Browsing by Author "Lazhar Merouani"

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    ANALYSIS OF CONJUGATED PROCESSES OF FILM EVAPORATION AND CONDENSATION IN A TUBULAR HEAT EXCHANGER †
    (2016-06-23) Lazhar Merouani
    This paper investigates coupled phase changes by forced convection from co-current flows of liquid films and vapour-air mixtures in a tubular heat exchanger. Evaporation occurs in the inner tube and condensation in the annulus region. Heat and mass transfers in the liquid films and the vapour-gas mixtures are described by the conservation equations of momentum, energy and diffusion. An appropriate change of coordinates is introduced in order to obtain a computational mesh with straight liquid-mixture interfaces along the walls. The governing equations are discretized by an implicit finite differences method and solved using an efficient numerical methodology. The distributions of axial velocity, temperature and vapour concentration in all regions of the tubes are determined from iterative procedures with a high convergence rate. The current analysis also provides the axial evolutions of film thicknesses, heat flux, condensation and evaporation rates in the whole domain. In addition, the effects of the inlet parameters of Reynolds number, relative humidity, pressure and liquid flow rate on the heat transfer characteristics, the evaporation and condensation rates are also investigated. This article is protected by copyright. All rights reserved
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    Convective Film Condensation in an Inclined Channel with Porous Layer
    (2013) Lazhar Merouani
    Abstract: The present work is a numerical study of laminar film condensation from vapor-gas mixtures in an inclined channel with an insulated upper wall and an isothermal lower wall coated with a thin porous material. A two-dimensional model is developed using a set of complete boundary layer equations for the liquid film and the steam-air mixture while the Darcy-Brinkman-Forchheimer approach is used for the porous material. The governing equations are discretized with an implicit finite difference scheme. The resulting systems of algebraic equations are numerically solved using Gauss and Thomas algorithms. The numerical results enable to determine the velocity, temperature and vapor concentration profiles in the steam-air mixture, the liquid film and the porous substrate. The axial evolution of the condensate flow rate and the wall heat flux are also presented and analyzed for different operating conditions. It is found that the inclination angle, the inlet values of relative humidity and the Reynolds number exert an influence on the condensation process much more significant than that coming from a change in the porous layer properties.
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    Etude numérique de la condensation en film par convection mixte dans un canal vertical
    (2007-08-29) Lazhar Merouani
    Une étude numérique de la condensation par convection mixte laminaire d’air humide dans un canal vertical à parois non isothermes est présentée. Les transferts dans la phase liquide et dans l’air sont décrits par les équations de conservation de masse, de quantité de mouvement, d’énergie et de diffusion. Le couplage entre les équations des deux phases est assuré par la continuité des contraintes de cisaillement, des densités de flux thermique et massique à l’interface liquide–air. Les équations sont discrétisées par la méthode des volumes finis et résolues par la méthode de Gauss (pour les équations de quantité de mouvement) et de Thomas (pour les équations d’énergie et de diffusion). Les résultats montrent notamment que le débit de condensat, l’épaisseur de film liquide et le flux thermique à la paroi augmentent avec le coefficient de transfert convectif entre la paroi et le milieu extérieur.