Spatio-temporal variability and dynamics in Sahelian agro-pastoral zones make each local situation a special case. These specificities must be considered to guide the dissemination of agricultural options with a view ...Spatio-temporal variability and dynamics in Sahelian agro-pastoral zones make each local situation a special case. These specificities must be considered to guide the dissemination of agricultural options with a view to sustainable development. The territorial scale of municipalities is not sufficient for this necessary contextualization;the scale of the “village terroir” seems to be a better option. This is the hypothesis we put forward in the framework of the Global Collaboration for Resilient Food Systems program (CRFS), i.e. local context is spatially defined by village terroir. The study is based on data collected through participatory mapping and surveys in “village terroirs” in three regions of Niger (Maradi, Dosso and Tillabéri). Then the links between farm managers and their cultivated land, as well as the spatio-temporal dynamics of local context are analyzed. This study provides evidence of the existence and functional usefulness of the village terroir for farmers, their land management and their activities. It demonstrates the usefulness of contextualizing agricultural options at this scale. Their analysis elucidates the links between “terroirs village” and the specific functioning of the agrosocio-ecosystems acting on each of them, thus laying the systemic and geographical foundations for a model of the spatio- temporal dynamics of “village terroirs”. This initial work has opened up new perspectives in modeling and sustainable development.展开更多
The present work deals with the study of the thermal performances of a convective dryer for fruits and vegetables. This dryer, operating with energy generated from the combustion of biomass in a boiler connected to a ...The present work deals with the study of the thermal performances of a convective dryer for fruits and vegetables. This dryer, operating with energy generated from the combustion of biomass in a boiler connected to a water/air heat exchanger could be a solution to the problematic of energy related to drying. An experimental and theoretical study is carried out on the temperature profile inside the dryer. For this purpose, 10.3 kg of tomatoes were dried on the experimental setup. The operation lasted about 16 hours and reduced the moisture content from 93.8% to 12% in wet basis. The overall thermal efficiency of the convective dryer during the trial is 10.76%. For the theoretical study, the dryer components (boiler, water/air exchanger and drying chamber) are first modeled individually;the different sub-programs are then coupled to form the convective dryer program. The method of global heat balances combined with the one called “ε-NUT” is used. The set of equations is discretized using the implicit method of finite differences, then solved with the Gauss algorithm in Fortran 90. The theoretical results obtained are in good agreement with those measured.展开更多
This work deals with the estimation of solar radiation through a solar tracker aimed at evaluating the effect of solar tracking on the solar deposit in Burkina Faso. Using a two-axis solar tracking system, we experime...This work deals with the estimation of solar radiation through a solar tracker aimed at evaluating the effect of solar tracking on the solar deposit in Burkina Faso. Using a two-axis solar tracking system, we experimentally measured solar radiation at our Joseph KI-ZERBO University site and compared it with that obtained by a numerical simulation run using Fortran programming software based on a mathematical model by Brichambaut. The results obtained from the mathematical and experimental studies show that, with a solar tracker, on a clear-sky day, solar irradiation is between 800 W·m−2 and 1000 W·m−2 between about 8 a.m. and 4 p.m., i.e. a duration of 8 hours of insolation. Analysis of the numerical and experimental results shows very good quantitative and qualitative agreement, with an average relative error of 18%.展开更多
A numerical approach to heat and mass transfer in a large water reservoir is presented. This water reservoir is likened to a parallelepiped reservoir whose vertical and lower walls are adiabatic and impermeable. The e...A numerical approach to heat and mass transfer in a large water reservoir is presented. This water reservoir is likened to a parallelepiped reservoir whose vertical and lower walls are adiabatic and impermeable. The equations that govern natural convection in water are solved by the finite volume method and Thomas’salgorithm. The adequacy between the velocity and pressure fields is ensured by the SIMPLE algorithm. We are going to evaluate the water losses by evaporation from three dams in the Nakanbé basin in Burkina Faso for a period of thirty years, that is to say from January 1, 1991, to March 15, 2020. The three dams have a rate of evaporation greater than 40% of the volume of water stored. Indeed the rate of evaporation in each dam increases with the water filling rate in the reservoir: we have observed the following results for each dam in the Nakanbé basin;for the date of 02/27/1988 to 03/13/2020., the Loumbila dam received a total volume of stored water of 22.02 Mm<sup>3</sup> and 10.57 Mm<sup>3</sup> as the total volume of water evaporated at the same date. At the Ouaga dam (2 + 3), it stored a water volume of 4.06 Mm<sup>3</sup> and evaporated 2.03 Mm<sup>3</sup> of its storage volume from 01/01/1988 to 05/07/2016. Finally, with regard to the Bagré dam, it stored 745.16 Mm<sup>3</sup> of water and 365.13 Mm<sup>3</sup> as the volume of water evaporated from 01/01/1993 to 03/31/2020.展开更多
