Emier Villanueva
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Chemical Engineering Problems on Diffusion (Mass Transfer)

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Emier Villanueva
Created by Emier Villanueva over 8 years ago
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Diffusion - Practice Problems_Villanueva

Diffusion - Practice Problems_Villanueva

Question 1 of 9

1

A gas of CH4 and He is contained in a tube at 101.32 kPa pressure and 298 K. At one point the partial pressure of methane is 60.79 kPa and at a point 0.02 m distance away, the partial pressure of methane is 20.26 kPa. If the total pressure is constant throughout the tube, calculate the flux of CH4 at steady state for equimolar counterdiffusion.

Select one of the following:

  • 5.52 E-05 kg mol CH4/m-2 s-1

  • 6.45 E-06 kg mol CH4/m-2 s-1

  • 6.03 E-05 kg mol CH4/m-2 s-1

  • 5.26 E-06 kg mol CH4/m-2 s-1

Explanation

Question 2 of 9

1

The gas CO2 is diffusing at steady state through a tube 0.20 m long having a diameter of 0.01 m and containing N2 at 298 K. The total pressure is constant at 101.32 kPa. the partial pressure of CO2 is 456 mmHgat one end and 76 mmHG at the other end. The diffusivity is 1.67 E-05 m2/s at 298 K. Calculate the flux of CO2 in SI units for equimolar counterdiffusion.

Select one of the following:

  • 1.34 E-10 kg mol/s

  • 2.56 E-10 kg mol/s

  • 2.68 E-10 kg mol/s

  • 1.76 E-10 kg mol/s

Explanation

Question 3 of 9

1

Helium and Nitrogen gas are contained in a conduit 5 mm in diameter and 0.1 m long at 298 K and a uniform constant pressure of 1.0 atm abs.The partial pressure of He at one end of the tube is 0.060 atm and at the other end is 0.020 atm. Calculate the following for steady-state equimolar counterdiffusion:

a) Flux of He in kgmol/s -1 m -2
b) Partial pressure of He at a point 0.05 m from either end in Pa

Select one or more of the following:

  • a) 3.46 E-11

  • a) 2.67 E-10

  • a) 2.21 E-11

  • a) 5.49 E-10

  • b) 5684 Pa

  • b) 4053 Pa

  • b) 4568 Pa

  • b) 3598 Pa

Explanation

Question 4 of 9

1

Geankoplis 6.2-4 Diffusion of Methane Through Nondiffusing Helium

Select one of the following:

  • 3.69 E-11 kgmol/m2 s

  • 3.86 E-11 kgmol/m2 s

  • 4.29 E-11 kgmol/m2 s

  • 3.12 E-11 kgmol/m2 s

Explanation

Question 5 of 9

1

Geankoplis 6.2-8 Evaporation Losses of Water in Irrigation Ditch

Answer in lbm/day

Select one of the following:

  • 1.235 E-14

  • 2.467 E-14

  • 2.649 E-14

  • 4.598 E-14

Explanation

Question 6 of 9

1

A drop of liquid toluene is kept at a uniform temperature of 25.9C and is suspended in air by a fine wire. The initial radius r1=2.00 mm. The vapor pressure of toluene at 25.9 C is 3.84 kPa and the density of liquid toluene is 866 kg/m3.

Calculate the time in seconds for complete evaporation.

Select one of the following:

  • 1390 s

  • 1450 s

  • 1210 s

  • 1490 s

Explanation

Question 7 of 9

1

Diffusion of Ethanol (A) through water (B)

An ethanol-water solution in the form of a stagnant film 2.0 mm thick at 293 is in contact at one surface with an organic solvent in which ethanol is soluble and water is insoluble. At point 1, the concentration of ethanol is 16.8 wt% and the solution density is 972.8 kg/m3. At point 2, the concentration of ethanol is 6.8 wt% and the solution density is 988.1 kg/m3. The diffusivity of ethanol is 0.740 E-09 m2/s. Caclulate the steady-state flux.

Select one of the following:

  • 9 E-07 kgmol/m2 s

  • 10 E-07 kgmol/m2 s

  • 11 E-07 kgmol/m2 s

  • 12 E-07 kgmol/m2 s

Explanation

Question 8 of 9

1

Vaporizing A and Convective Mass Transfer

A large volume of pure gas B at 2 atm pressure is flowing over a surface from which pure A is vaporizing. The liquid A completely wets the surface, which is a blotting paper. Hence, the partial pressure of A at the surface is the vapor pressure of A at 298 K, which is 0.20 atm. The k'y has been estimated to be 6.78 E-05 kgmol/s m2 mol frac. Calculate the vaporization rate.

Select one of the following:

  • 7.14 E-06 kgmol/sm2

  • 8.26 E-06 kgmol/sm2

  • 7.46 E-06 kgmol/sm2

  • 7.86 E-06 kgmol/sm2

Explanation

Question 9 of 9

1

Mass Transfer from a Flat Plate

A large volume of pure water at 26.1 C is flowing parallel to a flat plate of solid benzoic acid, where L = 0.244 m in the direction of flow. The water velocity is 0.061 m/s. The solubility of benzoic acid in water is 0.02948 kg mol/m3. The diffusivity of benzoic acid is 1.245 E-09 m2/s. Calculate the flux.

Select one of the following:

  • 1.16 E-04 kg mol/m2s

  • 1.54 E-04 kg mol/m2s

  • 2.89 E-04 kg mol/m2s

  • 3.76 E-04 kg mol/m2s

Explanation

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