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This work studied a multistage gasification system that is designed for producing a syngas with a low tar content. The proposed system is an atmospheric bubbling fluidized-bed gasifier and comprises mainly pyrolysis, combustion, and gasification zones. The numerical investigation is performed using Aspen Plus to study Prosopis Juliflora gasification. Chemical reactions as well as tar treatment in the process are investigated. Two different pyrolysis temperatures were considered: 500 and 600 °C, along with three different particle size ranges: 0.2-0.5, 0.5-1, and 1-2 mm. The effect of the air-to-biomass ratio, with values from 0.2 to 1.2, and the gasification reactor temperature, from 800 to 1000 °C, on the composition of product gas and tar species formation during the process (phenol, naphthalene, benzene, and toluene), its lower heating value (LHV), and cold gasification efficiency (CGE) were studied. Results showed that a pyrolysis temperature of 600 °C and a particle size range of 0.2-0.5 mm displayed less tar produced from both combustion and gasification zones and were associated with greater CO, H

This study presents a two and three-dimensional numerical simulations of a flow-through a sudden expansion and contraction microchannels. The finite element method was used to discretize the equations governing the physical model. By carrying out the numerical simulations, results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the microchannel for low Reynolds numbers. For high values of Reynolds number and expansion ratios, the vortex separation length increases. Also, the three-dimensional character of the flow is more pronounced for higher Reynolds numbers.

This study presents 2-D simulations of a flow-through a sudden expansion/contraction micro-channel with the existence of obstacles. The bottom wall is maintained at constant flux, while the other walls are adiabatic. Rectangular adiabatic obstacles are mounted before the expansion region on the upper and lower wall of the channel used. The finite element method was used to discretize the equations that govern the physical model. Results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the micro-channel for low Reynolds numbers. For higher values and expansion ratios, the vortex separation length increases. The obtained results show that the obstacles have a considerable effect on the dynamics of the flow and enhancement of heat transfer.

The electro-thermo-convection in a square cavity with incorporated hot solid body is numerically investigated. The finite volume method associated with Patankar’s “blocked-off-regions” technique is applied. A potential difference is applied between the hot obstacle and the horizontal walls in order to eliminate the so-called dead zone created at the bottom of the cavity. The flow movement is induced not only by thermal buoyancy forces but also by the electric Coulomb force. Calculations are made for several injection levels (1 ≤ C ≤ 10), various obstacle shape factors (1 ≤ l/w ≤ 9), different number of electric Rayleigh (0 ≤ T ≤ 800), multiple thermal Rayleigh numbers (2000 ≤ Ra≤ 30,000) and 03 obstacle positions. The results show that according to the intensity of the applied electrical forces, two types of regimes are identified: a thermally dominated regime characterized by a low heat exchange at the bottom of the obstacle and conversely an electrically dominated regime with an excellent heat exchange over the entire cavity. It has been demonstrated that it is possible to improve the heat transfer up to: 43% by changing the shape factor of the obstacle; 82% by varying the injection level and 532% by applying electrical forces.

The performance enhancement of an electrothermal effect-based biosensor is studied numerically in this research. Indeed, the study of a microfluidic biosensor is used to detect the C-reactive protein into a microchannel with considering electrothermal effect. In the presence of the electrical field, the produced Joule effect gives rise to a temperature gradient and causes homogeneities of electric permittivity and conductivity allowing the generation of flow motions. To improve the rate of reactant ransport via an on-surface-reaction in the microchannel, various pairs of electrodes under Alternating current (AC) are used and the effects of different arrangements and positions on flow structure, temperature and concentration fields, were investigated. In addition, the comparison with earliest results shows a good agreement.

The problem of electroconvection in an annular space between two elliptical concentric cylinders filled with a dielectric liquid and subjected to internal unipolar injection is considered. A finite volume method is used to solve the governing equations, including the Navier–Stokes ones and a simplified set of the Maxwell equations. For the first time the whole set of these coupled equations is solved, using the elliptical-cylindrical coordinates. We first validate numerical simulation in this field by comparing the results obtained with those available in the literature. The numerical solution of the electroconvection problem is then followed by a detailed analysis of the flow structure and electric charge distribution. It is shown that the multicellular convective pattern is observed. It is noticed that unipolar charge injection from the internal electrode significantly changes the topology of the fluid flow. Finally, the influence of various system parameters, such as the injection level and electric Rayleigh number, is also investigated.

