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The purification of hydrogen gas by diffusion through a palladium sheet was disc

ID: 898578 • Letter: T

Question

The purification of hydrogen gas by diffusion through a palladium sheet was discussed in Section 6.3. Compute the number of kilograms of hydrogen that pass per hour through a 5 mm-thick sheet of palladium having an area of 0.20 m^2 at 500 degree C. Assume a diffusion coefficient of 1.0 Times 10^-8 m^2/s; that the respective concentrations at the high- and low-pressure sides of the plate are 2.4 and 0.6 kg of hydrogen per cubic meter of palladium; and that steady-state conditions have been attained.

Explanation / Answer

For steady-state diffusion, from fick's first law,

J=diffusion flux=-D dc/dt               D=diffusion coefficient

                                                    dc/dt=concentration gradient of H2 across the sheet

J=-1.0*10^-8 m2/s * (0.6 kg/m3-2.4 kg/m3)/5*10^-3 m

J =-1.0*10^-8 m2/s*( -1.8 kg/m3) / 5*10^-3 m

    J=0.36 * 10^-5 kg/m2 sec

mass of hydrogen that pass per second through the given area=0.36 * 10^-5 kg/m2 sec* 0.20 m2

                                                                                             =0.072 * 10^-5 kg/m2 sec

therefore,mass of hydrogen that pass per hour =0.072 * 10^-5 kg/m2 sec * 3600 s/hour

                                                                    =259.20 * 10^-5 kg/ hour

                                                                   =2.592*10^-3 kg/ hour