The intermittent nature of renewable resources requires for most applications the development of efficient and cost-effective technologies for steady supply of electrical energy.The storage of energy in the form of hy...The intermittent nature of renewable resources requires for most applications the development of efficient and cost-effective technologies for steady supply of electrical energy.The storage of energy in the form of hydrogen chemically bound within organic molecules(rather than physically as compressed gas or cooled liquid)represents an alternative approach that is attracting great research interest.Compared to other liquid organic hydrogen carriers(LOHCs),dimethyl ether(DME)appears to have the largest potential impact on society,especially if inserted in technological chains of CO_(2) sequestration and utilization,so to determine an effective mitigation of environmental issues,without any net effect on the carbon footprint.Specifically,the steps of H2 storage and H2 release can take place in two coupled chemical processes,constituted by the exothermic synthesis of DME via CO_(2) hydrogenation and the endothermic steam reforming of DME,respectively.Herein,the latest advances in the development of heterogeneous bifunctional and hybrid catalysts for the direct hydrogenation of CO_(2) to DME are thoroughly reviewed,with special emphasis on thermodynamics,catalyst design and process feasibility.Despite many aspects behind the mechanism of DME synthesis from H2-CO_(2) streams are still to be uncovered,the recent progress in the research on H2 release by DME steam reforming is increasing the interest for effectively closing this binary H2 loop,in view of future green deals and sustainable research developments.展开更多
In order to select the best adsorbant for CO2 sequestration, this study deals the interaction between clay, Triassic sandstone and Jurassic evaporate and CO2. These materials have been used as sorbents. To choose the ...In order to select the best adsorbant for CO2 sequestration, this study deals the interaction between clay, Triassic sandstone and Jurassic evaporate and CO2. These materials have been used as sorbents. To choose the adequate geological layers for sequestration and with minimum risk of leakage, adsorbent characterizations were investigated using X-ray diffraction, SEM and surface area analysis, structural and textural shapes of these materials have been investigated too. The elution chromatography in gaseous phase has been employed to determine the adsorption isotherms of adsorbed CO2 for each adsorbent. Then, the treatment of the experimental data allowed us to compare each CO2/adsorbent couple. The adsorption isotherms were modeled using the Langmir and Freundlich models. A thermodynamic comparison between the different adsorbents will also be provided. Experimental results show that clay and Triassic sandstone have the highest rate of adsorption amount. It has been also found that the Langmuir model is the most appropriate one to describe the phenomenon of CO2 adsorption on clay. However, for the other adsorbents (i.e. Triassic sandstone and Jurassic evaporates) the two-models are adequate.展开更多
Operating in natural wind field, the horizontal axis wind turbines are subject to cyclical variation of aerodynamic loads. This cyclical loads fluctuation is a result of two aerodynamic phenomenon: the first one is th...Operating in natural wind field, the horizontal axis wind turbines are subject to cyclical variation of aerodynamic loads. This cyclical loads fluctuation is a result of two aerodynamic phenomenon: the first one is the advancing and retreating blade effect;the second one is related to the cyclical variation of induced velocity at the rotor plane. In these operating conditions, the correct prediction of this load variation is necessary to predict some important parameters linked to the fatigue and stability of free yawing turbines. The main objective of the present study is the evaluation of the azimuthal variation of normal force at different radial positions. To model the problem, the blade element momentum theory is used and wind turbine is supposed operate in yaw conditions. The aerodynamic coefficients are corrected using Chaviaropoulos and Hansen model to take into account the phenomenon of stall delay. A computer code was developed to obtain the numerical values and results are compared with measurements performed in the NASA Ames wind tunnel.展开更多
The present work is a study on the influence of temperature and the velocity of air on the drying kinetics of pineapple slices. The main objective is to define from this drying kinetics rules to help a designer choose...The present work is a study on the influence of temperature and the velocity of air on the drying kinetics of pineapple slices. The main objective is to define from this drying kinetics rules to help a designer choose an adequate principle or drying configuration and optimize the design of dryers adapted to the use of it. The experiments were made in an electric dryer using a parallel flow system. The air was used at three different temperatures （40, 50 and 60 ~C） and at four different velocities （0.27, 0.5, 1 and 1.8 m/s） during the experiment. The results show that an increase of 10 ℃ of the drying temperature reduced the drying time by 45% and increased the drying velocity by 30%. On the set of air velocities tested, it was noticed that the influence of air velocity on drying was more striking at the beginning than at the end of the drying process （variation of less than 20%）. Whatever the variation of parameters during the drying process, the best performance was observed when the products water content during the drying process was between 50% and 80%.展开更多
