Joseph Sarr

Renewable energy activities in Senegal: a review

Like many countries in Africa, Senegal is facing economical decline, energy crisis and serious desertification problem in rural areas. These issues could be removed if renewable energy is used as a primary source of energy in rural areas. What is required is a strategy to implement renewable energy technologies at large scale. The government and many non-governmental organisations (NGOs) have tried to comprehend and have strived to address the problem of energy. This paper presents a review of activities in the field of renewable energy applications in Senegal, which goes back to the mid 1970s and will discuss the socio-economic benefits that the country has derived from these environmentally sound and appropriate sources of energy. The development and trial of systems were mostly funded so far by donor agencies in collaboration with government and NGOs. Among the applications being supported are solar lighting, water pumping and small power plants. Recent efforts have been aimed at restructuring the programmes and giving them a market orientation. Future trends, some suggestions and recommendations for successful dissemination of renewable energy sources are also drawn. The present situation is seen to be much more promising and favourable for renewable energy.

Modelling recombination current in polysilicon solar cell grain boundaries

Abstract The recombination current in grain boundaries is theoretically investigated for a polycrystalline silicon solar cell n–p junction operating either in short-circuit or in open-circuit configurations. The analysis is carried out using results performed in earlier works, by means of numerical simulations including the presence of grain boundaries. The variation of grain boundary recombination current density with exciting light wavelength is reported for different cell parameters like grain boundary recombination velocity, base dopant density and base thickness. The objective of the present paper is to understand to what extend the light wavelength and the junction configuration allow an optimal measure of the grain boundary recombination parameter.

Numerical natural convection in a sector‐shaped enclosure

The purpose of this paper is to compare the numerical laminar two‐dimensional unsteady natural convection in a partial sector‐shaped enclosure submitted respectively to a constant heat flux density q1 and a uniform temperature T1 on the inner cylindrical wall. The numerical model performed in this paper is applied more particularly for high Grashof numbers, in order to point out the advent and the development of pre‐turbulent flows. Results of numerical runs are presented. The mean Nusselt number on active walls is represented as a function of the Grashof number Gr and the aspect ratio Fr. The results may be correlated very well with an expression of the form \overlineNu = k1 Gr1k2, for technical calculations.

Numerical Simulation of Two-Dimensional Natural Convection in a Confined Environment with the Vorticity-Stream Function Formulation

A numerical study is presented on the problem of 2D natural convection in a differentially heated cavity. The equations governing this unsteady flow phenomenon were solved using the vorticity-stream function formulation of the Navier-Stokes equations and heat. The results obtained are compared with the results of the literature and make it possible to validate this approach. In this work, we studied the heat transfer in a cavity and we determined the variation of the local Nusselt number which allows obtaining the rate of thermal transfer by convection in an enclosure. We analyzed thermal fields for different Rayleigh numbers by selecting two points to visualize temperature fluctuations over time. Thus, the creation of the ascending and descending movements of the fluid inside the cavity was analyzed. We have also established temperature histograms for the graphical presentation of the temperature distribution. The modeling of the two-dimensional problem was established using a “Fortran 90” calculation code. The results also show the different vorticity contour maps in laminar flow regime. We have presented our results of numerical simulations using a visualization tool. The Rayleigh number varies in the range of 103 to 106 for a Prandtl number equal to 0.72 corresponding to air.

Geometrical and Rayleigh number effects in the transient laminar free convection between two vertically eccentric spheres

Purpose – The purpose of this paper is to study the transient natural convection of a Newtonian fluid which develops in a closed spherical annulus delimited by two vertically eccentric spheres by using a bispherical coordinates system. The inner sphere is heated by a heat flux of constant density and the outer one is maintained isothermal.Design/methodology/approach – The transfer equations are written by using a bispherical coordinates system. The Navier‐Stokes equations are solved and coupled with the energy equation by using the alternating direction implicit (ADI) and the successive over relaxation (SOR) methods.Findings – The study of the stream function and the Nusselt number shows that the convection motion is reinforced for the geometries characterized by positive values of the eccentricity with heat exchange increasing. The Nusselt number increases with the modified Rayleigh number. The heat exchange increases with the radius ratio. The results show that the steady state is reached faster when th...