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1.
The current study addresses the mathematical modeling aspects of coupled conductive and radiative heat transfer in presence of absorbing, emitting and isotropic scattering gray medium within two-dimensional square enclosure. The walls of the enclosure are considered to be opaque, diffuse and gray. The enclosure comprised of isothermal vertical walls and insulated horizontal walls. A new hybrid method where the concepts of modified differential approximation employed by blending discrete ordinate method and spherical harmonics method, has been developed for modeling the radiative transport equation. The finite volume method has been adopted as the numerical technique. The effect of various influencing parameters i.e., radiation-conduction parameter, surface emissivity, single scattering albedo and optical thickness has been illustrated. The compatibility of the method with regard to solving coupled conduction and radiation has also been addressed. 相似文献
2.
The current study addresses the mathematical modeling aspects of transport phenomena in steady, two-dimensional, laminar flow accompanied by heat transfer in a lid-driven differentially heated cavity in presence of radiatively absorbing, emitting and scattering gray medium. The walls of the enclosure are considered to be opaque, diffusive and gray. Mixed convection is the outcome of the interaction of forced convection induced by the moving vertical hot and cold wall with the natural convection induced due to the differentially heated enclosure. Two different orientations of the wall movement have been considered to simulate opposing and aiding mixed convection phenomenon and to study its interaction with radiation. Vorticity-stream function formulation of N–S equation has been employed. The discrete ordinate method has been used in modeling the radiative transport equation followed with finite volume method as discretisation technique. The effect of influencing parameters on fluid flow and heat transfer has been studied. 相似文献
3.
Prabal Talukdar F. V. Issendorff D. Trimis C. J. Simonson 《Heat and Mass Transfer》2008,44(6):695-704
Interaction of conduction and radiation in 3D enclosures is carried out with a gray participating media. Application of block
structured grid is shown with the finite volume method (FVM). Radiation modeling is performed with the FVM and is coupled
with an ‘in-house’ code to solve the set of transport equations. The detailed numerical results are presented for a cubical
and a cylindrical enclosure as these results are not available in the literature. The numerical simulation for the cylindrical
enclosure is performed using a block-structured ‘O’ grid. Two additional geometries are considered in order to show the applicability
of the present work. Results of temperature, radiative heat flux and total heat flux distributions are presented for different
optical thicknesses, scattering albedoes, emissivities and conduction–radiation parameters. The 3D results are validated with
the available 2D results or results with pure radiation problems as limiting cases. 相似文献
4.
This paper deals with a numerical study of combined convective and radiative heat transfer in a three-dimensional rectangular
duct with hydrodynamically and thermally developing laminar flow. The gas is assumed to be an incompressible, absorbing, emitting,
isotropically scattering, gray medium. Isothermal, gray, diffuse boundary walls at different temperatures are assumed. The
finite-volume method (FVM) is adopted to describe both convective and radiative heat transfer.
The coupled continuity and momentum equations are solved by means of SIMPLER algorithm. Numerical results for the radiative
flux show very good agreement with the available data. The effects of aspect ratio, optical thickness, scattering albedo and
wall emissivity on the mean bulk temperature are also investigated.
By splitting the heat flux into convective and radiative contributions, the relative importance of these components is assessed
for a typical range of values of the parameters.
Received on 9 February 1999 相似文献
5.
In the present investigation, the coupled phenomenon of opposing mixed convection and radiation within differentially heated eccentric horizontal cylindrical annulus has been numerically simulated. The radiation transfer contributed from the participating medium is obtained by solving the nonlinear integro‐differential radiative transfer equation using discrete ordinate method. The participating gray medium is considered to be emitting, absorbing and isotropically scattering. The walls of the annulus are considered to be opaque, diffuse and gray. In the study it has been observed that the Richardson number ‘Ri’ has a small effect on the total Nusselt number ‘Nu’ in mixed convection heat transfer with or without radiation. From the present investigation it is found that substantial changes occur in isotherms as well as in flow patterns, when the Richardson number is allowed to vary in the range of 0.01–1. The influence of radiative parameters on the interaction phenomenon has been delineated through isotherm and streamline pattern. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
6.
