Thermal Transport and Flow in High-Speed Optical Fiber Drawing

1998 ◽  
Vol 120 (4) ◽  
pp. 916-930 ◽  
Author(s):  
Zhilong Yin ◽  
Y. Jaluria
Keyword(s):  
Optical Fiber ◽  
Thermal Transport ◽  
High Speed ◽  
Radiative Transport ◽  
Gas Velocity ◽  
Furnace Temperature ◽  
Fiber Drawing ◽  
Zonal Method ◽  
Optical Fiber Drawing ◽  
Purge Gas

The thermal transport associated with optical fiber drawing at relatively high drawing speeds, ranging up to around 15 m/s, has been numerically investigated. A conjugate problem involving the glass and the purge gas regions is solved. The transport in the preform/fiber is coupled, through the boundary conditions, with that in the purge gas, which is used to provide an inert environment in the furnace. The zonal method, which models radiative transport between finite zones in a participating medium, has been employed to compute the radiative heat transfer in the glass. The flow of glass due to the drawing process is modeled with a prescribed free-surface neck-down profile. The numerical results are compared with the few that are available in the literature. The effects of important physical variables such as draw speed, purge gas velocity and properties, furnace temperature, and preform diameter on the flow and the thermal field are investigated. It is found that the fiber drawing speed, the furnace temperature, and the preform diameter have significant effects on the temperature field in the preform/fiber, while the effects of the purge gas velocity and properties are relatively minor. The overall heating of the preform/fiber is largely due to radiative transport in the furnace and the changes needed in the furnace temperature distribution in order to heat the glass to its softening point at high speeds are determined.

Numerical Simulation of Transport in Optical Fiber Drawing With Core-Cladding Structure

2004 ◽  
Author(s):  
Chunming Chen ◽  
Yogesh Jaluria
Keyword(s):  
Optical Fiber ◽  
Optical Fibers ◽  
Numerical Results ◽  
Fiber Drawing ◽  
Zonal Method ◽  
The Core ◽  
Optical Fiber Drawing ◽  
Cylindrical Furnace ◽  
Purge Gas ◽  
Energy Equations

Optical fibers are typically heated and drawn from silica preforms, which usually consist of two concentric cylinders called the core and the cladding, in a high-temperature furnace. For optical communication purpose, the core always has a higher refractive index than the cladding. In order to investigate the effect of core-cladding structure on the optical fiber drawing, a numerical model has been developed in this work. Axisymmetric flows of a double-layer glass and aiding purge gas in a concentric cylindrical furnace are considered. The thermal and momentum transport in both glass layers and gas are coupled at the interface boundaries. The neck-down profile is generated using an iterative scheme. The zonal method is applied to model the radiation transfer in the glass preform and the gas. Coordinate transformations are used to convert complex domains into cylinders. Stream function, vorticity and energy equations for the core, the cladding and the purge gas are solved by finite different methods using a false transient method coupled with an alternating direction implicit (ADI) method. A second order differencing scheme is used for discretization. The numerical results are validated by comparing with experimental and numerical results available in the literature.

Numerical Simulation of Transport in Optical Fiber Drawing with Core–Cladding Structure

2006 ◽  
Vol 129 (4) ◽  
pp. 559-567 ◽  
Author(s):  
Chunming Chen ◽  
Yogesh Jaluria
Keyword(s):  
Refractive Index ◽  
Optical Fiber ◽  
Optical Fibers ◽  
Finite Difference Methods ◽  
Initial Study ◽  
Fiber Drawing ◽  
Zonal Method ◽  
The Core ◽  
Optical Fiber Drawing ◽  
Purge Gas

Optical fibers are typically drawn from silica preforms, which usually consist of two concentric cylinders called the core and the cladding, heated in a high-temperature furnace. For optical communication purposes, the core always has a higher refractive index than the cladding to obtain total internal reflection. In order to investigate the effect of this core–cladding structure on optical fiber drawing, a numerical model has been developed in this work. Axisymmetric flows of a double-layer glass and aiding purge gas in a concentric cylindrical furnace are considered. The thermal and momentum transport in both glass layers and gas are coupled at the interface boundaries. The neck-down profile is generated using an iterative numerical scheme. The zonal method is applied to model the radiation transfer in the glass preform. The gas is taken as nonparticipating. Coordinate transformations are used to convert the resulting complex domains into cylindrical regions. The stream function, vorticity, and energy equations for the core, the cladding, and the purge gas are solved by finite difference methods, using a false transient approach coupled with the alternating direction implicit method. A second-order differencing scheme is used for discretization. The numerical results are validated by comparing with results available in the literature. The effects of changes in the refractive index and absorption coefficient due to doping on fiber drawing are investigated. This problem has received very little attention in the literature, particularly with respect to modeling, and this paper presents an initial study of the underlying transport.