The lack of synergy between infrastructure financing mechanisms and mechanisms for combating climate change does not favor the definition of sustainable infrastructure in Cameroon. The definition of a sustainable infr...The lack of synergy between infrastructure financing mechanisms and mechanisms for combating climate change does not favor the definition of sustainable infrastructure in Cameroon. The definition of a sustainable infrastructure could meet the requirements of these mechanisms, thanks to the control of Greenhouse Gas (GHG) emissions during its installation, in relation to a predefined value. However, the promotion of efforts to reduce emissions from new infrastructures is not subject to a local market. This situation is a limit in the implementation of the policies defined in the Nationally Determined Contribution (NDC). This article proposes a framework for promoting reduction efforts for a national carbon market, in favor of hydroelectric infrastructures. Thanks to the Life Cycle Assessment (LCA) environmental assessment tool, we are going to determine the carbon quota for a specific power. The study carried out on the hydroelectric power station of Mekin (HydroMekin) leads us to a reduction effort of 68.2% compared to the threshold defined at 14.057 gCO<sub>2eq</sub>/kWh<sub>e</sub>. The framework, developed, contributes to defining the environmental parameters in the decarbonation strategy during the implementation of new hydroelectric infrastructures and the market carbon design elements special to the construction phase of these infrastructures.展开更多
Numerical modeling of sea states has been developed for years,and used for varied fields such as coastal work sizing,navigation safety,beaches and water leisure stability study.The third-generation ocean wind-wave spe...Numerical modeling of sea states has been developed for years,and used for varied fields such as coastal work sizing,navigation safety,beaches and water leisure stability study.The third-generation ocean wind-wave spectral model WAVEWATCH III(WW3)software was adopted and developed to simulate wave propagation in the Mediterranean basin.In this work,a more detailed study was carried out on the port of Algiers.Two different atmospheric models have been used to get the wind forcing:ALADIN(Area Limited Dynamic Adaptation Inter National Development)with an 8 km resolution.And AROME(Application to Operational Research at Meso-scale)with a 3 km resolution.The results obtained using both of the atmospheric models have been compared and analyzed.展开更多
The energy transition,validated by 194 countries at the end of CoP21 in Paris,requires new development design methods.This requirement,for the sub-Saharan African countries(SAC),could be an opportunity to finance thei...The energy transition,validated by 194 countries at the end of CoP21 in Paris,requires new development design methods.This requirement,for the sub-Saharan African countries(SAC),could be an opportunity to finance their development.Following the mixed results of the Clean Development Mechanism(CDM),partly due to its rather restrictive selection criterion,the desire to implement carbon asset transfer mechanisms is proposed by many countries including Cameroon.However,the success of such a mechanism would be guaranteed by encouraging policies to regulate emissions.It is in this perspective that our work falls.It aims at proposing a regulation approach for major projects.We have dwelt on hydroelectric projects.To do this,we ordered considering their quantitative feature,113 projects or visions proposed by 37 countries.Subsequently,a classification of projects according to compartments and trends was made.We finally pointed out 6 visions,including the mitigation in production,mitigation in distribution or service,adaptation in production,mitigation in transport,adaptation in distribution or service,and the adaptation in transport.The regulation methodology proposed for mitigation projects in the hydroelectric sector on a variable threshold hypothesis has led us to three trends in regulation.展开更多
In this paper,flow of slightly rarefied compressible nitrogen in microchannels has been investigated numerically for low values of Reynolds and Mach numbers.The 2D governing equations were solved using Finite Element ...In this paper,flow of slightly rarefied compressible nitrogen in microchannels has been investigated numerically for low values of Reynolds and Mach numbers.The 2D governing equations were solved using Finite Element Method with first-order slip boundary conditions(Comsol Multiphysics software).A validation was performed by comparing with similar configuration from the literature.It was found that our model can accurately predict the pressure driven flow in microchannels.Several interesting findings are reported about the Relative pressure,longitudinal velocity,Mach number,effect of gas rarefaction and flow rate.展开更多
