Competitive Exam Question Paper Mechanical Operations - Set 21

Practice Test: Question Set - 21

1. 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
2. Sphericity is the ratio of the surface area of a spherical particle having the same volume as the particle to the surface area of the particle. Which of the following has the maximum value of sphericity?
    (A) Sphere
    (B) Cube
    (C) Cylinder (L/D = 1)
    (D) Raschig rings
3. __________ mill is not used for grinding wheat into flour and for milling of cereals & other vegetable products.
    (A) Buhrstone
    (B) Roller
    (C) Attrition
    (D) Pebble
4. Vacuum filter is most suitable for the
    (A) Removal of fines from liquid
    (B) Liquids having high vapor pressure
    (C) Liquids of very high viscosity
    (D) None of these
5. Jigging is a technique by which different particles can be
    (A) Separated by particle size
    (B) Separated by particle density
    (C) Separated by particle shape
    (D) Mixed
6. The specific cake resistance for compressible sludges is a function of the pressure drop
    (A) Over cake
    (B) Over medium
    (C) Overall
    (D) None of these
7. For grinding of cereals, grains, spices, pigments, saw dust, cork etc., the most extensively used size reduction equipment is a
    (A) Buhrstone mill
    (B) Ball mill
    (C) Crushing rolls
    (D) Hammer mill
8. In case of grinding in a ball mill
    (A) Wet grinding achieves a finer product size than dry grinding
    (B) Its capacity decreases with increasing fineness of the products
    (C) Grinding cost and power requirement increases with increasing fineness of the products
    (D) All (a), (b) and (c)
9. __________ is the most commonly used 'filter aid'.
    (A) Diatomaceous earth
    (B) Fuller's earth
    (C) Vermiculite
    (D) Semi-plastic clay
10. A tube mill as compared to a ball mill
    (A) Employs smaller balls
    (B) Gives finer size reduction but consumes more power
    (C) Has larger length/diameter ratio (>2 as compared to 1 for ball mill)
    (D) All (a), (b) and (c)
11. Which of the following is not accomplished by agitation of liquids in agitators?
    (A) Dispersing gas in liquid
    (B) Blending of immiscible liquids
    (C) Dispersing immiscible liquid in form of emulsion
    (D) Suspending solid particles
12. The unit of filter medium resistance is
    (A) cm-1
    (B) gm/cm-1
    (C) cm/gm-1
    (D) gm-1
13. Equivalent diameter of a particle is the diameter of the sphere having the same
    (A) Ratio of surface to volume as the actual volume
    (B) Ratio of volume to surface as the particle
    (C) Volume as the particle
    (D) None of these
14. Bucket elevators are not suitable for the vertical lifting of __________ materials.
    (A) Fine (e.g. - 200 mesh size coal)
    (B) Sticky (e.g. clay paste)
    (C) Small lumpy (e.g. grains and sand)
    (D) Free flowing
15. 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)
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