Thermal transport due to material and gas flow in a furnace for drawing an optical fiber

1998 ◽  
Vol 13 (2) ◽  
pp. 494-503 ◽  
Author(s):  
S. Roy Choudhury ◽  
Y. Jaluria
Keyword(s):  
Heat Transfer ◽  
Optical Fiber ◽  
Temperature Difference ◽  
Thermal Transport ◽  
Transfer Rate ◽  
Gas Flow ◽  
Transport Processes ◽  
Inert Gas ◽  
Gas Velocity ◽  
Fiber Drawing

The transport processes involved in the neck-down region for optical fiber drawing are numerically investigated. In this manufacturing process, a moving glass rod is heated in a furnace containing an inert gas environment and drawn into a thin optical fiber. The conjugate problem is solved considering both radiation and convection, with focus on the latter. Two different flow configurations, involving inert gas flow in the same as well as in the opposite direction as the moving preform/fiber, are considered in this study. A coordinate transformation is used to change the complicated computational domains in the gas and the fiber to cylindrical ones. The transport in the fiber is coupled with that in the gas through the boundary conditions. The radiative thermal transport is calculated using an enclosure model developed in an earlier study. The numerical results on convective flow and transport are validated by comparing with results available in the literaturefor simpler configurations. The effects of several important parameters such as fiber draw speed, inert gas velocity, furnace dimensions, and gas properties on the flow and temperature distributions are investigated. For the aiding flow case, in which the inert gases flow in the same direction as the fiber, heat transfer to the fiber increases as the gas velocity increases. For opposing flow, a recirculating region appears in the gas, close to the moving fiber surface, causing reduction in heat transfer as compared to the aiding case. The thickness of this recirculating zone decreases with increasing inert gas velocity. Radiation is found to be the dominant mode of heat transfer in the overall heating of the preform/fiber, with nitrogen as the inert gas. However, near the edges of the furnace, radiation heat transfer is relatively small and convection becomes very important. Also, the convective transfer rate is relatively large near the flow entrance because of the large temperature difference between the gas and the fiber. However, away from the entrance, the gas heats up and the temperature difference relative to the fiber decreases, resulting in a smaller convective heat transfer rate. The relevance of the results to various aspects of the fiber-drawing process is discussed.

Feasibility of High Speed Furnace Drawing of Optical Fibers

2004 ◽  
Vol 126 (5) ◽  
pp. 852-857 ◽  
Author(s):  
Xu Cheng ◽  
Yogesh Jaluria
Keyword(s):  
Optical Fibers ◽  
High Speed ◽  
Flow Instability ◽  
Fiber Quality ◽  
Domain Boundary ◽  
Operating Conditions ◽  
Furnace Temperature ◽  
Fiber Drawing ◽  
Heated Zone ◽  
Additional Information

The domain of operating conditions, in which the optical fiber-drawing process is successful, is an important consideration. Such a domain is mainly determined by the stresses acting on the fiber and by the stability of the process. This paper considers an electrical resistance furnace for fiber drawing and examines conditions for process feasibility. In actual practice, it is known that only certain ranges of furnace temperature and draw speed lead to successful fiber drawing. The results obtained here show that the length of the heated zone and the furnace temperature distribution are other important parameters that can be varied to obtain a feasible process. Physical behavior close to the boundary of the feasible domain is also studied. It is found that the iterative scheme for neck-down profile determination diverges rapidly when the draw temperature is lower than that at the acceptable domain boundary due to the lack of material flow. However, the divergence rate becomes much smaller as the temperature is brought close to the domain boundary. Additional information on the profile determination as one approaches the acceptable region is obtained. It is found that it is computationally expensive and time-consuming to locate the exact boundary of the feasible drawing domain. From the results obtained, along with practical considerations of material rupture, defect concentration, and flow instability, an optimum design of a fiber-drawing system can be obtained for the best fiber quality.

Effect of Draw Furnace Geometry on High Speed Optical Fiber Manufacturing

2000 ◽  
Author(s):  
Xu Cheng ◽  
Yogesh Jaluria
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Optimal Design ◽  
Optical Fiber ◽  
High Speed ◽  
Graphite Furnace ◽  
Large Diameter ◽  
High Volume ◽  
Force Balance ◽  
Zonal Method

Abstract The motivation of manufacturers to pursue higher productivity and low costs in the fabrication of optical fibers requires large diameter silica-based preforms drawn into fiber at very high speed. An optimal design of the draw furnace is particularly desirable to meet the need of high-volume production in the optical fiber industry. This paper investigates optical fiber drawing at high draw speeds in a cylindrincal graphite furnace. A conjugate problem involving the glass and the purge gases is considered. The transport in the two regions is coupled through the boundary conditions at the free glass surface. The zonal method is used to model the radiative heat transfer in the glass. The neck-down profile of the preform at steady state is determined by a force balance, using an iterative numerical scheme. Thermally induced defects are also considered. To emphasize the effects of draw furnace geometry, the diameters of the preform and the fiber are kept fixed at 5 cm and 125 μm, respectively. The length and the diameter of the furnace are changed. For the purposes of comparison, a wide domain of draw speeds, ranging from 5 m/s to 20 m/s, is considered, and the form of the temperature distribution at the furnace surface is kept unchanged. The dependence of the preform/fiber characteristics, such as neckdown profile, velocity distribution and lag, temperature distribution and lag, heat transfer coefficent, defect concentration, and draw tension, on the furnace geometry is determined. Based on these numerical results, an optimal design of the draw furnace can be developed.

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