Homework Problem Set #1 Due January 23, 2002 1. Hydrogen at 1.0 MPa is to be stored at 400 o C in outer space, in a thin wall (0.1 mm) spherical iron tank of 0.1 m radius. Please calculate the rate of pressure drop (MPa/s) as a result of diffusion of hydrogen through the wall. Take D= 10-8 m 2 /s, and assume that the concentration of hydrogen in the iron at either side of the wall is the equilibrium solubility given by the equation c H ( p ) = 10-5 p 1/2 gmH/gmFe ( p in MPa). 2. A thin sheet of iron is in contact with a carburizing gas on one side and a decarburizing gas on the other at temperature of 1000 o C a) Sketch the resultant carbon concentration profile when a steady state has been reached, assuming that the surface concentrations are maintained at 0.15 and 0.14 wt% C and the diffusion coefficient of carbon increases concentration. b) If D c increases from 2.5x10-11 m 2 /s at 0.15%C to 7.7x10-11 m 2 /s at 1.4%C, what will be the quantitative relationship between the concentration gradients at the two surfaces? c)
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