Simulation of the flow in a coating applicator for optical fiber manufacture

Abstract

A detailed numerical study is carried out on the flow field generated in an open-cup coating applicator during the coating process in the manufacture of optical fibers. This is a critical problem in the manufacture of optical fibers and poses several challenges to numerical modeling. A finite volume numerical model, using multiple domains to represent the fluid chamber and the die, is employed to obtain results on the flow. A coordinate transformation is used to model the complex geometry of the flow region. Fairly generic configurations are considered and a wide range of fiber drawing speeds, ranging up to 15 m/s, is investigated. Different boundary conditions, such as free and solid surface, at the entrance of the moving fiber are considered. Several coating materials are simulated, along with wide ranges of operating conditions and geometric designs. Though different temperatures are considered for the coating material, to obtain different fluid viscosities, the flow is considered to be isothermal. The focus is on the flow pattern and on the velocity fields in the fluid chamber and the die. Also, of interest are the resulting mass flow rate, which yields the final coating thickness, and the effects of the inlet conditions. The characteristics of the recirculating flow that arises in many cases are investigated in detail. The results are presented in terms of streamlines, velocity distributions and flow rates. The effects of geometry, coating material and die shape are investigated in detail. This is the first part of an on-going detailed study on the simulation of coating applicators for the manufacture of optical fibers in order to improve uniformity, consistency, and quality of the coating.