The value of Lewis number (Le = Sc/Pr) for air-water vapour system is around_________________?

Related Mcqs:

1. An air-water vapour mixture has a dry bulb temperature of 60°C and a dew point temperature of 40°C. The total pressure is 101.3 kPa and the vapour pressure of water at 40°C and 60°C are 7.30 kPa and 19.91 kPa respectively. The humidity of air sample expressed as kg of water vapour/kg of dry air is__________________?

   A. 0.048
   B. 0.079
   C. 0.122
   D. 0.152

2. At equilibrium the concentration of water in vapour phase (C*) in kg/m3 of air space and the amount of water (m) adsorbed per kg of dry silica gel are related by, C* = 0.0667m. To maintain dry conditions in a room of air space 100m3 containing 2.2 kg of water vapour initially, 10 kg of dry silica gel is kept in the room. The fraction of initial water remaining in the air space after a long time (during which the temperature is maintained constant) is_________________?

   A. 0.0
   B. 0.2
   C. 0.4
   D. 1.0

3. Condensation of a vapour-gas mixture just begins, when (where, p = partial pressure of the vapour P = vapour pressure of the liquid) ?

   A. p = P
   B. p >>P
   C. p < P
   D. p << P

4. For the case of flow of air past a wet bulb thermometer (air water vapour system), the approximate value of h2/ky.Cz is around____________________?

   A. 0.60
   B. 0.24
   C. 1
   D. 0.72

5. Schmidt number and Lewis number for pure air at atmospheric conditions are respectively__________________?

   A. < 1 and ≈ 1
   B. 1 and 0
   C. > 1 and ≈ 1
   D. 0 and ≈ 1

6. Lewis number (Le) is____________________?

   A. Sc × Pr
   B. Pr × St
   C. Sh × Pr
   D. St × Sh

7. Lewis number (Le) is___________________?

   A. Sc × Pr
   B. Pr × St
   C. Sh × Pr
   D. St × Sh

8. Lewis number, which is important in problems involving simultaneous heat and mass transfer, is the ratio of__________________?

   A. Mass diffusivity to momentum diffusivity
   B. Thermal diffusivity to mass diffusivity
   C. Momentum diffusivity to thermal diffusivity
   D. None of these

9. If mass diffusivity in a mixture is equal to the thermal diffusivity, then the Lewis number is____________________

   A. 0
   B. 1
   C. 1

10. For which of the following unit operations, Lewis number is of significance ?

    A. Adsorption
    B. Binary distillation
    C. Gas absorption
    D. Humidification