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old_exam_1 - B Name FIRST HOUR EXAMINATION TAM 324/CEE300...

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Name ____________________________ F IRST H OUR E XAMINATION - TAM 324/CEE300 Friday February 16, 2007 • Work all problems in spaces provided • One page of hand-written notes permitted. 1. (10 points) Nitrogen gas can be used to improve the properties of steel. A sheet of steel 1.5 mm thick has Nitrogen atmospheres on both sides at 1200 o C and is permitted to achieve a steady-state diffusion condition The diffusion coefficient for Nitrogen in steel at this temperature is 6x10 -11 m 2 /s, and the diffusion flux is found to be 1.2x10 -7 kg/m 2 -s. Also, it is known that the concentration of Nitrogen at the in the steel at the high-pressure surface is 4 kg/m 3 . (a) (3pts) Write out the appropriate governing equation that describes this diffusion process. (b) (7pts) Compute the distance into the sheet from this high- pressure side that the concentration will be 2.0 kg/m 3 . B

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