Due to the large amounts of pesticides commonly used and their impact on health, prompt and accurate pesticide analysis is important. This review gives an overview of recent advances and new trends in biosensors for p...Due to the large amounts of pesticides commonly used and their impact on health, prompt and accurate pesticide analysis is important. This review gives an overview of recent advances and new trends in biosensors for pesticide detection. Optical, electrochemical and piezoelectric biosensors have been reported based on the detection method. In this review biosensors have been classified according to the immobilized biorecognition element: enzymes, cells, antibodies and, more rarely, DNA. The use of tailor-designed biomolecules, such as aptamers and molecularly imprinted polymers, is reviewed. Artificial Neural Networks, that allow the analysis of pesticide mixtures are also presented. Recent advances in the field of nanomaterials merit special mention. The incorporation of nanomaterials provides highly sensitive sensing devices allowing the efficient detection of pesticides.展开更多
The two-phase thermosyphon loop is an efficient solution for space cooling. This paper presents the simulation results of numerical studies on the heat transfer and thermal performance of a two-phase thermosiphon loop...The two-phase thermosyphon loop is an efficient solution for space cooling. This paper presents the simulation results of numerical studies on the heat transfer and thermal performance of a two-phase thermosiphon loop for passive air-conditioning of a house. The fluid considered in this study is methanol, which is compatible with copper and is environmentally friendly. These numerical results show that the temperature at the evaporator wall drops from 23<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C to 13<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C and increases at the condenser. The solar flux density has a strong influence on the condenser temperature. The mass flow rates and masses at the evaporator and condenser increase with temperature. The variation of evaporating and condensing temperature affects the performance of the system. For a constant evaporating and condensing temperature of 2<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C and 29<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C, the COP is 0.77 and 0.84 respectively. With these results, the use of the two-phase thermosyphon loop in air conditioning is possible to obtain a thermal comfort of the occupants acceptable by the standards but with a large exchange surface of the evaporator.展开更多
In this work, a numerical study of heat transfers in a metallic pressure cooker isolated with kapok wool was carried out. This equipment works like a thermos, allowing finishing cooking meals only thanks to the heat s...In this work, a numerical study of heat transfers in a metallic pressure cooker isolated with kapok wool was carried out. This equipment works like a thermos, allowing finishing cooking meals only thanks to the heat stored at the beginning of cooking, which generates energy savings. Cooked meals are also kept hot for long hours. In our previous work, we have highlighted the performances of the pressure cooker when making common dishes in Burkina Faso. Also, the parameters (thickness and density) of the insulating matrix allowing having such performances as well as the influence of the climatic conditions on the pressure cooker operation were analyzed in detail in this present work. The numerical methodology is based on the nodal method and the transfer equations obtained by making an energy balance on each node have been discretized using an implicit scheme with finite differences and resolved by the Gauss algorithm. Numerical results validated experimentally show that the thickness of the kapok wool as well as its density play an important role in the pressure cooker operation. In addition, equipment performances are very little influenced by the weather conditions of the city of Ouagadougou (Burkina Faso).展开更多
This work gives tools to overcome the difficulty to determine experimentally physical properties for vegetable oils within the range of temperature typically observed during the injection phase in a diesel engine. Kno...This work gives tools to overcome the difficulty to determine experimentally physical properties for vegetable oils within the range of temperature typically observed during the injection phase in a diesel engine. Knowing vegetable oils’ physical properties to these ranges of temperature is of fundamental importance when modeling their combustion in diesel engine. However, vegetable oils’ experimental physical properties data are rare in the literature for temperature above 523 K. This paper describes experimental measurements and estimation methods for density, dynamic viscosity, thermal conductivity and heat capacity of vegetable oils for this particular range of temperature. The methodology uses several correlative methods using group contribution approach for each property and compares experimental data with predicted one to select the more accurate model. This work has shown the rapeseed and jatropha oils’ physical properties can be satisfactorily predicted as a function of temperature using group contribution approach.展开更多
The accelerated depletion of oil reserves and the often exorbitant cost of fossil fuels contribute to the development of fuels from renewable sources. The objective of this work is to analyze the influence of the prop...The accelerated depletion of oil reserves and the often exorbitant cost of fossil fuels contribute to the development of fuels from renewable sources. The objective of this work is to analyze the influence of the properties of renewable fuels on their evaporation in natural convection, their combustion and their use in internal combustion engines. A summary of the various numerical and experimental works from the literature has been presented in this work. This work focuses on the numerical modelling of the natural convection evaporation of an isolated drop of a liquid fuel in natural convection. The transfers in the liquid and vapour phases are described by the conservation equations of mass and species, momentum and energy. The main feature of this work is the consideration of advection, azimuthal angle and thickness of the vapour phase of the drop during evaporation of the drop.展开更多
