Work index is the gross energy (kWh/tonne of feed) necessary to reduce a very large feed to such a size that 80% of product particles will pass through a 0.1 mm screen. The value of work index determined for wet grinding should be multiplied with ______________ to get the same for dry grinding?

Related Mcqs:

1. The value of work index does not change materially from one equipment to another. If the value of work index determined for close circuit grinding is Wi, then the same for open circuit grinding will be_________________?

   A. 0.5 Wi
   B. Wi
   C. 1.34 Wi
   D. 3.34 Wi

2. The energy required per unit mass to grind limestone particles of very large size to 100 μm is 12.7 kWh/ton. An estimate (using Bond’s law) of the energy to grind the particles from a very large size to 50 μm is________________?

   A. 6.35 kWh/ton
   B. 9.0 kWh/ton
   C. 18 kWh/ton
   D. 25.4 kWh/ton

3. Wet grinding in a revolving mill ______________ as compared to dry grinding ?

   A. Gives less wear on chamber walls
   B. Requires more energy
   C. Increases capacity
   D. Complicates handling of the product

4. 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) ?

   A. (S/V)p
   B. √(S/V)p
   C. (S/V)2p
   D. (S/V)f

5. Higher is the mesh number, smaller will be the aperture size of the screen. It means that the aperture size of a 200 mesh screen will be smaller than that of 20 mesh screen. This is valid for__________________?

   A. British standard screens
   B. German standard screens (DIN 1171) etc
   C. American standard screens (ASTM and Tyler standard screens)
   D. All A., B. and C.

6. A sand mixture was screened through a standard 10-mesh screen. The mass fraction of the oversize material in feed, overflow and underflow were found to be 0.38, 0.79 and 0.22 respectively. The screen effectiveness based on the oversize is_________________?

   A. 0.50
   B. 0.58
   C. 0.68
   D. 0.62

7. Which of the following grinding mills has the horizontally arranged rods as the grinding elements thereby delivering more uniform granular products with minimum fines ?

   A. Compartment mill
   B. Rod mill
   C. Pebble mill
   D. Tube mill

8. Use of ‘grinding aids’ is done in _______________ grinding?

   A. Dry
   B. Wet
   C. Ultrafine
   D. Intermediate

9. A _____________ mill is a revolving mill divided into two or more sections by perforated partitions in which preliminary grinding takes place at one end and the finishing grinding at the discharge end?

   A. Compartment
   B. Tube
   C. Rod
   D. Pebble

10. In closed circuit grinding as compared to open circuit grinding, the_________________?

    A. Specific surface of product is more
    B. Product has lesser size uniformity
    C. Production rate at a given limiting size is lower
    D. Operation is economical