A new three-stage biomass gasifier is proposed to generate product gas with low tar content. The first stage is dedicated for biomass pyrolysis. While the main roles of the second and third stages, which are superposed and separated by a gas distributor plate, are product pyrolysis gases combustion and gasification, respectively; noting that gasification is realized in a fluidized bed. In order to study and improve the process fundamentals, a cold flow model is developed to understand system dynamics and parameters. A computational fluid dynamics (CFD) study has been conducted using the Eulerian-multiphase model approach applied within the combustion and gasification zones. A complete CFD simulation of flow through the gas distributor is realized. Three values of the distributor perforated area: 1%, 3% and 5% and three bed materials were investigated to study the effect of the solid density and particle size on the fluidized bed. The aim of this work is to study the effect different parameters such as the distributor design, gas flow rate, fluidization velocity, solid density and solid particle size. In this work, gas and solid velocities above the distributor, pressure drop across the distributor, distributor to bed pressure drop ratio, solid volume fraction, bed pressure drop and the bed expansion ratio have been examined. Results show that the perforated area of a distributor has a great influence on the uniformity of the fluidization. The hydrodynamics of solid-gas fluidized beds are shown strongly affected by the gas flow rate and the properties of the bed material.

A multistage atmospheric fluidized bed gasifier was developed using the Aspen Plus simulation process. The innovative gasification reactor aims to yield a high-quality product gas as it conducts pyrolysis, combustion, and reduction in different zones. In addition, it uses gas as a heat carrier and has a fluidized char bed in the reduction zone to enhance the in-situ tar reduction. In order to study the feasibility of the gasifier, an evaluation of the product gas and the process efficiency is required. The proposed model was based on the reaction rates and hydrodynamic parameters of the bubbling bed. Four different stages were initially considered in the simulation process: decomposition of the feed, partial volatile combustion, char reduction, and gas solid separation. The gasification reactor was operated over a temperature range of 800&ndash, 1000 &deg, C and an isothermal combustion reactor was operated at 1000 &deg, C. In addition, the air to biomass mass ratio was varied from 0.2 to 0.5. It has been validated and displayed very good agreement with published data. Effects of gasification reactor temperature, air to biomass ratio, and gasifier dimensions on the composition of product gas were investigated Results showed that the principal component is CO and its concentration in the product gas increases with increase in gasifier temperature but decreases with increasing air to biomass ratio. The results also gave a relatively high value of the lowered gas caloric value and acceptable cold gas efficiency which help the sizing of gasifiers and the choice of optimal operating conditions.

This work presents a three-dimensional numerical study on double-diffusive natural convection in a cubic cavity filled with a micropolar fluid. The flow is driven by buoyancy forces due to temperat...

Purpose The purpose of this work is to highlight the effects of partial unipolar injection on electro-thermo-convection (ETC) in dielectric liquid contained between two eccentric cylinders. Design/methodology/approach A finite volume method was used to solve governing equations. The study is performed for different parameters, such as radius ratio (0.2 ≤ Γ ≤ 0.6), dimensionless electric Rayleigh number (0 ≤ T ≤ 900), eccentricity (−0.4 ≤ e ≤ 0.4) and thermal Rayleigh number (10 ≤ Ra ≤ 5.105). Findings It is found that heat transfer increases with increase in dimensionless electric Rayleigh number and eccentricity ratio. Originality/value The originality of this work is to analyze the ETC in dielectric liquid subjected to partial unipolar injection between two eccentric cylinders

Effect of magnetic field on combined surface tension and buoyancy convection in an enclosure with partially active vertical walls is investigated numerically. The active part of the left side wall is at a higher temperature than the active part of the right side wall. The bottom and the inactive parts of the side walls are adiabatic and capillary forces occur at the top free surface. The governing equations are discretized by the finite volume method. The results are obtained for Pr = 0.054, 0 ? Ha ? 100, 0 ? Ma ? 10000, and 2.104 ? Gr ? 2.106. The flow structure and temperature field were presented by streamlines and isotherms respectively. The surface tension effect of is manifested by increasing Marangoni number. The application of magnetic field was found to control the flow and to oppose the capillary effects.

