&lt;title&gt;Mixed-convection effects during the drawing of optical fibers&lt;/title&gt;

Papamichael, Haris; Miaoulis, Ioannis N.

doi:10.1117/12.50206

Cited by 3 publications

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“…log(/.L) = 1.456 x 10 (T21993(4) The temperature distribution within the glass can be described by the following energy equation61:SP1E Vol. 2287 / 13 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/16/2015 Terms of Use: http://spiedl.org/terms…”

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confidence: 99%

<title>Heat transfer in the heating region of the optical fiber drawing process</title>

Papamichael

Miaoulis

1994

Properties and Characteristics of Optical Glass III

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The use and applications of optical fibers have been increased dramatically over the years. A need to improve the quality and increase the yield of optical fibers and optical multifiber systems lead to studies related to the manufacturing process of optical fibers. This paper presents a combination of analytical and numerical work on the thermal analysis of the heating region. During the process various phenomena occur in the heating region: As the glass rod is pulled downward, it stretches and a neckdown shape is formed at its lower end. This stretching affects the air flow patterns in the furnace as well as the heat transfer in the glass and its surroundings. The preform is heated radially by a radiative heater. The radiation effects were taken into consideration. Axial and radial heat conduction, and convective heat transfer from the surface of the preform were also accounted for. A coupled form of the boundary layer equations combined with the conduction equation in the glass was solved considering the above phenomena. The temperature distribution in the glass for various drawing conditions was calculated. The flow patterns in the glass were observed and a sample study of the air flow in the furnace is presented. Also, the shape of the glass preform was evaluated for various drawing parameters.

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<title>Heat transfer in the heating region of the optical fiber drawing process</title>

Papamichael

Miaoulis

1994

Properties and Characteristics of Optical Glass III

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Neck Down and Thermally Induced Defects in High-Speed Optical Fiber Drawing

Yin

Jaluria

1999

Journal of Heat Transfer

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The drawing speeds employed in the manufacturing of optical fibers have been rising in recent years due to growing worldwide demand. However, increasing speeds have placed stringent demands on the manufacturing process, mainly because of large temperature gradients that can generate thermally induced defects and undesirable variations in fiber characteristics. Heat transfer and glass flow that arise in drawing fibers of diameters 100–125 microns from cylindrical silica preforms of diameters 5–10 cm play a critical role in the success of the process and in the maintenance of fiber quality. This paper presents an analytical and numerical study of the optical fiber drawing process for relatively large diameter preforms and draw speeds as high as 20 m/s. The free surface, which defines the neck-down profile, is not assumed but is determined by using a balance of forces. An iterative numerical scheme is employed to obtain the profile under steady conditions. The transport in the glass is calculated to obtain the temperature, velocity and defect distributions. A zone radiation model, developed earlier, is used for calculating radiative transport within the glass. Because of the large reduction in the diameter of the preform/fiber, the velocity level increases dramatically and the geometry becomes complicated. A coordinate transformation is used to convert the computational domains to cylindrical ones. The numerical results are compared with experimental and numerical results in the literature for smaller draw speeds for validation. The effects of high draw speeds and of other physical variables on defects generated in the fiber, on the neck-down profile, and on the feasible domain for the process are determined. [S0022-1481(00)02302-1]

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

Choudhury

Jaluria

1998

J. Mater. Res.

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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.

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<title>Mixed-convection effects during the drawing of optical fibers</title>

Cited by 3 publications

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<title>Heat transfer in the heating region of the optical fiber drawing process</title>

<title>Heat transfer in the heating region of the optical fiber drawing process</title>

Neck Down and Thermally Induced Defects in High-Speed Optical Fiber Drawing

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

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