Heat transfer analysis of viscous incompressible fluid by combined natural convection and radiation in an open cavity (original) (raw)
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Thermal Science, 2018
A numerical study of the natural convection combined with thermal radiation inside a square porous cavity filled with a fluid of temperature-dependent viscosity is carried out. The side horizontal walls are assumed to be adiabatic while both the left and right vertical walls are kept at constant but different temperatures. The Rosseland diffusion approximation is used to describe the radiative heat flux in the energy equation. The governing equations formulated in dimensionless stream function, vorticity, and temperature variables are solved using finite difference method. A parametric analysis illustrating the effects of the radiation parameter (0 ? Rd ? 10), Darcy number (10?5 ? Da ? 10?2), and viscosity variation parameter (0 ? C ? 6) on fluid flow and heat transfer is implemented. The results show an essential intensification of convective flow with an increase in the radiation parameter.
Effect of radiation on the flow structure and heat transfer in a two-dimensional gray medium
Thermal Science
A numerical study of combined natural convection and radiation in a square cavity filled with a gray non-scattering semi-transparent fluid is conducted. The horizontal walls are adiabatic and the vertical are differentially heated. Convection is treated by the finite volumes approach and the discrete ordinates method is used to solve radiative transfer equation using S6 order of angular quadrature. Representative results illustrating the effects of the Rayleigh number, the optical thickness and the Planck number on the flow and temperature distribution are reported. In addition, the results in terms of the average Nusselt number obtained for various parametric conditions show that radiation modifies significantly the thermal behavior of the fluid within the enclosure.
Forschung Im Ingenieurwesen-engineering Research, 2008
The present article considers a numerical study on the combined effect of thermal dispersion and thermal radiation on the non-Darcy natural convection flow over a vertical flat plate kept at higher and constant temperature in a fluid saturated porous medium. Forchheimer extension is used in the flow equations. The coefficient of thermal diffusivity has been assumed to be the sum of molecular diffusivity and the dispersion thermal diffusivity due to mechanical dispersion. Rosseland approximation is used to describe the radiative heat flux in the energy equation. The non-dimensional governing equations are solved by the finite element method (FEM). The resulting non-linear integral equations are linearized and solved by the Newton–Raphson iteration. The finite element implementations are prepared using Matlab software packages. Numerical results for the details of the stream function, velocity and temperature contours as well as heat transfer rates in terms of Nusselt number are presented and discussed.
Effects of radiation on natural convection flow around a sphere with uniform surface heat flux
Journal of Mechanical Engineering, 2009
The effects of radiation on natural convection flow around a sphere with uniform surface heat flux have been investigated in this paper. We have considered here a sphere with uniform surface heat flux immersed in a viscous incompressible optically thick fluid. The governing equations are first transformed into non-dimensional form and the resulting nonlinear systems of partial differential equations are then solved numerically using Finite-difference method with Keller-box scheme. We have focused our attention on the evolution of the shear stress in terms of local skin friction coefficient and the rate of heat transfer in terms of local Nusselt number. Also, velocity as well as temperature profiles are shown graphically for some selected values of radiation parameter (Rd), surface temperature parameter (D) and Prandtl number (Pr). Keywords: Thermal radiation, Prandtl number, natural convection, uniform surface heat flux. doi:10.3329/jme.v39i1.1834 Journal of Mechanical Engineering, ...
Solar Energy, 2012
In this work the numerical results of natural convection and surface thermal radiation in an open cavity receiver considering large temperature differences and variable fluid properties are presented. Numerical calculations were conducted for Rayleigh number (Ra) values in the range of 10 4 -10 6 . The temperature difference between the hot wall and the bulk fluid (DT) was varied between 100 and 400 K, and was represented as a dimensionless temperature difference (u) for the purpose of generalization of the trends observed. Noticeable differences are observed between the streamlines and temperature fields obtained for u = 1.333 (DT = 400 K) and u = 0.333 (DT = 100 K). The total average Nusselt number in the cavity increased by 79.8% (Ra = 10 6 ) and 88.0% (Ra = 10 4 ) as u was varied from 0.333 to 1.333. Furthermore the results indicate that for large temperature differences (0.667 6 u 6 1.333) the radiative heat transfer is more important that convective heat transfer.
