Mass Transfer > Diffusion In Solids

LIQUIDS AND GASES MCQs

Total Questions : 71

Page 1 of 8 pages
Question 1. For a steady state equimolar counter diffusion of A and B. The N flux of A is ________
  1.    – N flux of A
  2.    N flux of A
  3.    – N flux of B
  4.    N flux of B
 Discuss Question
Answer is Option C. -> – N flux of B
Answer: (c).– N flux of B
Question 2. In sulphuric acid plants dry air is used for burning of sulphur. Air is dried in contact with concentrated Sulphuric acid. Moisture diffuses through a layer of air, reaches the surface and gets absorbed in it. Here air is said to be non-diffusing were as moisture is diffusing. Which of the following statements are correct?
  1.    Moisture has a source and a sink whereas dry air has a source but no sink
  2.    Moisture as well as dry air have a sink
  3.    Moisture has a source but no sink whereas dry air has a source as well as sink
  4.    Moisture as well as dry sir have no sink
 Discuss Question
Answer is Option A. -> Moisture has a source and a sink whereas dry air has a source but no sink
Answer: (a).Moisture has a source and a sink whereas dry air has a source but no sink
Question 3. The value of a ratio of N flux of A to the total N flux for a steady state equimolar counter diffusion is
  1.    0
  2.    Infinity
  3.    1
  4.    None of the mentioned
 Discuss Question
Answer is Option B. -> Infinity
Answer: (b).Infinity
Question 4. A mixture of 60% hydrogen and 40% oxygen is blowing over a pan of water at 1atm pressure. The bulk gas temperature is 30°C and the water temperature is 20°C. The vapor pressure of water at this temperature is 17.53mm Hg. The concentration of moisture in the bulk gas is negligible and the diffusivity values are DO₂-H₂O=0.357cm²/s, DH₂-H₂O=0.972cm²/s at 34°C and DH₂-O₂=0.891cm²/s at 43°C.

What is the value of the flux (kmol/m³.s) of water vapor through a stagnant film of estimated thickness 1.5mm on the water surface?
  1.    1.36*10⁻⁵
  2.    1.96*10⁻⁵
  3.    1.96*10⁻¹
  4.    1.96*10⁻⁷
 Discuss Question
Answer is Option B. -> 1.96*10⁻⁵
Answer: (b).1.96*10⁻⁵
Question 5. Consider steady-state equimolar counterdiffusion through the converging-diverging tube. Given: r₁=1cm; r₂=2cm; Nᴀ=10⁻⁶ kmol/m².s at the vessel 1 end of the tube. The rate of transport of B at the vessel 2 end of the tube is
  1.    2*10⁻⁶ kmol/s, towards vessel 1
  2.    2.5*10⁻⁷ kmol/s, towards vessel 1
  3.    5*10⁻⁶ kmol/s, towards vessel 2
  4.    9*10⁻⁷ kmol/s, towards vessel 2
 Discuss Question
Answer is Option B. -> 2.5*10⁻⁷ kmol/s, towards vessel 1
Answer: (b).2.5*10⁻⁷ kmol/s, towards vessel 1
Question 6. The molar average velocity of the components in a binary mixture in which they are in equimolar counter diffusion is
  1.    Equal to mass average velocity
  2.    Zero
  3.    Always negative
  4.    Always positive
 Discuss Question
Answer is Option B. -> Zero
Answer: (b).Zero
Question 7. Find the number of stages.Find The Number Of Stages.....
  1.    1
  2.    2
  3.    3
  4.    4
 Discuss Question
Answer is Option C. -> 3
Answer: (c).3
Question 8. In an accident a container containing ethanol(s.g 0.789) falls down in a room of dimension 1*1*2(all in m). Ethanol forms a layer of 2mm. Ethanol vaporizes and diffuses through a stagnant film of air of thickness 2.5mm. What will be the time required for the water layer to disappear completely, if the floor has micro pores and water penetrates the floor at a constant rate of 0.1kg/m²h. The diffusivity of ethanol in air is 2.567*10⁻⁵ m²/s. The total pressure is 1.013 bar and the pressure of ethanol in bulk air is 0.02244 bar and at the ethanol-air interface is 0.02718bar. The temperature is 25.2°C.
  1.    3.64h
  2.    4.73h
  3.    5.94h
  4.    2.36h
 Discuss Question
Answer is Option A. -> 3.64h
Answer: (a).3.64h
Question 9. A cylinder of sulfur is kept in a large volume of stagnant air for sublimation. How much time will be required for its complete sublimation?
  1.    One fourth the time required by sphere of same mass
  2.    Half the time required by a cube of same mass
  3.    One fourth the time required by a cube of same mass
  4.    Infinite
 Discuss Question
Answer is Option D. -> Infinite
Answer: (d).Infinite
Question 10. For a gas mixture (A+B) equimolar counterdiffusion takes place. Which among the following statements are correct for molar flux?
  1.    If temperature is doubled, the flux will get halved
  2.    If diffusion length is halved, the flux will get halved
  3.    If temperature is halved, the flux will get halved
  4.    If temperature is doubled and length is halved, the flux will become four times
 Discuss Question
Answer is Option A. -> If temperature is doubled, the flux will get halved
Answer: (a).If temperature is doubled, the flux will get halved