Foued Halouani

EXPERIMENTAL STUDY OF THERMAL EFFECT ON OLIVE WOOD POROUS STRUCTURE DURING CARBONIZATION

The study presented in this paper is an investigation on the porosity changes induced by the carbonization of Tunisian olive wood. The porosity is measured by mercury porosimetry. The experimental results show that the total porosity of carbonized wood increases with the temperature. It should be underlined that the formation of some macropores during the increase of the temperature is certainly due to the breaking of the cell wall by the mercury penetration. The weakness of the cell wall is observed when the degradation rate of the three pseudo components of wood, the notion of which has been introduced by the authors in a previous article [Grioui et al. 2006], becomes high which corresponds to the temperature range between 523 K and 548 K.

Analysis of Degradation and Failure Mechanisms that Develop in Hot Forging Die

A failed die, used to forge gas valves, was analyzed using macroscopic and microscopic equipment on some specimens. Fatigue cracks on the die were evidently observed on all the surfaces of the die. Many processes were found to be major contributors to have caused the die failure. Oxidation was observed in some areas, especially on plane surfaces and thin sections. Surface layers of tools at the tool-workpiece interface were not only exposed to high mechanical stresses but also to severe temperature cycles, which could have led to loss of strength and hardness. Metallographic analysis revealed that the oxide layers consisted of different diffusion layers which accelerated thermal fatigue mechanisms.

Étude hydrodynamique et thermique de la condensation en film à l'intérieur d'un tube horizontal

Condensation of pure vapor inside a horizontal tube is investigated for a stratified two-phase flow. The proposed theoretical model takes into account the effect of the equivalent gravitational and interphase friction forces applied to the condensate film on film hydrodynamics. A numerical model is developed to study the motion of the film due to liquid removal from the vapor flow and to permit the determination of the average local and overall heat transfer coefficients. A simulation is made of the effects of vapor velocity, saturation temperature level and driving temperature difference on the intensity of the process. Our results are compared with those obtained by another theoretical model and are found to be in better agreement with the reported experimental data and give a coherent description of heat transfer mechanisms.