Kamel Halouani | University of Sfax (original) (raw)

Vol 9, No 1 (2007) by Kamel Halouani

The study presented in this paper is an investigation on the porosity changes induced by the carb... more The study presented in this paper is an investigation on the porosity changes induced by the carbonization of Tunisian olive wood. The porosity is measured by mercury porosimetry. The experimental results show that the total porosity of carbonized wood increases with the temperature. It should be underlined that the formation of some macropores during the increase of the temperature is certainly due to the breaking of the cell wall by the mercury penetration. The weakness of the cell wall is observed when the degradation rate of the three pseudo components of wood, the notion of which has been introduced by the authors in a previous article ], becomes high which corresponds to the temperature range between 523 K and 548 K.

Papers by Kamel Halouani

Fire Dynamics Simulator (FDS) and global thermochemical modelling are used to solve numerically p... more Fire Dynamics Simulator (FDS) and global thermochemical modelling are used to solve numerically pyrolysis, combustion and heat recuperation in a pilot plant of biomass pyrolysis using pyrolysis products as fuel. Obtained results are validated with experimental measurements. In the case of FDS modelling, three different treatments of radiation are considered: without radiation, with gray gas radiation and with non gray gas radiation. The results of numerical simulations are compared with the global model results and with the experimental results. It was shown that the FDS results are in good qualitative and quantitative agreement with the experimental results. The global model gives qualitative results in agreement with experimental results with less CPU time compared with FDS results. Whereas FDS results are more accurate than those of the global model. At the end of the process FDS results are better than global model results this is due to the fact that global model doesn't take into account the thermal inertia of the pilot plant. The global model is used to study the racing reaction in the pilot plant and to study the case with and without catalyser. FDS is used to predict CO and CO2 emissions. The effect of the non gray gas behaviour is emphasised and demonstrated to affect pollutant emissions.

A pilot downdraft gasifier is investigated experimentally using almond shell biomass as feedstock... more A pilot downdraft gasifier is investigated experimentally using almond shell biomass as feedstock. Experimental temperature profiles along the different zones of the gasifier are measured and overlapping regions between the different gasifier stratified zones is proved: we identified two main zones (drying-pyrolysis zone and partial oxidation-reduction zone) instead of four stratified zones as proposed in the literature. In light of this experimental finding, a two dimensional mathematical model is developed for the combined partial oxidation-reduction zone based on conservation equations coupled to the heterogeneous and homogeneous chemistry. Partial oxidation and thermal cracking mechanisms of tar are proposed based on the available kinetic data. The model is developed for the quasi-steady state period of the experiment and used to simulate the heat and mass transport fields within the computational domain, analyze the interaction between the heterogeneous and homogeneous reactions and evaluate the performance of the gasifier in terms of tar conversion and syngas composition. Validation against the mean experimental temperature data and the producer gas composition at the outlet of the reactor are presented and a satisfactory agreement is observed. The influence of pyrolysis gas composition, air flow rate and bed porosity on the process and its outputs is also investigated.

A numerical study of isothermal carbonization of thick wood particles has been developed. The pro... more A numerical study of isothermal carbonization of thick wood particles has been developed. The proposed model takes into account the heat and mass transfer and chemical kinetics simultaneously. The thermal properties of wood are considered to be linear functions of the local temperature and have been estimated from literature data or by fitting the model with experimental data. The carbonization process has been described by a kinetic scheme based on a two stage semi-global kinetic model developed in a previous work of the authors. The mathematical formulation leads to a coupled nonlinear partial differential equations system, which has been solved iteratively by an implicit finite differences method. The residual mass as well as the temperature profile inside the thick particle are predicted numerically. The obtained results are in good agreement with the available experimental data. Then, the model is used to study the effect of reactor temperature and particle size on the evolution of the local temperature and mass loss inside the wood particle.