A computational study has been performed to see the heat transfer intensification induced by electrically generated convection in a two co-focal elliptical cylinder layers for dielectric liquid. Temperature of the inner cylinder is higher than of outer one. Finite volume method is used to solve the governing equations by writing a homemade computer code. The study is performed for dimensionless electric Rayleigh number (0 ≤ T ≤ 700), Rayleigh numbers (102≤ Ra ≤105), eccentricity ratio (0.4 ≤ e ≤ 1). It is observed that the unipolar charge injection by the internal electrode changes significantly the topology of the fluid flow. Moreover, the computations highlight an important effect of the eccentricity value on the intensity and circulation cell number. Finally, it is found that heat transfer is improved with increasing dimensionless electric Rayleigh number.

In this paper, the effect electric field on the flow induced by the combined buoyancy and thermocapillary forces is carried out. Calculations are performed for a strong unipolar injection (C = 10) and different values of Marangoni number (−10000 ≤ Ma ≤ 10000), thermal Rayleigh number (5000 ≤ Ra ≤ 50,000) and electric Rayleigh number (0 ≤ T ≤ 800). The Prandtl number (Pr) and the mobility parameter (M) are fixed at 116.6 and 49, respectively. These values correspond to the Silicone oil used as working liquid several practical applications. The full set of coupled equations: Navier–Stokes, Electro-hydrodynamic (EHD) and heat transfer equations are directly solved using stream function-vorticity formalism. Obtained results show that the electric forces can control the thermocapillary instabilities. According to the intensity and the direction of the applied electric forces, it is demonstrated that these instabilities can be accentuated, attenuated, or even completely eliminated.

The kinetics of antigen–antibody binding reaction, in the electrokinetically controlled microfluidic heterogeneous immunoassays, have been numerically simulated and discussed. The aim of this study is to demonstrate how to model phenomena defined in different 2D and 3D dimensions in a fully coupled manner using COMSOL Multiphysics. Moreover, we explain how to examine a convection-diffusion phenomenon present in a 2D domain (respectively 3D) coupled to diffusion-reaction phenomenon which is occurring only on a 1D boundary of this same area (respectively 2D). In our developed model, microfluidic networks for surface immunoassays were used. Antibodies, immobilized on one wall of a microchannel, absorb the employed analytes. The reaction rates in the modification area function of the reactants' concentration in the phase that transports the chemicals. Nevertheless, for surface reactions it is necessary to highlight the surface concentrations of the active sites and surface adsorbed species. The obtained results show that the increase of the concentration can reduce the growth of the diffusion boundary layer and raise the biosensor performance. Finally, the 2D simulations are described as crucial in predicting more accurate results.

Numerical simulations of the cold flow of a gas–solid mixture in a G-Volution circulating dual gasification reactor are conducted by using the commercial software package ANSYS FLUENT. Isothermal non-reactive, turbulent, unsteady gas–solid flow is assumed and the Eulerian–Eulerian fluid model is adopted. The effect of restricted cross sections on the pressure gradient and the solids holdup in the fuel reactor of this Circulating Fluidized G-Volution Gasification dispositive is investigated. Computation of the reactor without internals is also conducted for comparison. In addition, segregation in a fluidized binary biomass –sand bed is considered for different inlet velocities.

A computational study has been performed to investigate the effects of partially active magnetic field on natural convection heat transfer in CNT-nanofluid filled and three-dimensional differentially heated closed space. Two cases are considered to see this effect as magnetic field is applied to upper half (Case I) and lower half (Case II) while remaining walls are insulated. The finite volume method is used to solve governing equations and results are obtained for different governing parameters as Hartmann number (0 ≤ Ha ≤ 100), nanoparticle volume fraction (0 ≤ φ ≤ 0.05) and height of the active zone (0 ≤ L B ≤ 1). It is found that location of magnetic field plays an important role even at the same Hartmann number. Thus, it can be a good parameter to control heat and fluid flow inside the closed space.