In this paper a new model and computer code is presented by considering singular and discontinuous heat flow divergence. A hybrid model including Smith’s WSGG model and Coppale and Vervish’s model is used for calculating gas radiative properties. Energy equation is solved simultaneously to reach temperature field which specify gas radiative properties. S 8 order of discrete ordinate method is used to solve RTE. It is assumed that walls of enclosure are gray, diffuse and opaque with specified temperature. Boundary conditions are corrected in each iteration that change temperature field. 相似文献
7.
Coupled laminar natural convection with radiation in air-filled square enclosure heated from below and cooled from above is
studied numerically for a wide variety of radiative boundary conditions at the sidewalls. A numerical model based on the finite
difference method was used for the solution of mass, momentum and energy equations. The surface-to-surface method was used
to calculate the radiative heat transfer. Simulations were performed for two values of the emissivities of the active and
insulated walls (ɛ1=0.05 or 0.85, ɛ2=0.05 or 0.85) and Rayleigh numbers ranging from 103 to 2.3×106 . The influence of those parameters on the flow and temperature patterns and heat transfer rates are analyzed and discussed
for different steady-state solutions. The existing ranges of these solutions are reported for the four different cases considered.
It is founded that, for a fixed Ra, the global heat transfer across the enclosure depends only on the magnitude of the emissivity
of the active walls. The oscillatory behavior, characterizing the unsteady-state solutions during the transitions from bicellular
flows to the unicellular flow are observed and discussed. 相似文献
8.
Ahmed Boutoub Hazem Ettouati Hmaïed Benticha Mohamed Sassi 《Heat and Mass Transfer》2007,43(7):613-622
This paper discusses the radiative transfer effects of an axisymmetric gas-particles jet into a cylindrical pipe. The medium
is gray and it participates to radiation by emission, absorption and scattering. The two-phase flow problem is solved numerically
by the finite volume method. We investigate the radiative transfer through a sensitivity analysis which considers the effects
of the particle radiative properties and the particle number density on the temperature field and on the radiative heat fluxes
of the two-phase flow domain. Analysis of the temperature profile in the cylinder, without and then with particle radiation
effects, shows a decrease in the medium temperatures and thus an important role of the radiative transfer. These results also
show that the presence of scattering makes the medium temperature more uniform. Finally, analysis of the particle number density,
through the variation of the injection velocity, shows that a decrease in the injection velocity decreases the temperatures
of the gas and particles and rapidly equilibrates the gas and particle temperatures. 相似文献
9.
10.
This work is focused on the numerical modeling of steady laminar mixed convection flow in a lid-driven inclined square enclosure filled with water–Al2O3 nanofluid. The left and right walls of the enclosure are kept insulated while the bottom and top walls are maintained at constant temperatures with the top surface being the hot wall and moving at a constant speed. The developed equations are given in terms of the stream function–vorticity formulation and are non-dimensionalized and then solved numerically subject to appropriate boundary conditions by a second-order accurate finite-volume method. Comparisons with previously published work are performed and found to be in good agreement. A parametric study is conducted and a set of graphical results is presented and discussed to illustrate the effects of the presence of nanoparticles and enclosure inclination angle on the flow and heat transfer characteristics. It is found that significant heat transfer enhancement can be obtained due to the presence of nanoparticles and that this is accentuated by inclination of the enclosure at moderate and large Richardson numbers. 相似文献
11.
