Diffusion - Practice Problems_Villanueva

Emier Villanueva
Quiz by Emier Villanueva, updated more than 1 year ago
Emier Villanueva
Created by Emier Villanueva over 5 years ago
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Chemical Engineering Problems on Diffusion (Mass Transfer)

Resource summary

Question 1

Question
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.
Answer
  • 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

Question 2

Question
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.
Answer
  • 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

Question 3

Question
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
Answer
  • 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

Question 4

Question
Geankoplis 6.2-4 Diffusion of Methane Through Nondiffusing Helium
Answer
  • 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

Question 5

Question
Geankoplis 6.2-8 Evaporation Losses of Water in Irrigation Ditch Answer in lbm/day
Answer
  • 1.235 E-14
  • 2.467 E-14
  • 2.649 E-14
  • 4.598 E-14

Question 6

Question
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.
Answer
  • 1390 s
  • 1450 s
  • 1210 s
  • 1490 s

Question 7

Question
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.
Answer
  • 9 E-07 kgmol/m2 s
  • 10 E-07 kgmol/m2 s
  • 11 E-07 kgmol/m2 s
  • 12 E-07 kgmol/m2 s

Question 8

Question
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.
Answer
  • 7.14 E-06 kgmol/sm2
  • 8.26 E-06 kgmol/sm2
  • 7.46 E-06 kgmol/sm2
  • 7.86 E-06 kgmol/sm2

Question 9

Question
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.
Answer
  • 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
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