With hypothesis that radiation is incoherent, based on Planek's definition of radiative entropy, radiative entropy transfer equation and local radiative entropy generation in semitransparent graded index medium are derived. A calculation method based on discrete-ordinates approach is used to solve radiative entropy transfer equation in semitransparent graded index medium. A one-dimensional slab system filled with semitransparent graded index medium is taken as an example to verify the radiative entropy transfer equation and the calculation method. Numerical results of dimensionless radiative entropy generation of the slab system agree well with entire thermodynamics analysis.

The coupled heat transfer processes of radiation, conduction and convection in semitransparent planar slab are analyzed. An inverse method is presented for estimating the unknown boundary incident radiation heat flux in semitransparent planar slab with transparent boundaries from the knowledge of the radiation intensities exiting the boundaries. The effects of anisotropic scattering, absorption coefficient, scattering coefficient, fluid temperature outside the boundaries, convection heat transfer coefficients, conduction coefficient of semitransparent media and slab thickness on the accuracy of the inverse analysis are investigated. The results show that this method is praticable.

The discrete ordinate approximation method of three-dimensional radiative transfer equation in absorbing scattering medium is expounded. The selection of quadrature sets of in-scattering term are analysed. The causes about the formation of false scattering and ray effect and its influence on the accuracy of solutions are also analysed. By detailed comparison, it is shown that false scattering and ray effect exact not only in discrete-ordinates method, but also in zone method, discrete transfer method, etc., and the influence of false scattering and ray effect on solution accuracy of radiative transfer equation can be reduced by decreasing grid size and increasing the number of solid angle discretation. The process of radiative heat transfer in a three-dimension rectangular furnace is simulated using discrete ordinates method. By comparison with zone method and discrete transfer method, it is found that discrete ordinates method has a good accuracy, and recently is one of the best method to simulate the process of radiative heat transfer in furnace.