This paper presents an experimental comparative study on the thermal performance and heat exchange of two single pass solar air heaters models (SAHs); we have proceeded to reversing the flow direction in the solar air heater. Initially, to determine the best performing model and to improve the efficiency factor of the SAH. Secondly, to evaluate the convective heat transfer coefficient of both models, named: N-1 and N-2. The indices (1) and (2) indicate, respectively, that the air was blown up or blown down in the channel duct of the SAH. Therefore, we have compared between the efficiencies, the convective heat transfer coefficient, Nusselt number curves and the distribution of air temperatures in the channel ducts of both solar air heaters. Both collectors were designed, constructed and tested in the University of Biskra (Algeria) in a stand facing south at an inclination angle equal to the local latitude. The results show that N-2 model (air blown down) is more efficient than N-1 model (air blown up), and the improvements in the heat exchange due to this technological solution are about 10-20%.
This paper presents an experimental study by comparing between the thermal performance of three types of solar air flat plate collectors, FPCs: (i) without obstacles, (ii) with rectangular obstacles, and (iii) with trapezoidal obstacles in the air flow duct. In order to determine the best performing model, we have proceeded to reversing the flow direction, in each collector, and comparing the six obtained models under outdoor conditions. All collectors were designed, constructed, and tested in the University of Biskra (Algeria) in a stand facing south at an inclination angle equal to the local latitude. Thus, we have proceeded to the application of the best system for the drying of the green chili. We have sought to determine the moisture content and loss of mass for the forced convection hot air drying of the product and their temperature dependence. In comparison with the recent literature, at different air mass flow, the highest efficiencies (77%) were obtained from the FPC with trapezoidal obstacles, when the air was blown down at air flow rate 0.043 kg/s. In addition, this study has allowed us to show that (i) for a same geometry, the highest efficiencies were always obtained when the air was blown down in the solar air FPC and (ii) the use of obstacles, in the air flow duct of the FPCs, is an efficient method to improve their performances, especially when the air is blown down. The obstacles ensure a good air flow under the absorber plate, create the turbulence, and reduce the dead zones in the collector.
This paper presents an experimental investigation of damage in sandwich structures. These sandwich panels are result of the combination of glass-polyester as skins and cork agglomerate as core. For this purpose, delamination test (mode I) is carried on double cantilever beams (DCB) in sandwich beams. The initiation crack is characterized by toughness obtained from the determination of energy release rate (GIC) by modified beam theory method. The skins of these sandwiches are considered as orthotropic materials while the core as isotropic transverse material. The results show that, the energy release rate at the initiation of the crack of (DCB) specimens remains almost constant despite the variation of the initial crack, a good adhesion (skins -core) is also noticed.
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