Global temperature is predicted to increase in the end of the century and one of the primary consequences of this warming is the sea level rise. Considering the vulnerabilities on coastal systems and water resources, ...Global temperature is predicted to increase in the end of the century and one of the primary consequences of this warming is the sea level rise. Considering the vulnerabilities on coastal systems and water resources, it is important to evaluate the potential effects of this rising in coastal areas, since the saline intrusion on rivers would be intensified, leading to problems related to water quality. In this context, the present work aimed to verify saline intrusion changes along an important river, São Francisco Canal, located in Rio de Janeiro State, Brazil. For this purpose, a hydrodynamic modeling was performed using SisBaHiA, considering different sea levels and tide conditions. According to the results, it was verified the intensification on saline intrusion and higher salinity values due to a sea level rise of 0.5 m. These results show that new licenses for water withdrawals must be carefully analyzed as the fluvial flow plays an important role to contain the saltwater intrusion on the studied river. Accordingly, it is recommended the evaluation of climate change effects in order to choose best strategies to reduce coastal vulnerability, and the use of this theme on environmental licensing and territorial planning, integrating water planning with coastal management.展开更多
The production process of clean hydrogen by iso-octane steam reforming in a micro-reactor under atmospheric pressure,and the high temperature was investigated.The simulation is done using momentum conservation,mass co...The production process of clean hydrogen by iso-octane steam reforming in a micro-reactor under atmospheric pressure,and the high temperature was investigated.The simulation is done using momentum conservation,mass conservation,and convection-diffusion equations,represented by the Navier-Stocks equations,the continuity equation,and the Steffan-Maxwell equation respectively.The resolution was performed using a differential equations discretization into their conservative by the finite element method with an unconditionally stable scheme.An analysis of the hydrodynamics of the flow effect shows that the hydrogen produced by iso-octane reforming is proportional to the mixed flow Reynolds number.展开更多
The goal of this study is to examine the energetic,entransy,and exergetic methodologies employed to estimate the ideal insulation thickness for construction walls in terms of cost and ecological impact.To achieve thes...The goal of this study is to examine the energetic,entransy,and exergetic methodologies employed to estimate the ideal insulation thickness for construction walls in terms of cost and ecological impact.To achieve these goals,the life cycle cost analysis-based insulating thicknesses of the various methods are evaluated along with the overall costs,yearly cost reductions,and total expenses.The fuel consumption,CO_(2) emissions,and ecological effects are then compared using an environmental analysis based on the three methodologies.The savings of hollow concrete brick(HCB),compressed stabilized earth brick(CSEB),and sundried earth brick(SEB)walls are evaluated along with the insulation thicknesses in terms of cost and ecological impact.As a result,it is determined that the exergetic technique is better suited for optimizing insulating thickness.For CSEB,SEB,and HCB walls,the economic ideal insulation thicknesses are 0.01 m,0.016 m,and 0.02 m,with yearly financial savings of 5$⋅m^(-2),7.5$⋅m^(-2),and 9$⋅m^(-2).For CSEB,SEB,and HCB walls,accordingly,the ecological optimal insulation thicknesses are 0.023 m,0.032 m,and 0.040 m,with net savings of exergetic ecological impact equal to 59 mPts⋅m^(-2),55 mPts⋅m^(-2),and 51 mPts⋅m^(-2).展开更多
文摘The intermittent nature of renewable resources requires for most applications the development of efficient and cost-effective technologies for steady supply of electrical energy.The storage of energy in the form of hydrogen chemically bound within organic molecules(rather than physically as compressed gas or cooled liquid)represents an alternative approach that is attracting great research interest.Compared to other liquid organic hydrogen carriers(LOHCs),dimethyl ether(DME)appears to have the largest potential impact on society,especially if inserted in technological chains of CO_(2) sequestration and utilization,so to determine an effective mitigation of environmental issues,without any net effect on the carbon footprint.Specifically,the steps of H2 storage and H2 release can take place in two coupled chemical processes,constituted by the exothermic synthesis of DME via CO_(2) hydrogenation and the endothermic steam reforming of DME,respectively.Herein,the latest advances in the development of heterogeneous bifunctional and hybrid catalysts for the direct hydrogenation of CO_(2) to DME are thoroughly reviewed,with special emphasis on thermodynamics,catalyst design and process feasibility.Despite many aspects behind the mechanism of DME synthesis from H2-CO_(2) streams are still to be uncovered,the recent progress in the research on H2 release by DME steam reforming is increasing the interest for effectively closing this binary H2 loop,in view of future green deals and sustainable research developments.