Entropy generation inside an inclined cubical differentially heated cavity filled with CNT-water nanofluid is evaluated numerically using FVM based on 3D vorticity-vector potential formalism. A conductive Ahmed body is incorporated at the center of the enclosure. The effects of several parameters such as Rayleigh number (10 3 ≤ Ra ≤ 10 5 ), volumetric fraction (0 ≤ φ ≤ 0.05) of nanoparticles, angle of inclination of cavity (0° ≤ α ≤ 180°) and thermal conductivity ratio (0.01 ≤ R c ≤ 100) on entropy generation are analyzed. The results are elucidated with local and total entropy generations and Bejan number. Entropy generation increases when Raleigh number increases due to buoyancy. Entropy declines when the inclination angle is increased up to 90°, after that entropy generation surges.

A computational analysis has been performed in this work to solve three-dimensional magnetohydrodynamic natural convection in an open cubical enclosure filled with CNT-water nanofluid. The cavity is heated from left vertical wall and an inclined plate is attached inside the cavity with finite length. The study is solved for different governing parameters as Rayleigh number (10 3 ≤ Ra ≤ 10 5 ), nanoparticle volume fraction (0% ≤ φ ≤ 5%), Hartmann number (0 ≤ Ha ≤ 100) and inclination angle of the fin (0° ≤ θ ≤ 360°). It is observed that all of these parameters can be used as passive control element for heat and fluid flow and the maximum heat transfer is formed when θ = 180° but minimal value of average Nusselt number is changed according to nanoparticle addition into base fluid.

Three-dimensional computational analysis of entropy generation due to natural convection in partially open enclosure has been performed in this work by using finite volume method. A written computer code was developed to solve governing equations of this three-dimensional problem. The study has been performed for different governing parameters such as opening ratio 0. 25 ≤ h ≤ 0.75, center of opening 0.25 ≤ d ≤ 0.75 and Rayleigh number 10 3 ≤ Ra ≤ 10 5 . It is observed that edge of openings is the most effective parameter on entropy generation and after comparing many cases, both the highest heat transfer and entropy generation were observed for the fully opened cavity.

Three-dimensional natural convection in an inclined solar collector equipped with partitions has been investigated numerically. The presence of partitions improves the performances of the collector by increasing the heat transfer near the absorber. A parametric study was done for various partitions length and Rayleigh numbers, while Prandtl number and inclination angle were fixed at 0.71 and 45°, respectively. Results are reported in terms of isosurfaces of temperature, isotherms, particles trajectories, velocity vector projection, average Nusselt number along the absorber plate and entropies generation contours.

A computational study has been performed to see the effects of electro-thermo-convection induced via a strong unipolar injection between two concentric or eccentric cylinders using the finite volum...

A numerical study of the 3D double-diffusive natural convection in an inclined solar distiller was established. The flow is considered laminar and caused by the interaction of thermal energy and the chemical species diffusions. The governing equations of the problem, are formulated using vector potential-vorticity formalism in its three-dimensional form, then solved by the finite volumes method. The Rayleigh number is fixed at Ra=105 and effects of the buoyancy ratio and inclinationare studied for opposed temperature and concentration gradients. The main purpose of the study is to find the optimum inclination angle of the distiller which promotes the maximum mass and heat transfer.

In this work, the heat and mass transfers in 3D lid driven cavity is analyzed. Double-diffusive convective flow in a cubic enclosure with moving left side in −y (Case I) or +y (Case II) directions is studied numerically. The cavity is heated from left side and cooled from right and constant different concentration is imposed, while remaining surfaces are adiabatic. The FVM based on the 3D vector-potential – vorticity formalism is used as numerical method. Prandtl number and Lewis number are fixed at 10, 0.7 and 2, respectively. The study covers a wide range for Richardson number 0.1 ≤ Ri ≤ 10 and Buoyancy ratio −10 ≤ Ri ≤ 10. Results are presented by particle trajectories, isotherms, Iso-concentration and local and mean Nusselt and Sherwood numbers.

In the present work, the effect of magnetic field on double diffusive natural convection in a cubic cavity filled with a binary mixture is numerically studied using the finite volume method. Two vertical walls are maintained at different temperatures and concentrations. The study is focused on the determination of the entropy generation due to heat and mass transfer, fluid friction and magnetic effect. The influence of the magnetic field on the three-dimensional flow, temperature and concentration fields, entropy generation and heat and mass transfer are revealed. The main important result of this study is that the increase of Hartmann number damped the flow and homogenized the entropy generation distribution in the entire cavity.

