Effects of Variable Properties and Viscous Dissipation During Optical Fiber Drawing

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Abstract
The axisymmetric free-surface flow and thermal transport of fused silica during optical fiber drawing was considered with variable properties, prescribed heat flux, and neck shape. Experimental data from previous researchers were adapted or used as the basis for assumptions in order to enable a realistic analysis. The main objectives were to model the neck-down process in order to clarify the effects of the variable properties and the associated viscous dissipation. Due to the large changes in dimension and viscosity, this system poses severe nonlinearities, and a new solution algorithm was necessarily developed. Validation was achieved and several important results were obtained. Among these, it was shown that the viscous dissipation has considerable impact on the fiber temperature due to its localization to a small volume near the fiber section. Also, it was shown that a variable viscosity generated vorticity, which was localized to the region where the preform radius undergoes large changes.