We consider a differential variational-hemivariational inequality with constraints,in the framework of reflexive Banach spaces.The existence of a unique mild solution of the inequality,together with its stability,was ...We consider a differential variational-hemivariational inequality with constraints,in the framework of reflexive Banach spaces.The existence of a unique mild solution of the inequality,together with its stability,was proved in[1].Here,we complete these results with existence,uniqueness and convergence results for an associated penalty-type method.To this end,we construct a sequence of perturbed differential variational-hemivariational inequalities governed by perturbed sets of constraints and penalty coefficients.We prove the unique solvability of each perturbed inequality as well as the convergence of its solution to the solution of the original inequality.Then,we consider a mathematical model which describes the equilibrium of a viscoelastic rod in unilateral contact.The weak formulation of the model is in a form of a differential variational-hemivariational inequality in which the unknowns are the displacement field and the history of the deformation.We apply our abstract penalty method in the study of this inequality and provide the corresponding mechanical interpretations.展开更多
Solar cookers are a good option in developing countries with high solar potential for environmentally friendly cooking and reduced pressure on forests. However, they are still affected by the intermittency of the sun....Solar cookers are a good option in developing countries with high solar potential for environmentally friendly cooking and reduced pressure on forests. However, they are still affected by the intermittency of the sun. In order to overcome this problem, in this work, a box type solar cooker integrated Jatropha oil as a heat storage material is fabricated and experimented with. The design was examined with a maximum stagnation temperature of 157.7°C. The recorded cooking power vanished between 78.4 and 103.6 W, while thermal efficiency varied from 41.26% to 58.78%. The energy transfer cycle test, including charge and discharge revealed that 91.18% of the heat lost through the cooker could be recovered by the heat storage unit and a large amount is restored to the system during cloudiness or a temperature perturbation.展开更多
<span style="font-family:Verdana;">This work concerns a modeling of habitat equipped with an adsorption cooling unit powered by a geothermal heat pump in the context of the climate of the Comoros Islan...<span style="font-family:Verdana;">This work concerns a modeling of habitat equipped with an adsorption cooling unit powered by a geothermal heat pump in the context of the climate of the Comoros Islands. Cooling unit is a simple system consisting of an a</span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">d</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">sorber, </span><span style="font-family:Verdana;">condenser and evaporator. The modeling of the habitat-air conditioning system was based on a description of heat and mass transfers. The first</span><sup> </sup><span style="font-family:Verdana;">law of thermodynamics on the energy conservation using the analogies between heat and electrical transfers is used to establish the equations of the model. Zeolite-methanol pair and Dubinin-Astakhov adsorption model are used to describe the amount of adsorbed mass. The finite difference method applied to a point of the considered exchange surface is used to discretize equations and </span><span style="font-family:Verdana;">resolve them. The coupling of the system takes place through a convective tr</span><span style="font-family:Verdana;">ansfer betw</span><span style="font-family:Verdana;">een the air inside habitat and the evaporator</span><span style="font-family:Verdana;">’s surface. This article </span><span style="font-family:Verdana;">presents results for typical November days in Comoros. Different temperatu</span><span style="font-family:Verdana;">res </span><span style="font-family:Verdana;">of habitat with and without a cooling unit show that using the adsorption co</span><span style="font-family:Verdana;">oling unit can help lower internal temperatures. We observe a temperature difference of 2.14 K in particular at 2 p.m., if the air conditioning starts at 8 a.m. The influence of the input parameters on the air inside the habitat makes it possible to assess the impact on indoor comfort. The COP<sub>th</sub> can reach 0.46. </span><span style="font-family:Verdana;">However, we can get a high performance if we optimize temperature thresh</span><span style="font-family:Verdana;">olds. </span><span style="font-family:Verdana;">These show that this type of cooling unit can help improve the habitat therm</span><span style="font-family:Verdana;">al comfort in a tropical and dry climate.</span></span></span></span>展开更多
This work concerns an experimental and numerical study of energy losses in a typical oven usually used in the agro-food craft sector in Burkina Faso. The experimental results were obtained by infrared thermography of ...This work concerns an experimental and numerical study of energy losses in a typical oven usually used in the agro-food craft sector in Burkina Faso. The experimental results were obtained by infrared thermography of the oven and by monitoring the evolution of the wall temperatures using thermocouples connected to a data acquisition system. These results indicate that the energy losses are mainly through the walls of the oven. The numerical study based on the energy balance and corroborated by the experimental study made it possible to quantify these losses of energy which represents almost half of the fuel used. These results will allow us to work on a new, more efficient oven model for the grilling sector in Burkina Faso.展开更多
