Gaseous hydrogen at a constant pressure of 0.658 MPa is to flow within the inside of a thin-walled cylindrical tube of nickel that has a radius of 0.125 m. The temperature of the tube is to be 350°C and the pressure of hydrogen outside of the tube will be maintained at 0.0127 MPa.
Calculate the minimum wall thickness if the diffusion flux is to be no greater than 1.25 × 10–7 mol/m2/s. The concentration of hydrogen in the nickel, CH (in moles hydrogen per cubic meter of Ni), is a function of hydrogen pressure, PH2 (in MPa), and absolute temperature T according to
CH = 30.8√(p_(H_2 ) ) exp^((12,300J/mol)/RT) (6.34)
Furthermore, the diffusion coefficient for the diffusion of H in Ni depends on temperature as
D_H (m^2/s) = (4.76×〖10〗^(-7) )exp(-(39,560J/mol)/RT) (6.35)
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