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4. 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. The thickness of the polymer film is initially uniform at l, = 0.02 cm. In the present process, a volumetric flow rate of 30 cm³/s of MEK liquid solvent is added 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. It may be assumed that the concentration of dissolved polymer in the bulk solvent is essentially zero even though in reality the concentration of dissolved polymer in the solvent increases very slightly from the entrance to the exit of the pan. It may also be assumed that the change in film thickness during the dissolution process does not affect the convection mass-transfer process. Let A = polymer (solute), B = MEK (liquid solvent). M (a) What is the Schmidt number for the mass-transfer process? (4%) (b) What is the average Sherwood number for the mass-transfer process? (4%) (4%) (b) What is the average flux of dissolved polymer (in units of g/cm³-s) from the surface? (c) What are the hydrodynamic (8) and concentration boundary-layer (&) thicknesses at x = 10 cm? (8%) Potentially useful data: the diffusion coefficient of dissolved polymer in liquid MEK solvent at 25 °C 3.0 x 10 cm²/s; mass density of solid polymer film material = 1.05 g/cm³; maximum solubility of dissolved polymer in MEK solvent at 25 °C -0.04 g/cm³; kinematic viscosity of liquid MEK at 25 °C 6.0 x 10 cm²/s; mass density of liquid MEK solvent at 25 °C -0.80 g/cm³. 5x (Hint: 8= 30 cm liquid MEK polymer film (initially 0.2 mm thick) 2 cm exiting MEK inn of X = L = 20 cm x=0 width of pan= 10 cm