Mechanical Operations

41. A suspension of glass beads in ethylene glycol has a hindered settling velocity of 1.7 mm/s, while the terminal settling velocity of a single glass bead in ethylene glycol is 17 mm/s. If the Richardson-Zaki hindered settling index is 4.5, the volume fraction of solids in the suspension is

1. 0.1
2. 0.4
3. 0.6
4. None of these

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42. A tube mill as compared to a ball mill

1. Employs smaller balls
2. Gives finer size reduction but consumes more power
3. Has larger length/diameter ratio (>2 as compared to 1 for ball mill)
4. All (A), (B) and (C)

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43. A tube mill compared to a ball mill

1. Has a higher length/diameter ratio
2. Produces a coarser product
3. Has a higher diameter/length ratio
4. Uses much larger balls

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44. A widely used size reduction equipment for _________ is Bradford breaker.

1. Talc
2. Coal
3. Iron core
4. Wheat

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45. About 2-3 hp, power per gallon of a thin liquid provides vigorous agitation in an agitator. 'Power number' in agitation is given by

1. P. g_c/N³. D². ρ
2. P. g_c. ρ/μ2
3. N³. D³. ρ/P. g_c
4. P. g_c/n2. D². ρ

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46. According to Bond crushing law, the work required to form particle of size 'D' from very large feed is (where (S/V)p and (S/V)f are surface to volume ratio of the product and feed respectively).

1. (S/V)_p
2. √(S/V)_p
3. (S/V)² _p
4. (S/V)_f

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47. According to Taggart's rule for selecting between a gyratory crusher and a jaw crusher; the later should be used, if the hourly tonnage to be crushed divided by the square of the gape expressed in cm is less than

1. 0.00184
2. 0.0184
3. 0.184
4. 1.84

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48. Activators are those chemicals which help buoying up one mineral in preference to the other in the froth floatation process. Which of the following is an activator?

1. Cresylic acid
2. Copper sulphate
3. Calcium carbonate
4. Sodium carbonate

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49. 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?

1. Wet grinding in low viscous suspension
2. Wet grinding in high viscous suspension
3. Dry grinding of large particles (upto 1.25 cms)
4. Dry grinding of large particles in un-baffed mills

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50. AD⁵ition of filter aid to the slurry before filtration is done to _________ of the cake.

1. Increase the porosity
2. Increase the compressibility co-efficient
3. Decrease the porosity
4. Decrease the compressibility co-efficient

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