Modélisation de la vitesse de séchage du maïs

Cet article consiste à présenter un autre modèle appliqué à la détermination de la vitesse de séchage du produit hygroscopique. Ce modèle est obtenu par la ressemblance entre la cinétique chimique et la cinétique de séchage. L’intérêt de ce présent travail c’est de trouver un modèle simple, facile et fiable pour caractériser la vitesse de séchage du produit. En adoptant ce modèle, nous avons obtenu un autre modèle mathématique de la cinétique de séchage du maïs. Nous validons le modèle adopté par rapport à l’autre modèle, nous observons que les résultats sont en accords.Mots-clés : Modèle, vitesse séchage, cinétique de séchage, produitshygroscopiques, maïs

Natural Convection Heat and Mass Transfer in the Boundary Layer along a Vertical Cylinder with Opposing Buoyancies

The effects of opposing buoyancies on natural convection heat and mass transfer in the boundary layer over a vertical cylinder immersed in a quiescent Newtonian fluid are presented in this paper. The surface of the cylinder is maintained at a constant temperature and concentration. The homotopic transformation is proposed to transform the physical domain into a flat plate. The boundary layer equations and the boundary conditions are solved numerically using an implicit finite difference scheme and the Gauss-Seidel algorithm. The buoyancy ratio N, Prandtl number Pr and Schmidt number Sc are important parameters for this problem. The numerical results for Pr=Sc and Pr≠ Sc, including the velocity, temperature, concentration fields and the Nusselt number as well as the Sherwood number along the surface of the cylinder are discussed for aiding and opposing buoyancies. Results show that the Nusselt (Sherwood) number increases with positive or negative buoyancies ration N (N=Grc/Grt). Moreover, for opposing flows with Sc<Pr , the flow is completely downward, the thickness of the concentration layer is larger than that of the thermal layer . For Pr<Sc , the velocity are weak and the thermal layer thickness is much larger

Numerical and experimental study of an air-soil heat exchanger for cooling habitat in Sahelian zone: case of Ouagadougou

The use of air-soil heat exchangers for the cooling home has developed considerably in recent years. In this work, we have leaded the numerical study of an air-soil heat exchanger by using a nodal approach. We have also presented our experimental prototype implemented in Ouagadougou. This study has allowed determining the evolution of air temperature along the exchanger and also validating our numerical results with those of the literature and the experiment

Modeling Submicron Particles Collec-tion in Laminar Forced Convection Gas Flow by a Rectangular Venturi Scrubber

Abstract Venturi scrubbers are usually used for large particles cleaning in turbulent gaseous flow. In this work, submicron particles scrubbing in laminar forced convection dusty air flow in a rectangular venturi scrubber have been numerically simulated. Hydrodynamics effects and scrubbing process are investigated in detail. Results are presented as flow velocity, axial pressure, streamlines pattern, particles and droplets mass fraction profile, and collect efficiency. They show that venturi scrubbers can be efficient for submicron particles scrubbing. In fact, a better collect efficiency is obtained at high particles-droplets residence time, high ratio droplets concentration/particles concentration, low venturi diameter ratioand low Reynolds numbers. There is a critical Reynolds number value for which the collect efficiency becomes very low and tends to be constant

The Effect of Combined Convective and Microwave Heating on Mechanical Behaviour of Wood during Drying

ABSTRACT: A numerical study is performed in order to analyse the effect of combined microwave and convective drying on the wood rheology behaviour. The stress model takes into account the free shrinkage, elastic deformation, viscoelasticity and mechanosorptive creep. Stress equations were solved using an implicit finite differential scheme and Thomas algorithm. Results showed that, combined convective and microwave drying reduce the drying time of wood and increasing the drying efficiency. It was found that the moisture content of wood below the fiber saturation point affect the drying stress and there was a significant effect between the drying condition and the mechanical properties of wood. The variation of moisture content during drying intended to produce a mechano-sorptive creep that is able to reduce drying stress. The stress model is used to optimize drying process and to effectively relieve the residual stresses after drying

Modélisation des isothermes de sorption des feuilles de Marjolaine

Les teneurs en eau d’équilibre de désorption et d’adsorption des feuilles de marjolaine (Origanum majorana) ont été déterminées à 30, 40, et 50 °C par la méthode gravimétrique statique. L’équilibre a été obtenu après 12 jours pour la désorption et 9 jours pour l’adsorption. L’effet d’hystérésis thermique est observé dans la gamme des températures testées. Pour la modélisation des isothermes de sorption, et pour la prédiction du comportement hygroscopique lors du stockage ou du séchage, quatre modèles mathématiques ont été utilisés. Le modèle de Peleg à quatre paramètres optimise le lissage des points expérimentaux dans un domaine des activités de l’eau assez important. Des changements relativement importants se font sentir dans les propriétés thermodynamiques de la marjolaine en termes d’enthalpie différentielle et d’entropie Toutefois, ces derniers se compensent et il est possible qu’ils soient principalement le résultat de différences dans la structure de l’eau autour de la périphérie de la plante et du site qui se combine, tant avant qu’après la sorptio

An efficient parallel high-order compact scheme for the 3D incompressible Navier–Stokes equations

International audienc

Turbulent mixed convection of heat and water vapor transfers in a two-dimensional vegetation canopy

The present study consists in a numerical investigation of turbulent mixed-convection of heat and water vapor transfers inside two-dimensional (2-D) vegetation canopy, in the surrounding atmosphere and in a wet underground. The time-averaged Navier-Stokes equations are used to characterize the flow field surrounding the canopy and within it. Reynolds shear stresses are calculated using the eddy turbulence model and the Prandtl mixing length. The governing equations are solved numerically using an implicit finite difference method and Thomas algorithm. The present model is used for the determination of the micro climatic profiles such as streamlines, isotherms and iso-concentration. Special emphasis is laid on the systematic analysis of the total evaporation rate (evapotranspiration), the local and average heat fluxes, the Nusselt and Sherwood numbers. The effects of Leaf Area Density distribution, the canopy stomata regulation, as well as the atmospheric forcing conditions on the transfers, are presented and analysed. The results show that buoyancy force caused by properties variation reduces the local heat and mass transfer coefficients, and that this reduction increases at lower wind velocities

Convection heat and mass transfers in a vertical duct

Abstract Heat and mass transfers are analysed in a vertical duct where an air flow is established. One of the plates is heated and cooled by a falling water film. Temperatures at the wall and at the water-air interface are measured using thermocouples and an infrared thermography system. It is shown that the infrared camera measures the water surface temperature. From temperature measurements, local Nusselt numbers are calculated for different wall heat flux densities and liquid mass rates. From these Sherwood numbers are deduced using Lewis function assumption