Question 71 : Pebble mills are tumbling mills widely used for grinding in the manufacture of paints & pigments and cosmetic industries, where iron contamination in the product is highly objectionable. Pebbles used in pebble mill are made of
1. stainless steel
2. bronze
3. concrete
4. flint or porcelain
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Question 72 : In continuous filtration (at a constant pressure drop), filtrate flow rate varies inversely as the
1. square root of the velocity.
2. square of the viscosity.
3. washing time only.
4. filtration time only.
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Question 73 : Which of the following is not an ultrafine grinder (colloid mill)?
1. Toothed roll crusher
2. Micronizers
3. Agitated mills and fluid energy mills
4. Hammer mills with internal classification
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Question 74 : For sizing of fine materials, the most suitable equipment is a
1. grizzly
2. trommel
3. vibrating screen
4. shaking screen
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Question 75 : Pick out the wrong statement.
1. Wear and tear in wet crushing is more than that in dry crushing of materials.
2. Recycled coarse material to the grinder by a classifier is termed as circulating load.
3. A 'dust catcher' is simply an enlargement in a pipeline which permits the solids to settle down due to reduction in velocity of the dust laden gas.
4. Size enlargement (opposite of size reduction) is not a mechanical operation.
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Question 76 : Which of the following is not categorised as a ''mechanical operation'' ?
1. Humidification
2. Size enlargement
3. Filtration
4. Agitation
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Question 77 : Which of the following is a pressure filter ?
1. Rotary drum filter.
2. Leaf filter (Moore filter).
3. Plate and flame filter.
4. Sand filter.
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Question 78 : Equivalent diameter of a particle is the diameter of the sphere having the same
1. ratio of surface to volume as the actual volume.
2. ratio of volume to surface as the particle.
3. volume as the particle.
4. none of these.
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Question 79 : Short distance transportation of grain, gravel, sand, ash, asphalt etc. is done by using a __________ conveyor.
1. ribbon
2. screw
3. slat or drag
4. flight
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