4. Chloroform is used to remove a polystyrene (PS) film from a nonporous flat surface of length 30 cm and width 8cm. Initially, the thickness of the PS film is 0.02cm. The PS film is placed in an open flat pan of length 40cm and width of 10cm. Subsequently, chloroform at a volumetric flow rate of 20cm3/s is added to the pan, and the depth of chloroform in the pan is maintained at 2.0cm. It is assumed that the concentration of dissolved PS in bulk chloroform is essentially zero. It is also assumed that the change in film thickness during the dissolution process does not affeet the convection mass-transfer process. (a) What are the Schmidt number and the average Sherwood number for the mass-transfer process? (6%) (b) What is the average flux of dissolved PS from the surface? (4\%) (c) Develop a relationship between the local convective mass-transfer coefficient (k)) and film (d) Eventually, the PS film will completely dissolve away from the flat surface. However, before this position (x)(4%) time the thickness of the PS film remaining on the flat surface will not be uniform. Find the change in PS film thickness (l) with regard to the film position and time (t).(4%) (c) What are the hydrodynamic () and concentration boundary-layer () thicknesses at x15cm ? (4%) Diffusion coefficient of dissolved PS in chloroform: 2.0100cm2/s; Mass density of PS: 1.0g/cm3; Mass density of chloroform: 1.5g/cm3; Kinematic viscosity of chloroform: 6.0103cm2/s; Maximum solubility of dissolved PS in chloroform: 0.05g/cm3. [Hint: =Rex5x]