Effects Of Mass Diffusion Research Articles

Entropy generation analysis of fuel premixed CH4/H2/air flames using multistep kinetics

The volumetric entropy generation rate distributions and exergy losses of premixed methane/air with hydrogen addition in a micro-planar combustor were numerically investigated. Detailed reaction mechanism for methane/hydrogen/air was considered. The analysis identified reactions contributing most of the entropy generated in combustion. The entropy generation rates due to the effects of chemical reaction, thermal conduction and mass diffusion are calculated based on the gas properties. A detailed parametric study of the influence of flow velocity and hydrogen mass fraction on the volumetric entropy generation rate is performed. With the increase of H2 addition to methane fuel, the entropy generation rates induced by thermal conduction and mass diffusion decrease, however, the chemical reaction induced entropy generation rate is less sensitive to H2 addition. The total entropy generation rate rises with the inlet velocity. The availability reduction by wall heat losses increases with increasing H2 addition and inlet velocity. The exergy efficiency remains nearly constant with H2 addition.

A Comparison of the Pyrolysis of Olive Kernel Biomass in Fluidised and Fixed Bed Conditions

The use of thermogravimetric analysis to describe biomass kinetics often uses bench top thermogravimetric analyser (TGA) analysers which are only capable of low heating rates. The aim of this research was to compare experimental fast pyrolysis of Olive kernels in a bespoke laboratory thermogravimetric fluidised bed reactor (TGFBR) characterised by rapid heating rates at high flow rates, compared to a smaller bench scale fixed bed TGA system. The pyrolysis in the TGFBR was analysed by using the isothermal kinetic approach and it was theorised that the pyrolysis decomposition reactions occurred by two mechanisms depending on the temperature, resulting in an activation energy of 67.4 kJ/mol at temperatures below <500 °C and 60.8 kJ/mol at temperatures >500 °C. For comparison, a bench scale TGA was used to look at the thermal behaviour in different fixed bed thermal conditions giving a higher activation energy of 74.4 kJ/mol due to the effect of external particle gas diffusion. The effect of biomass particle size (0.3–4.0 mm) on the conversion of biomass at different temperatures, was investigated between 300 and 660 °C in the TGFBR. The results suggested inhibition of internal gas diffusion was more important at lower temperatures, but in comparison had no significant effect when measured in the fixed bed TGA at lower heating rates. Bench top TGA analysis of pyrolysis is a rapid and valuable method, but is limited by smaller sample sizes and lower heating rates. In comparison, the conditions encountered with the laboratory scale TGFBR are more likely to be relevant to larger scale systems where heat distribution, heat transfer and mass diffusion effects play major roles in the reactivity of biomass.

Solutions with special functions for time fractional free convection flow of Brinkman-type fluid

The objective of this paper is to report the combined effect of heat and mass diffusion on time fractional free convectional incompressible flow of Brinkman-type fluid over an oscillating plate in the presence of first-order chemical reaction. The Laplace transform has been used to obtain the exact solutions for the fractional-order distributions. Exact expressions for temperature, concentration and velocity have been presented in terms of special functions. For instance, we presented temperature in terms of Wright function, concentration in the form of Fox-H function and velocity in terms of Mittag-Leffler and general Wright functions. The effects of various physical parameters on the fluid motion are sketched and discussed graphically. The present solutions have been reduced by taking one or more parameters approaching to zero and an excellent agreement is observed with the published work. The numerical results for skin-friction, Nusselt and Sherwood numbers have been shown in tabular form.

