THERMAL TRANSPORT IN OPTICAL FIBER MANUFACTURING

A numerical model of combined radiative and convective heat transfer in a fiber draw furnace was formulated and solved. The model was used to predict glass temperatures and identify important heat transfer modes. The energy equation, which included conductive, convective, and radiative terms, was discretized using a control-volume-based finite element technique. Thermal radiation within the glass was approximated by the P1 method using a two-band spectral absorption coefficient. Surface-to-surface radiation from the muffle wall to the outer surface of the glass was computed by a full enclosure analysis. A cosinusoidal glass profile was assumed and a continuity-satisfying velocity field was specified. The results of the calculation showed that radiation was an important mode for air, argon and carbon dioxide purge gases, but that conduction was dominant for the case of a helium purge gas. The glass preform attains its asymptotic temperature higher in the furnace with helium than with any of the other gases studied. Temperatures are relatively insensitive to final fiber velocity and to the spacing between the glass and the furnace wall.