Radiative transfer modeling: Numerical techniques and applications in fiber optics manufacturing

Radiative transfer is an important heat transfer mode for many scientific and engineering applications. For example, radiative heat transfer can be orders of magnitude higher than other modes of heat transfer in optical fiber drawing process. Therefore, modeling of radiative transfer is very important to understand the physical phenomena as well as process control and optimization. However, accurate modeling of radiative transfer in semitransparent media has been proven to be extremely challenging. Solving the radiative transfer equation requires solution for an integral-differential equation with five independent variables (three in spatial domain and two in directional domain) even for gray media. Analytical solutions for the radiative transfer equation are limited to only a few extremely simplified cases and numerical modelings are sometimes prohibitively expensive. ^ This dissertation proposes several numerical techniques to improve the efficiency and accuracy in radiative transfer modeling. Two numerical techniques are proposed and demonstrated to reduce the computational cost of evaluating direct exchange areas for the zonal method. A modified scheme is proposed for modeling axisymmetric radiative transfer using finite volume method to improve compatibility with finite volume method in CFD analysis, as well as to remove sources of error in existing schemes. Numerical models to investigate radiative transfer related to fiber optics manufacturing are also presented. The radiative transfer in laser heating of fused silica rods and microstructured optical fiber fabrication is investigated to gain physical insights of processes involved. The effects of radiative heat transfer modeling and Fresnel boundary conditions are demonstrated. Finally, the thermal radiative properties of a submicron thick film coated semi-transparent fiber is determined using the ray tracing method and wave optics. The predicted radiative properties are incorporated into a detailed conjugate heat transfer model to study chemical vapor deposition carbon coating of optical fiber.