Departement of Physic

Aims: The present work is the use of Scheffler technology to melt plastic waste to produce composite materials using an oven type receiver. The composite material in this study contains polyethylene as a matrix and sand as reinforcement. Study Design: The fusion temperature of polyethylene is about 200°C and is obtained by solar concentration. The experimental plastic melting unit in Saaba (latitude 12.38° N; longitude -1.43° E), Burkina Faso, uses two 8 m² Scheffler concentrators sharing a cubic receiver. Three types of mirrors with a reflectivity of at least 90% are used as reflecting facets to equip the Scheffler dishes at the site. Methodology: The thermal behavior of the receiver is analyzed experimentally. Temperatures are measured on the inner and outer walls as well as the internal air temperature with 5 K-type thermocouples. When the fusion temperature is reached on the inside, we introduce the plastic waste which has been previously washed, crushed, dried and weighed. Resu...

The study of thermal and ventilation parameters, obtained in a transient, laminar solar chimney of reduced dimensions, (1 < m <3) m with a square collector (side = 2m) is presented. Experimental measurements has been made to determine the temperature of the absorber and the fluid in the collector, it is shown that at the entrance of the chimney, the temperature of the absorber decreases slightly while that of the fluid is maintained at a maximum level. Temperature differences were observed up to 32°C between the atmosphere and the fluid in April. A temperature variation at the absorber depending on the stack height is presented. Temperature measurements in the chimney, at various heights depending on the axial coordinate, show a variable temperature profile. It is, from these, shown that, in the selected interval of stack height, the average speeds of output increase linearly as a function of stack height. For a chimney of 3m in height and 20cm in diameter, a maximum speed of approximately 0.7 ms-1 was observed. The lack of appropriate equipment handicaps the velocity measurement at the chimney entrance. Thus, the results of simulations with the computer code COMSOL 5.1 has confirmed temperature values measured at the chimney entrance and after this, velocity values are determined.

In this paper, optical analysis of spherical concentrator is made to determine the local and the global geometric concentration, as knowing the geometric concentration of a system can help predict what temperatures can possibly be obtained with it.This leads to conclude that spherical collectors may produce higher temperatures than parabolic trough, and they could even be sharply improved by using a mixt cylindrical and cavity (or flat) absorber. A craft prototype of a steady spherical concentrator made with concreteand having a smooth inner surface mapped with mirror tape is presented. Its absorber is made with blacken steel sheets and shaped like a moon crescent to be aligned with the declination plan and to avoid motorization for the tracking of the sun from East to West. Experimental measurements lead to temperatures reaching 686°C on the curve of the least diffusion, and 252°C in the absorber oven-like reservoir. Overall, the resultsuggests higher potentialities of spherical collectors,which also show possibility of use with much reduced tracking system and less vulnerability to bad weather.

This manuscript presents a theoretical modeling of conversion efficiency improvement in a typical polycrystalline Si solar cell in 1D assumptions under multispectral sunlight illumination. The improvement is brought by the increase in the collection of the minority carriers charge in excess. This increase is the consequence of the integration of the electric field provided by the use of the open-circuit photovoltage of another silicon solar cell. We assume that two silicon solar cells are integrated to the system. The first solar cell provides the open-circuit photovoltage which is connected to two aluminum planar armatures creating a planar capacitor. The second solar cell is placed under the uniform electric field created between the two aluminum armatures. This study has shown that the photocurrent generated is improved by the conduction current given by this electric field. It shows that an improvement in the electric power, particularly its maximum value, leads to the improvement in the conversion efficiency and the fill factor. We observe an improvement in the second silicon solar cell performances for the shortest distance between both aluminum conductors.

In this publication, a hemispherical concentrator, containing a transparent component of refractive index n 2 greater than or equal to the refractive index n 1 of the surrounding environment and having a flat diopter on its upper side, is studied. Then a hemispherical concentrator built in the same way as the previous concentrator but with a hemispherical diopter on its upper side is also studied. A comparison with the Rawlemon spherical concentrator is finally made by drawing the local, global geometric and geometric mean concentrations curves of all these systems. The medium n 1 is air with a refractive index n 1 = 1, while the medium n 2 is varied: 1 (air-like), 1.33 (water-like) and 1.5 (glass-like). In conclusion, a flat diopter on a hemispherical concentrator reduces the receiver positioning hour and declination angles, while a hemispherical diopter on a hemispherical concentrator increases the geometric and geometric mean concentration of the system.