Bio-oil from fast pyrolysis of Tunisian almond shell (TN-AS) in fluidized bed reactor was investi... more Bio-oil from fast pyrolysis of Tunisian almond shell (TN-AS) in fluidized bed reactor was investigated. TG (Thermogravimetric) and DTG (Derivative Thermogravimetric) analyses were performed to quantify the kinetic of its thermal degradation by comparison with other Mediterranean almond shell feedstocks from Spain (SPAS) and Turkey (TR-AS). The obtained bio-oil was characterized in terms of its composition and energy content using FTIR, 13 C NMR and GC-MS. The analyses showed that TN-AS bio-oil was similar to the Turkish one and was slightly different from the Spanish bio-oil. Aging effect at room temperature over a long storage period (5 years) was also investigated to assess bio-oil stability. The aged TN-AS bio-oil had a higher viscosity (705.16 ± 3.76 mm 2 ·s −1 at 50 °C) while pH, water content and HHV remained unchanged. The increase of viscosity may be due to the increase in the molecular weight resulting of re-polymerization reactions taking place during the long storage period.

A pilot plant of biomass pyrolysis using pyrolysis products as fuel has been tested and shown to ... more A pilot plant of biomass pyrolysis using pyrolysis products as fuel has been tested and shown to improve energy balance of the process and to be environmentally friendly by avoiding rejection of pyrolysis pollutants fumes into the atmosphere. The high number of parameters involved in a pyrolysis process makes it difficult to specify an optimum procedure for charcoal yield and pyrolysis cycle durability. So the knowledge of the essential parameters which govern the kinetics mechanisms of the biomass thermal decomposition and the combustion of pyrolysis gases is very useful to understand the operating cycle of the plant. In the present study a thermochemical model is developed in order to simulate and control the operating cycle of the system. The effect of the inlet molar air flow rate on the temporal evolution of biomass mass loss rate and temperatures in the different active zones of the pilot plant as well as the determination of the critical inlet molar air flow rate for which accidental runaway of combustion reactions occurs are presented. To avoid this accidental phenomenon a Proportional-Integral-Derived (PID) anticipated regulation is used in order to control temperatures evolution in the different zones of the device and avoid the runaway of combustion reactions.

The effect of radiative heat transfer on the hydromagnetic double-diffusive convection in two-dim... more The effect of radiative heat transfer on the hydromagnetic double-diffusive convection in two-dimensional rectangular enclosure is studied numerically for fixed Prandtl, Rayleigh, and Lewis numbers, Pr = 13.6, Ra = 10 5 , Le = 2. Uniform temperatures and concentrations are imposed along the vertical walls while the horizontal walls are assumed to be adiabatic and impermeable to mass transfer. The influences of the optical thickness and scattering albedo of the semitransparent fluid on heat and mass transfer with and without magnetic damping are depicted. When progressively varying the optical thickness, multiple solutions are obtained which are steady or oscil-latory accordingly to the initial conditions. the mechanisms of the transitions between steady compositionally dominated flow and unsteady thermally dominated flow are analyzed.

This article presents a numerical study of the effect of the radiative heat transfer on the three... more This article presents a numerical study of the effect of the radiative heat transfer on the three-dimensional convection in a cubic differentially heated cavity for different optical parameters of the medium, Pr = 13.6 and Ra = 10 5. The natural convection equations, using the Boussinesq approximation for the treatment of buoyancy term in the momentum equation, are expressed using the vorticity-stream function formulation. These equations and the radiative transfer equation are discretized, respectively, with the control volume finite difference method and the FTn finite volume method. The successive relaxation-iterating scheme is used to solve the resultant algebraic system equations. Results show that the structure of the main flow is considerably altered by of the conduction–radiation parameter. The inner spiraling flows are found very sensible in location and direction to the radiative heat transfer. However, the peripheral spiraling motion is qualitatively insensitive to these parameters. It is also found that radiation favorites the merging of the vortices near the front and back walls.

