At low Reynold’s number, the power (P) required for agitating a fluid in a stirred tank becomes independent of inertial forces. In this limit, indicate which of the following relations is satisfied: Po = ρ/ρN3 D5: Power number Re = ρ N D2/μ: Reynold’s number N is the impeller rotational speed, and D is the impeller diameter ?

Related Mcqs:

1. The power number for a stirred tank becomes constant at high Reynolds number. In this limit, the variation of power input with impeller rotational speed (N) is proportional to___________________?

   A. N°
   B. N1
   C. N2
   D. N3

2. Height of liquid in agitation tank is normally maintained equal to the tank diameter. However, if the tank is too tall and a large liquid hold up is desired, then two or more impellers mounted on the same shaft may be used. The clearance between the tank bottom and the bottom most impeller should be about (where, D = impeller diameter) ?

   A. 0.5 D
   B. D
   C. 1.5 D
   D. 2 D

3. For a turbine agitated and baffled tank, operating at low Reynold’s number (based on impeller diameter), the power number (Np) varies with NRe as_________________?

   A. Np ∝ NRe
   B. Np ∝ √NRe
   C. Np → constant
   D. Np ∝ 1/NRe

4. Velocity of a small particle of diameter ‘Dp’ at a distance ‘r’ from the rotational axis of a cyclone rotating at an angular speed ‘ω’ is given by (the other symbols are as per standard notation) ?

   A. [(DP/18). (ρs – ρ/μ)] ω2r
   B. [(DP2/18). (ρs – ρ/μ)] ω2r
   C. [(DP/18). (ρs – ρ/μ)] ω2r2
   D. [(DP2/18). (ρs – ρ/μ)] ω2r

5. A centrifugal filtration unit operating at a rotational speed of w has inner surface of the liquid (density ρL) located at a radial distance R from the axis of rotation. The thickness of the liquid film is δ and no cake is formed. The initial pressure drop during filtration is ___________________?

   A. ½w2 . R2 . ρL
   B. ½w2 . δ2 . ρL
   C. ½w2 . δρL (2R + δ)
   D. ½w2 . R . ρL(R + 2δ)

6. Actual operating speed of a ball mill may vary from 65 to 80% of the critical speed. Which of the following duties would require the ball mill to be operated at maximum percentage of critical speed ?

   A. Wet grinding in low viscous suspension
   B. Wet grinding in high viscous suspension
   C. Dry grinding of large particles (upto 1.25 cms)
   D. Dry grinding of large particles in un-baffed mills

7. Power consumption during turbulent flow in agitation tank is proportional to the ______________ of the liquid?

   A. Viscosity
   B. Thermal conductivity
   C. Surface tension
   D. Density

8. Laminar flow region is said to exist during agitation of a liquid in an agitator, when the value of Reynolds number is________________?

   A. > 10
   B. < 10
   C. > 100
   D. < 100

9. Optimum ratio of operating speed to critical speed of a trommel is_____________________?

   A. 0.33-0.45
   B. 1.33-1.45
   C. 0.5-2
   D. 1.5-2.5

10. The operating speed of a ball mill should be ______________ the critical speed?

    A. Less than
    B. Much more than
    C. At least equal to
    D. Slightly more than