A cylinder of vision correcting glass is being extruded from a four cm diameter hot die initially at 250 degrees Celsiu

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A cylinder of vision correcting glass is being extruded
from a four cm diameter hot die initially at 250 degrees Celsius. A
cooling fan provides circulating air at 28 degrees Celsius,
producing a convection heat transfer coefficient of seven. The
glass can be approximated as silicone dioxide it can be considered
complete when the cylinder has cooled to 50 degrees Celsius. How
many seconds will a technician have before the material is ready to
use?