A wide variety of abundant low cost carbonaceous fuels such as coal-derived coke, petroleum coke ... more A wide variety of abundant low cost carbonaceous fuels such as coal-derived coke, petroleum coke (refinery wastes) and biochar from biomass carbonization can be utilized to generate electricity in a Direct Carbon Fuel Cell (DCFC) system. In this paper, a promising IntermediateeTemperature DCFC based on ceria-carbonate composite electrolyte is successfully tested at 600e750 C using as fuel a biochar issued from almond shell carbon-ization. This bio-resource fuel gives the best open circuit cell potential (1.07 V) at 700 C. Measurements of the cell performance indicate a peak power density of 127 mW cm À2 for the almond shell biochar fuel, which is compared favorably with a peak power density of 100 mW cm À2 for activated carbon fuel used in previous work. Obtained results show that the electrochemical performance of the almond shell biochar as fuel is highly dependent on their intrinsic physico-chemical properties, such as chemical composition, surface area, the nature of mineral matter and content of oxygen-functional groups not only on the edges but also in the interior of the graphite structure of the almond shell biochar where the degree of coverage is higher. The cell performance is showed maintained due to the replenishment of oxygen-containing reactive sites which continuously appear at the reactive edge of the carbon crystal, as the edge continuously advances.

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright a b s t r a c t A radiation model is proposed to extend the zonal method of Hottel to semi-transparent inhomogeneous real combusting gas–soot mixture in a 2-D black-walled rectangular enclosure. The direct exchange areas are carried out by direct numerical integration and then adjusted to meet the conservation constraints using two smoothing processes namely the Larsen and Howell's least squares and generalized Lawson's improved smoothing methods, which has not been previously done to the best knowledge of the authors. The predicted net radiative heat flux distributions compare favorably with benchmark solutions for two test cases dealing with isothermal and non-isothermal homogeneous mediums. It is concluded from this investigation that there is no significant effect of the smoothing method on the computed wall heat fluxes for the homogeneous and inhomogeneous test cases using different grey gases number. The grid dependence study depicts that the numerical solutions fully achieve grid independence. It is worth noting that it can be proceeded with the present extended zonal method and computer code to more complex cases. The results based on the generalized Lawson's smoothing method compare favorably with those yielded by the popular least squares method and, consequently, can be considered as a benchmark solution for other investigations.

International Journal of Hydrogen …, Jan 1, 2009

Heat Mass and charge transfer a b s t r a c t A two-dimensional CFD model of PEM fuel cell is dev... more Heat Mass and charge transfer a b s t r a c t A two-dimensional CFD model of PEM fuel cell is developed by taking into account the electrochemical, mass and heat transfer phenomena occurring in all of its regions simultaneously. The catalyst layers and membrane are each considered as distinct regions with finite thickness and calculated properties such as permeability, local protonic conductivity, and local dissolved water diffusion. This finite thickness model enables to model accurately the protonic current in these regions with higher accuracy than using an infinitesimal interface. In addition, this model takes into account the effect of osmotic drag in the membrane and catalyst layers. General boundary conditions are implemented in a way taking into consideration any given species concentration at the fuel cell inlet, such as water vapor which is a very important parameter in determining the efficiency of fuel cells.

The radiative heat transfer problem is investigated numerically for 2D complex geometry biomass p... more The radiative heat transfer problem is investigated numerically for 2D complex geometry biomass pyrolysis reactor composed of two pyrolysis chambers and a heat recuperator. The fumes are a mixture of carbon dioxide and water vapor charged with absorbing and scattering particles and soot. In order to increase gases residence time and heat transfer, the heat recuperator is provided with many inclined, vertical, horizontal, diffuse and grey baffles of finite thickness and has a complex geometry. The Finite Volume Method (FVM) is applied to study radiative heat transfer. The blocked-off region procedure is used to treat the geometrical irregularities. Eight cases are considered in order to demonstrate the effect of adding baffles on the walls of the heat recuperator and on the walls of the pyrolysis rooms then choose the best case giving the maximum heat flux transferred to the biomass in the pyrolysis chambers. Ray effect due to the presence of baffles is studied and demonstrated to have a crucial effect on radiative heat flux on the walls of the pyrolysis rooms. Shadow effect caused by the presence of the baffles is also studied. The non grey radiative heat transfer is studied for the real existent configuration. The Weighted Sum of The Grey Gases (WSGG) Model of Kim and Song is used as non grey model. The effect of soot volumetric fraction on the non grey radiative heat flux is investigated and discussed.

This paper presents the study of natural heat Method (LBM). A D2Q9 lattice model was coupled with... more This paper presents the study of natural heat Method (LBM). A D2Q9 lattice model was coupled with the D2Q4 lattice model to represent density and internal energy distribution function, respectively. The enclosure is filled with air heated by a sma source of heat situated at the bottom wall. with results from literature. The effec studied for Ra=10 6 .

