Combined natural convection and radiation in a triangular enclosure

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منو

" Combined natural convection and radiation in a triangular enclosure "
S. M. F. Hasani B. T. F. Chung

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113083
Doc. No	:	TLpq304409510
Main Entry	:	B. T. F. Chung
	:	S. M. F. Hasani
Title & Author	:	Combined natural convection and radiation in a triangular enclosure\ S. M. F. HasaniB. T. F. Chung
College	:	The University of Akron
Date	:	1998
student score	:	1998
Degree	:	Ph.D.
Page No	:	145
Abstract	:	The problem of combined natural convection and radiation heat transfer of a gray absorbing-emitting and isotropically scattering medium in a triangular enclosure is solved numerically in this dissertation. Interactions of natural convection and radiation occur in many engineering applications such as electronic cooling, solar heating, crystal growth, fire propagation etc. The radiation effect was neglected from many of the previous studies due to the complexities associated with radiation modeling. The triangular enclosure considered in the present study has been used by researchers in the past to model flows inside attic spaces, solar stills and near shore water circulation in lakes and rivers. Previous pure natural convection studies in this geometry had produced conflicting results and the effect of radiation was not considered prior to this study. The objectives of this study are: (i) to obtain a numerical solution for the combined natural convection and radiation problem in a triangular enclosure, (ii) to study the influence of radiation on thermal instabilities present in pure natural convection flow in this geometry, (iii) to perform parametric study and (iv) to verify the results of pure natural convection flow using more accurate QUICK scheme. The problem is mathematically formulated and a Fortran computer program is developed to meet the desired objectives. The two dimensional stream function equation, the time-dependent vorticity transport and energy equations, and the radiative transport equation are solved simultaneously for uniform temperature boundary conditions. Two different sets of boundary conditions are employed with inclined surfaces considered hot for one and cold for the other. The stream function equation is solved using successive overrelaxation whereas the vorticity transport and energy equations are solved using third-order upwinding QUICK scheme while the radiative transport solution is sought by means of Discrete Ordinates Method. Two different orders of approximation namely S4 and S8 have been used to obtain the radiative solution. The problem is studied in depth and the effect of radiation has been found to suppress thermal instabilities present in pure natural convection flow, thus delaying the cell bifurcation and hence raising the critical Rayleigh number. It is also observed that higher Rayleigh numbers make the flow unstable and increase the heat transfer while larger aspect ratios reduce the number of flow instabilities. Lower Planck numbers contribute to more radiative transfer, thus increasing the total heat transfer. As Planck number increases, the radiation effect decreases and the combined solution approaches pure natural convection solution. Larger optical thicknesses reduce heat transfer while higher surface emissivities and higher scattering effects increase the heat transfer. The effect of scattering in increasing the heat transfer is however much less than the effect due to wall emissivity. The pure natural convection results of the present study seemed to have resolved the conflicts of the previous studies and these in general, confirm the results published earlier by Salmun. Finally, in this dissertation, detailed numerical results along with an extensive parametric study are presented for the first time for combined natural convection and radiation heat transfer in a triangular enclosure. In addition, this research has also provided a deep insight into the mechanism of buoyancy driven pure convective motion in this geometry. All the results presented in this dissertation are an important addition to the existing heat transfer literature.
Subject	:	Applied sciences
	:	Emissivity
	:	Heat transfer
	:	Mechanical engineering
	:	Natural convection
	:	Triangular enclosure