Mechanical Operations Flashcards
Short distance transportation of grain, gravel, sand, ash, asphalt etc. is done by using a __________ conveyor.
flight
slat or drag
ribbon
screw
screw
Equivalent diameter of a particle is the diameter of the sphere having the same
ratio of surface to volume as the actual volume.
ratio of volume to surface as the particle.
volume as the particle.
none of these.
ratio of surface to volume as the actual volume.
If dp is the equivalent diameter of a non-spherical particle, Vp its volume and sp its surface area, then its sphericity is Φs is defined by
Φs = 6 Vp/dp sp
Φs = Vp/dp sp
Φs = 6 dp Sp/Vp
Φs = dp Sp/Vp
Φs = 6 Vp/dp sp
Power required to drive a ball mill with a particular ball load is proportional to (where, D = diameter of ball mill )
D
1/D
D^2.5
1/D^2.5
D^2.5
Pick out the wrong statement.
A. Recycled coarse material to the grinder by a classifier is termed as circulating load.
B. Wear and tear in wet crushing is more than that in dry crushing of materials.
C. Size enlargement (opposite of size reduction) is not a mechanical operation.
D. 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.
Size enlargement (opposite of size reduction) is not a mechanical operation.
In continuous filtration (at a constant pressure drop), filtrate flow rate varies inversely as the
square root of the velocity.
square of the viscosity.
filtration time only.
washing time only.
square root of the velocity.
For sizing of fine materials, the most suitable equipment is a
trommel
grizzly
shaking screen
vibrating screen
vibrating screen
Which of the following is not categorised as a “mechanical operation” ?
Agitation
Filtration
Size enlargement
Humidification
Humidification
Which of the following is a pressure filter ?
Leaf filter (Moore filter).
Plate and flame filter.
Rotary drum filter.
Sand filter.
Plate and flame filter.
Tabular bowl centrifuges as compared to disk bowl centrifuges
operate at higher speed.
employ bowl of larger diameter.
can not be operated under pressure/vacuum.
can’t be used for separation of fine suspended solids from a liquid.
operate at higher speed.
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
bronze
stainless steel
flint or porcelain
concrete
flint or porcelain
Which of the following relationships between co-efficinet of friction (μ) between rock & roll and a (half of the angle of nip) of the particle to be crushed is correct ?
μ > tan α
μ ≥ tan α
μ > tan 2α
μ ≤ tan α
μ ≥ tan α
Pick out the wrong statement pertaining to the roll crushers.
A. Maximum feed size determines the required roll diameter.
B. For hard material’s crushing, the reduction ratio should not exceed 4.
C. Both the rolls run necessarily at the same speed.
D. Reduction ratio and differential roll speed affect production rate & energy consumed per unit of surface produced.
Both the rolls run necessarily at the same speed.
Which of the following is not an ultrafine grinder (colloid mill)?
Micronizers
Agitated mills and fluid energy mills
Toothed roll crusher
Hammer mills with internal classification
Toothed roll crusher
Two particles are called to be equal settling, if they are having the same.
size.
specific gravity.
terminal velocities in the same fluid & in the same field of force.
none of these.
terminal velocities in the same fluid & in the same field of force.
18.
__________ centrifuge is normally used in sugar mills.
Tubular bowl
Disc-bowl
Suspended batch basket
Perforated horizontal basket continuous
Suspended batch basket
Solid particles separation based on the difference in their flow velocities through fluids is termed as the
classification
Diatomaceous earth is a/an
explosive
filter aid
filter medium
catalyst
filter aid
The distribution given by microscopic analysis of powder is
number
length
area
volume
number
Number of particles in a crushed solid sample is given by (where, m = mass of particles in a sample, Vp = volume of one particle, ρ= density of particles)
m/ρ . Vp
m. ρ/Vp
m . Vp/ρ
Vp/m . ρ
m/ρ . Vp
For a non-spherical particle, the sphericity
A. is defined as the ratio of surface area of a sphere having the same volume as the particle to the actual surface area of the particle.
B. has the dimension of length.
C. is always less than 1.
D. is the ratio of volume of a sphere having the same surface area as the particle to the actual volume of the particle.
is defined as the ratio of surface area of a sphere having the same volume as the particle to the actual surface area of the particle.
In washing type plate and frame filter press, the ratio of washing rate to the final filtrate rate is
1/4
Ball mills and tube mills with flint or porcelain balls are used for size reduction of
asbestos
rubber
non-metallic ores
limestone
non-metallic ores
Size reduction of __________ is accomplished in steam heated rollers and roll crushers.
resins
gums
hard rubber
waxes
hard rubber
The capacity of a belt conveyor depends upon two factors. If one is the cross-section of the load, the other is the __________ of the belt.
speed
Which of the following is not a part of the Blake jaw crusher?
Hanger
If a force greater than that of gravity is used to separate solids & fluids of different densities, the process is termed as the
centrifugation
Filter aid is used to
increase the porosity of the cake.
Which of the following mineral dressing operations is termed as ‘comminution’?
Panning
Spiralling
Tabling
None of these
None of these
Pick out the wrong statement.
Close circuit grinding is more economical than open circuit grinding.
Cod oil, beef tallow or aluminium stearates are used as grinding aids in cement ‘industries’.
The equipment used for the removal of traces of solids from a liquid is called a classifier.
Size enlargement is a mechanical operation exemplified by medicinal tablet making.
The equipment used for the removal of traces of solids from a liquid is called a classifier.
—A clarifier is generally used to remove solid particulates or suspended solids from liquid for clarification and/or thickening.
Gravity settling process is not involved in the working of a
hydrocyclone
Froth floatation is the most suitable for treating
sulphide ores
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 μrn is
18 kWh/ton
Which of the following is the most suitable for cleaning of fine coal dust (<0.5 mm) ?
Froth floatation
Pick out the correct statement:
Removal of iron from ceramic material is necessitated (by magnetic separation method) so as to avoid discolouration of ceramic products.
The operating cost of shaking screen is more than that of a vibrating screen.
Screen capacity does not depend upon the specific gravity of the minerals.
Asphalt is best crushed using toothed roll crusher.
Removal of iron from ceramic material is necessitated (by magnetic separation method) so as to avoid discolouration of ceramic products.
Range of compressibility co-efficient of the commercial compressible cake obtained in filtration operation is
0.01 to 0.1
0.1 to 0.3
0.2 to 0.8
0.2 to 0.4
0.2 to 0.8
Highly viscous liquids & pastes are agitated by
propellers
turbine agitators
multiple blade paddles
none of these
multiple blade paddles
The value of ‘angle of nip’ is generally about ____deg
32°