2017
We analyze the effect of radiation on mixed convective heat and mass transfer flow of a viscous fluid ,incompressible fluid through a porous medium in a vertical channel bounded by flat walls. A non-uniform temperature is imposed on the walls and the concentration on these walls is taken to be constant. The viscous dissipation is taken in to account in the energy equation. Assuming the slope of the boundary temperature to be small. We solve the governing momentum, energy and diffusion equations by a perturbation technique. The velocity ,the temperature ,the concentration ,the shear stress and the rate of heat transfer have been analyzed for different variations of the governing parameters. The dissipative effects on the flow, heat and mass transfer are clearly brought out.
2006
This paper describes a numerical study of the radiation-natural convection interactions in a differentially-heated cavity with an inner body. A specifically developed numerical model, based on the finite-volume method, is used for the solutions of the governing differential-equations. The SIMPLER algorithm for the pressure-velocity coupling is adopted. The fluid (air) is perfectly transparent to the radiation. The surface emissivity e, the Rayleigh number Ra, and the thermal conductivity ratio R k were varied parametrically. For Pr = 0.71 and relatively wide ranges of the other parameters, results are reported in terms of isotherms, streamlines, average Nusselt-numbers across the enclosure, local Nusselt-numbers at the hot and cold walls, vertical and horizontal median velocities and horizontal walls, temperature distributions. It is found that: (i) the radiation exchange homogenizes the temperature inside the cavity and produces an increase in the average Nusselt-number, particularly when R k and Ra are high and (ii) the average Nusselt-number increases with increasing surface emissivity, especially at high Rayleigh numbers.
The paper deals with Simultaneous heat transfer by convection and radiation in a channel flow between two infinite black parallel plates is investigated. The effect of radiation on the heat transfer and the full thermal development of the flow is studied. The effect of scattering albedo, conductionradiation parameter and the optical thickness are examined. The radiation is shown to substantially alter the heat transfer downstream before the thermally fully developed conditions. The full thermal development is shown to exist for the constant wall temperature case, while it is pushed further downstream and could not be seen for the constant wall heat flux case. While the radiation greatly affects the heat transfer when the fluid is heated, for the cooling case radiation effect decreases along the stream wise direction and vanishes at the fully developed conditions.
2010 14th International Heat Transfer Conference, IHTC 14, 2010
Combined heat transfer of natural convection-conduction and surface radiation in an open cavity heated by constant flux is studied in this paper. Flow model is laminar and SIMPLE algorithm and QUICK scheme are employed. The relevant parameters are as follows, Prandtl number is 0.7 and dimensionless solid thickness is 0.2, conductivity ratio rangs from 0 to 1000, Rayleigh number ranges from 10 3 to 10 9 , surface emissivity ranges from 0 to 1. The numerical results shows secondary circular formed as an effect of radiation which increased the average Nusselt number about from 54.1% to 100.3%. INTRODUCTION Natural convection in an open cavity is a topic of significant interest in a range of engineering applications such as building insulation, solar thermal central receivers, geothermal reservoirs, electronic cooling devices, fire spread in rooms, etc. During the past decades, both experimental and computational studies have been conducted into the cavity-flow physics. These studies were mainly focused on flow and heat transfer of different Rayleigh numbers, aspect ratios, and tilt angles. Also, they studied the occurrence of transition to turbulence and turbulence and how the boundary conditions in the aperture are considered. In a realistic case with any open cavity system, conduction of solid walls and surface thermal radiation always exist, and can both strongly interact with natural convection, because of the coupling between the surface temperature and the flow fields in the cavity.