The final step of a manufacturing process in which a protective coating is applied to the inner surface of a circular tube involves passage of dry, atmosphere air through the tube to remove a residual liquid associated with the process. Consider a coated 5-m-long tube with an inner diameter of 50 mm. The tube is maintained at a temperature of 300 K, and the residual liquid exists as a thin film whose corresponding vapor pressure is 15 mm Hg. The molecular weight and diffusion coefficient of the vapor are M_A = 70 kg/kmol and D_AB = 10^-5 m²/s, respectively. Air enters the tube at a mean velocity of 0.5 m/s and a temperature of 300 K.

  (a) Estimate the partial pressure and mass density of vapor in the air exiting the tube. 

  (b) What is the rate of liquid removal from the tube in kg/s?