In a manufacturing process, an organic solvent (methyl ethyl ketone, MEK) is used to dissolve a thin coating of a polymer film away from a nonporous flat surface of length 20 cm and width 10 cm as shown in the figure below. The thickness of the polymer film is initially uniform at 0.2 mm. In the process, MEK solvent is added at a flow rate of 30 cm3/s to an open flat pan of length 30 cm and width 10 cm. The depth of the liquid MEK solvent in the pan is maintained at 2.0 cm. You may assume
that the concentration of the dissolved polymer in the bulk solvent is essentially zero,
even though in reality the concentration of dissolved polymer in the solvent increases very slightly as it flows from the entrance to the exit of the pan. At the temperature and pressure of the process, the following data area available:
· Diffusion coefficient of dissolved polymer (solute A) in the MEK solvent (B)
· Kinematic viscosity of liquid MEK
.
· Density of solid polymer film material
.
· Density of liquid MEK
· Maximum solubility of dissolved polymer in the MEK solvent
.
(a) Determine the average flux, g A/cm2
s, from the surface.
(b) How long will it take for the polymer film to completely disappear?