Thermal Modeling of the Optical Fiber Drawing Process
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THERMAL MODELING OF THE OPTICAL FIBER DRAWING PROCESS
HARIS PAPAMICHAEL and IOANNIS N. MIAOULIS* Mechanical Engineering Department, Tufts University, Medford MA 02155
ABSTRACT
A new general method for determining the local dimensionless heat convection coefficient (Nusselt number) and the temperature distribution in thin and thick optical fibers during the drawing process was developed. The axial heat transfer by conduction was included in the analysis as an addition to previously developed models. The developed model can serve as a general thermal solver for thin (200gm in dia.) fibers. The general method was compared with existing methods and it was found to be in agreement in the case of thin fiber analysis but not in the case of thick fiber analysis, where axial conduction effects are significant. Results of a parametric study to examine the effects of diameter of fiber and drawing speed on the temperature distribution are presented. INTRODUCTION
Numerous studies on the modeling and analysis of fabrication of optical fibers have been conducted during the last 15 years. These studies were motivated by the need to improve the quality and increase the yield of optical fibers and optical multifiber systems. The majority of the investigations have focused on the optical properties and performance of the optical fibers. The amount of work done in the area of thermal modeling of optical fiber processes is significantly less than in the area of optical performance. Thermal modeling on the other hand is essential for process improvement and new product design. A fiber exiting the cylindrical furnace used in most of fiber drawing processes can be modeled as a long thin moving cylinder. The viscous air boundary layer on such cylinders has been the subject of many previous investigations. Sakiadis 11] derived the boundary layer thickness on a moving continuous cylinder in an infinite stationary fluid, using the Karman-Pohlhausen momentum integral technique with an assumed logarithmic velocity
profile. Bourne and Elliston 12] analyzed the development of both the momentum and thermal laminar boundary layers on drawn fibers. The authors considered the fiber to have a constant radius and a uniform temperature and used the Karman-Pohlhausen method to evaluate the local Nusselt number for several Prandtl numbers. Bourne and Dixon 131 predicted the temperature distribution of the fiber as a function of distance from the orifice using the same method. In this analysis a temperature profile analogous to the logarithmic velocity profile was assumed for the boundary layer. The results obtained matched closely with experimental findings. All previous thermal analyses focused on thin fibers (
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