Papers by Keyword: Natural Convection

Abstract: This paper deals with the study of the heat and mass transfer characteristics of natural convection from a horizontalsurface embedded in a radiating fluid saturated porous medium. Similarity solutions for buoyancy induced heat and masstransfer from a horizontal surface, where the wall temperature and concentration are a power function of distance fromthe origin, are obtained by using an integral approach of Von Karman type. The effects of the governing parameters suchas buoyancy ratio, Lewis number, radiation parameter and the power-law exponent on local Nusselt and local Sherwoodnumbers have been investigated both numerically and graphically.

Abstract: In this paper, a numerical simulation was conducted to investigate the steady laminar natural convective heat transfer and surface radiation from a heated rectangular body in a triangular enclosure. The coupled equations of Navier-stockes and energy are both solved using the finite volume method. The velocity-pressure coupling is insured by the SIMPLER algorithm. The fluid used in this study is a dry air of Prandtl number Pr = 0.71.In such way that, the radiative exchanges are made only through solid walls and which are assumed to be gray and diffuse. The physical parameters characterizing the problem and influencing heat transfer are Rayleigh number Ra, aspect ratio A, height h and width w of the body. The results are presented in terms of isotherms, streamlines and average Nusselt number.

Abstract: The work in this manuscript deals with the numerical simulation of natural convection in a staggered cavity with the help of a recently developed two-dimensional double Multiple-Relaxation-Time (MRT) thermal Lattice Boltzmann method (LBM). In the last decade, there has been a rapid rise in the development of Lattice Boltzmann methods. However, its application in the simulation of natural convection from a staggered cavity has been carried out for the first time in this study. A careful undermining into the existing literature of heat and mass transfer reveal that study of natural convections in cross-sectional cavities is notably absent. Therefore, in this manuscript, we attempt to review the recently developed method and tried to analyze its implementation on natural convection in a staggered cavity with four differentially heated vertical walls. The problem geometry has eight boundaries. It is a staggered cavity with adiabatic horizontal walls and differentially heated vertical walls. The flow inside the thermally driven staggered cavity has been carefully studied for Rayleigh numbers 10³, 10⁴ and 10⁵. The velocity and pressure boundary conditions are determined by a non-equilibrium extrapolation rule. As no benchmark results are available in the literature for this relatively new problem, we carry out its simulation with the help of a yet another well established scheme. This scheme is a higher-order compact (HOC) scheme with fourth order spatial accuracy and second order temporal accuracy. Our results show that there is a very good agreement between both these methods which exemplifies the accuracy and credibility of our results.

Abstract: An analytical study of transient natural convective flow of a viscous incompressible optically thick radiating fluid past a moving vertical plate with ramped heat and mass fluxes in the presence of thermal radiation is performed. Exact solution of the governing equations under Boussinesq approximation, is obtained in closed form by Laplace transform technique. The expressions for the shear stress and at the plate temperature and concentration are also derived. The velocity profiles, temperature and species concentration are studied as functions of different physical parameters like radiation parameter, thermal Grashof number, mass Grashof number, Schmidt number, Prandtl number and time. The physical aspects of the problem are discussed.

Abstract: In the present study, an integral method of Von Karman type has been used to analyse the phenomenon of natural convection heat and mass transfer near a vertical surface embedded in a fluidsaturated porous medium considering the viscous dissipation and radiation effects. The buoyancy effect is due to the variation of temperature and concentration across the boundary layer. The effects of the governing parameters e.g. buoyancy ratio (N), Lewis number (Le), Eckert number (Ec) and radiation parameter (R) on local Nusselt number, local Sherwood number, velocity profile, temperature profile and concentration profile have been investigated. The results obtained in the present analysis have been compared with the published results available in the literature and they have been found in precise agreement.

Abstract: In the present research study a mathematical analysis has been presented for unsteady MHD natural convective flow of a rotating fluid over an infinite vertical plate immersed in a fluid saturated porous medium with oscillating free-stream. The effects of Hall and ion-slip currents also considered on the fluid flow. The unsteady MHD flow over the vertical plate is induced due to thermal and concentration buoyancy forces and oscillatory movement of the free-stream. The partial differential equations governing the motion for the fluid flow are solved analytically. The effects of various pertinent flow parameters on the fluid velocity, fluid temperature and species concentration are presented in graphical form whereas that on skin friction and rate of heat and mass transfer at the plate are presented in tabular form. An interesting observation recorded from the present analysis that there appears reversal flow in the secondary flow direction due to presence of thermal and/or concentration buoyancy forces. However, in the absence of both reversals flow does not exist in the secondary flow direction. It is also noted that the thickness of momentum boundary layer decreases with rise in frequency of oscillations of the free-stream.

Abstract: A numerical study of a natural convection flow coupled with radiation was carried out in a double-skin façade. The solar radiation flux to which the double-skin façade is subjected has been chosen for a cold season month (φ = 66.9 W/m² ). The double-skin façade is installed on a building whose interior temperature is 293 K given that the temperature at the inlet in winter conditions is 255 K. This study focuses on 5 different widths of the double-skin façade (4, 6, 8, 10 and 12 cm). Three-dimensional numerical simulations have been carried out for a steady and turbulent flow. Transport equations of mass, momentum and energy are solved numerically using finite volume method. Velocity and temperature profiles show the differences between all the above mentioned 5 cases in order to highlight the optimal width of the double-skin façade.

Abstract: Understanding of the natural convection flow in hydrothermal autoclaves is essential for the control of the growth rate and the quality of the grown crystals. This paper presents an analysis of the natural convection fluid flow and heat transfer and show the comparison between simulation and experimental results for the experimental model in a small size autoclaves, fill with water. A numerical model based on finite volume method has been developed to simulate the heat transfer and fluid convection in the vessel. Results show that the flow will strongly affect the temperature distribution. It can be observed that in the upper region the liquid flows up in the middle of the vessel and flows down in lateral parts near the walls. The temperature difference between experimental and simulation results is less than 1 °C in the upper part and between 2 and 3 °C in the bottom part. Velocity measurements show a good qualitative agreement between simulation and experimental results. The value of the z-component of velocity along the symmetry axis slightly increase with the increases of temperature difference ΔT .

Abstract: The buoyancy-induced air flow through a two-dimensional vertical ventilation channel is calculated. One of the channel walls is heated uniformly, and the other wall is adiabatic. A thin baffle is placed on the heated wall to manipulate the air flow through the channel. Numerical results are obtained for baffles of different lengths and placed at various heights along the heated wall. It is found that the baffle is effective in weakening a reverse flow at the exit of the channel, and significant enhancement of ventilation performance may be achieved with the presence of the baffle.

Abstract: The three-dimensional numerical study of natural convection in a cubical enclosure, discretely heated, was carried out in this study. Two heating square sections, similar to the integrated electronic components, are placed on the vertical wall of the enclosure. The imposed heating fluxes vary sinusoidally with time, in phase and in opposition of phase. The temperature of the opposite vertical wall is maintained at a cold uniform temperature and the other walls are adiabatic. The governing equations are solved using Control volume method by SIMPLEC algorithm. The sections dimension ε = D / H and the Rayleigh number Ra were fixed respectively at 0,35 and 10⁶. The average heat transfer and the maximum temperature on the active portions will be examined for a given set of the governing parameters, namely the amplitude of the variable temperatures a and their period τ_p. The obtained results show significant changes in terms of heat transfer, by proper choice of the heating mode and the governing parameters.