Papers by Keyword: Natural Convection

Abstract: The effect of buoyancy ratio on the two dimensional natural convection heat and mass transfer generated in an inclined square bi-L-shaped layered porous cavity filled with Newtonian fluid has been investigated numerically. Each porous layer is considered isotropic, homogeneous and saturated with the same fluid. The cavity is heated and salted from below where as the vertical walls are assumed to be adiabatic and impermeable. The physical model for the momentum conservation equation makes use of the Darcy-Brinkman-Forcheimer model, and the set of coupled equations is solved using a finite volume approach. The power-law scheme is used to evaluate the flow, heat and mass fluxes across each of the control volume boundaries. Tri diagonal matrix algorithm with under-relaxation is used in conjunction with iterations to solve the nonlinear discretized equations. An in-house code developed for this study is validated using previous studies. The results are presented graphically in terms of streamlines, isotherms and iso-concentrations. In addition, the heat and mass transfer rate in the cavity is measured in terms of the average Nusselt and Sherwood numbers.

Abstract: A numerical study of the natural convection of laminar heat transfers in the stationary state in a half-elliptic inclined cavity, which represents a continuation of the work done, we studied the influence of the tilt of the cavity by varying the angle — entered 0 degrees, which corresponds to the horizontal cavity, up to 15 degrees. For each value of δ we varied the Rayleigh number from 2.13 10³ to 10⁶. The system of equations governing the problem solved numerically by the fluent calculation code based on the finite volume method. Based on the Boussinesq approximation. Both bottom and upper walls maintained at a constant temperature. The interest of this study is to see the influence of the tilt of the half-elliptic cavity on the structure of the flow and the distribution of temperature. These results can exploited in semi-elliptic agricultural greenhouses that rest on sloping soils. We chose a Prandtl number 0.71 that corresponds to the air. Keywords: Heat transfer; half-elliptical; Natural convection; Laminar flow; Multicellular; CFD simulation

Abstract: The present study relates to numerical investigation of natural convection heat transfer in a nanofluid filled square enclosure. One side of the enclosure is maintained at high temperature and the other side at a low temperature; while the top and bottom sides are adiabatic. The commercial CFD software ANSYS-FLUENT© was used to solve this numerical problem with the governing differential equations discretized by a control volume approach. nanofluids of Cu-water, Al₂O₃-water and TiO₂-water have been simulated for a range of Rayleigh numbers and volume fractions. The results were obtained in the form of streamlines and isotherms. Interpretations of the results are done based on heat transfer rates, volume fraction, Rayleigh number and Nusselt number. It is to be noted that addition of nanoparticles enhances the heat transfer rate. It is also observed that the Nusselt number is highly affected by volume fraction and Rayleigh number.

Abstract: Nonlinear density and temperature variation’s role (NDT) on the magnetohydrodynamic (MHD) natural convective flow of couple stress fluid with nanoparticles through a vertical porous channel modeled as Darcy-Forchheimer flow is the purpose of our work. The nanoparticles volume fraction is taken into consideration (Buongiorno model). The nonlinear partial differential equations governing this flow were transformed into ordinary differential equations via the similarity technique and simulated numerically using Matlab, following boundary value problem (BVP4c) code. Graphical illustrations, including non-dimensional velocity, temperature, concentration, nanoparticle’s concentration and numerical results containing Nusselt and Sherwood numbers were presented for different values of the non-linear part of the Boussinesq approximation; couple stress parameter, and the Biot number on the walls.

Abstract: Keywords: Natural convection, anisotropic porous medium, inversion of density.Abstract. The natural convection in the porous medium has attracted considerable attention with its applications in various industrial sectors, such as the agro-alimentary, the pharmaceutical and oil processing industries. The present work is about the study of the phenomenon of natural convection at 4°C on the vertical plate lining in an anisotropic porous medium in permeability. The wall of the vertical surface is subjected to a constant temperature with defined hydrodynamic conditions and thermal limits. Generalized Darcy’s law was used to establish the governing equations of the system. The control parameters governing the system are respectively the permeability ratio K*, the angle ϴ of the major axis and the inversion parameter R. The general basic equations were solved numerically using Runge-Kutta and shooting method. There was validated against previous work. The effect of these parameters on the heat transfer was highlighted. From the analysis result, it comes out the following conclusions: The convective flow is significantly affected by the anisotropic parameter; heat transfer along the vertical surface is maximum (minimum) when the main shaft having the high permeability is oriented parallel (perpendicular) to the gravitational field; the rate of heat transfer is depending on the inversion parameter R. The convective transfer rate illustrated by the local Nusselt number is symmetric with respect to R=0.45, where it reaches its smallest value. It is inversely proportional to the distribution of the thickness of boundary layer. A high convective transfer rate corresponds to a low boundary layer thickness and this inversely.

