Theoretical study on thermal radiative properties of semitransparent porous media

Thermal radiative properties are significant to radiative transfer processes in semitransparent media.In order to calculate thermal radiative properties,conventional Mie formulism and its various abbreviations are generally used,which are based upon electromagnetic scattering by a sphere submerged in a non absorbing medium.For some semitransparent porous media such as ceramics where the matrix is absorbing,the conventional Mie solution is no longer valid.In this study a rigid Mie solution of electromagnetic scattering by a sphere in an absorbing medium is introduced to analyze the radiative properties of such a medium,and reliability of conventional Mie formulism is also tested.Parametric studies show that scattering coefficient and phase function of porous media are influenced significantly by matrix refractive index and size parameter.The matrix absorbing index usually has little influence.But when the absorbing index is greater than 0.01,especially under the condition where the size parameter is greater than 30,the conventional Mie formulism is not appropriate.Such a porous media may exhibit scattering or absorbing dominated characters under different conditions and an optimal pore diameter exists for a specified wavelength,which decreases with the matrix refractive index.