Generation of neck-down profile for furnace drawing of optical fiber

An analytical and numerical approach has been developed for the generation of the neck-down profile of an optical fiber during the drawing process, based on the transport equations and surface force balance. An axisymmetric, laminar flow circumstance is assumed. The governing transport equations are solved employing the finite difference method. The axial velocity is radially lumped and the normal force balance and vertical momentum equations are used to obtain a correction scheme for the neck-down profile. After a new profile is obtained, the full governing equations are solved, considering both radiation and convection transport. This process is continued till the necking shape does not change from one iteration to the next. The necking shape obtained has been validated by comparisons with experimental results available in the literature. Also, the robustness of the numerical scheme is verified by starting with different initial profiles, each of which yielded the same final shape. Also, it was verified that for the converged solution, the draw tension is essentially constant throughout the necking region. Among the interesting are the limitations imposed on fiber diameter and speed for practical operating conditions. Some fully conjugate results, considering coupled convection in the inert fluid inside the furnace are also presented.