THERMAL TRANSPORT IN THE MANUFACTURE OF OPTICAL FIBERS
This review discusses the fabrication of optical fibers, which are of considerable importance in many applications such as telecommunications, computer networking, sensors, lasers, and diagnostics. The various steps involved in the manufacturing process are outlined and the review focuses on the drawing, cooling, and coating of optical fibers. Heat transfer and fluid flow considerations play an important role in determining the properties and characteristics of the final product as well as the rate of production. The basic transport mechanisms that arise are discussed, along with the governing equations and relevant boundary conditions. The various practical concerns that must be considered for a satisfactory optical fiber are discussed. The challenges posed by relevant aspects such as strong temperature dependence of glass viscosity, complex geometry, free surface flow, and large changes in cross-sectional area are considered and some of the important methods to address these are presented. A few characteristic numerical results are presented and discussed. These are validated by comparisons with experimental results. Micro- and nanoscale transport mechanisms play a critical role in the process because changes in the structure and characteristics of the fiber, as well as thermally induced defects and other imperfections, largely occur at these small length scales. These mechanisms must be coupled with transport at the macro- or engineering scales, which apply to the overall system, resulting in a multiscale problem. Besides solid fibers, hollow fibers, which are used for sensors and power delivery and typically need fairly precise wall thicknesses and core diameters for satisfactory operation, are also considered. The implications of such results in improving practical systems and processes, including enhanced process feasibility, production rate, and product quality, are also discussed.
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