文摘In order to select the best adsorbant for CO2 sequestration, this study deals the interaction between clay, Triassic sandstone and Jurassic evaporate and CO2. These materials have been used as sorbents. To choose the adequate geological layers for sequestration and with minimum risk of leakage, adsorbent characterizations were investigated using X-ray diffraction, SEM and surface area analysis, structural and textural shapes of these materials have been investigated too. The elution chromatography in gaseous phase has been employed to determine the adsorption isotherms of adsorbed CO2 for each adsorbent. Then, the treatment of the experimental data allowed us to compare each CO2/adsorbent couple. The adsorption isotherms were modeled using the Langmir and Freundlich models. A thermodynamic comparison between the different adsorbents will also be provided. Experimental results show that clay and Triassic sandstone have the highest rate of adsorption amount. It has been also found that the Langmuir model is the most appropriate one to describe the phenomenon of CO2 adsorption on clay. However, for the other adsorbents (i.e. Triassic sandstone and Jurassic evaporates) the two-models are adequate.
文摘Operating in natural wind field, the horizontal axis wind turbines are subject to cyclical variation of aerodynamic loads. This cyclical loads fluctuation is a result of two aerodynamic phenomenon: the first one is the advancing and retreating blade effect;the second one is related to the cyclical variation of induced velocity at the rotor plane. In these operating conditions, the correct prediction of this load variation is necessary to predict some important parameters linked to the fatigue and stability of free yawing turbines. The main objective of the present study is the evaluation of the azimuthal variation of normal force at different radial positions. To model the problem, the blade element momentum theory is used and wind turbine is supposed operate in yaw conditions. The aerodynamic coefficients are corrected using Chaviaropoulos and Hansen model to take into account the phenomenon of stall delay. A computer code was developed to obtain the numerical values and results are compared with measurements performed in the NASA Ames wind tunnel.
文摘The present work is a study on the influence of temperature and the velocity of air on the drying kinetics of pineapple slices. The main objective is to define from this drying kinetics rules to help a designer choose an adequate principle or drying configuration and optimize the design of dryers adapted to the use of it. The experiments were made in an electric dryer using a parallel flow system. The air was used at three different temperatures （40, 50 and 60 ~C） and at four different velocities （0.27, 0.5, 1 and 1.8 m/s） during the experiment. The results show that an increase of 10 ℃ of the drying temperature reduced the drying time by 45% and increased the drying velocity by 30%. On the set of air velocities tested, it was noticed that the influence of air velocity on drying was more striking at the beginning than at the end of the drying process （variation of less than 20%）. Whatever the variation of parameters during the drying process, the best performance was observed when the products water content during the drying process was between 50% and 80%.
文摘The lack of synergy between infrastructure financing mechanisms and mechanisms for combating climate change does not favor the definition of sustainable infrastructure in Cameroon. The definition of a sustainable infrastructure could meet the requirements of these mechanisms, thanks to the control of Greenhouse Gas (GHG) emissions during its installation, in relation to a predefined value. However, the promotion of efforts to reduce emissions from new infrastructures is not subject to a local market. This situation is a limit in the implementation of the policies defined in the Nationally Determined Contribution (NDC). This article proposes a framework for promoting reduction efforts for a national carbon market, in favor of hydroelectric infrastructures. Thanks to the Life Cycle Assessment (LCA) environmental assessment tool, we are going to determine the carbon quota for a specific power. The study carried out on the hydroelectric power station of Mekin (HydroMekin) leads us to a reduction effort of 68.2% compared to the threshold defined at 14.057 gCO<sub>2eq</sub>/kWh<sub>e</sub>. The framework, developed, contributes to defining the environmental parameters in the decarbonation strategy during the implementation of new hydroelectric infrastructures and the market carbon design elements special to the construction phase of these infrastructures.
文摘Numerical modeling of sea states has been developed for years,and used for varied fields such as coastal work sizing,navigation safety,beaches and water leisure stability study.The third-generation ocean wind-wave spectral model WAVEWATCH III(WW3)software was adopted and developed to simulate wave propagation in the Mediterranean basin.In this work,a more detailed study was carried out on the port of Algiers.Two different atmospheric models have been used to get the wind forcing:ALADIN(Area Limited Dynamic Adaptation Inter National Development)with an 8 km resolution.And AROME(Application to Operational Research at Meso-scale)with a 3 km resolution.The results obtained using both of the atmospheric models have been compared and analyzed.