International Journal of Energy, Environment and Economics

In this study an attempt to base the wood gasification process calculations on equilibrium princi... more In this study an attempt to base the wood gasification process calculations on equilibrium principles has been made. This leads to a simple model based on chemical principles. The system model gives the composition of the produced gas and its low calorific value as functions of wood's moisture and final temperature of reaction so the model constitute a software energy simulation tools to the optimization of gasification plants performances. Agreement between the computed results and the observed data is good with an overall average deviation of about 2.7% for the contents of gases and 3.5% for the low calorific value.

A theoretical study of the carbonization of thick wood particles has been developed. The proposed... more A theoretical study of the carbonization of thick wood particles has been developed. The proposed model takes into account heat and mass transfer and chemical kinetics simultaneously. The thermal properties of wood are considered to be linear functions of the temperature and have been estimated from literature data or by fitting the model with experimental data. Carbonization process have been simulated by a scheme consisting of three parallel reactions of the virgin wood decomposition and secondary reaction of the primary tar. The kinetic parameters have been determined experimentally by thermogravimetric analysis. The mathematical formulation leads to a system of coupled nonlinear partial differential equations, which have been solved iteratively by an implicit finite differences method. The residual mass as well as the temperature profile inside the thick particle are simulated. The obtained results are in good agreement with the available experimental data.

The need for energy is increasing sharply due to the rapid increase in the world’s population and... more The need for energy is increasing sharply due to the rapid increase in the world’s population and developing technologies, while the current energy resources with limited reserves are decreasing. However, there is a great concern with the environment problems associated with great CO2, NOx and SOx emissions resulting from the rising use of fossil fuels. For all these reasons, more attention is being paid to renewable energy. In fact, biomass is becoming increasingly important as a renewable source of energy compared with other renewable energy resources to substitute declining fossil fuel resources [1]. Among the processes of energy production from biomass, pyrolysis is the most viable process for biomass upgrading by cracking polymeric structure of lignocellulosic materials and converting it, under inert atmosphere, into volatile fraction consisting of gases, vapors and tar components and a carbon solid residue (biochar) fractions. The knowledge and understanding of the chemical an...

The socio-economic importance of the olive oil production is significant especially in the Medite... more The socio-economic importance of the olive oil production is significant especially in the Mediterranean region, both in terms of wealth and tradition. Spain is the main world producer followed by Italy, Greece, Turkey, Syria and Tunisia. Hence, this area is especially affected by olive mill waste pollution. The extraction of olive oil generates huge quantities of wastes that may have a great impact on land and water environments because of their high phytotoxicity. In fact, several by-products are generated during the olive oil production process which includes spent olives (fruit pits and solids after pressing, olive leaves from harvesting), and process wastewater that has high organic loading. By-products of olive oil production (wastewater and spent olives) require specialized management to reduce environmental pollution. The economical and environmentally sustainable methods of disposing these classes of wastes are still a challenge for the olive oil industry. In fact, olive oi...

The radiative heat transfer problem is investigated numerically for 2D complex pilot plant of bio... more The radiative heat transfer problem is investigated numerically for 2D complex pilot plant of biomass pyrolysis composed by two pyrolysis chambers and a heat recuperator. In order to increase gases residence time and heat transfer, the heat recuperator is provided with many inclined, vertical, horizontal, diffuse and gray baffles of finite thickness and has a complex geometry. The Finite Volume Method (FVM) is applied to study radiative heat transfer. The blocked-off region procedure is used to treat the geometrical irregularities. Seven cases are considered in order to demonstrate the effect of adding baffles on the walls of the heat recuperator and on the walls of the pyrolysis rooms then choose the best case giving the maximum heat flux transferred to the biomass in the pyrolysis chambers. Shadow effect caused by the presence of the baffles is also studied.

The study presented in this paper is an investigation on the porosity changes induced by the carb... more The study presented in this paper is an investigation on the porosity changes induced by the carbonization of Tunisian olive wood. The porosity is measured by mercury porosimetry. The experimental results show that the total porosity of carbonized wood increases with the temperature. It should be underlined that the formation of some macropores during the increase of the temperature is certainly due to the breaking of the cell wall by the mercury penetration. The weakness of the cell wall is observed when the degradation rate of the three pseudo components of wood, the notion of which has been introduced by the authors in a previous article ], becomes high which corresponds to the temperature range between 523 K and 548 K.

