Tut (5)

1. A stream of air at 100 kPa pressure and 300 K is flowing on the top surface of a thin flat sheet of solid naphthalene of length 0.2 m with a velocity of 20 m/sec. The other data are: Mass diffusivity of naphthalene vapor in air DAB= 6 x 10 6 m2/sec Kinematic viscosity of air = 1.5 x105 m2/s Concentration of naphthalene at the air-solid naphthalene interface = 1x10 5 kmol/m3. Calculate: a) The mass transfer coefficient over the flat plate b) The rate of loss of naphthalene from the surface per unit width neglecting the naphthalene concentration in the bulk air stream

2. A 1-m square thin plate of solid naphthalene is oriented parallel to a stream of air flowing at 20 m/s. The air is at 310 K and 1.013*105 Pa. The naphthalene remains at 290 K; at this temperature, the diffusivity of naphthalene in air is 5.61*10-6m2/s and its vapor pressure is 26 Pa. Determine a. the value of the mass-transfer coefficient at a point 0.3 m downstream from the leading edge.

3. Consider a circular pipe of inner diameter D = 0.015 m whose inner surface is covered with a layer of liquid water as a result of condensation In order to dry the pipe, air at 300 K and 1 atm is forced to flow through it with an average velocity of 1.2 m/s. Using the analogy between heat and mass transfer, determine the mass transfer coefficient inside the pipe = 1.58x10-5 m2/s , DAB = 2.54x10-5m2/s