文摘The energy transition,validated by 194 countries at the end of CoP21 in Paris,requires new development design methods.This requirement,for the sub-Saharan African countries(SAC),could be an opportunity to finance their development.Following the mixed results of the Clean Development Mechanism(CDM),partly due to its rather restrictive selection criterion,the desire to implement carbon asset transfer mechanisms is proposed by many countries including Cameroon.However,the success of such a mechanism would be guaranteed by encouraging policies to regulate emissions.It is in this perspective that our work falls.It aims at proposing a regulation approach for major projects.We have dwelt on hydroelectric projects.To do this,we ordered considering their quantitative feature,113 projects or visions proposed by 37 countries.Subsequently,a classification of projects according to compartments and trends was made.We finally pointed out 6 visions,including the mitigation in production,mitigation in distribution or service,adaptation in production,mitigation in transport,adaptation in distribution or service,and the adaptation in transport.The regulation methodology proposed for mitigation projects in the hydroelectric sector on a variable threshold hypothesis has led us to three trends in regulation.
文摘In this paper,flow of slightly rarefied compressible nitrogen in microchannels has been investigated numerically for low values of Reynolds and Mach numbers.The 2D governing equations were solved using Finite Element Method with first-order slip boundary conditions(Comsol Multiphysics software).A validation was performed by comparing with similar configuration from the literature.It was found that our model can accurately predict the pressure driven flow in microchannels.Several interesting findings are reported about the Relative pressure,longitudinal velocity,Mach number,effect of gas rarefaction and flow rate.
文摘Global temperature is predicted to increase in the end of the century and one of the primary consequences of this warming is the sea level rise. Considering the vulnerabilities on coastal systems and water resources, it is important to evaluate the potential effects of this rising in coastal areas, since the saline intrusion on rivers would be intensified, leading to problems related to water quality. In this context, the present work aimed to verify saline intrusion changes along an important river, São Francisco Canal, located in Rio de Janeiro State, Brazil. For this purpose, a hydrodynamic modeling was performed using SisBaHiA, considering different sea levels and tide conditions. According to the results, it was verified the intensification on saline intrusion and higher salinity values due to a sea level rise of 0.5 m. These results show that new licenses for water withdrawals must be carefully analyzed as the fluvial flow plays an important role to contain the saltwater intrusion on the studied river. Accordingly, it is recommended the evaluation of climate change effects in order to choose best strategies to reduce coastal vulnerability, and the use of this theme on environmental licensing and territorial planning, integrating water planning with coastal management.
文摘The production process of clean hydrogen by iso-octane steam reforming in a micro-reactor under atmospheric pressure,and the high temperature was investigated.The simulation is done using momentum conservation,mass conservation,and convection-diffusion equations,represented by the Navier-Stocks equations,the continuity equation,and the Steffan-Maxwell equation respectively.The resolution was performed using a differential equations discretization into their conservative by the finite element method with an unconditionally stable scheme.An analysis of the hydrodynamics of the flow effect shows that the hydrogen produced by iso-octane reforming is proportional to the mixed flow Reynolds number.
文摘The goal of this study is to examine the energetic,entransy,and exergetic methodologies employed to estimate the ideal insulation thickness for construction walls in terms of cost and ecological impact.To achieve these goals,the life cycle cost analysis-based insulating thicknesses of the various methods are evaluated along with the overall costs,yearly cost reductions,and total expenses.The fuel consumption,CO_(2) emissions,and ecological effects are then compared using an environmental analysis based on the three methodologies.The savings of hollow concrete brick(HCB),compressed stabilized earth brick(CSEB),and sundried earth brick(SEB)walls are evaluated along with the insulation thicknesses in terms of cost and ecological impact.As a result,it is determined that the exergetic technique is better suited for optimizing insulating thickness.For CSEB,SEB,and HCB walls,the economic ideal insulation thicknesses are 0.01 m,0.016 m,and 0.02 m,with yearly financial savings of 5$⋅m^(-2),7.5$⋅m^(-2),and 9$⋅m^(-2).For CSEB,SEB,and HCB walls,accordingly,the ecological optimal insulation thicknesses are 0.023 m,0.032 m,and 0.040 m,with net savings of exergetic ecological impact equal to 59 mPts⋅m^(-2),55 mPts⋅m^(-2),and 51 mPts⋅m^(-2).
