Computational Model for Predicting the Location of Glass Solidification in Optic Fiber Drawing

Abstract

This paper presents a computational model for predicting the location at which the glass fiber solidifies during a high-speed drawing process. Although modeling of the optic fiber drawing process has been of interest for the past two decades, traditional fiber drawing process uses small diameter preforms and low draw speeds, where the glass usually solidifies and turns into fiber inside the furnace. Much larger preforms drawn at higher speeds have been used in the state-of-the-art fiber drawing systems to improve production efficiency and reduce cost. Insulated post-chambers are often added below the furnace to reduce the glass cooling rate so that the optical loss in the fiber is low. To provide a basis for design optimization of the post-chamber, we have solved the conjugate problem of the glass free surface flow and the air convection to determine the location where the glass solidifies. As radiation is the dominant mode of heat transfer in the glass, the radiative transfer equation (RTE) is solved directly by discrete ordinate method (DOM). The heat flux due to the mixed convection of the air is also numerically calculated along the glass free surface, which involves the boundary layer flow around a continuously moving fiber and the buoyancy driven flow through the open-ended channel. The calculated free shapes are compared against the experimentally measured data to verify the computational model.