Fire Dynamics Simulator (FDS) and global thermochemical modelling are used to solve numerically p... more Fire Dynamics Simulator (FDS) and global thermochemical modelling are used to solve numerically pyrolysis, combustion and heat recuperation in a pilot plant of biomass pyrolysis using pyrolysis products as fuel. Obtained results are validated with experimental measurements. In the case of FDS modelling, three different treatments of radiation are considered: without radiation, with gray gas radiation and with non gray gas radiation. The results of numerical simulations are compared with the global model results and with the experimental results. It was shown that the FDS results are in good qualitative and quantitative agreement with the experimental results. The global model gives qualitative results in agreement with experimental results with less CPU time compared with FDS results. Whereas FDS results are more accurate than those of the global model. At the end of the process FDS results are better than global model results this is due to the fact that global model doesn't take into account the thermal inertia of the pilot plant. The global model is used to study the racing reaction in the pilot plant and to study the case with and without catalyser. FDS is used to predict CO and CO2 emissions. The effect of the non gray gas behaviour is emphasised and demonstrated to affect pollutant emissions.

A pilot downdraft gasifier is investigated experimentally using almond shell biomass as feedstock... more A pilot downdraft gasifier is investigated experimentally using almond shell biomass as feedstock. Experimental temperature profiles along the different zones of the gasifier are measured and overlapping regions between the different gasifier stratified zones is proved: we identified two main zones (drying-pyrolysis zone and partial oxidation-reduction zone) instead of four stratified zones as proposed in the literature. In light of this experimental finding, a two dimensional mathematical model is developed for the combined partial oxidation-reduction zone based on conservation equations coupled to the heterogeneous and homogeneous chemistry. Partial oxidation and thermal cracking mechanisms of tar are proposed based on the available kinetic data. The model is developed for the quasi-steady state period of the experiment and used to simulate the heat and mass transport fields within the computational domain, analyze the interaction between the heterogeneous and homogeneous reactions and evaluate the performance of the gasifier in terms of tar conversion and syngas composition. Validation against the mean experimental temperature data and the producer gas composition at the outlet of the reactor are presented and a satisfactory agreement is observed. The influence of pyrolysis gas composition, air flow rate and bed porosity on the process and its outputs is also investigated.

A numerical study of isothermal carbonization of thick wood particles has been developed. The pro... more A numerical study of isothermal carbonization of thick wood particles has been developed. The proposed model takes into account the heat and mass transfer and chemical kinetics simultaneously. The thermal properties of wood are considered to be linear functions of the local temperature and have been estimated from literature data or by fitting the model with experimental data. The carbonization process has been described by a kinetic scheme based on a two stage semi-global kinetic model developed in a previous work of the authors. The mathematical formulation leads to a coupled nonlinear partial differential equations system, which has been solved iteratively by an implicit finite differences method. The residual mass as well as the temperature profile inside the thick particle are predicted numerically. The obtained results are in good agreement with the available experimental data. Then, the model is used to study the effect of reactor temperature and particle size on the evolution of the local temperature and mass loss inside the wood particle.

Bio-oil from fast pyrolysis of Tunisian almond shell (TN-AS) in fluidized bed reactor was investi... more Bio-oil from fast pyrolysis of Tunisian almond shell (TN-AS) in fluidized bed reactor was investigated. TG (Thermogravimetric) and DTG (Derivative Thermogravimetric) analyses were performed to quantify the kinetic of its thermal degradation by comparison with other Mediterranean almond shell feedstocks from Spain (SPAS) and Turkey (TR-AS). The obtained bio-oil was characterized in terms of its composition and energy content using FTIR, 13 C NMR and GC-MS. The analyses showed that TN-AS bio-oil was similar to the Turkish one and was slightly different from the Spanish bio-oil. Aging effect at room temperature over a long storage period (5 years) was also investigated to assess bio-oil stability. The aged TN-AS bio-oil had a higher viscosity (705.16 ± 3.76 mm 2 ·s −1 at 50 °C) while pH, water content and HHV remained unchanged. The increase of viscosity may be due to the increase in the molecular weight resulting of re-polymerization reactions taking place during the long storage period.

