Effect of unsteady natural convection on the diameter of drawn polymer optical fiber

This paper presents experimental results showing the effect various natural convection heating regimes have on the diameter of drawn polymer optical fiber. The airflow, adjacent to the polymer, can be either laminar, oscillatory, or chaotic, depending on the imposed thermal boundary conditions at the furnace and iris walls. When subject to oscillatory and chaotic natural convection, the drawn fiber varies in diameter 2.5 to 10 times more than that measured under laminar heating conditions. Particle image velocimetry shows that unsteady natural convection occurs with the interplay between two asymmetric counter-rotating convective cells. This represents a significant instability mechanism, one that has not been previously identified.