In this work, a model of convective drying of mango slices was developed and validated by experiments. This model was established by considering slices shrinkage in the energy and the mass balances during the thin lay...In this work, a model of convective drying of mango slices was developed and validated by experiments. This model was established by considering slices shrinkage in the energy and the mass balances during the thin layer drying. The drying kinetics and the temperature curves of the product were simulated using the model at various drying temperatures. The simulated curves were then compared to the experimental curves obtained using a convective dryer controlled in temperature and moisture. The results showed that the drying curves were suitably fitted by the thin layer drying model with a correlation coefficient r<sup>2</sup> = 0.997. Thus, taking shrinkage into account, it is possible to predict more effectively the thin layer drying kinetics of mango slices. This study therefore contributed to the mango drying modelling and to the mango dryer setting.展开更多
In the present work, the mass transfer characteristics, namely moisture diffusivity and moisture transfer coefficient of “Violet de Galmi” variety of onions were evaluated using the analytical model. Onions were dri...In the present work, the mass transfer characteristics, namely moisture diffusivity and moisture transfer coefficient of “Violet de Galmi” variety of onions were evaluated using the analytical model. Onions were dried in a single layer at different temperatures (40℃, 50℃, 60℃, and 70℃) and for a relative humidity of drying air of 20%. The results showed a reasonably good agreement between the values predicted by the correlation and the experimental observations. This model computed the Biot number, effective moisture diffusivity, and mass transfer coefficient. Effective diffusion coefficient values are obtained between 0.2578 × 10<sup>-9</sup> m<sup>2</sup>·s<sup>-1</sup> and 0.5460 × 10<sup>-9</sup> m<sup>2</sup>·s<sup>-1</sup>. Mass transfer coefficients of “Violet de Galmi” onion drying vary between 3.37 × 10<sup>-7</sup> m·s<sup>-1</sup> and 13.38 × 10<sup>-7</sup> m·s<sup>-1</sup>. Numbers of mass transfer Biot are found between 0.9797 and 2.9397. The activation energy E<sub>a</sub> is 31.73 kJ·mol<sup>-1</sup>.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
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
This work concerns a dynamic modeling and a numerical simulation of the operation of an adsorption solar refrigeration system using the zeolite-water couple. For this, a mathematical model representing the evolution o...This work concerns a dynamic modeling and a numerical simulation of the operation of an adsorption solar refrigeration system using the zeolite-water couple. For this, a mathematical model representing the evolution of heat and mass transfer at each component of the solar adsorption refrigerator has been developed. We have adopted the Dubinin-Astakhov model for the adsorption kinetics of the zeolite/water pair. This model allows to describe the phenomenon of adsorption and to calculate the rate of adsorbate (water) in the zeolite (adsorbent) as a function of the temperature and the pressure. The equations governing the operation of the solar adsorption refrigerator, deduced from the thermal and mass balances established at the collector adsorber, condenser and evaporator components, were solved by an implicit finite difference scheme and Gauss Seidel’s iterative method. We have validated the model established by applying it to the model of Allouhi et al. 2014. We analyzed the influence of the adsorbate/adsorbent couples, the solar flux, the ambient temperature on the adsorption and desorption process. The temperature profiles obtained representing the temperature evolution of the glass, the absorbent plate, the zeolite-water mixture, the condenser, the evaporator, as well as the pressure and the adsorbed mass allowed us to evaluate the performance of the solar adsorption refrigerator. SCOP is higher the higher the solar flux captured by the collector-adsorber.展开更多
The sorption behaviour and water transport mechanisms inside Spirulina platensis samples were experimentally analysed during isothermal drying at 25℃ and 50℃. Two different products grown in semi-industrial farms fr...The sorption behaviour and water transport mechanisms inside Spirulina platensis samples were experimentally analysed during isothermal drying at 25℃ and 50℃. Two different products grown in semi-industrial farms from Burkina Faso and France with initial water contents respectively of the range from 2.73 kg w /kg dm to 3.12 kg w /kg dm were characterized. A novel procedure has been developed to determine the water content profiles inside samples during isothermal drying. At both temperatures, experimental results underlined that the physical properties of Spirulina are not sensitive to the geographical origin, Burkina-Faso or France. To keep Spirulina at an water activity below 0.6 in order to preserve it from micro-organisms development, sorption isotherm curves show that a sufficient requirement is to lower the water content until an upper limit of w = 0.075 db. The evolution of water transport coefficient as a function of water content highlights a monotonous exponential dependence with a transport coefficient ranging from 1.70 × 10–10 to 94 × 10–10 m2/s. The contribution of solid phase shrinkage to the transport of water is negligible for the last drying steps.展开更多
This paper concerns the study of the influence of the proportion of plastic from polyethylene, on the yields of gas emissions during the combustion of the mixture of “millet stalks and polyethylene plastic bags”, in...This paper concerns the study of the influence of the proportion of plastic from polyethylene, on the yields of gas emissions during the combustion of the mixture of “millet stalks and polyethylene plastic bags”, in a prototype of kiln of potters. During these investigations, we looked at the rate of residual oxygen (O2) and emissions of carbon dioxide (CO2) and nitrogen monoxide (NO), as a function of primary air flow (Q1) and secondary airflow (Q2). The potter’s kilns are considered those fueled by natural air flow. The primary air flows ranging from 45 to 85 Nm3?h 1 and secondary air flows from 20 to 60 Nm3?h 1. To conduct this numerical study, the model used is “reactor” based on the code CHEMKIN II. The modeled area is composed into a multitude of perfectly stirred reactors (PSR) and the kinetic model has 893 species and 113 reversible chemical reactions. The results show that in our test conditions, the increasing of the rate of plastic in the mixture produces a decrease of the residual oxygen content, due to higher oxygen consumption regardless of the airflow. The CO2 emissions are an increasing function of the rate of plastic (polyethylene) in the fuel mixture. Finally, NO emissions are increasing functions of the mass of plastic for a proportions less than or equal to 20%, and are essentially controlled by the temperature of the reactional medium.展开更多
文摘In this work, a model of convective drying of mango slices was developed and validated by experiments. This model was established by considering slices shrinkage in the energy and the mass balances during the thin layer drying. The drying kinetics and the temperature curves of the product were simulated using the model at various drying temperatures. The simulated curves were then compared to the experimental curves obtained using a convective dryer controlled in temperature and moisture. The results showed that the drying curves were suitably fitted by the thin layer drying model with a correlation coefficient r<sup>2</sup> = 0.997. Thus, taking shrinkage into account, it is possible to predict more effectively the thin layer drying kinetics of mango slices. This study therefore contributed to the mango drying modelling and to the mango dryer setting.