A pilot plant of biomass pyrolysis using pyrolysis products as fuel has been tested and shown to ... more A pilot plant of biomass pyrolysis using pyrolysis products as fuel has been tested and shown to improve energy balance of the process and to be environmentally friendly by avoiding rejection of pyrolysis pollutants fumes into the atmosphere. The high number of parameters involved in a pyrolysis process makes it difficult to specify an optimum procedure for charcoal yield and pyrolysis cycle durability. So the knowledge of the essential parameters which govern the kinetics mechanisms of the biomass thermal decomposition and the combustion of pyrolysis gases is very useful to understand the operating cycle of the plant. In the present study a thermochemical model is developed in order to simulate and control the operating cycle of the system. The effect of the inlet molar air flow rate on the temporal evolution of biomass mass loss rate and temperatures in the different active zones of the pilot plant as well as the determination of the critical inlet molar air flow rate for which accidental runaway of combustion reactions occurs are presented. To avoid this accidental phenomenon a Proportional-Integral-Derived (PID) anticipated regulation is used in order to control temperatures evolution in the different zones of the device and avoid the runaway of combustion reactions.

The effect of radiative heat transfer on the hydromagnetic double-diffusive convection in two-dim... more The effect of radiative heat transfer on the hydromagnetic double-diffusive convection in two-dimensional rectangular enclosure is studied numerically for fixed Prandtl, Rayleigh, and Lewis numbers, Pr = 13.6, Ra = 10 5 , Le = 2. Uniform temperatures and concentrations are imposed along the vertical walls while the horizontal walls are assumed to be adiabatic and impermeable to mass transfer. The influences of the optical thickness and scattering albedo of the semitransparent fluid on heat and mass transfer with and without magnetic damping are depicted. When progressively varying the optical thickness, multiple solutions are obtained which are steady or oscil-latory accordingly to the initial conditions. the mechanisms of the transitions between steady compositionally dominated flow and unsteady thermally dominated flow are analyzed.

This article presents a numerical study of the effect of the radiative heat transfer on the three... more This article presents a numerical study of the effect of the radiative heat transfer on the three-dimensional convection in a cubic differentially heated cavity for different optical parameters of the medium, Pr = 13.6 and Ra = 10 5. The natural convection equations, using the Boussinesq approximation for the treatment of buoyancy term in the momentum equation, are expressed using the vorticity-stream function formulation. These equations and the radiative transfer equation are discretized, respectively, with the control volume finite difference method and the FTn finite volume method. The successive relaxation-iterating scheme is used to solve the resultant algebraic system equations. Results show that the structure of the main flow is considerably altered by of the conduction–radiation parameter. The inner spiraling flows are found very sensible in location and direction to the radiative heat transfer. However, the peripheral spiraling motion is qualitatively insensitive to these parameters. It is also found that radiation favorites the merging of the vortices near the front and back walls.

A wide variety of abundant low cost carbonaceous fuels such as coal-derived coke, petroleum coke ... more A wide variety of abundant low cost carbonaceous fuels such as coal-derived coke, petroleum coke (refinery wastes) and biochar from biomass carbonization can be utilized to generate electricity in a Direct Carbon Fuel Cell (DCFC) system. In this paper, a promising IntermediateeTemperature DCFC based on ceria-carbonate composite electrolyte is successfully tested at 600e750 C using as fuel a biochar issued from almond shell carbon-ization. This bio-resource fuel gives the best open circuit cell potential (1.07 V) at 700 C. Measurements of the cell performance indicate a peak power density of 127 mW cm À2 for the almond shell biochar fuel, which is compared favorably with a peak power density of 100 mW cm À2 for activated carbon fuel used in previous work. Obtained results show that the electrochemical performance of the almond shell biochar as fuel is highly dependent on their intrinsic physico-chemical properties, such as chemical composition, surface area, the nature of mineral matter and content of oxygen-functional groups not only on the edges but also in the interior of the graphite structure of the almond shell biochar where the degree of coverage is higher. The cell performance is showed maintained due to the replenishment of oxygen-containing reactive sites which continuously appear at the reactive edge of the carbon crystal, as the edge continuously advances.

