Ahmed Omri

Control volume finite element numerical simulation of mixed convection in an air-cooled cavity

The knowledge of flow structure and heat transfer by mixed convection in an open cavity is of interest in relation to a number of physical and technological applications such as ventilation, heat or pollution agent clearance, and electronic cooling. This paper presents a numerical study of transient mixed convection of laminar flows in an air-cooled cavity in which a fluid is injected at a temperature lower than the initial temperature of the cavity. A control volume finite element method (CVFEM) using triangular elements is employed to discretize the governing equations. The performance of the numerical algorithm is first tested. In order to investigate the quality of the ventilation and cooling, the dynamic and thermal fields are numerically determined for a large range of Reynolds and Richardson numbers and for different inlet-outlet locations. Cooling efficiency is examined at transient and at steady regimes.

Numerical Analysis of Natural Buoyancy-Induced Regimes in Isosceles Triangular Cavities

This article deals with a numerical simulation of natural-convection flows using the control-volume finite-element method in isosceles triangular cavities, submitted to a uniform heat flux from below when inclined sides are maintained isothermal, without symmetry assumptions for the flow structure. The aim of the study is to examine a pitchfork bifurcation occurrence. The study provides useful information on the thermal exchange sensitivity to two governing parameters, the Rayleigh number and the tilt angle in a basin still receiving a uniform heat flux. Results show that the heated wall is not isothermal and the flow structure is sensitive to the cover tilt angle. Three regimes with two vortices or more, symmetrical or asymmetrical, can be observed. Results can be constructive for design enhancements in energy systems such as solar water distillers and air conditioning processes.

Lattice Boltzmann simulation of MHD natural convection in a nanofluid-filled enclosure with non-uniform heating on both side walls

This paper examines the natural convection in a square enclosure filled with a water-Al₂O₃ nanofluid and is subjected to a magnetic field. The side walls of the cavity have spatially varying sinusoidal temperature distributions. The horizontal walls are adiabatic. Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature fields. This study has been carried out for the pertinent parameters in the following ranges: Rayleigh number of the base fluid, Ra=10³ to 10⁵, Hartmann number varied from Ha=0 to 90, phase deviation (γ=0, π/4, π/2, 3π/4 and π) and the solid volume fraction of the nanoparticles between φ = 0 and 6%. The results show that the heat transfer rate increases with an increase of the Rayleigh number but it decreases with an increase of the Hartmann number. For γ=π/2 and Ra=10⁵ the magnetic field augments the effect of nanoparticles. At Ha=0, the greatest effects of nanoparticles are obtained at γ = 0 and π/4 for Ra=10⁴ and 10⁵ respectively.

MHD natural convection in a nanofluid-filled cavity with linear temperature distribution

This paper examines the natural convection in a square enclosure filled with a water-Al2O3 nanofluid and is subjected to a magnetic field. The bottom wall is uniformly heated and vertical walls are linearly heated whereas the top wall is well insulated. Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature fields. This study has been carried out for the pertinent parameters in the following ranges: Rayleigh number of the base fluid, Ra=103 to 105, Hartmann number varied from Ha=0 to 60, the inclination angle of the magnetic field relative to the horizontal plane γ = 0° to 180° and the solid volume fraction of the nanoparticles between φ = 0 and 6%. The results show that the heat transfer and fluid flow depends strongly upon the direction of magnetic field. In addition, according the Hartmann number, it observed that the magnetic field direction controls the effects of nanoparticles.

Slip flow effect on laminar convection inside micro-tubes with permeable walls

Abstract In this study, a two-dimensional steady state simultaneously developing laminar flow along a permeable micro-tube is investigated numerically under slip flow conditions. The constant wall temperature boundary condition and the case of uniform suction at the entire tube wall were considered. The set of governing equations subjected to the appropriate boundary conditions for the hydrodynamic and thermal fields was solved by using the Finite Volume Method. The numerical model was validated using the available data for developing and fully developed continuum flow. The results show that increasing the Knudsen number reduces the axial velocity of the tube center and increases the streamwise fluid velocity at the wall, inducing a flattening of the velocity profiles. This leads to a reduced friction coefficient compared to the continuum case. Furthermore, the study reveals a significant effect on the rarefaction on the hydrodynamic and thermal fields especially for high values of the suction Reynolds nu...