This work is devoted to an experimental study of metallic pressure cooker insulated with kapok wool, a vegetal biodegradable fiber. Experiments conducted on the cooling of hot water in the equipment revealed very low ...This work is devoted to an experimental study of metallic pressure cooker insulated with kapok wool, a vegetal biodegradable fiber. Experiments conducted on the cooling of hot water in the equipment revealed very low heat losses and a time constant of 60 hours on average. As a result, the equipment makes it possible to finish cooking meals only thanks to the heat stored at the beginning of cooking and keeps cooked dishes warm for long hours. The thermal phase shift of the pressure cooker is around 7?h. Cooking tests conducted on some local dishes revealed about 70% butane gas savings for cooking cowpea and white rice, 38% for cooking fatty rice, 75% for pasta and couscous, and 30% for cooking potato stew. These results show that this technology can contribute to minimizing?energy consumption in the restaurant sector.展开更多
This work presents a contribution to the study of the process of cold production by adsorption from solar energy. In this paper, we discuss a comparative study of the operation of a solar adsorption refrigerator using...This work presents a contribution to the study of the process of cold production by adsorption from solar energy. In this paper, we discuss a comparative study of the operation of a solar adsorption refrigerator using the silica gel-water couple and the zeolite-water couple through dynamic modeling and simulation. The mathematical model representing the evolution of heat and mass transfer at each component of the adsorption solar refrigerator has been developed. It appears from this study that the evolution of the temperature of the two adsorbents (zeolite and silica gel) is quasi-similar throughout the operating cycle. However, the maximum mass of water vapor adsorbed by the silicagel (0.24 kg/kg) is higher than that adsorbed by the zeolite (0.201 kg/kg). In the same way, the mass of water vapor cycled, obtained with the silicagel-water couple which is 0.14 kg/kg, is higher than that obtained with the zeolite-water couple which is 0.081 kg/kg. Therefore, the amount of cold produced 9.178 MJ and the solar coefficient of performance 0.378 obtained with the solar refrigerator using the silica gel-water couple, are better.展开更多
Fresh water is one of the most significant resources for human activities and survival,and irrigation is among the most important uses of water.The sustainibility and performance of irrigation canals can be greatly af...Fresh water is one of the most significant resources for human activities and survival,and irrigation is among the most important uses of water.The sustainibility and performance of irrigation canals can be greatly affected by sediment transport and deposition.In our previous works,we proposed a Lattice Boltzmann model for simulating a free surface flow in an irrigation canal,as an alternative to more traditional models mainly based on shallow water equations.Here we introduce the sedimentation phenomenon into our model by adding a new algorithm,based on the earlier work by B.Chopard,A.Dupuis and A.Masselot[9,11,12,27].Transport,erosion,deposition and toppling of sediments are taken into account and enable the global sedimentation algorithm to simulate different transport modes such as bed load and suspended load.In the present work,we study both the behaviour of a sediment deposit located at an underflow submerged gate(depending on the gate opening and the flow discharge)and the influence of the presence of such a deposit on the flow.Both numerical and experimental validations have been performed.The experiments were realized on the micro-canal of the LCIS laboratory at Valence,France.The comparisons between simulations and experiments give good qualitative agreement.展开更多
Pollen analysis was carried out on the Core MD982194 of 29.78 m retrieved from the Middle Okinawa Trough which was dated as old as -200 ka BP. The results revealed that pollen assemblages mainly presented an alternati...Pollen analysis was carried out on the Core MD982194 of 29.78 m retrieved from the Middle Okinawa Trough which was dated as old as -200 ka BP. The results revealed that pollen assemblages mainly presented an alternation of coniferous and herb pollen. The coniferous saccate pollen, principally Pinus and Tsuga, predominated in most parts of the core, especially highlighted in the interstadial stages including MIS 1,3, 5 and MIS7, whereas the herb pollen significantly increased in the gla- cial periods. Thus the pollen flora and their percentages showed the sensitive changes under the influence of ice volume during the glacial and interglacial periods. Our record from this core has first documented that the percentage of Cyperaceae was ex- tremely high in the glacial stages with a notable increase in Artemisia, Gramineae, Asteraceae, Cbenopodiaceae, and freshwa- ter algae, which can be used as a proxy for sea-level change at the study site because of their close negative correlation of the orbital-scale changes in sea level. The distance between the continental coastline and the Okinawa Trough has deeply short- ened due to the sea-level drop in the LGM. As a result, the sediment materials from Yangtze River were extensively deposited on the flat, exposed continental shelf owing to the rapid decline of river flow speed, leading to that pollen grains from Okinawa Trough are derived mainly from the flat coastal vegetation of exposed continental shelf at glacial stages. Changes of pollen as- semblage were consistent with the variation of temperature and humidity, which showed that the percentage of arboreal pollen was highly augmented at MIS 7, 5 and MIS 1, corresponding to the strengthening of the East Asian summer monsoon and in- creasing of rainfall. Moreover, the peak of Pinus percentage in MIS 5.3, 5.1 and MIS 3.3 may be closely linked by orbital and sub-orbital cycles of solar radiation and monsoonal variability. The present study of core MD981294 implied lower tempera- ture and precipitation during the lowest sea-level stage (LGM), and more visibly testified that the vegetation of the flat plain on the exposed continental shelf was dominated by intrazonal communities such as halophyte grasslands and freshwater wetlands instead of zonal steppe or semi-arid desert. All above evidence demonstrated that the fundamental changes of pollen assem- blage and their origins in Okinawa Trough since -200 ka BP were affected by combine factors including the coastline position and climate fluctuation. Moreover, the substantial shortening of distance between shoreline and the Okinawa Trough driven by orbital insolation cycles was clearly indicated by the pollen spectra, whereas the source-area climate signal of the pollen record was largely weakened.展开更多