The present paper is about an experimental evaluation of the terrestrial silicon single-crystalline solar PV module behavior under low gamma radiation. The simultanous proliferation of radioactive sources in Burkina Faso dominated by gamma type and the photovoltaic (PV) systems installations in both urban and rural areas justify this study. There is also high background radiation compared to normal in some region of the country. It has been shown that the photocurrent and the electric power increase while the photovoltage stays constant for an extremely low gamma radiation doses. This work proves that long time exposition to any low radiation can cause the reduction of the performance of the solar PV module. However for greater values of the dose, the photocurrent, the photovoltage and the electric power decrease. Hence, it is so important to protect PV equipments against gamma radiation by adjusting the PV installation height from the ground where high background radiation is notified or by putting reinforced concrete at their bottom faces. The two ways can be combinated adding the respect to radiation protection principle As Low As Reasonably Achievable (ALARA).

This paper deals with the climatology of aerosols in West Africa based on satellite and in situ measurements between 2001 and 2016 and covers four sites in the Sahelian zone. There are indeed Banizoumbou (13.541˚N, 02.665˚E), Cinzana (13.278˚N, 05.934˚W), Dakar (14.394˚N, 16.959˚W) and Ouagadougou (12.20˚N, 1.40˚W) located respectively in Niger, Mali, Senegal and Burkina Faso. Thus, an intercomparison between the satellite observations and the in situ measurements shows a good correlation between MODIS and AERONET with a correlation coefficient R = 0.86 at Cinzana, R = 0.85 at Banizounbou, R = 0.84 at Ouagadougou and a low correlation coefficient R = 0.66 calculated on the Dakar site. Like MODIS, SeaWiFS shows a very good correspondence with measurements of the ground photometer especially for Banizoumbou (R = 0.89), Cinzana (R = 0.88) and Dakar (R = 0.75) followed by a low correlation coefficient calculated on the Ouagadougou site (R = 0.64). The performance of these airborne sensors is also corroborated by the calculation of root mean square error (RMSE) and the mean absolute error (MAE). Following this validation, a climatological analysis based on aerosol optical depth (AOD) shows the seasonality of aerosols in West Africa strongly influenced by the climate dynamics illustrated by the MERRA model reanalysis. This seasonal spatial distribution of aerosols justifies the temporal variability of the particles observed at the different sites in the Sahel.

Indirect solar dryers with solar collectors, do not always make it possible to reach the desired temperature level and drying time. As part of the improvement of the thermal performance of these systems, a study of the caustic zone is first presented. It is in this zone that the tubular receiver of the studied insolator is placed. The system of equations obtained results from the division of the insolator into fictitious slices of length dz, in which the thermal balance is established. It is solved using an iterative method with finite differences. The volumetric flow rate and the temperature of the heat transfer fluid which can be injected into the drying cage during a day are thus determined at the outlet.

A cylindrical-parabolic solar-thermal converter, with 0.5m2 of capture surface, was manufactured and attached to a furnace, constituting an indirect solar dryer. Thermal balances of the elements of the receiver, housed in the focal point of this collector, are settled. A campaign of vacuum tests of this dryer indicated temperatures of the heat-bearing air in natural convection, along the absorber tube (70°C) and inside the drying cage (almost 60°C,on average). The average thermal efficiency of said converter has been evaluated at 50%.The higher the efficiency, the less the converter&#39;s capture surface is required and, therefore, less investment is required. These promising results testify to the effective performance of this new dryer compared to dryers with flat collectors, whose efficiencies could not exceed 40% despite the large surface area of these collectors.

Thermal comfort is one of the most important requirements that scientists and building designers must meet to ensure the indoor air quality knowing its importance on productivity and the health of occupants. However, it has never been of great concern for architects and architectural historians and seldom explores it. Buildings are the large consumer of the most energy consumption (around 40% worldwide) and generate around 35% of GHGs like CO2 that leads to extreme climate change. Hence, general and specific eco-friendly solutions in the field of building construction are required. Analysis of this study shows that air conditioning consumption can be significantly reduced thanks to the compressed earth bricks and by taking into account the climate and the orientation of the facades. However, this paper establishes viable low-cost option of building energy consumption while maintaining the thermal comfort and good indoor air quality. This work explains the effect of a single resident...

Aims: This paper is about a solar collector made of hemispherical concentrators. This collector is sun tracking free, and used for natural convection. Lenses are used on top of each concentrator to improve its efficiency. Study Design: The Solar collector is made of hemispherical concentrators with Fresnel lenses axially-centered to those concentrators and placed on top of each one of them. Those concentrators are covered with a 4 mm glass for a greenhouse effect. The concentrators generate hot spots that heat the inside air. There is no need for receivers at the hot spots. Methodology: from Inlet to outlet, temperatures are measured as well as inlet air speed, which allow the efficiency evaluation. Results: Although those measurements were conducted in a cloudy period, temperature difference Original Research Article Ky et al.; PSIJ, 25(1): 8-22, 2021; Article no.PSIJ.66543 9 from the inlet to the outlet was around 55°C to 65°C. This result is superior to previous studies of the sa...

