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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 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.

This article provides a numerical study on carbon nanotube-water nanofluid convection in a three-dimensional cavity under a magnetic field effect. Two walls are kept at a hot temperature, and the upper and lower horizontal walls are considered adiabatic. As a new configuration, the beneficial effect of using a nanofluid is coupled with the incorporation of cold V-shape obstacle placed in the cubic cavity; in addition, an external magnetic field is applied toward the horizontal

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.

International audience; In this study, the combined impact of carbon nanotube volume fractions and the electric field on the enhancement of dielectric oil heat transfer is investigated. The geometry studied is an annular layer filled with the dielectric oil and bounded by two eccentric or concentric cylinders. A temperature gradient and an electrical potential difference are applied between the two cylindrical walls. The goal is to analyse the flow behaviour and the heat transfer improvement using a double enhancement technique by combining an active (electric field) and passive (nanoparticles) approach. An in-house numerical simulation code using the finite volume method was developed to solve the set of coupled equations describing the conservation laws of the electro-thermo-hydrodynamic flow associated with the oil. A parametric study, outlining the influence of different relevant variables has been performed. The parameters investigated are the thermal Rayleigh number , the electrical Rayleigh number , the radius ratio , the eccentricity , the nanotubes volume fraction and the injection level respectively. The effect of these variables on the heat transfer intensification is examined in detail. According to the adopted configuration, heat transfer intensifications between 3% and 77% have been recorded essentially when an electric field was applied. Also, the addition of a 0.5% volume fraction of carbon nanotubes provides a heat transfer improvement of around 27%. Furthermore, for a first time a multiparameter correlation has been developed. This correlation can be useful to better understand the impact of various physical parameters on the heat transfer in annular spaces and also to predict exact values of the Nusselt number.

Impacts of using double rotating cylinders and partly porous layers in the bifurcating channels on the hydro-thermal performance were numerically assessed. Hybrid nanoparticles were used in water and finite element method was selected as the solver. Effects of Reynolds number, rotational speeds of the cylinders and their locations in the bifurcating channels, porous layer sizes and nanoparticle solid volume fractions on the hydro-thermal performance features were explored. The contribution of different hot wall parts was changed with varying Reynolds number and rotational velocity of the cylinders. Depending upon the rotational direction of the cylinders, the vortex occurrence and size at the bifurcations change significantly. Heat transfer considering all hot walls rise with higher rotational speeds in both directions. The amount of improvement in the heat transfer rate becomes 25 % and 19 % with varying speeds of the cylinders as compared to motionless cylinders. The pressure coefficient reduces with increasing the second cylinder speed in clockwise direction and this is favorable for thermal performance since the heat transfer also increases. The overall impact of the varying horizontal locations of the cylinders on the heat transfer rate is slight. The separated zones at the branching depends on the porous layer sizes. The overall heat transfer behavior becomes opposite when varying the sizes of the porous layers in the horizontal and vertical channels. By using nanoparticles in the base fluid, 35.75 % improvement in the heat transfer rate is achieved for vertical wall at Re = 350 while pressure drop coefficient rises by about 8.5 % . The overall improvement in the heat transfer rate by using nanofluid is 26 % . Owing to diverse use of bifurcating channels in thermal engineering from fuel cells to electronic cooling, the proposed methods of heat transfer enhancement techniques can be considered simultaneously for effective control the thermal performance of those systems.

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 numerical study based on the finite volume method has been performed to study the three-dimension natural convection in a parallelogrammic top side opened cavity filled nanofluid with partially heated square at the bottom side. Results are obtained for different governing parameters such as nanoparticle concentration (φ) from 0 to 0.05, inclination angle of the back and front walls (α) from 5° to 75°, Rayleigh number from 103 to 105, and length of heater changer from 0.1 to 1. The main finding from the obtained result showed that the inclination angle and nanoparticle volume fraction affect the flow structure and enhance the heat transfer.

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.

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.

A numerical study is performed to investigate the effects of adding Carbon Nano Tube (CNT) and applying a magnetic field in two directions (vertical and horizontal) on the 3D-thermo-capillary natural convection. The cavity is differentially heated with a free upper surface. Governing equations are solved using the finite volume method. Results are presented in term of flow structure, temperature field and rate of heat transfer. In fact, results revealed that the flow structure and heat transfer rate are considerably affected by the magnitude and the direction of the magnetic field, the presence of thermocapillary forces and by increasing nanoparticles volume fraction. In opposition, the increase of the magnetic field magnitude leads to the control the flow causing flow stabilization by merging vortexes and reducing heat transfer rate.