In this work, we perform a numerical study of a water flow over a stepped spillway. This flow is described by the Reynolds averaged Navier-Stokes equation (RANS) associated with the turbulence k - model. These equat...In this work, we perform a numerical study of a water flow over a stepped spillway. This flow is described by the Reynolds averaged Navier-Stokes equation (RANS) associated with the turbulence k - model. These equations are solved using a commercial software based on the finite volume scheme and an unstructured mesh. The air-water flow was modeled using volume of fluid (VOF) and multiphasic methods. The characteristics of the profile, etc.. We analyze the effects on the flow structure of the flow were investigated including the total pressure, the velocity steps and countermarch inclination, the air injection through the countermarch into the water flow and the dynamics water discharges. Results show that the inclination of the countermarch relative to the vertical and the air injection into the water flow increase the total pressure in the neighbourhood of the steps.展开更多
文摘Spatio-temporal variability and dynamics in Sahelian agro-pastoral zones make each local situation a special case. These specificities must be considered to guide the dissemination of agricultural options with a view to sustainable development. The territorial scale of municipalities is not sufficient for this necessary contextualization;the scale of the “village terroir” seems to be a better option. This is the hypothesis we put forward in the framework of the Global Collaboration for Resilient Food Systems program (CRFS), i.e. local context is spatially defined by village terroir. The study is based on data collected through participatory mapping and surveys in “village terroirs” in three regions of Niger (Maradi, Dosso and Tillabéri). Then the links between farm managers and their cultivated land, as well as the spatio-temporal dynamics of local context are analyzed. This study provides evidence of the existence and functional usefulness of the village terroir for farmers, their land management and their activities. It demonstrates the usefulness of contextualizing agricultural options at this scale. Their analysis elucidates the links between “terroirs village” and the specific functioning of the agrosocio-ecosystems acting on each of them, thus laying the systemic and geographical foundations for a model of the spatio- temporal dynamics of “village terroirs”. This initial work has opened up new perspectives in modeling and sustainable development.
文摘The present work deals with the study of the thermal performances of a convective dryer for fruits and vegetables. This dryer, operating with energy generated from the combustion of biomass in a boiler connected to a water/air heat exchanger could be a solution to the problematic of energy related to drying. An experimental and theoretical study is carried out on the temperature profile inside the dryer. For this purpose, 10.3 kg of tomatoes were dried on the experimental setup. The operation lasted about 16 hours and reduced the moisture content from 93.8% to 12% in wet basis. The overall thermal efficiency of the convective dryer during the trial is 10.76%. For the theoretical study, the dryer components (boiler, water/air exchanger and drying chamber) are first modeled individually;the different sub-programs are then coupled to form the convective dryer program. The method of global heat balances combined with the one called “ε-NUT” is used. The set of equations is discretized using the implicit method of finite differences, then solved with the Gauss algorithm in Fortran 90. The theoretical results obtained are in good agreement with those measured.
文摘This work deals with the estimation of solar radiation through a solar tracker aimed at evaluating the effect of solar tracking on the solar deposit in Burkina Faso. Using a two-axis solar tracking system, we experimentally measured solar radiation at our Joseph KI-ZERBO University site and compared it with that obtained by a numerical simulation run using Fortran programming software based on a mathematical model by Brichambaut. The results obtained from the mathematical and experimental studies show that, with a solar tracker, on a clear-sky day, solar irradiation is between 800 W·m−2 and 1000 W·m−2 between about 8 a.m. and 4 p.m., i.e. a duration of 8 hours of insolation. Analysis of the numerical and experimental results shows very good quantitative and qualitative agreement, with an average relative error of 18%.
文摘A numerical approach to heat and mass transfer in a large water reservoir is presented. This water reservoir is likened to a parallelepiped reservoir whose vertical and lower walls are adiabatic and impermeable. The equations that govern natural convection in water are solved by the finite volume method and Thomas’salgorithm. The adequacy between the velocity and pressure fields is ensured by the SIMPLE algorithm. We are going to evaluate the water losses by evaporation from three dams in the Nakanbé basin in Burkina Faso for a period of thirty years, that is to say from January 1, 1991, to March 15, 2020. The three dams have a rate of evaporation greater than 40% of the volume of water stored. Indeed the rate of evaporation in each dam increases with the water filling rate in the reservoir: we have observed the following results for each dam in the Nakanbé basin;for the date of 02/27/1988 to 03/13/2020., the Loumbila dam received a total volume of stored water of 22.02 Mm<sup>3</sup> and 10.57 Mm<sup>3</sup> as the total volume of water evaporated at the same date. At the Ouaga dam (2 + 3), it stored a water volume of 4.06 Mm<sup>3</sup> and evaporated 2.03 Mm<sup>3</sup> of its storage volume from 01/01/1988 to 05/07/2016. Finally, with regard to the Bagré dam, it stored 745.16 Mm<sup>3</sup> of water and 365.13 Mm<sup>3</sup> as the volume of water evaporated from 01/01/1993 to 03/31/2020.