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright a b s t r a c t A radiation model is proposed to extend the zonal method of Hottel to semi-transparent inhomogeneous real combusting gas–soot mixture in a 2-D black-walled rectangular enclosure. The direct exchange areas are carried out by direct numerical integration and then adjusted to meet the conservation constraints using two smoothing processes namely the Larsen and Howell's least squares and generalized Lawson's improved smoothing methods, which has not been previously done to the best knowledge of the authors. The predicted net radiative heat flux distributions compare favorably with benchmark solutions for two test cases dealing with isothermal and non-isothermal homogeneous mediums. It is concluded from this investigation that there is no significant effect of the smoothing method on the computed wall heat fluxes for the homogeneous and inhomogeneous test cases using different grey gases number. The grid dependence study depicts that the numerical solutions fully achieve grid independence. It is worth noting that it can be proceeded with the present extended zonal method and computer code to more complex cases. The results based on the generalized Lawson's smoothing method compare favorably with those yielded by the popular least squares method and, consequently, can be considered as a benchmark solution for other investigations.

International Journal of Hydrogen …, Jan 1, 2009

Heat Mass and charge transfer a b s t r a c t A two-dimensional CFD model of PEM fuel cell is dev... more Heat Mass and charge transfer a b s t r a c t A two-dimensional CFD model of PEM fuel cell is developed by taking into account the electrochemical, mass and heat transfer phenomena occurring in all of its regions simultaneously. The catalyst layers and membrane are each considered as distinct regions with finite thickness and calculated properties such as permeability, local protonic conductivity, and local dissolved water diffusion. This finite thickness model enables to model accurately the protonic current in these regions with higher accuracy than using an infinitesimal interface. In addition, this model takes into account the effect of osmotic drag in the membrane and catalyst layers. General boundary conditions are implemented in a way taking into consideration any given species concentration at the fuel cell inlet, such as water vapor which is a very important parameter in determining the efficiency of fuel cells.

The radiative heat transfer problem is investigated numerically for 2D complex geometry biomass p... more The radiative heat transfer problem is investigated numerically for 2D complex geometry biomass pyrolysis reactor composed of two pyrolysis chambers and a heat recuperator. The fumes are a mixture of carbon dioxide and water vapor charged with absorbing and scattering particles and soot. In order to increase gases residence time and heat transfer, the heat recuperator is provided with many inclined, vertical, horizontal, diffuse and grey baffles of finite thickness and has a complex geometry. The Finite Volume Method (FVM) is applied to study radiative heat transfer. The blocked-off region procedure is used to treat the geometrical irregularities. Eight cases are considered in order to demonstrate the effect of adding baffles on the walls of the heat recuperator and on the walls of the pyrolysis rooms then choose the best case giving the maximum heat flux transferred to the biomass in the pyrolysis chambers. Ray effect due to the presence of baffles is studied and demonstrated to have a crucial effect on radiative heat flux on the walls of the pyrolysis rooms. Shadow effect caused by the presence of the baffles is also studied. The non grey radiative heat transfer is studied for the real existent configuration. The Weighted Sum of The Grey Gases (WSGG) Model of Kim and Song is used as non grey model. The effect of soot volumetric fraction on the non grey radiative heat flux is investigated and discussed.

This paper presents the study of natural heat Method (LBM). A D2Q9 lattice model was coupled with... more This paper presents the study of natural heat Method (LBM). A D2Q9 lattice model was coupled with the D2Q4 lattice model to represent density and internal energy distribution function, respectively. The enclosure is filled with air heated by a sma source of heat situated at the bottom wall. with results from literature. The effec studied for Ra=10 6 .

International Journal of Energy, Environment and Economics

In this study an attempt to base the wood gasification process calculations on equilibrium princi... more In this study an attempt to base the wood gasification process calculations on equilibrium principles has been made. This leads to a simple model based on chemical principles. The system model gives the composition of the produced gas and its low calorific value as functions of wood's moisture and final temperature of reaction so the model constitute a software energy simulation tools to the optimization of gasification plants performances. Agreement between the computed results and the observed data is good with an overall average deviation of about 2.7% for the contents of gases and 3.5% for the low calorific value.