In this study, a 3D numerical study of free ventilated room equipped with a discrete heat source was performed using the Finite Volume Method (FVM). To ensure good ventilation, two parallel openings were created in the room. A suction opening was located at the bottom of the left wall and another opening was located at the top of the opposite wall; the heat source was placed at various positions in order to compare the heating efficiency. The effects of Rayleigh number (103 ≤ Ra ≤ 106) for six heater positions was studied. The results focus on the impact of these parameters on the particle trajectories, temperature fields and on the heat transfer inside the room. It was found that the position of the heater has a dramatic effect on the behavior and topography of the flow in the room. When the heat source was placed on the wall with the suction opening, two antagonistic behaviors were recorded: an improvement in heat transfer of about 31.6%, compared to the other positions, and a low Rayleigh number against 22% attenuation for high Ra values was noted.

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 see the effects of electro-thermo-convection induced via a strong unipolar injection between two concentric or eccentric cylinders using the finite volum...

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 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.

A computational research was performed to analyze the electrohydrodynamic (EHD) convective heat transfer in a differentially heated dielectric-MWCNT nanofluid layer. The study was conducted on a square enclosure subjected to a temperature gradient between these two vertical walls as well as a potential difference between these horizontal walls. The enclosure was filled with MWCNT oil-based nanofluid; the MWCNT nanoparticles were dispersed in a perfectly insulating thermal oil with a volume fraction of hardly exceeded 0.4%. The governing equations were derived with the assumption of homogeneous nanofluid and were solved with employing finite volume method. Based on the obtained results, it was found that the increase of Rayleigh number, electric Rayleigh number and nanoparticle concentration enhanced the heat transfer. For high thermal and electric Rayleigh number values, the flow and heat transfer became time dependent and accordingly a frequency study was also performed. It was found that the inclusion of an electric field with the addition of nanoparticles led to a significant heat transfer enhancement of about 43%.

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 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.

The study of heat transfer on shear flows around an obstacle presents a great interest in determination of the influence of water on buildings and port infrastructures. The variation of the inlet temperatures and the influence of an obstacle placed at the bottom of a channel were analyzed. The obtained results supported by numerical simulations have shown that the doubling of the fluid inlet temperature significantly modifies all the dynamic characteristics of the shear flow. Pressure distribution, turbulent kinetic energy, dissipation rate, turbulent viscosity, and strain rate in the water channel were exposed. These results can help us to better exploit the flow of hot water discharged by power plants.

This study deals with the electroconvection phenomenon that takes place in a dielectric liquid layer placed between two annular electrodes and subjected to the action of an electric field. The full set of governing equations describing the combined Electro-Hydro-Dynamic (EHD) flow is directly solved with the finite volume method. The development of electroconvective motion is investigated in details in the case of strong injection when the emitter electrode is the inner cylinder. We first examine the stability of such flow. As in the plane–plane configuration we have highlighted the existence of a linear and non-linear critical electric Rayleigh numbers giving rise to a hysteresis loop. The flow structure under the effect of the electric field is analyzed and the distribution of electric charge density is presented. In particular we investigate the effect of various parameters involved in this configuration, such as the radius ratio, injection strength and electric Rayleigh number. A multicellular convective pattern is particularly observed and it is shown that the number of cells is increased when the annular gap is narrower. Finally a significant increase of the rotational speed of the vortex with the electric Rayleigh number is recorded.

The purpose of this study is to show the effect of some physical parameters on a parallel shear flow. The variation of the velocity inlet and the influence of an obstacle placed at the bottom of a channel were analyzed. The governing equations based on K –e model in a line source downstream around a three-dimensional obstacle are determined by the finite volume method with SIMPLEC algorithm. The obtained results have allowed to establish the dynamic characteristics of this kind of flow. Horizontal and vertical velocity fields, Reynolds shear stress field, turbulence intensity and scalar concentration in the water channel and a wind tunnel were exposed. These results permit us to localize the maximum and minimum zones of turbulence, which help us to exploit those fields for different purposes such as energy extraction and port infrastructure.