文摘Due to the large amounts of pesticides commonly used and their impact on health, prompt and accurate pesticide analysis is important. This review gives an overview of recent advances and new trends in biosensors for pesticide detection. Optical, electrochemical and piezoelectric biosensors have been reported based on the detection method. In this review biosensors have been classified according to the immobilized biorecognition element: enzymes, cells, antibodies and, more rarely, DNA. The use of tailor-designed biomolecules, such as aptamers and molecularly imprinted polymers, is reviewed. Artificial Neural Networks, that allow the analysis of pesticide mixtures are also presented. Recent advances in the field of nanomaterials merit special mention. The incorporation of nanomaterials provides highly sensitive sensing devices allowing the efficient detection of pesticides.
文摘The two-phase thermosyphon loop is an efficient solution for space cooling. This paper presents the simulation results of numerical studies on the heat transfer and thermal performance of a two-phase thermosiphon loop for passive air-conditioning of a house. The fluid considered in this study is methanol, which is compatible with copper and is environmentally friendly. These numerical results show that the temperature at the evaporator wall drops from 23<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C to 13<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C and increases at the condenser. The solar flux density has a strong influence on the condenser temperature. The mass flow rates and masses at the evaporator and condenser increase with temperature. The variation of evaporating and condensing temperature affects the performance of the system. For a constant evaporating and condensing temperature of 2<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C and 29<span style="color:#111111;font-family:Roboto, sans-serif;font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>C, the COP is 0.77 and 0.84 respectively. With these results, the use of the two-phase thermosyphon loop in air conditioning is possible to obtain a thermal comfort of the occupants acceptable by the standards but with a large exchange surface of the evaporator.
基金the Embassy of France in Burkina Faso,the National Research Fund for Innovation and Development(FONRID)and the International Science Program(ISP)of UPPSALA University for their financial support which allowed the realization of this work.
文摘In this work, a numerical study of heat transfers in a metallic pressure cooker isolated with kapok wool was carried out. This equipment works like a thermos, allowing finishing cooking meals only thanks to the heat stored at the beginning of cooking, which generates energy savings. Cooked meals are also kept hot for long hours. In our previous work, we have highlighted the performances of the pressure cooker when making common dishes in Burkina Faso. Also, the parameters (thickness and density) of the insulating matrix allowing having such performances as well as the influence of the climatic conditions on the pressure cooker operation were analyzed in detail in this present work. The numerical methodology is based on the nodal method and the transfer equations obtained by making an energy balance on each node have been discretized using an implicit scheme with finite differences and resolved by the Gauss algorithm. Numerical results validated experimentally show that the thickness of the kapok wool as well as its density play an important role in the pressure cooker operation. In addition, equipment performances are very little influenced by the weather conditions of the city of Ouagadougou (Burkina Faso).
基金A.S.Zongo expresses his gratitude to French Cooperation in Burkina Faso who,through the Service for Cooperation and Cultural Action(SCAC),financed this study by awarding an internship fellowship in 2017 at CIRAD Montpellier.
文摘This work gives tools to overcome the difficulty to determine experimentally physical properties for vegetable oils within the range of temperature typically observed during the injection phase in a diesel engine. Knowing vegetable oils’ physical properties to these ranges of temperature is of fundamental importance when modeling their combustion in diesel engine. However, vegetable oils’ experimental physical properties data are rare in the literature for temperature above 523 K. This paper describes experimental measurements and estimation methods for density, dynamic viscosity, thermal conductivity and heat capacity of vegetable oils for this particular range of temperature. The methodology uses several correlative methods using group contribution approach for each property and compares experimental data with predicted one to select the more accurate model. This work has shown the rapeseed and jatropha oils’ physical properties can be satisfactorily predicted as a function of temperature using group contribution approach.
文摘The accelerated depletion of oil reserves and the often exorbitant cost of fossil fuels contribute to the development of fuels from renewable sources. The objective of this work is to analyze the influence of the properties of renewable fuels on their evaporation in natural convection, their combustion and their use in internal combustion engines. A summary of the various numerical and experimental works from the literature has been presented in this work. This work focuses on the numerical modelling of the natural convection evaporation of an isolated drop of a liquid fuel in natural convection. The transfers in the liquid and vapour phases are described by the conservation equations of mass and species, momentum and energy. The main feature of this work is the consideration of advection, azimuthal angle and thickness of the vapour phase of the drop during evaporation of the drop.