Different modes of reaction front propagation in n-heptane/air mixture with concentration non-uniformity

According to the reactivity gradient theory of Zel'dovich, the non-uniformity in temperature or concentration can lead to detonation development under certain conditions. In the literature, there are many studies on detonation development caused by temperature gradient or hot spot. However, the modes of supersonic reaction front propagation and detonation development regime caused by concentration non-uniformity have not been investigated previously. In this study, one-dimensional simulations were conducted to investigate the transient autoignition and reaction front propagation processes in n-heptane/air mixture with concentration non-uniformity. With the increase of equivalence ratio gradient, three modes (supersonic autoignitive reaction front, developing detonation and subsonic reaction front) of reaction front propagation induced by concentration non-uniformity were identified. The effects of heat conduction and mass diffusion on these three modes were examined and it was demonstrated that molecular diffusion has little influence on the first two modes. The detonation development regime caused by concentration non-uniformity was reported in this paper. This regime was found to be similar to the one caused by temperature gradient. A non-dimensional parameter was proposed to characterize the lower limit of the detonation regime. Furthermore, the effects of initial temperature on the detonation development regime were examined. It was found that the detonation development regime becomes wider as the initial temperature decreases. The initial temperature was shown to only have great impact on the upper limit of the detonation development regime while it has little influence on the lower limit. The influence of initial temperature was explained using the volumetric energy density of the mixture.

Combined Buoyancy Effects of Thermal and Mass Diffusion on Laminar Mixed Convection in Vertical and Horizontal Semicircular Ducts

The development of laminar mixed convection with heat and mass transfer in vertical and horizontal semicircular ducts has been investigated for the case of thermal boundary conditions of uniform heat input, concentration at the fluid–solid interface axially, and uniform peripheral wall temperature at any axial station. The governing equations were solved numerically over the following conditions: Pr = 0.7, Le = 1, Re = 500, Grt = 1.66 × 105, and Grc = 1.66 × 105. The combined effects of solutal and thermal Grashof numbers on the flow and thermal fields were observed in terms of the axial velocity, temperature, and concentration distributions, as well as, friction factor, Nusselt number, and Sherwood number. Further, the development of velocity, temperature, and concentration at different axial stations was found to be influenced by the solutal and thermal Grashof numbers. The results also showed that the forced-convection boundary layer development dominates very close to the duct inlet, while further downstream, the heat and mass transfer rates are enhanced due to the effect of solutal buoyancy.

EFFECTS OF NEWTONIAN HEATING AND MASS DIFFUSION ON MHD FREE CONVECTION FLOW OVER VERTICAL PLATE WITH SHEAR STRESS AT THE WALL

Effects of Newtonian heating and mass diffusion on magnetohydrodynamic free convection flow over a vertical plate that applies arbitrary shear stress to the fluid is studied. The fluid is considered electrically conducting and passing through a porous medium. The influence of thermal radiation in the energy equations is also considered. General solutions of the problem are obtained in closed form using the Laplace transform technique. They satisfy the governing equations, initial and boundary conditions and can set up a huge number of exact solutions correlatives to various fluid motions. The effects of various parameters on velocity profiles are shown graphically and discussed in details

Stagnation electrical MHD nanofluid mixed convection with slip boundary on a stretching sheet

In this study, the stagnation nano energy conversion problems have been completed for conjugate mixed convection heat and mass transfer with electrical magneto hydrodynamic (EMHD) and heat source/sink effects nanofluid flow field over a slip boundary stretching sheet surface. The physical phenomena varied which depended on different factors. All of the important nano energy conversion parameters S0, M, E, Gt, Gc, λ, Pr, Sc, Ncc, S and δ have represented the dominance of the magnetic energy effect, electric effect, mixed convection effect, heat generation/absorption energy effect, heat transfer effect, mass diffusion effect, heat conduction–convection effect and slip boundary effects, respectively. The similarity transformation and a modified Finite-Difference method are used to analyze the present nano energy conversion system's thermal energy conversion problem. The non-linear ordinary equations of the corresponding flow field momentum, temperature, concentration equations and plate sheet heat conduction equation are derived by employing the similarity transformation technology. The dimensionless non-linear ordinary equations are composed of momentum, temperature, concentration and plate sheet heat conduction equations which have been solved numerically by an improved finite difference technique.

