Numerical investigation on He and Ar gas convective cooling for optical fiber glass drawing at short draw towers

Abstract

The inert purge gas plays an important role in mass manufacturing of optical fibers, as it is usually the mixture gas of helium and argon. The natural and forced convective effects of purge gas are numerically investigated through the process simulation of glass fiber drawing in a short draw tower furnace by employing an iterative computational scheme of neck-down prediction formulation and computational fluid dynamics simulation of purge gas flow. The furnace geometric model and process conditions are based on realistic manufacturing process. It is found that neck-down shape and draw tension are quite insensitive to change of gas flow rate and helium contents level. In contrast, the recirculatory flow pattern around preform neck-down region is observed when helium contents are low, suggesting the difficulty in flushing of contamination particles out of furnace system. The increase of helium contents combined with increased flow rate in purge gas mixture could completely remove such undesirable flow patterns.