基金supported by the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement(823731CONMECH)supported by National Natural Science Foundation of China(11671101),supported by National Natural Science Foundation of China(11961074)+2 种基金Guangxi Natural Science Foundation(2021GXNSFAA075022)Project of Guangxi Education Department(2020KY16017)Yulin normal university of scientific research fund for high-level talents(G2019ZK39,G2021ZK06)。
文摘We consider a differential variational-hemivariational inequality with constraints,in the framework of reflexive Banach spaces.The existence of a unique mild solution of the inequality,together with its stability,was proved in[1].Here,we complete these results with existence,uniqueness and convergence results for an associated penalty-type method.To this end,we construct a sequence of perturbed differential variational-hemivariational inequalities governed by perturbed sets of constraints and penalty coefficients.We prove the unique solvability of each perturbed inequality as well as the convergence of its solution to the solution of the original inequality.Then,we consider a mathematical model which describes the equilibrium of a viscoelastic rod in unilateral contact.The weak formulation of the model is in a form of a differential variational-hemivariational inequality in which the unknowns are the displacement field and the history of the deformation.We apply our abstract penalty method in the study of this inequality and provide the corresponding mechanical interpretations.
文摘Solar cookers are a good option in developing countries with high solar potential for environmentally friendly cooking and reduced pressure on forests. However, they are still affected by the intermittency of the sun. In order to overcome this problem, in this work, a box type solar cooker integrated Jatropha oil as a heat storage material is fabricated and experimented with. The design was examined with a maximum stagnation temperature of 157.7°C. The recorded cooking power vanished between 78.4 and 103.6 W, while thermal efficiency varied from 41.26% to 58.78%. The energy transfer cycle test, including charge and discharge revealed that 91.18% of the heat lost through the cooker could be recovered by the heat storage unit and a large amount is restored to the system during cloudiness or a temperature perturbation.
文摘<span style="font-family:Verdana;">This work concerns a modeling of habitat equipped with an adsorption cooling unit powered by a geothermal heat pump in the context of the climate of the Comoros Islands. Cooling unit is a simple system consisting of an a</span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">d</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">sorber, </span><span style="font-family:Verdana;">condenser and evaporator. The modeling of the habitat-air conditioning system was based on a description of heat and mass transfers. The first</span><sup> </sup><span style="font-family:Verdana;">law of thermodynamics on the energy conservation using the analogies between heat and electrical transfers is used to establish the equations of the model. Zeolite-methanol pair and Dubinin-Astakhov adsorption model are used to describe the amount of adsorbed mass. The finite difference method applied to a point of the considered exchange surface is used to discretize equations and </span><span style="font-family:Verdana;">resolve them. The coupling of the system takes place through a convective tr</span><span style="font-family:Verdana;">ansfer betw</span><span style="font-family:Verdana;">een the air inside habitat and the evaporator</span><span style="font-family:Verdana;">’s surface. This article </span><span style="font-family:Verdana;">presents results for typical November days in Comoros. Different temperatu</span><span style="font-family:Verdana;">res </span><span style="font-family:Verdana;">of habitat with and without a cooling unit show that using the adsorption co</span><span style="font-family:Verdana;">oling unit can help lower internal temperatures. We observe a temperature difference of 2.14 K in particular at 2 p.m., if the air conditioning starts at 8 a.m. The influence of the input parameters on the air inside the habitat makes it possible to assess the impact on indoor comfort. The COP<sub>th</sub> can reach 0.46. </span><span style="font-family:Verdana;">However, we can get a high performance if we optimize temperature thresh</span><span style="font-family:Verdana;">olds. </span><span style="font-family:Verdana;">These show that this type of cooling unit can help improve the habitat therm</span><span style="font-family:Verdana;">al comfort in a tropical and dry climate.</span></span></span></span>
文摘This work concerns an experimental and numerical study of energy losses in a typical oven usually used in the agro-food craft sector in Burkina Faso. The experimental results were obtained by infrared thermography of the oven and by monitoring the evolution of the wall temperatures using thermocouples connected to a data acquisition system. These results indicate that the energy losses are mainly through the walls of the oven. The numerical study based on the energy balance and corroborated by the experimental study made it possible to quantify these losses of energy which represents almost half of the fuel used. These results will allow us to work on a new, more efficient oven model for the grilling sector in Burkina Faso.
基金the National Research Fund for Innovation and Development(FONRID)the International Science Program(ISP)for their financial support.
文摘This work is devoted to an experimental study of metallic pressure cooker insulated with kapok wool, a vegetal biodegradable fiber. Experiments conducted on the cooling of hot water in the equipment revealed very low heat losses and a time constant of 60 hours on average. As a result, the equipment makes it possible to finish cooking meals only thanks to the heat stored at the beginning of cooking and keeps cooked dishes warm for long hours. The thermal phase shift of the pressure cooker is around 7?h. Cooking tests conducted on some local dishes revealed about 70% butane gas savings for cooking cowpea and white rice, 38% for cooking fatty rice, 75% for pasta and couscous, and 30% for cooking potato stew. These results show that this technology can contribute to minimizing?energy consumption in the restaurant sector.
