3. A storage tank with a surface area of 35 m2 and a wall thickness of 100 mm contains 2000 kg of hydrogen gas at a concentration of 110 kg/m3. The atmosphere outside the tank has a hydrogen concentration of 0.2 kg/m3. If D = 810-11 m2/s, how long will it take (in years) for 4% of the hydrogen to diffuse out of the tank? Assume steady-state conditions.

Suppose the tank in Problem 3 had initial hydrogen concentration in the metal of 0.2 kg/m3. Assuming nonsteady state conditions, how long would it take for the hydrogen concentration halfway through the wall thickness to reach its steady-state value? Based on your answer, how accurate is the steady state assumption in Problem 3.