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Effect of unsteady natural convection on the diameter of drawn polymer optical fiber

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Abstract

This paper presents experimental results showing the effect various natural convection heating regimes have on the diameter of drawn polymer optical fiber. The airflow, adjacent to the polymer, can be either laminar, oscillatory, or chaotic, depending on the imposed thermal boundary conditions at the furnace and iris walls. When subject to oscillatory and chaotic natural convection, the drawn fiber varies in diameter 2.5 to 10 times more than that measured under laminar heating conditions. Particle image velocimetry shows that unsteady natural convection occurs with the interplay between two asymmetric counter-rotating convective cells. This represents a significant instability mechanism, one that has not been previously identified.

©2003 Optical Society of America

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Supplementary Material (2)

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Media 2: AVI (4498 KB)     

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Figures (9)

Fig. 1.
Fig. 1. The polymer optical fiber draw furnace. Thermocouple locations are marked with ‘x’.
Fig. 2.
Fig. 2. Axial variation of: (a) the polymer neck-down profile, η(z)=Rp/Rw, (including the radial and axial location of the thermocouples in air) and (b) the wall temperature profile, Tw(z).
Fig. 3.
Fig. 3. The model furnace. The inset of frame ‘A’ shows a sample raw PIV image in which the ‘necking’ polymer preform and olive oil particles can be seen.
Fig. 4.
Fig. 4. Excursion of the air temperature and fiber diameter histories from the sample mean, illustrating: (a,b) laminar, (c,d) oscillatory, and (e,f) chaotic natural convection conditions. Note different scales on the y-axes.
Fig. 5.
Fig. 5. Frequency spectrums of: (a) the air temperature and (b) the fiber diameter observations for the oscillatory (Tt=114.5°C) and chaotic (Tt=104.8°C) flow regimes.
Fig. 6.
Fig. 6. Air temperature and fiber diameter histories recorded at: (a, b) Tt=108°C and (c, d) Tt=106°C, illustrating the occurrence of period doubling and its effect on the fiber diameter.
Fig. 7.
Fig. 7. PIV vector plot of time-invariant, axi-symmetric, laminar flow in the furnace model.
Fig. 8.
Fig. 8. Time history of the axial velocity measured at x=-0.018 m and z=0.096 m showing unsteady natural convection. A movie of one complete oscillation is shown in Fig. 9.
Fig. 9.
Fig. 9. (1.21 MB) Movie showing the asymmetric oscillating flow field within the model furnace (4.50 MB version). (Location x=-0.018 m, z=0.096 m is marked with a white cross.)
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