kinetics. [ABSTRACT FROM PUBLISHER]

An adjoint distributed mathematical model is proposed to describe the ignition and combustion of a magnesium particle with allowance for the gas area surrounding the particle. The combustion process is modeled within the framework of the single-phase Stefan problem. Verification of the model on the basis of available experimental values of ignition and combustion times under various conditions is performed. [ABSTRACT FROM AUTHOR]

A distributed two-dimensional mathematical model of ignition and combustion of magnesium particles with allowance for the heterogeneous chemical reaction and for the region of the thermal influence of the particle on the gas is developed. Problems of particle ignition under the action of uniform and nonuniform thermal fields in a rectangular microchannel are solved. [ABSTRACT FROM AUTHOR]

Pyrolysis of woody biomass was studied experimentally with the aim of investigating heat transfer and heterogeneous chemical reactions. In rapid pyrolysis, two different pyrolysis rates were obtained, with different reactions taking place depending on the temperature (a process producing gas and a process producing tar + water). However, the temperature at the transit stage between the two steps for gas differs from the temperature for tar + water. The fact means that there are two processes for gas generation. The experimental results obtained for slow pyrolysis showed that the average temperature in the biomass layer increased slowly as compared with the change in the set temperature. This tendency does not vary over a mean particle size range of 1.1 < Dp,50 (mean particle size) < 11 mm. Numerical simulation of heat transfer in a tubular reactor, without considering chemical enthalpy, was carried out. Comparison of the calculated results with the experimental heat flow rates in the biomass layer revealed two endothermic regions and two exothermic regions. The flow rate of gas generated in the reaction showed two peaks at the exothermic regions. Thus, it was concluded that heat transfer by pyrolysis consists of many processes. Furthermore, we propose a new mechanism representing the heterogeneous chemical reactions involved in pyrolysis, which is divided into four processes: (i) evaporation of water, (ii) decomposition of cellulose, (iii) decomposition of generated tar and (iv) decomposition of lignin. [ABSTRACT FROM AUTHOR]

A distributed mathematical model of ignition of a magnesium particle with allowance for the heterogeneous chemical reaction and the region of the thermal influence of the particle on the gas is developed. A solution of the problem in a steady formulation is found, which allows expanding the classification of the thermal history of the particle-gas system. A numerical model for solving the considered class of boundary-value problems of magnesium-particle ignition is proposed, and the mathematical model is verified in terms of the ignition delay as a function of the Nusselt number. A limiting size of the gas layer near the particle, which determines the ignition mode, is identified. Stability of some heating regimes to finite and infinitesimal disturbances is demonstrated. It is shown that the ignition process can be controlled by a high-frequency thermal action on unstable states of the particle-gas system. [ABSTRACT FROM AUTHOR]