Laminar three dimensional flow and heat transfer in a nanofluid filled cavity with solid insert at the corners is analyzed computationaly by using finite volume method. Entropy generation is also presented from the obtained results of velocity and temperature values. In order to simulate nanofluids, an in-house numerical method was developed based on the solution of three dimensional solution of Navier–Stokes equations.Three cases are studied based on number and location of solid inserts. Effects of Rayleigh number (10 4 ≤ Ra ≤ 10 6 ), nanoparticle volume fraction (0 ≤ φ ≤ 0.15) and thermal conductivity ratio (0.01 ≤ Rc ≤ 100) are analyzed on natural convection and entropy generation. It is observed that a three dimensional solution brings a more understanding work for the study. Higher heat transfer and entropy generation are observed in the case of nanoparticle addition into base fluid. In any case, partitions can be used as a control element for heat and fluid flow and energy consumption.

In the original publication of the article, under the section ‘Affiliation’ number 1, the sentence that read as “Department of Industrial Engineering and Systems, College of Engineering, Princess Noura bint Abdu Rahman University, Riyadh, 84428, Saudi Arabia” should read as “Department of Industrial Engineering and Systems, College of Engineering, Princess Nourah bint Abdulrahman University, Riyadh, 84428, Saudi Arabia”.

In this paper, we carry out a numerical study of the Coulomb-driven electro-convection flow in a dielectric liquid using the finite volume method (FVM). The system under study consists of an eccentric annulus layer subjected to strong unipolar injection from an inner cylinder. All equations are written in bi-cylindrical coordinate system and are expressed using the vorticity–stream function method. The behavior of the fluid for different system parameters is well studied. The taken parameters are in the range of eccentricity 0 ≤ e ≤ 80%, injection strength in the range of 0.5 ≤ C ≤ 10 and electric Rayleigh number in the range of 30 ≤ T ≤ 1600. The distributions of the electric charge density and stream function are carefully examined. The computations highlight a significant effect of the eccentricity value on the flow topography. Indeed, increasing the eccentricity value leads to a significant reduction in electro-plumes as well as circulation cells number. Furthermore, an intensification in cells rotation, of about 116%, was recorded when eccentricity reaches 80%. Depending on torque values e-T, we observe the existence of multicellular regime made of counter-rotating vortexes.

In this work, A new multi-stage biomass gasifier with three compartments is proposed. The aim of the design is to generate a low tar content product gas. Therefore, the system is composed of biomass pyrolysis zone, product pyrolysis gases combustion zone and gasification zone. Second and third zones are superposed and separated by a gas distributor. A computational fluid dynamics (CFD) study has been conducted using the software ANSYS Fluent to simulate the hydrodynamics behavior of flow inside the combustion and gasification zones. Based on a two-dimensional cold flow configuration, the Eulerian-multiphase model approach has been used. Sand is chosen as the bed materiel, belonging to Geldart B group, and fluidized by the air. The flow through the distributor is accurately modeled. The ultimate aim of this work is to study the effects of the gas distributor and some geometrical modifications in the gasifier on the pressure drop, the bed expansion ratio and the bed behavior. Results show that the pressure drop and the bed expansion are affected by the distributor's diameter and its holes diameter. Also, a combination of these changes could be used to optimize the fluidization and avoid slugging of the bed.

Convective heat transfer and entropy generation in a 3D closed cavity, equipped with adiabatic-driven baffle and filled with CNT (carbon nanotube)-water nanofluid, are numerically investigated for a range of Rayleigh numbers from 103 to 105. This research is conducted for three configurations; fixed baffle (V = 0), rotating baffle clockwise (V+) and rotating baffle counterclockwise (V−) and a range of CNT concentrations from 0 to 15%. Governing equations are formulated using potential vector vorticity formulation in its three-dimensional form, then solved by the finite volume method. The effects of motion direction of the inserted driven baffle and CNT concentration on heat transfer and entropy generation are studied. It was observed that for low Rayleigh numbers, the motion of the driven baffle enhances heat transfer regardless of its direction and the CNT concentration effect is negligible. However, with an increasing Rayleigh number, adding driven baffle increases the heat transfer only when it moves in the direction of the decreasing temperature gradient; elsewhere, convective heat transfer cannot be enhanced due to flow blockage at the corners of the baffle.