文摘In the present work, the mass transfer characteristics, namely moisture diffusivity and moisture transfer coefficient of “Violet de Galmi” variety of onions were evaluated using the analytical model. Onions were dried in a single layer at different temperatures (40℃, 50℃, 60℃, and 70℃) and for a relative humidity of drying air of 20%. The results showed a reasonably good agreement between the values predicted by the correlation and the experimental observations. This model computed the Biot number, effective moisture diffusivity, and mass transfer coefficient. Effective diffusion coefficient values are obtained between 0.2578 × 10<sup>-9</sup> m<sup>2</sup>·s<sup>-1</sup> and 0.5460 × 10<sup>-9</sup> m<sup>2</sup>·s<sup>-1</sup>. Mass transfer coefficients of “Violet de Galmi” onion drying vary between 3.37 × 10<sup>-7</sup> m·s<sup>-1</sup> and 13.38 × 10<sup>-7</sup> m·s<sup>-1</sup>. Numbers of mass transfer Biot are found between 0.9797 and 2.9397. The activation energy E<sub>a</sub> is 31.73 kJ·mol<sup>-1</sup>.
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This work concerns a dynamic modeling and a numerical simulation of the operation of an adsorption solar refrigeration system using the zeolite-water couple. For this, a mathematical model representing the evolution of heat and mass transfer at each component of the solar adsorption refrigerator has been developed. We have adopted the Dubinin-Astakhov model for the adsorption kinetics of the zeolite/water pair. This model allows to describe the phenomenon of adsorption and to calculate the rate of adsorbate (water) in the zeolite (adsorbent) as a function of the temperature and the pressure. The equations governing the operation of the solar adsorption refrigerator, deduced from the thermal and mass balances established at the collector adsorber, condenser and evaporator components, were solved by an implicit finite difference scheme and Gauss Seidel’s iterative method. We have validated the model established by applying it to the model of Allouhi et al. 2014. We analyzed the influence of the adsorbate/adsorbent couples, the solar flux, the ambient temperature on the adsorption and desorption process. The temperature profiles obtained representing the temperature evolution of the glass, the absorbent plate, the zeolite-water mixture, the condenser, the evaporator, as well as the pressure and the adsorbed mass allowed us to evaluate the performance of the solar adsorption refrigerator. SCOP is higher the higher the solar flux captured by the collector-adsorber.
文摘The sorption behaviour and water transport mechanisms inside Spirulina platensis samples were experimentally analysed during isothermal drying at 25℃ and 50℃. Two different products grown in semi-industrial farms from Burkina Faso and France with initial water contents respectively of the range from 2.73 kg w /kg dm to 3.12 kg w /kg dm were characterized. A novel procedure has been developed to determine the water content profiles inside samples during isothermal drying. At both temperatures, experimental results underlined that the physical properties of Spirulina are not sensitive to the geographical origin, Burkina-Faso or France. To keep Spirulina at an water activity below 0.6 in order to preserve it from micro-organisms development, sorption isotherm curves show that a sufficient requirement is to lower the water content until an upper limit of w = 0.075 db. The evolution of water transport coefficient as a function of water content highlights a monotonous exponential dependence with a transport coefficient ranging from 1.70 × 10–10 to 94 × 10–10 m2/s. The contribution of solid phase shrinkage to the transport of water is negligible for the last drying steps.
文摘This paper concerns the study of the influence of the proportion of plastic from polyethylene, on the yields of gas emissions during the combustion of the mixture of “millet stalks and polyethylene plastic bags”, in a prototype of kiln of potters. During these investigations, we looked at the rate of residual oxygen (O2) and emissions of carbon dioxide (CO2) and nitrogen monoxide (NO), as a function of primary air flow (Q1) and secondary airflow (Q2). The potter’s kilns are considered those fueled by natural air flow. The primary air flows ranging from 45 to 85 Nm3?h 1 and secondary air flows from 20 to 60 Nm3?h 1. To conduct this numerical study, the model used is “reactor” based on the code CHEMKIN II. The modeled area is composed into a multitude of perfectly stirred reactors (PSR) and the kinetic model has 893 species and 113 reversible chemical reactions. The results show that in our test conditions, the increasing of the rate of plastic in the mixture produces a decrease of the residual oxygen content, due to higher oxygen consumption regardless of the airflow. The CO2 emissions are an increasing function of the rate of plastic (polyethylene) in the fuel mixture. Finally, NO emissions are increasing functions of the mass of plastic for a proportions less than or equal to 20%, and are essentially controlled by the temperature of the reactional medium.
