A rectangular metal plate is sprayed uniformly with a thin layer of coating of approximately 0.2...

 

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A rectangular metal plate is sprayed uniformly with a thin layer of coating of approximately 0.2 mm in thickness. The rectangular surface has a length of 50 cm and a width of 14 cm. The coating contains acetone that evaporates from the layer to cure the coating. Initially, there is 0.001 mole of acetone per cm of coating loaded in the coating. The plate is heated to maintain a uniform temperature of 40°C, and the vapour pressure exerted by the solvent is 55 kPa at 40°C. Air gently flows parallel to the surface at a velocity of 5.0 cm/s, 1.0 atm pressure and 20°C. You may neglect any molecular diffusion of the solvent through the very thin polymeric film and focus only on the convection aspects of the problem. 3.1. Calculate the mass transfer coefficient (10) 3.2. How long will it take for the acetone to evaporate completely? (10) The following correlations may be used without proof, although you must give reasons in support of your answer: Corelation Conditions Sh = 0.664 Re5 Sc.33 (laminar) Re, <2 x 10 Sh, = 0.0365 Re Sc33 ,0.33 (turbulent) Re, >2 x 105 %3D Properties at 303 K: Diffusivity DAB = 0.0232 cm2/s A rectangular metal plate is sprayed uniformly with a thin layer of coating of approximately 0.2 mm in thickness. The rectangular surface has a length of 50 cm and a width of 14 cm. The coating contains acetone that evaporates from the layer to cure the coating. Initially, there is 0.001 mole of acetone per cm of coating loaded in the coating. The plate is heated to maintain a uniform temperature of 40°C, and the vapour pressure exerted by the solvent is 55 kPa at 40°C. Air gently flows parallel to the surface at a velocity of 5.0 cm/s, 1.0 atm pressure and 20°C. You may neglect any molecular diffusion of the solvent through the very thin polymeric film and focus only on the convection aspects of the problem. 3.1. Calculate the mass transfer coefficient (10) 3.2. How long will it take for the acetone to evaporate completely? (10) The following correlations may be used without proof, although you must give reasons in support of your answer: Corelation Conditions Sh = 0.664 Re5 Sc.33 (laminar) Re, <2 x 10 Sh, = 0.0365 Re Sc33 ,0.33 (turbulent) Re, >2 x 105 %3D Properties at 303 K: Diffusivity DAB = 0.0232 cm2/s

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