文摘This work presents a contribution to the study of the process of cold production by adsorption from solar energy. In this paper, we discuss a comparative study of the operation of a solar adsorption refrigerator using the silica gel-water couple and the zeolite-water couple through dynamic modeling and simulation. The mathematical model representing the evolution of heat and mass transfer at each component of the adsorption solar refrigerator has been developed. It appears from this study that the evolution of the temperature of the two adsorbents (zeolite and silica gel) is quasi-similar throughout the operating cycle. However, the maximum mass of water vapor adsorbed by the silicagel (0.24 kg/kg) is higher than that adsorbed by the zeolite (0.201 kg/kg). In the same way, the mass of water vapor cycled, obtained with the silicagel-water couple which is 0.14 kg/kg, is higher than that obtained with the zeolite-water couple which is 0.081 kg/kg. Therefore, the amount of cold produced 9.178 MJ and the solar coefficient of performance 0.378 obtained with the solar refrigerator using the silica gel-water couple, are better.
文摘Fresh water is one of the most significant resources for human activities and survival,and irrigation is among the most important uses of water.The sustainibility and performance of irrigation canals can be greatly affected by sediment transport and deposition.In our previous works,we proposed a Lattice Boltzmann model for simulating a free surface flow in an irrigation canal,as an alternative to more traditional models mainly based on shallow water equations.Here we introduce the sedimentation phenomenon into our model by adding a new algorithm,based on the earlier work by B.Chopard,A.Dupuis and A.Masselot[9,11,12,27].Transport,erosion,deposition and toppling of sediments are taken into account and enable the global sedimentation algorithm to simulate different transport modes such as bed load and suspended load.In the present work,we study both the behaviour of a sediment deposit located at an underflow submerged gate(depending on the gate opening and the flow discharge)and the influence of the presence of such a deposit on the flow.Both numerical and experimental validations have been performed.The experiments were realized on the micro-canal of the LCIS laboratory at Valence,France.The comparisons between simulations and experiments give good qualitative agreement.
基金supported by the National Natural Science Foundation of China(Grant Nos.41072128 and 40772113)the Fundamental Research Funds for the Central Universities(Grant Nos.11LGJC13 and 10LGZD08)Young Scientist’s Fund of the State Oceanic Administration of China
文摘Pollen analysis was carried out on the Core MD982194 of 29.78 m retrieved from the Middle Okinawa Trough which was dated as old as -200 ka BP. The results revealed that pollen assemblages mainly presented an alternation of coniferous and herb pollen. The coniferous saccate pollen, principally Pinus and Tsuga, predominated in most parts of the core, especially highlighted in the interstadial stages including MIS 1,3, 5 and MIS7, whereas the herb pollen significantly increased in the gla- cial periods. Thus the pollen flora and their percentages showed the sensitive changes under the influence of ice volume during the glacial and interglacial periods. Our record from this core has first documented that the percentage of Cyperaceae was ex- tremely high in the glacial stages with a notable increase in Artemisia, Gramineae, Asteraceae, Cbenopodiaceae, and freshwa- ter algae, which can be used as a proxy for sea-level change at the study site because of their close negative correlation of the orbital-scale changes in sea level. The distance between the continental coastline and the Okinawa Trough has deeply short- ened due to the sea-level drop in the LGM. As a result, the sediment materials from Yangtze River were extensively deposited on the flat, exposed continental shelf owing to the rapid decline of river flow speed, leading to that pollen grains from Okinawa Trough are derived mainly from the flat coastal vegetation of exposed continental shelf at glacial stages. Changes of pollen as- semblage were consistent with the variation of temperature and humidity, which showed that the percentage of arboreal pollen was highly augmented at MIS 7, 5 and MIS 1, corresponding to the strengthening of the East Asian summer monsoon and in- creasing of rainfall. Moreover, the peak of Pinus percentage in MIS 5.3, 5.1 and MIS 3.3 may be closely linked by orbital and sub-orbital cycles of solar radiation and monsoonal variability. The present study of core MD981294 implied lower tempera- ture and precipitation during the lowest sea-level stage (LGM), and more visibly testified that the vegetation of the flat plain on the exposed continental shelf was dominated by intrazonal communities such as halophyte grasslands and freshwater wetlands instead of zonal steppe or semi-arid desert. All above evidence demonstrated that the fundamental changes of pollen assem- blage and their origins in Okinawa Trough since -200 ka BP were affected by combine factors including the coastline position and climate fluctuation. Moreover, the substantial shortening of distance between shoreline and the Okinawa Trough driven by orbital insolation cycles was clearly indicated by the pollen spectra, whereas the source-area climate signal of the pollen record was largely weakened.
基金the ERASMUS MUNDUS AVERROES Program,for the financial support off this study
文摘In this work, we perform a numerical study of a water flow over a stepped spillway. This flow is described by the Reynolds averaged Navier-Stokes equation (RANS) associated with the turbulence k - model. These equations are solved using a commercial software based on the finite volume scheme and an unstructured mesh. The air-water flow was modeled using volume of fluid (VOF) and multiphasic methods. The characteristics of the profile, etc.. We analyze the effects on the flow structure of the flow were investigated including the total pressure, the velocity steps and countermarch inclination, the air injection through the countermarch into the water flow and the dynamics water discharges. Results show that the inclination of the countermarch relative to the vertical and the air injection into the water flow increase the total pressure in the neighbourhood of the steps.