Question

A very thin polymeric coating of thickness 0.1 mmuniformly coats a rectangular surface. The rectangular surfacehas a length of 20 cm and a width of 10 cm. the coating contains asolvent that must be evaporated away from the coating in order tocure the coating. Initially, there is 0.001 mole of solvent per cm3of coating loaded in the coating. A heated plate just beneath thesurface maintains the coating at a uniform temperature of 40C,and the vapor pressure exerted by the solvent is 0.05 atm at 40C.Air gently flows parallel to the surface at a velocity of 5.0 cm/s.The surrounding air at 1.0 atm total system pressure and 20Crepresents an ‘‘infinite sink’’ for mass transfer. You may neglectany molecular diffusion of the solvent through the very thinpolymeric film and focus only on the convection aspects of theproblem. The diffusion coefficient of species in air at 20C is0.1 cm2/s. a. Determine the Reynolds, Schmidt, and Sherwood numbersassociated with this process. b. What is the film mass-transfer coefficient, ky, (mole fractionbased driving force) associated with this process? c. How long will it take for the solvent to completely evaporatefrom the coating? 30.2 A 1-m square thin plate of solid naphthalene is orientedparallel to a stream of air flowing at 20 m/s. The air is at 310 Kand 1.013 x 105 Pa. The naphthalene remains at 290 K; at thistemperature, the diffusivity of naphthalene in air is 5.61 x 10-6 m2/s and its vapor pressure is 26 Pa. Determine a. the value of the mass-transfer coefficient at a point 0.3 mdownstream from the leading edge. b. the moles of naphthalene per hour lost from the section ofthe plate 0.5–0.75 m downstream from the leading edge.

A very thin polymeric coating of thickness 0.1 mmuniformly coats a rectangular surface. The rectangular surfacehas a length of 20 cm and a width of 10 cm. the coating contains asolvent that must be evaporated away from the coating in order tocure the coating. Initially, there is 0.001 mole of solvent per cm3of coating loaded in the coating. A heated plate just beneath thesurface maintains the coating at a uniform temperature of 40C,and the vapor pressure exerted by the solvent is 0.05 atm at 40C.Air gently flows parallel to the surface at a velocity of 5.0 cm/s.The surrounding air at 1.0 atm total system pressure and 20Crepresents an ‘‘infinite sink’’ for mass transfer. You may neglectany molecular diffusion of the solvent through the very thinpolymeric film and focus only on the convection aspects of theproblem. The diffusion coefficient of species in air at 20C is0.1 cm2/s.
a. Determine the Reynolds, Schmidt, and Sherwood numbersassociated with this process.
b. What is the film mass-transfer coefficient, ky, (mole fractionbased driving force) associated with this process?
c. How long will it take for the solvent to completely evaporatefrom the coating?

30.2 A 1-m square thin plate of solid naphthalene is orientedparallel to a stream of air flowing at 20 m/s. The air is at 310 Kand 1.013 x 105 Pa. The naphthalene remains at 290 K; at thistemperature, the diffusivity of naphthalene in air is 5.61 x 10-6 m2/s and its vapor pressure is 26 Pa. Determine
a. the value of the mass-transfer coefficient at a point 0.3 mdownstream from the leading edge.
b. the moles of naphthalene per hour lost from the section ofthe plate 0.5–0.75 m downstream from the leading edge.

Added by John E.

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