Dispersion of water sprays in a transverse air jet and the aging of spray nozzles
Author(s)Eletribi, Shereen, 1975-
John H. Lienhard, V.
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This thesis explores spray cooling methods used in the manufacturing process of glass fibers. At the onset of the manufacturing process glass fibers are extruded from a pool of molten glass through an array of holes in a heated bushing plate. Before the fibers can be wound onto a spool, the fibers must be coated with a sizing compound. In order for the sizing compound to be applied, the glass fibers must be cooled to a temperature below 90°C or so. Heat losses through convection and radiation to the environment are not sufficient to achieve this temperature over a reasonable distance, so supplemental cooling in the form of water sprays is used in the manufacturing process. The sprays provide evaporative cooling to the fiber bundle. This work explores ways to optimize the spray cooling process so the fibers can be cooled more uniformly and with lower water consumption. The spray atomization qualities and the spray dispersion patterns of the nozzles used on the glass production lines are examined. The droplet diameter, velocity and number flux are measured with a Phase Doppler Particle Analyzer. When the fibers are pulled from the bushing plate, they move at very high velocities and generate a bulk air flow around the fiber bundle. This induced air flow appears to be a determining factor in the dispersion of the spray into the fiber bundle. An experimental apparatus was built to measure the entrainment of the spray into a transverse air jet (simulated fiber air flow). The spray nozzle operating pressure and the spray nozzle distance from the simulated bulk air flow were varied to determine the optimal spray configuration. Increasing the nozzle operating pressure from 276 kPa (40 psi) to 690 kPa (100 psi) was found to increase the quality of atomization, while further increases in pressure to 1000 kPa (145 psi) produced insignificant effects. The best spray dispersion was achieved at a separation of 15 cm between the spray nozzle and the edge of the fiber bundle. Furthermore, the characteristics of the spray interaction with the bulk air flow were compared to the behavior of the spray in still air. The effect of aging on the spray nozzles is also examined. The spray characteristics were measured at three different positions within the spray cone for a range of operating pressures from 276 kPa (40 psi) to 1000 kPa (145 psi) for nozzles aged zero, two, four and six weeks on an actual glass fiber production line. It was found that increasing the nozzle operating pressure above 690 kPa (100 psi) did not provide significant improvement in spray atomization, as was also found in the bulk air flow case. Aging was found to cause inferior atomization and more scatter in the droplet parameters. Aging effects are due to corrosion of the spray nozzles and to scale deposits within the nozzle water passage.
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (leaf 116).
DepartmentMassachusetts Institute of Technology. Department of Mechanical Engineering
Massachusetts Institute of Technology