The unsteady conjugate conduction-natural convection in enclosure is of great theoretical significance and is widely encountered in engineering applications in the areas of fluid dynamics and heat transfer. However, there are relatively few efforts to investigate the unsteady flow physics and heat transfer characteristics in the inclined enclosure of finite thickness walls. In the present work, this problem is numerically investigated by a high accuracy multidomain temporal-spatial pseudospectral method. The enclosure is filled with Boussinesq fluid and is bounded by four finite thickness and conductive walls; one of the vertical sidewall is exposed to time-periodic temperature environment while the opposite sidewall holds constant temperature; the top and bottom walls are assumed to be adiabatic. Particular efforts are focused on the effects of three types of influential factors: the wall thermophysical properties, the time-periodic temperature patterns and the inclination, and the time-periodic flow patterns and heat transfer characteristics are presented. Numerical results reveal that within the present parameter range, the heat transfer rate increases almost linearly with the thermal conductivity ratio and thermal diffusivity ratio but decreases with the inclination angle. Moreover, the heat transfer could be enhanced or weakened by selecting different temperature pulsating period in the case of finite thickness wall, while it is always enhanced if the walls are zero thickness. The back heat transfer and heat transfer resonance phenomena are observed, and their relationships with the time-periodic flow patterns and temperature distributions are analyzed. The findings are helpful to the understandings of the fluid flow and heat transfer mechanisms in the related enclosure configurations, and may be of engineering use in thermal design improvement. 相似文献
12.
In the present work, the interaction between non-gray radiation and forced convection in a laminar radiating gas flow over a recess including two backward and forward facing steps in a duct is investigated numerically. Distributions of absorption coefficients across the spectrum (50 cm?1 < η < 20,000 cm?1) are obtained from the HITRAN2008 database. The full-spectrum k-distribution method is used to account for non-gray radiation properties, while the gray radiation calculations are carried out using the Planck mean absorption coefficient. To find the divergence of radiative heat flux distribution, the radiative transfer equation is solved by the discrete ordinates method. The effects of radiation–conduction parameter, wall emissivity, scattering coefficient and recess length on heat transfer behaviors of the convection–radiation system are investigated for both gray and non-gray mediums. In addition, the results of gray medium are compared with non-gray results in order to judge if the differences between these two approaches are significant enough to justify the usage of non-gray models. Results show that for air mixture with 10 % CO2 and 20 % H2O, use of gray model for the radiative properties may cause significant errors and should be avoided. 相似文献
13.
A complete analysis of heat transfer in rectangular fin arrays has been conducted taking into consideration convection and
radiation at all surfaces, as well as radiative exchange between the fins and all neighboring surfaces. The analysis assumes
diffuse nongray surfaces and uses the spectral optical properties of stainless steel AISI 430. Three different gray models
were proposed in order to assess the effect of the gray assumption on the heat-transfer characteristics. Results are presented
for the temperature and radiative-flux distributions along the fin, the radiative flux along the base, the contribution of
the radiative component to the overall heat transfer, and the effectiveness of the fin array. Significant deviations in some
of these results were found between the nongray model and the gray models. In general, convection was found to be the more
effective mode of heat transfer in fin arrays and the effectiveness of the array decreases as the contribution of the radiative
component increases. 相似文献
14.
The interaction between conduction, convection and radiation heat transfer in molten glass has been studied with specific reference to the forehearth units of a glass tank furnace. In shallow molten glass flows as typically encountered in forehearth units, the radiation-conductivity approach for modelling the radiative transfer process is found inappropriate. This is especially so for colourless glasses which are not optically thick below 2.8 microns. In the present work radiative heat transfer process in molten glass has been treated more rigourously by incorporating both optically thick and thin limits. The radiative interaction at the boundaries is treated more realistically. In the case of colourless glasses, the results obtained by the present method show the necessacity to account for the direct radiative interaction between the interior layers of the glass and refractory walls at the top and the bottom. The forehearth exit temperature profiles obtained by using the present method are quite different with those obtained using the radiation conductivity approach. 相似文献
15.
