The drying kinetics of fresh beef (approximately 12-cm long and 7-cm wide) were determined for different temperatures (40, 50 and 60C), air velocities (1, 2 and 3 m/s), relative humidity (15, 30 and 60%) and thicknesses of the product (2, 3 and 4 mm). Temperature showed a high influence on the drying kinetics compared with other drying parameters. Two drying periods were identified according to the shape of the drying curves: a first period during which the drying rate falls slowly and a second period with significant decrease of drying rate. The drying kinetics of beef was modeled using the drying characteristic curve method and the model obtained fits accurately with the experimental data as the residuals between experimental and modeled values are inferior to 10% and the root mean square error is less than 5%. This model showed a higher performance compared with the semi-empirical models generally used to fit the drying kinetics of food products. PRACTICAL APPLICATIONSMeat preservation in hot countries is difficult because of the very perishable nature of this product. Drying is generally used for the conservation of the meat or to obtain some traditional based dried meat products. The information provided in this paper are important to manage the drying operations and for a good modeling of convective drying kinetics of beef, particularly in tropical conditions. Good knowledge and modeling of the drying kinetics, in conditions close to those encountered in the real processes, are basic requirements to achieve appropriate modeling and design of drying processes.

This work is part of the dynamic of proposing a solution to the problem of access to electricity in Chad, which has a rate of access to electricity of 3%. N’Djamena has significant solar potential that can be harnessed to generate electricity. In this paper, we present a theoretical study of the performances of the Dish/Stirling system with the purpose of producing electricity, based on a mathematical model taking into account each of the subparts of the system (concentrator, solar cavity receiver, and Stirling engine). Hydrogen is preferred to helium as the working fluid for operating the Stirling engine at high temperatures. This coupled model made it possible to estimate the monthly average of the electric power produced by this modular system and also its overall solar electricity yield.

This study aims to evaluate the long-term variations of sunshine duration and to estimate its interaction with meteorogical parameters from 1950 to 2010 in Chad, Central Africa. The results show that Chad is the one of world's sunniest countries. Each year, Chad receives more than 3030.91 ± 176.33 hours of sunning corresponding to 8.9 hours daily. Likewise, a strong north-south gradient is noted over Chad. For instance, the daily insolation is 10 ± 0.41 hours in the north, 8.85 ± 1.1 hours in the center and 7.75 ± 1.8 hours in the south. Furthermore, there is a marked seasonality of sunshine duration with maximums in dry season and minimums during the rainy season. The lowest values of sunshine duration are found in August. On the contrary, maximums are recorded from November to February with values greater than 9.5 hours per day. Moreover, the annual anomalies study allowed determining three great periods in terms of sunshine variability in Chad. Firstly, the period between 1950 to 1970 (named humid period) is characterized by the lowest values of sunshine duration in Chad. Secondly, from 1970 and 1990, the region suffered an unprecedented drought which resulted in an increase of sunstroke duration in Chad. And finally, the period from 1990 to 2010 called the return period is characterized by a rapid year-to-year fluctuations of insolation duration. Unlike to surface temperature, we have also shown that there is a direct relation between the duration of insolation and the meteorological parameters such as precipitations and relative humidity.

Polyethylene oxide solutions have a behavioral flexibility that provides researchers with the opportunity to use constitutive law models in a variety of ways for their MRI characterization. Our results obtained in numerical simulation carried out in 2D and 3D for speed profiles of a solution of PEO deployed by the simple method of the cylindrical Couette geometry considering the fluid Newtonian defect, allowed to identify the behavior of fluid complex (rheo-fluidifying threshold fluid). The relevance and the interest of the method are examined by analyzing these results generated by the numerical data obtained, since these profiles depend on the non-Newtonian properties of the fluid which one does not know a priori and which one seeks to measure by postulating first to the power law of Ostwald, then to the truncated power law.

This manuscript deals with a quasi-steady regime thermal analysis of a solar parabolic trough collector in the climatic conditions of the city of N'Djamena located in a Sahelian region of the Chad Republic. The objective is to develop the solar electricity potential of N'Djamena and contribute to the development of renewable energies in the country. A one-dimensional numerical model was developed in a quasi-steady regime to simulate and analyze the thermal behavior of the system. The energy balance equations governing the thermal behavior of the collector are solved by the implicit finite difference method, while considering the variation of the solar radiation over time. Initially, the model was validated by experimental data existing in the literature. Excellent agreement is observed when comparing the numerical results to experimental data. The effect of various parameters, including the type of heat transfer fluids, wind speed, and mass flow rate of fluid, on the thermal performance of the parabolic trough solar collector in quasi-steady regime operation was observed. It is shown that the variation of wind speed has a very slight effect on the thermal performance of the collector. Four fluids (therminol 66, therminolV-P1, untreated water, and treated water) were simulated between 11:00 and 15:00 local time. Through the simulation of four fluids, it was shown that the energy efficiency of the collector when using oil is much better than with water.