A.     Helium gas is stored at 20°C in a spherical container of fused silica, which has an inner diameter of 0.20 m and a wall thickness of 2 mm. If the container is charged to an initial pressure of 4 bar, what is the rate at which this pressure de creases with time?

B.     To maintain a pressure close to atmosphere, an industrial pipeline containing ammonia gas is vented to ambient air. Venting is achieved by tapping the pipe and inserting a 3 mm diameter tube, which extends for 20 m into the atmosphere. With the entire system operating at 25°C, determine the mass rate at which ammonia is lost to the atmosphere and the mass rate of contamination of the pipe with air. What are the mole and mass fractions of air in the pipe when the ammonia fl ow rate is 5 kg/h. Given: For ammonia-air system at 298 K, D = 0.28 ¥ 10–4 m2/s.