Advanced Model of Radiative Heat Transfer in a Rod Geometry

2007 ◽  
Author(s):  
Gennadii V. Kobelev ◽  
Valerii F. Strizhov ◽  
Alexander D. Vasiliev
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Reactor Vessel ◽  
Severe Accident ◽  
Radiative Heat Exchange ◽  
Pressurized Water ◽  
Vessel Elements ◽  
View Factors

Radiative heat transfer is very important in different fields of mechanical engineering and related technologies including heat transfer in furnaces, aerospace, nuclear reactors, different high-temperature assemblies. In particular, in the course of a hypothetical severe accident at pressurized water reactor (PWR) the temperatures inside the reactor vessel reach high values at which taking into account of radiative heat exchange between the structures of reactor (including core and other reactor vessel elements) gets important. Existing models of radiative heat exchange use many limitations and approximations like approximate estimation of view factors and beam lengths. The module MRAD was used in this paper to model the radiative heat exchange in rod-like geometry typical of PWR. Radiative heat exchange is computed using dividing on zones (zonal method) as in existing radiation models implemented to severe accident numerical codes such as ICARE, SCDAP/RELAP, MELCOR but improved in following aspects: • new approach to evaluation of view factors and mean beam length; • detailed evaluation of gas absorptivity and emissivity; • account of effective radiative thermal conductivity for the large core; • account of geometry modification in the course of severe accident. Special attention is paid to deriving of exact analytical values of view factors and mean beam lengths (which are a good tool in radiative heat transfer concerning gas media) for a number of “standard” geometries. Generalized Hottel’s method of strings is used for rods of finite lengths. Monte-Carlo method is used for validation of new model in application to “standard” geometries. The developed model is successfully applied for modeling of PARAMETER-SF1 and QUENCH-06 tests, which use the triangular and square rod assembly respectively.

Coupling a Discrete Transfer Method to a View Factors Technique for Radiative Heat Transfer Modeling in Industrial Furnaces

2005 ◽  
Author(s):  
Youssef Joumani ◽  
Guillaume Mougin ◽  
Fouad Ammouri ◽  
Marc Till
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Three Dimensional ◽  
Analytical Formula ◽  
Two Dimensions ◽  
Radiation Model ◽  
Participating Media ◽  
View Factors ◽  
Transfer Method

Air Liquide has been involved in the design of industrial furnaces (glass melting, reheating, aluminum, …) for several years. Thanks to that experience, known-how and expertise in modeling such applications have been developed. Dedicated simulation tools — 0D for global heat and mass balance, 1D for the prediction of longitudinal temperature profiles and 3D for detailed analysis — have been built. Each of them is very helpful when used relevantly and offers numerous opportunities at each step of the design of a furnace. In such kind of applications, the temperature levels are very high (up to 2500 K). As a consequence it is very crucial to simulate the radiative heat transfer as accurately as possible. This requires the use of a radiation model that can take into account complex geometries, non-isothermal media and various gas mixture compositions. Very often, three-dimensional simulations are necessary and reduction to smaller dimension problems is difficult or inadequate. The present paper introduces a new radiation model for computing two-dimensionally radiative heat transfer in an industrial furnace with a piecewise distributed load. To reduce the three-dimensional problem to two dimensions, the method consists in coupling the 2D radiation transport equation to a boundary condition based on view factors through an imaginary plane to homogenize the radiative behavior of the load surface. A solution procedure using the discrete transfer method associated to a weighted-sum-of-gray-gases database to deal with absorption and emission of a CO2-H2O mixture is proposed. Simulation results are finally compared to an analytical formula and then to a full-3D approach taking into account participating media, non-isothermal and gray walls. All tests show that this model can be used to simulate industrial configurations with a good accuracy.

Modeling of Radiative Heat Transfer during a PWR Severe Accident

2006 ◽  
Vol 154 (2) ◽  
pp. 194-214
Author(s):  
M. Zabiégo ◽  
F. Fichot ◽  
P. Rubiolo
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Severe Accident

Numerical Study of the Heat Radiation from the Porous Cylindrical Burner with Radiative Heat Exchange

2014 ◽  
Vol 1040 ◽  
pp. 553-558 ◽  
Author(s):  
F.S. Palesskiy ◽  
R.V. Fursenko ◽  
S.S. Minaev
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Power Distribution ◽  
Radiative Heat ◽  
Spectral Power ◽  
Numerical Study ◽  
Heat Radiation ◽  
Radiative Heat Exchange ◽  
Burner Surface ◽  
Cylindrical Burner

The problem of premixed gas combustion in porous cylindrical burner is investigated numerically. Two-temperature diffusional-thermal model taking into account radiative heat transfer described in the framework of Eddington model is applied. It was found that radiative heat transfer affects the characteristics of filtration combustion, such as temperature distribution and the flame radius, substantially. It is demonstrated that the overall heat flux from outer burner surface is significantly caused by heat radiation from the inner regions of the porous media. Account of the thermal radiation from the burner interior leads to the shift of the spectral power distribution maximum towards the short wave region in comparison with spectral density calculated on the base of burner outlet surface temperature.

scholarly journals Influence of the gray gases number in the weighted sum of gray gases model on the radiative heat exchange calculation inside pulverized coal-fired furnaces

2016 ◽  
Vol 20 (suppl. 1) ◽  
pp. 197-206 ◽  
Author(s):  
Nenad Crnomarkovic ◽  
Srdjan Belosevic ◽  
Ivan Tomanovic ◽  
Aleksandar Milicevic
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Radiative Heat ◽  
Computer Code ◽  
Pulverized Coal ◽  
Radiative Properties ◽  
Radiative Heat Exchange ◽  
Weighted Sum ◽  
Approximation Accuracy ◽  
Relative Differences

The influence of the number of gray gases in the weighted sum in the gray gases model on the calculation of the radiative heat transfer is discussed in the paper. A computer code which solved the set of equations of the mathematical model describing the reactive two-phase turbulent flow with radiative heat exchange and with thermal equilibrium between phases inside the pulverized coal-fired furnace was used. Gas-phase radiative properties were determined by the simple gray gas model and two combinations of the weighted sum of the gray gases models: one gray gas plus a clear gas and two gray gases plus a clear gas. Investigation was carried out for two values of the total extinction coefficient of the dispersed phase, for the clean furnace walls and furnace walls covered by an ash layer deposit, and for three levels of the approximation accuracy of the weighting coefficients. The influence of the number of gray gases was analyzed through the relative differences of the wall fluxes, wall temperatures, medium temperatures, and heat transfer rate through all furnace walls. The investigation showed that there were conditions of the numerical investigations for which the relative differences of the variables describing the radiative heat exchange decrease with the increase in the number of gray gases. The results of this investigation show that if the weighted sum of the gray gases model is used, the complexity of the computer code and calculation time can be reduced by optimizing the number of gray gases.

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