Emier Villanueva
Quiz by , created more than 1 year ago

Unit Operations (Diffusion) Quiz on Diffusion Quiz 3_Villanueva, created by Emier Villanueva on 05/08/2015.

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Emier Villanueva
Created by Emier Villanueva almost 9 years ago
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Diffusion Quiz 3_Villanueva

Question 1 of 10

1

A dimensionless number that represents the ratio of the molecular momentum diffusivity and the molecular mass diffusivity.

Select one of the following:

  • Schmidt Number

  • Biot Number

  • Sherwood Number

  • Prandtl Number

Explanation

Question 2 of 10

1

When a detailed comparison of mass-transfer correlations is not available, which of the following heuristics may be useful?

Select one of the following:

  • Semiempirical correlations are often preferred to purely empirical or purely theoretical correlations.

  • Correlations with broader data bases are often preferred.

  • More recent data is often preferred to older data.

  • All of the choices.

  • None of the choices.

Explanation

Question 3 of 10

1

The quantity obtained by dividing each mass-transfer coefficient by the flow rate of the phase is called the:

Select one of the following:

  • HTU

  • NTU

  • J*

  • NOG

Explanation

Question 4 of 10

1

What is the diffusivity of caproic acid in air at 250 kPa and 30 C?

Select one of the following:

  • 0.0948 ft2/hr

  • 0.0794 ft2/hr

  • 0.0468 cm2/s

  • 0.0864 cm2/s

Explanation

Question 5 of 10

1

Prediction of Liquid Diffusivity. Predict the diffusion coefficient of acetone in water at 25C with up to 20% error.

Select one of the following:

  • 2.4 E-06

  • 2.8 E-06

  • 3.2 E-06

  • 3.6 E-06

Explanation

Question 6 of 10

1

Acetic acid is flowing through air and it is contained in a 5-m long tube at 101.325 kPa and at 25C. At one point, the partial pressure of acetic acid is PA1 = 70.4 kPa and at the other end, PA2 = 30.6 kPa. If the total pressure inside the tube is constant, calculate the flux of acetic acid at steady state for equimolar counterdiffusion.

Select one of the following:

  • 4

  • 5

  • 6

  • 7

Explanation

Question 7 of 10

1

The gaseous molecular diffusion flux of A is 4.0 E-07 gmoles/s-cm2 at 298 K and 1 atm. What will be the bulk velocity in cm/s if the diffusion flux relative to a stationary observer is 8.0 E-07 gmole/s-cm2 and the mole fraction of A is 0.015?

Select one of the following:

  • 0.65

  • 0.32

  • 1.45

  • 0.18

Explanation

Question 8 of 10

1

Ethyl alcohol is diffusing into an alcohol-water solution at 18C. The concentration of alcohol in the bulk of the solution is negligible, while that at the surface of the solution is 2.6 M. The film thickness is 0.15 m and the diffusivity is 1 E-05 cm2/s. The mass of alcohol diffusing through 100 ft2 of interface per hour is:

Select one of the following:

  • 5.61lb

  • 6.64 lb

  • 3264 g

  • 1654 g

Explanation

Question 9 of 10

1

The diffusivity of hydrogen peroxide in air at 60 C and 1 atm is 0.188 cm2/s. How much estimated error does Chen and Othmer diffusivity empirical correlation have based on the Wilke-Lee diffusivity correlation?

Select one of the following:

  • 7.3 %

  • 7.0 %

  • 6.8 %

  • 7.6 %

Explanation

Question 10 of 10

1

Carbon dioxide (solute) and air found inside a 0.5-m long tube. At one end, the partial pressure of water is 15.325 kPa and 58.325 kPa at the other end. What is the flux assuming that the total pressure inside the tube is constant. The total pressure of the tube is 101.325 kPa at 25 C. Assume 5.4 % error for the diffusivity constant.

Select one of the following:

  • 0.0054

  • 0.0068

  • 0.0076

  • 0.0043

Explanation

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