Mixed convection flow over a slender cylinder due to the combined effects of thermal and mass diffusion

This paper deals with the similarity solution of double-diffusive mixed convection flow over a vertical slender cylinder due to the combined effects of thermal and mass diffusion. Local similarity method has been used to transform governing nonlinear partial differential equations into ordinary differential equations. With the help of a set of suitable similarity transformations, the nonlinear coupled partial differential equations governing select phenomena (such as flow, thermal and concentration field) have been reduced to a set of nonlinear coupled ordinary differential equations. Numerical solution of system of nonlinear ordinary differential equations are derived using an implicit finite difference scheme along with quasilinearisation technique. The significant observations of the study are as follows: 1) strong effect of buoyancy parameter λ on the flow and thermal field; 2) strong influence of Prandtl number (Pr) and Sherwood number (Sc) on heat transfer and mass transfer respectively.

Mixed convection flow over a slender cylinder due to the combined effects of thermal and mass diffusion

This paper deals with the similarity solution of double-diffusive mixed convection flow over a vertical slender cylinder due to the combined effects of thermal and mass diffusion. Local similarity method has been used to transform governing nonlinear partial differential equations into ordinary differential equations. With the help of a set of suitable similarity transformations, the nonlinear coupled partial differential equations governing select phenomena (such as flow, thermal and concentration field) have been reduced to a set of nonlinear coupled ordinary differential equations. Numerical solution of system of nonlinear ordinary differential equations are derived using an implicit finite difference scheme along with quasilinearisation technique. The significant observations of the study are as follows: 1) strong effect of buoyancy parameter λ on the flow and thermal field; 2) strong influence of Prandtl number (Pr) and Sherwood number (Sc) on heat transfer and mass transfer respectively.

The Approximate Analytical Solution of Non-Linear Equation for Simultaneous Internal Mass and Heat Diffusion Effects

For the first time a mathematical modelling of porous catalyst particles subject to both internal mass concentration gradients as well as temperature gradients, in endothermic or exothermic reactions has been reported. This model contains a non-linear mass balance equation which is related to rate expression. This paper presents an approximate analytical method (Modified Adomian decomposition method) to solve the non-linear differential equations for chemical kinetics with diffusion effects. A simple and closed form of expressions pertaining to substrate concentration and utilization factor is presented for all value of diffusion parameters. These analytical results are compared with numerical results and found to be in good agreement.

Generalized thermoelastic diffusion in a nanoscale beam using eigenvalue approach

In this paper, the effect of mass diffusion in a thermoelastic nanoscale beam in context Lord and Shulman theory is studied. The analytical solution in the Laplace domain is obtained for lateral deflection, temperature, displacement, concentration, stress and chemical potential. The both ends of the nanoscale beam are simply supported. The basic equations have been written in the form of a vector-matrix differential equation in the Laplace transform domain, which is then solved by an eigenvalue approach. The results obtained are presented graphically for the effect of time and mass diffusion to display the phenomena physical meaning.

Heating and evaporation of a new gasoline surrogate fuel: A discrete multicomponent modeling study

In Gasoline Direct Injection (GDI) engines, a fuel spray is injected directly into the cylinder during the compression stroke, creating a fuel–air mixture with an ignitable composition at the spark gap at the time of ignition. Spraying droplet breakup, heating and evaporation is essential for the mixture preparation and the ignition/combustion. For numerical modeling of spray evaporation and combustion, it is impractical to include all real components. In this study, a new 6-component surrogate mixture composed of i-pentane/n-heptane/toluene/iso-octane/n-propyl cyclohexane/iso-undecane is developed to match the targeted gasoline in terms of thermo-physical properties and experimental distillation curve. This new surrogate also covers TRF (toluene reference fuel) components, which are the three basic components for ignition modeling. This allows both physical and chemical modeling of gasoline using only one surrogate. This new surrogate fuel is implemented into an existing modeling methodology which simultaneously accounts for finite conductivity, finite mass diffusivity and turbulence effects within atomizing multicomponent liquid fuel sprays. The main purpose of this study is to perform analysis of heating and evaporation of the new surrogate gasoline. Both normal evaporation and flash boiling evaporating processes are investigated.