Steady, laminar, natural-convection flow in the presence of a magnetic field in an inclined square enclosure differentially
heated along the bottom and left vertical walls while the other walls are kept isothermal was considered. The governing equations
were solved numerically for the stream function, vorticity and temperature ratio using the differential quadrature method
for various Grashof and Hartmann numbers, inclination angle of the enclosure and direction of the magnetic field. The orientation
of the enclosure changes the temperature gradient inside and has a significant effect on the flow pattern. Magnetic field
suppresses the convective flow and its direction also influences the flow pattern, causing the appearance of inner loops and
multiple eddies. The surface heat flux along the bottom wall is slightly increased by clockwise inclination and reduced by
half by the counterclockwise inclination. The surface heat flux along the upper portion of the left side wall is reversed
by the rise of warmer fluids due to the convection currents for no inclination and clockwise inclination of the enclosure. 相似文献
16.
The problem of steady, laminar, natural convective flow of a viscous fluid in an inclined enclosure with partitions is considered.
Transverse gradient of temperature is applied on the two opposing regular walls of the inclined enclosure while the other
walls are maintained adiabatic. The problem is formulated in terms of the vorticity-stream function procedure. A numerical
solution based on the finite volume method is obtained. Representative results illustrating the effects of the enclosure inclination
angle and the degree of irregularity on the contour maps of the streamlines and temperature are reported and discussed. In
addition, results for the average Nusselt number at the heated wall of the enclosure and the difference of extreme stream-function
values are presented and discussed for various Rayleigh numbers, inclination angles and dimensionless partition heights. 相似文献
17.
Giovanni Mascali 《Continuum Mechanics and Thermodynamics》2002,14(6):549-561
Recently [1], a procedure has been proposed in order to close the set of the moment equations of relativistic radiative fluid
dynamics. In particular explicit expressions for the moments of the bremsstrahlung and Thomson scattering source terms have
been given. In this work, as anticipated in [1], we shall treat in a systematic way Comptonization and double Compton scattering
too. Numerical results relative to the Compton cooling of hot electrons are shown.
Received November 14, 2001 / Published online June 4, 2002
RID="a"
ID="a" e-mail: mascali@dmi.unict.it
Communicated by Ingo Müller, Berlin 相似文献
18.
A study of the application of the discrete-ordinate method (DOM) with remedy for the ray effects to the solution of surface radiation exchange is presented in this paper. The remedy for the ray effects is achieved by dividing the radiative intensity into the attenuated incident and the medium emitting components. To demonstrate the application of the technique, this work considers radiative heat transfer in a two-dimensional cylindrical enclosure filled with a nearly transparent medium. The results obtained by the present DOM are in excellent agreement with those by the radiosity/irradiation method. 相似文献
19.
G. Wang M. ZengY.C. Ren H. Ozoe Q.W. Wang 《Experimental Thermal and Fluid Science》2011,35(1):105-111
The transient natural convection in an inclined enclosure filled with water is studied experimentally for the time-periodically-varying wall temperature on one side wall and constant average temperature on the opposing side wall. This system has no temperature difference between the opposing two side walls in time-averaged sense. The temperatures of two opposing walls and the heat flux across the enclosure are measured by a heat flux meter. Based on the experimental results, the effects of time-periodically-varying wall temperature and inclined angles of the enclosure on heat transfer characteristics are studied. The experimental results show that, with the upper wall temperature oscillating, the heat flux across the enclosure is also periodically varied with time, and the net heat flux is from the lower wall to the upper wall. Numerical computations are also conducted and numerical results are qualitatively assured by the experimental measurements. 相似文献
20.
In this study, a discussion of the fluid dynamics in the attic space is reported, focusing on its transient response to sudden
and linear changes of temperature along the two inclined walls. The transient behaviour of an attic space is relevant to our
daily life. The instantaneous and non-instantaneous (ramp) heating boundary condition is applied on the sloping walls of the
attic space. A theoretical understanding of the transient behaviour of the flow in the enclosure is performed through scaling
analysis. A proper identification of the timescales, the velocity and the thickness relevant to the flow that develops inside
the cavity makes it possible to predict theoretically the basic flow features that will survive once the thermal flow in the
enclosure reaches a steady state. A time scale for the heating-up of the whole cavity together with the heat transfer scales
through the inclined walls has also been obtained through scaling analysis. All scales are verified by the numerical simulations. 相似文献