This technology is used in drying, domestic water heating or in the production of electricity. However, it uses a solar tracking system that is too complex and expensive for countries with less equipment and high solar potential. In this study, we are interested in the experimentation and thermal analysis of a stationary hemispheric concentrator. The numerical resolution of the caustic equations of a spherical concentrator allowed to determine the dimensions and the position of the receiver, necessary for the design of the physical model and the assembly of the experimental device. The results of the 3D numerical simulation with the Comsol5.3a software allowed to highlight the ray tracing and the profile of the flow concentrated on the receiver. The results obtained experimentally show that the receiver and the air inside reached a maximum temperature of 224°C and 97.6°C respectively. The solar concentration device studied is therefore technically favorable for thermal applications ...

In this paper, an indirect solar dryer using a new type of collector is studied. The collector is built with hemispherical concentrators with an axially-centered Fresnel lens placed on top of each. That allows the collector’s aperture area of 0.32m2 to fully contribute to the hot spot generated in the hemispherical concentrators. The dryer was installed permanently, sun-tracking free, and drying experiments were taken at a cloudy period (From the end of May to the beginning of June) to correspond to the most-needed time of crops conservation in Ouagadougou, Burkina Faso. Mango and ginger were charged in the chamber, weighted separately and without tray permutation to see the weight loss for each of the 5 trays’ products. As outcomes, dryer’s collector efficiency was evaluated at 42.45%. Mango was 74 Thierry Sikoudouin Maurice Ky et al. dried with temperatures ranging from 57 to 67°C around the trays with a dryer’s efficiency of 41.2% and in 8 hours. In conclusion, the novel collecto...

This work focuses on the convective drying of tomato slices with hot air at temperatures of 50 and 60°C and at velocities of 0.1, 0.25 and 0.5 m.s-1. The kinetics and drying rates are determined according to the temperature and velocity of the drying air. The equation of “Gaussian”, used for the first time and in this work, is more adaptable to the drying curves. Two methods have been used to determine the coefficient of effective diffusion (with and without the effect of shrinkage). The energy of activation is evaluated with the Arrhenius relationship. In this study, we are interested in the phenomenon of shrinkage, in particular, and the evolution of the relative thickness of the slice of tomato according to drying duration and moisture content. The study shows that on hot air drying, the influence of velocity is dominant as compared to temperature. We observed that for the same final moisture content, the final relative thickness of the product is not constant. It varies dependin...

A particular solar cooker namely the parabolic trough solar cooker (low concentration) called &quot;blazing tube&quot; is studied in the present work. It is about determining experimentally its performances. Several tests were conducted, tests while empty, water hea tests, temperature readings of the various components were also carried out. The cooking time of certain dishes has also been determined. It emerges from these experiments that the outlet temperature of the flu used all day as needed, even in slightly unfavorable times.

Objectives: We present in this study a modeling of thermal laminar convection airflow in a solar tower. Methods: To formulate with precision, the boundary conditions of the solar chimney model chosen, the Cartesian equations are transformed into hyperbolic coordinates. An orthogonal grid is elaborated. It then makes it possible to draw up the diagrams of physique and calculation fields. The computer code uses the heat equation, the vorticity, and the stream function formalism as the boundary conditions for pressure are difficult to set. We use the Boussinesq approximation, which consists in considering that the density (ρ) of the fluid varies only in the term of the gravity forces, whose variations with temperature, assumed to be linear, generate natural convection. These variations are then translated into an equation of state which relates density to temperature. The system of dimensionless equations is solved by using an intégro-interpolation method referring to finite differences scheme. Findings: The solutions obtained from the dimensionless equations enabled us to determine the space evolution parameters (temperatures and velocities) in the tower according to the Rayleigh number. The fluid temperature and velocity evolution in the collector increase when one moves in the direction of radius decrease. The fluid temperature evolution in the chimney showed that the highest temperature is located at the chimney base while we obtained a parabolic profile of the transverse temperature distribution within the chimney. Finally, the evolution of the fluid velocity in the chimney showed that there was a preferred zone for turbine installation. Novelty : The use of dimensionless geometric parameters is unique and in general, the approach adopted in this paper differs from that encountered in the literature.

The evaluation of the solar deposit is essential for the sizing of photovoltaic systems. This requires the availability of radiation data. In Burkina Faso, weather data doesn’t cover all the country. That makes that solar radiation measured are not available for the all country. Theorical methods can help about it. This paper is written to fill the gap of adapted solar models for the country. In this work, an analysis of the results provided by four models for the estimation of hourly values ​​of global radiation on a horizontal plane was made. The radiation data for the year 2017 comes from the Burkina weather forecast. The validation of the models is carried out by a comparison between the radiation measured and that given by the various models provided by MATLAB code. The different models have been validated by several statistical indicators (RMSE and normalized MAE) and graphs for a clear sky. Scoring criteria have been established to assess the relative quality of each model. T...