Abstract: In the building, roof is a major element contributing to the space thermal load. Due to its importance, this component has been widely studies in the literature and under various climatic conditions. In this paper, a numerical study was carried out for the coupling of natural convection and surface radiation heat transfer in a triangular shaped roof with eave (Gabel roof) for cold climates. The numerical solution is obtained using a finite volume method based on the SIMPLER algorithm for the treatment of velocity-pressure coupling. Concerning the radiation exchange, the working fluid (air) is assumed to be transparent, so only the solid surfaces (assumed diffuse-grey) give a contribute to such exchange. Governing parameters on heat transfer and flow fields are Rayleigh number (Ra), aspect ratio (A) and eave lengths (e^*). Numerical results are obtained to display the isotherms, streamlines and the heat transfer rate in terms of local and average Nusselt numbers. We found that the production of several circular cells is proportional to the decrease of aspect ratio and the increase of Rayleigh number. In addition, the heat transfer is much more pronounced in the presence of thermal radiation.

Abstract: The two dimensional study of natural convection in vertical cylindrical annular enclosure filled with Cu-water nanofluid under magnetic fields is numerically analyzed. The vertical walls are maintained at different uniform hot and cold temperatures, T_H and T_C, respectively. The top and bottom walls of the enclosure are thermally insulated. The governing equations are solved numerically by using a finite volume method. The coupling between the continuity and momentum equations is effected using the SIMPLER algorithm. Numerical analysis has been carried out for a wide range of Rayleigh number (10³ ≤Ra≤10⁶), Hartmann number (1 ≤Ha≤100) and nanoparticles volume fraction (0 ≤φ≤0.08). The influence of theses physical parameters on the streamlines, isotherms and average Nusselt has been numerically investigated.

Abstract: A numerical analysis was performed to study the effects of combined double diffusive and viscous dissipation under non-uniform wall boundary conditions on heat and mass transfer for a viscous nanofluid past a semi-infinite vertical plate embedded in porous medium which descriped by Darcy-Forchheimer extension. The mathematical model of nanofluid incorporate the Brownian motion and thermophoresis mechanisms. The nonlinear governing equations are reduced to a set of nonsimilar ordinary differential equations and the resulting system of equations is then solved numerically by Keller-Box method. A parametric study is achieved and obtained numerical results are presented with the help of graphical illustrations, in order to ride how the governing parameters affects the flow field, temperature, concentration and solide volume fraction profiles. Furthermore, some interesting data for the local Nusselt and Sherwood numbers are also illustrated.

Abstract: The main topic of this paper is the development of a mathematical model, based on the Lattice Boltzmann equations (LBE), which is proposed for the simulation of the complex convective flow, held in an electrically conducting melt, driven by the combined action of buoyancy, surface-tension, and electromagnetic forces. The lattice Boltzmann method (LBM) is relatively novel and contrasts with the usual well-known methods to physical modeling in the domain of computational fluid dynamics (CFD). Indeed, the LBM describes the fluid (i.e. lattice fluid) at a microscopic level (molecular) and proposes models for the collision between molecules. The full continuum-level physics (i.e. the macroscopic hydrodynamic fields) is implicitly contained in the LB model. Indeed those macroscopic quantities are defined as moments of the so-called particle distribution functions. In the present work, a two-dimensions (2D) LBE-based model is developed to the simulation of convection melt flow driven by the combination of natural buoyancy, surface tension, and electromagnetic forces. The model is applied to numerical modeling of the problems of buoyancy, surface-tension, and electromagnetic driven convection melt flow in an enclosure. The melt system used has a low Prandtl number, which is appropriate to crystal growth melts.

Abstract: The oscillatory natural convection between two concentric cylinders is numerically investigated. The effect of Prandtl number on flow and heat transfer characteristics with considering the magnetic field effects is investigated. For different values of physical parameters, critical Rayleigh numbers are determined. For buoyancy term, the Boussinesq approximation is used, and the numerical solutions are obtained using the finite volume method. For this kind of Prandtl number, the flow and heat transfer characteristics are unique and independent of the Prandtl number. Stability diagram (Ra_Cr-Pr) highlights the dependence of Ra_Cr via Prandtl numbers and various Hartmann number. The importance of this modeling is its practical application for stabilizing or weakening the convective effects in the design of magnetic systems.