A theoretical study of the carbonization of thick wood particles has been developed. The proposed... more A theoretical study of the carbonization of thick wood particles has been developed. The proposed model takes into account heat and mass transfer and chemical kinetics simultaneously. The thermal properties of wood are considered to be linear functions of the temperature and have been estimated from literature data or by fitting the model with experimental data. Carbonization process have been simulated by a scheme consisting of three parallel reactions of the virgin wood decomposition and secondary reaction of the primary tar. The kinetic parameters have been determined experimentally by thermogravimetric analysis. The mathematical formulation leads to a system of coupled nonlinear partial differential equations, which have been solved iteratively by an implicit finite differences method. The residual mass as well as the temperature profile inside the thick particle are simulated. The obtained results are in good agreement with the available experimental data.

The need for energy is increasing sharply due to the rapid increase in the world’s population and... more The need for energy is increasing sharply due to the rapid increase in the world’s population and developing technologies, while the current energy resources with limited reserves are decreasing. However, there is a great concern with the environment problems associated with great CO2, NOx and SOx emissions resulting from the rising use of fossil fuels. For all these reasons, more attention is being paid to renewable energy. In fact, biomass is becoming increasingly important as a renewable source of energy compared with other renewable energy resources to substitute declining fossil fuel resources [1]. Among the processes of energy production from biomass, pyrolysis is the most viable process for biomass upgrading by cracking polymeric structure of lignocellulosic materials and converting it, under inert atmosphere, into volatile fraction consisting of gases, vapors and tar components and a carbon solid residue (biochar) fractions. The knowledge and understanding of the chemical an...

The socio-economic importance of the olive oil production is significant especially in the Medite... more The socio-economic importance of the olive oil production is significant especially in the Mediterranean region, both in terms of wealth and tradition. Spain is the main world producer followed by Italy, Greece, Turkey, Syria and Tunisia. Hence, this area is especially affected by olive mill waste pollution. The extraction of olive oil generates huge quantities of wastes that may have a great impact on land and water environments because of their high phytotoxicity. In fact, several by-products are generated during the olive oil production process which includes spent olives (fruit pits and solids after pressing, olive leaves from harvesting), and process wastewater that has high organic loading. By-products of olive oil production (wastewater and spent olives) require specialized management to reduce environmental pollution. The economical and environmentally sustainable methods of disposing these classes of wastes are still a challenge for the olive oil industry. In fact, olive oi...

The radiative heat transfer problem is investigated numerically for 2D complex pilot plant of bio... more The radiative heat transfer problem is investigated numerically for 2D complex pilot plant of biomass pyrolysis composed by two pyrolysis chambers and a heat recuperator. In order to increase gases residence time and heat transfer, the heat recuperator is provided with many inclined, vertical, horizontal, diffuse and gray baffles of finite thickness and has a complex geometry. The Finite Volume Method (FVM) is applied to study radiative heat transfer. The blocked-off region procedure is used to treat the geometrical irregularities. Seven cases are considered in order to demonstrate the effect of adding baffles on the walls of the heat recuperator and on the walls of the pyrolysis rooms then choose the best case giving the maximum heat flux transferred to the biomass in the pyrolysis chambers. Shadow effect caused by the presence of the baffles is also studied.

The economic development in the world has faced mankind with two major energy challenges: the sub... more The economic development in the world has faced mankind with two major energy challenges: the substitution of fossil fuels and the reduction of greenhouse gas emissions. Hydrogen has the potential to solve these challenges. A great effort is therefore made to develop new technologies of production, delivery, storage, conversion, and end-use of hydrogen. One of the promising ways for hydrogen production is biomass gasification. In this work, this process is studied experimentally in attempt to ameliorate its efficiency in term of hydrogen or syngas yield. Three liquid catalysts were used for that purpose. Analysis of the gas produced was performed and the results show that the catalysts improved the carbon monoxide yield through low temperature carbon dioxide gasification, whereas no remarkable improvement was found for hydrogen yield. Experiments at higher temperatures could reveal higher catalyst effect on the products of the process and on the hydrogen yield particularly.