Problem 1: A spherical solid air freshener is suspended from the ceiling of a room. The deodorant sublimes into the air. The sphere is 4 cm in diameter. The deodorant has a mole weight of 100. The surrounding air is motionless. The saturation mole fraction of deodorant in air is 0.001, and the average mole fraction in the surrounding air can be considered to be zero. Use 1 atm and 20^o C for the conditions of the air. The diffusivity of this deodorant in the air is 100 cm²/hr. Sphere area = ΠD².

Using an appropriate mass transfer coefficient correlation, estimate the gas phase mass transfer coefficient (k_c).

Using the value from the previous problem, estimate the initial rate of sublimation of this deodorant (Kg/hr)? (If you do not have an answer for the first problem, use 0.01 cm/hr for the gas phase mass transfer coefficient.)

Problem 2: A gas contains 0.1 mole percent H2S, and this must be reduced to 0.001 mole percent. One thousand (1000) kg-moles/hr of this gas is to be treated in an absorption column with a solvent that contains no H2S. The gas enters at 500 kPa. The column is isothermal at 30^oC. Henry's law can be used for equilibrium calculations with a constant of 250 kPa.

Calculate the minimum allowable solvent rate for this separation.

Using a solvent flow of 800 kg-moles/hr, estimate the Noy value for this column.

Problem 3: . A wetted wall column is used to humidify a dry air stream. The air enters the bottom of the column with 0.1 mole percent water, and exits at the top containing 1.0 mole percent water. The column operates at 760 mm Hg and 50^oC. The vapor pressure of water at this condition is 90 mm Hg. The column inner diameter is 0.1 m, and the air is flowing with a velocity of 0.4 m/sec.

Where is the controlling resistance to the mass transfer of water vapor located, gas phase, liquid phase, or both phases? Provide a reason for your answer.

Calculate the saturation (equilibrium) mole fraction of water vapor in the air?

Estimate a mass transfer coefficient, Ky (kgmol/m²-sec), for this column using relation 17.70.

Estimate the mass transfer area per unit volume (a) for this column.

Estimate the Hoy value for this column.

Calculate Noy and estimate the height of the column using your answer for Hoy. (Assume a value if you do not have an answer to the previous problem.)

Problem 4: An experimental apparatus is used to measure the rate of the decomposition of species A on a catalyst. In the experiment, A diffuses through a film of fluid to the catalyst surface. On the catalyst, A decomposes to form two moles of B: A -> 2B. The B diffuses back through the film to the bulk fluid. The experiment is conducted so that the bulk fluid is pure A, with no B. Measurement indicates that the mole fraction of A next to the catalyst surface is 0.2. The film thickness is 0.1 cm, the diffusivity is 5.0 x 10^-5cm²/sec, and the molar density of the A/B fluid mixture is 0.01 gm-moles/cm³.

Is this an example of equimolar counter diffusion? If not, what is the magnitude and direction of the molar flux of B in comparison to the molar flux of A?

What is the rate of A decomposition per unit area of catalyst (gm-mole/cm²)?