Mixed Convection Heat and Mass Transfer from a Vertical Surface Embedded in a Porous Medium

An analysis is performed to study the heat and mass transfer characteristics of mixed convection flow along a vertical flat plate embedded in a fluid-saturated porous medium under the combined buoyancy effects of thermal and mass diffusion. The plate is impermeable and is maintained at a uniform temperature/concentration. The boundary-layer partial differential equations are transformed into a set of nonlinear ordinary differential equations using a similarity transformation and then are solved numerically using the function bvp4c from MATLAB for different values of the governing parameters. Results show that dual solutions exist for a certain range of these parameters. Very interesting analytical solutions have also been included in the paper. The results have been compared with the ones from the open literature.

Combined Effect of Variable Viscosity and Variable Thermal Conductivity on Double-Diffusive Convection Flow of a Permeable Fluid in a Vertical Channel

This paper reports a detailed analytical and numerical investigation on free convection flow of viscous fluid through a porous medium due to the combined effects of thermal and mass diffusion. Effect of temperature-dependent viscosity and thermal conductivity is investigated in the presence of first-order chemical reaction. The non-Darcy model is applied to define the porous matrix. The effects of viscous and Darcy dissipations are taken into account. The governing equations of continuity, momentum, energy, and concentration which are coupled nonlinear ordinary differential equations are solved analytically using regular perturbation method and numerically using Runge–Kutta shooting method. Brinkman number and variable thermal conductivity parameters are used as perturbation parameters. The velocity, temperature, and concentration distributions are discussed numerically and plotted in graphs. The effects of variable viscosity parameter, variable thermal conductivity parameter, thermal Grashof number, mass Grashof number, Brinkman number, wall temperature ratio, and first-order chemical reaction parameter on the flow fields are explored. The effects of physical parameters such as skin friction and Nusselt number at both the plates are derived and discussed, and the numerical values for various values of physical parameters are presented in tables. The solutions obtained using Runge–Kutta shooting method and using perturbation method are compared and the solutions agree very well in the absence of perturbation parameter.

Entropy generation analysis of fuel lean premixed CO/H2/air flames

The volumetric entropy generation rate distributions and exergy losses of fuel lean premixed CO/H2/air flames are investigated numerically in a micro-scale cylindrical channel at atmospheric pressure. The numerical simulation predicts the gas properties such as temperature, density and species concentrations by the detailed gas phase chemistry and transport. The entropy generation rates due to the effects of chemical reaction, thermal conduction and mass diffusion are calculated based on the gas properties. A detailed parametric study of the influence of CO/H2/air flow velocity and CO mass fraction on the volumetric entropy generation rate is performed. The entropy generation rate induced by chemical reaction is suppressed by adding more CO to the mixture. However, higher thermal conduction induced entropy generation is inspected in the mixture with more CO. The total entropy generation rate rises with the inlet velocity. This is the first systematical analysis of the volumetric entropy generation rates distributions of CO/H2/air flames in the micro channel. The analysis could be applied to other power conversion systems which utilize CO/H2/air mixture.

BUOYANCY EFFECTS OF THERMAL AND MASS DIFFUSION ON MHD NATURAL CONVECTION PAST FINITE VERTICAL, POROUS FLAT PLATE

The flow of an electrically conducting incompressible fluid due to buoyancy effects of thermal and mass diffusion past a finite vertical porous plate with constant suction was investigated in the presence of uniform transverse magnetic field. The problem has been solved for velocity, temperature and concentration profiles. The equations governing the flow are solved numerically using finite difference method for various values of Grashof parameter ranging from 0 to - 1. The results obtained are then presented using tables and graphs. It was noted that a decrease in Grashof parameter leads to an increase in primary, secondary, temperature and concentration profile.

