1. Helium gas at 25°C and 4 bars is contained in a glass cylinder of 100-mm inside diameter and 5-mm thick- ness. What is the rate of mass loss per unit length of the cylinder?

2. Helium gas at 25°C and 4 bars is stored in a spherical Pyrex container of 200-mm inside diameter and 10- mm thickness. What is the rate of mass loss from the container?

(a) Under the same conditions as in the example, determine the solubility of the polymer material (kmol/m3 · bar) if the temperature is 295 K and the relative humidity inside and outside the package is 2 = 0.1 and 1 = 0.9, respectively.

(b) By selecting a different packaging material, the diffusivity of the film may be changed. Determine the total water vapor transfer rate associated with reducing the diffusivity to 10% of its original value.

(c) The solubility of the material adjacent to its exposed surface may be modified by coating it with various thin films. Determine the water vapor transfer rate after coating both sides of the original polymer sheet and, in turn, reducing the solubility near both surfaces to 10% of the original value.

(d) Determine the water vapor transfer rate after coating the exterior of the original polymer sheet and reducing its solubility by a factor of 9, while leaving the interior surface untreated.