Numerical Study On Microstructural Effect On The Radiative Properties Of Thermal Barrier Caotings (TBCs)

In essence, radiation is one kind of electromagnetic wave which can bedescribed by the Maxwell equations. The traditional radiation transferequations are not completely applicable when the microstructure is smallerthan the wavelength. In this paper, the conventional geometrical opticsray-tracing approach is improved by considering the interference effect. Fourdifferent rough surfaces are generated, and their reflection properties arestudied by using the geometrical optics ray-tracing method and the finitedifferent time domain method. Through the analysis and comparison of theresults, the effect of the interference effect is evaluated in the geometricaloptics ray-tracing method. Except for small incidence angles or weakroughness, the interference effect has a significant effect on the resultspredicted by the geometrical optics method. Therefore, it cannot beneglected in such conditions. Compared with the conventional geometricaloptics ray-tracing method, the improved geometrical optics ray-tracingmethod has a higher precision and wider applications.Thermal barrier coatings (TBCs) are not the pure bulk materials, andthey contain many different micro/nano structures caused by the sprayingprocess. The microstructures in the coatings play a very important role onmechanical and thermal properties, therefore, the coating properties differhugely from those of the corresponding bulk materials. The influence of microstructures on thermal conductivity has been investigated by manyresearchers, however their effect on radiative heat transfer is seldom studied.The radiative heat transfer will become increasingly important as thetemperature rises, and this warrant the study on the influence ofmicrostructures on radiative properties. In the present paper,Finite-Difference-Time-Domain (FDTD) method was employed to simulatethe radiative heat transfer behaviors of TBCs with different types ofmicrostructures. The relationship between microstructures and radiativeproperties of the coating is investigated. Furthermore, the parameters ofmicrostructures such as defect size, shape coefficient, porosity andorientation angle are examined in detail. The results will help us to furtherunderstand the radiative heat transfer process across the TBCs and willprovide us a theoretical guide to design TBCs with a high thermal insulationproperty.