Magnetic field effect on heat and mass transfer of mixed convection of shear-thinning fluids in a lid-driven enclosure with non-uniform boundary conditions

In this paper, the effect of a magnetic field on mixed convection of shear-thinning fluids in a square lid-driven cavity with sinusoidal boundary conditions under the combined buoyancy effects of thermal and mass diffusion has been analyzed by finite difference lattice Boltzmann method (FDLBM). This study has been conducted for the certain pertinent parameters of Richardson number (Ri = 0.00062–1), Hartmann number (Ha = 0–100), Lewis number (Le = 5 and 50), power-law index (n = 0.2–1) as the buoyancy ratio is studied from N = −10 to 10. Results indicate that the augmentation of Richardson number causes heat and mass transfer to drop. The enhancement of Hartmann number declines heat and mass transfer for multifarious buoyancy ratios and power-law indexes steadily at Ri = 0.00062 and 0.01. The fall of the power law index declines heat and mass transfer at Ri = 0.00062 and 0.01 for various Hartmann numbers and buoyancy ratios. The increase in power-law index and Hartmann number influence heat and mass transfer differently at Ri = 1 for various buoyancy ratios and Lewis numbers. The growth of Lewis number enhances mass transfer for the studied Hartmann numbers and buoyancy ratios.

Topological disorder of microstructure in fiber-reinforced polymer composites: Diffusion response

Influence of microarchitectural fiber matrix arrangement in representative volume element is studied to assess the effect of mass diffusion in the fiber-reinforced polymer composites. A novel approach has been proposed to illustrate the quantitative definition of the representative volume element heterogeneity using topological descriptor of clustering. Average fiber center distance from the fixed representative volume element center is described to compute the clustering in different representative volume elements, followed by finite element method simulation to model and visualize two-dimensional microstructures of fiber-reinforced matrix composites with moisture boundary conditions. The suggested topology descriptor shows good correlation with diffusion response in relation to saturation time, whereas a fair degree of correlation was observed for mass accumulation and mass flux characteristics. The results indicate that microstructural heterogeneity has a strong influence on typical moisture diffusion characteristics and hence, an overall diffusion-induced damage. The observations should serve as a clue to design the fiber-reinforced polymer composites with the moisture barrier properties.

Transverse Vibrations in Thermoelastic-Diffusive Thin Micro-Beam Resonators

This article deals with the transverse vibrations in a homogeneous isotropic, thermoelastic-diffusive thin beam based on the Euler–Bernoulli theory under clamped–clamped boundary conditions. The analytical expressions for deflection, thermal moment, mass moment, frequency shift, and damping due to thermoelastic-diffusion in the beam has been derived. The effects of mass diffusion, thermomechanical coupling, surface conditions, and beam dimensions on energy dissipation and other field quantities induced by thermoelastic-diffusion have been investigated. The analytical results have been numerically analyzed with the help of MATLAB software. The numerically computed results for deflection, temperature change, thermal moment, mass moment, damping factor, and frequency shift have been presented graphically. The computed values of effective flexural rigidity have been given in tabular form. The study may find applications in medical science, engineering, accelerometers, sensors, resonators, etc.

Mesoscopic simulation of magnetic field effect on double-diffusive mixed convection of shear-thinning fluids in a two sided lid-driven cavity

In this paper, the effect of magnetic field on mixed convection of shear-thinning fluids in a square two sided lid-driven cavity under the combined buoyancy effects of thermal and mass diffusion has been analyzed by finite difference lattice Boltzmann method (FDLBM). This study has been conducted for the certain pertinent parameters of Richardson number (Ri=0.00062–1), Hartmann number (Ha=0–90), Lewis number (Le=5 and 10), power-law index (n=0.2–1) as the buoyancy ratio is studied from N=−20 to 20. Grashof number is fixed at Gr=100 in this study. Results indicate that the augmentation of Richardson number decreases heat and mass transfer. The enhancement of Hartmann number declines heat and mass transfer for multifarious buoyancy ratios and power-law indexes. The fall of the power law index declines heat and mass transfer at Ri=0.00062 and 0.01 for various Hartmann numbers and buoyancy ratios. The power-law index change influences heat and mass transfer differently at Ri=1 for various buoyancy ratios, Lewis and Hartmann numbers. The growth of Lewis number enhances the mass transfer for the studied Hartmann numbers and buoyancy ratios. The rise of Hartmann number decreases the effect of power-law index on heat and mass transfer gradually.