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Unformatted text preview: Numerical Example Quasi-steady State where c is in ppm and the hydrogen pressure, p H , is in atm. The density of steel is 7.73 g/cm 3 . The diffusion coefficient of hydrogen in steel is taken to be 10-8 cm 2 /s. What is the rate of pressure drop (atm/s) as a result of diffusion of hydrogen through the wall? SOLUTION A cubic steel tank of volume 1 liter and wall thickness 0.1 cm is used to store hydrogen with an initial pressure of 8.7 atm. The tank is placed in outer space at 673 K. The hydrogen concentration on the steel surface is given by , H p c 3 = Diffusion Under an External Field v velocity of mass flow or drift velocity under external force, F . v c x c D J + = Diffusion Mass flow or drift due to an external field MF = v where M is the atom mobility which is related to diffusivity through the Nernst-Einstein relation, T k D M B = Examples of External Forces, F elastic potential- d /dx Elastic potential gradient activity coefficient-k B Td (...
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This note was uploaded on 01/19/2010 for the course MAT SCI 503 taught by Professor Chen during the Spring '02 term at Pennsylvania State University, University Park.
- Spring '02