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4 a 5 m long plastic tube with an outer...

Question: 4 a 5 m long plastic tube with an outer...

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4) A 5 m long plastic tube with an outer diameter of 8 mm and a wall thickness of 1 mm is used to deliver N2 at 1 atm pressure to a furnace in a laboratory. Oxy- gen molecules can dissolve into the plastic when it is exposed to room tempera ture air. As O2 molecules diffuse across the the wall of the tubing, oxygen is into the otherwise pure N2 gas stream, which flows to the furnace at a rate of 0.1 1/s. The diffusivity of O2 in the plastic is 10-12 cm2/s at room tem perature. At the outer surface of the tube, O2 is incorporated into the plastic at a rate consistent with a first order chemical reaction:ノ= k-p(02) with a rate con- stant k = 1010 molecules/(cm2.s-atm) and p(O) = 0.2 atm for air. a) Estimate the difference in oxygen concentration within the plastic across the wall of the tubing. Determine the concentration in parts per billion (ppb) of O2 present in the gas stream as it enters the furnace. b)

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