Related Mcqs:

1. 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

2. The critical speed of a trommel (N) is related to its dia D. as _____________________?

   A. N ∝ 1/√D
   B. N ∝ √D
   C. N ∝ D
   D. N ∝ 1/D

3. 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

4. Critical Speed (Nc) of a ball mill is given by (where R1 and R2 are radii of ball mill and the ball respectively) ?

   A. Nc = (1/4π). √(g/R1 – R2)
   B. Nc = (1/2π). √(g/R1 – R2)
   C. Nc = (1/π). √(g/R1 – R2)
   D. Nc = (1/2π). √(R1 – R2/g)

5. Critical speed of rotation, N (in rps – rotation per second) of a trammel is equal to (where, g = acceleration due to gravity = 9.81 m/sec2 and, r = radius of trammel, metre.) ?

   A. (1/2π). √(g/r)
   B. (1/π). √(g/r)
   C. ½ √(g/r)
   D. 2π. √(g/r)

6. What is the critical rotation speed in revolutions per second, for a ball mill of 1.2 m diameter charged with 70 mm dia balls ?

   A. 0.5
   B. 1.0
   C. 2.76
   D. 0.66

7. 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)

8. The optimum moisture content in solids to be crushed/ground ranges from _______________ percent?

   A. 3 to 4
   B. 8 to 10
   C. 10 to 15
   D. 15 to 20

9. For raschig rings, the sphericity is_____________________?

   A. 0.5
   B. 1
   C. < 1
   D. √3

10. Range of compressibility co-efficient of the commercial compressible cake obtained in filtration operation is_____________________?

    A. 0.01 to 0.1
    B. 0.1 to 0.3
    C. 0.2 to 0.8
    D. 0.2 to 0.4