Mechanical Operations Flashcards
Concepts and heuristics necessary for unit operations and processes involving solids (or with fluids) requiring mechanical operations. (450 cards)
1
Q
Short distance transportation of grain, gravel, sand, ash, asphalt etc. is done by using a ____ conveyor.
A
screw
2
Q
Equivalent diameter of a particle is the diameter of the sphere having the same
A
ratio of surface to volume as the actual volume
3
Q
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
A
Φs = 6 Vp/dp sp
4
Q
Power required to drive a ball mill with a particular ball load is proportional to (where, D = diameter of ball mill )
A
D2.5
5
Q
Pick out the wrong statement.
A
Size enlargement (opposite of size reduction) is not a mechanical operation
6
Q
In continuous filtration (at a constant pressure drop), filtrate flow rate varies inversely as the
A
square root of the velocity
7
Q
For sizing of fine materials, the most suitable equipment is a
A
vibrating screen
8
Q
Which of the following is not categorised as a “mechanical operation” ?
A
Humidification
9
Q
Which of the following is a pressure filter?
A
Plate and flame filter
10
Q
Tabular bowl centrifuges as compared to disk bowl centrifuges
A
operate at higher speed
11
Q
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
A
flint or porcelain
12
Q
Filter aids like asbestos, kieselguhr, diatomaceous earth etc. are used to increase the porosity of the final filter cake & reducing the cake resistance during filtration. Filter aid is
a. added to the feed slurry.
b. precoated on the filter medium prior to filtration.
c. separated from the cake by dissolving solids or by burning it off.
A
all ‘a’, ‘b’&’c’
13
Q
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?
A
μ ≥ tan α
14
Q
Pick out the wrong statement pertaining to the roll crushers.
A
Both the rolls run necessarily at the same speed
15
Q
Which of the following is not an ultrafine grinder (colloid mill)?
A
Toothed roll crusher
16
Q
Two particles are called to be equal settling, if they are having the same.
A
terminal velocities in the same fluid & in the same field of force
17
Q
Which of the following is the most suitable for handling fibrous and dense slurries?
A
Cone type agitator
18
Q
____ centrifuge is normally used in sugar mills.
A
Suspended batch basket
19
Q
Solid particles separation based on the difference in their flow velocities through fluids is termed as the
A
classification
20
Q
Diatomaceous earth is a/an
A
filter aid
21
Q
The distribution given by microscopic analysis of powder is
A
number
22
Q
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)
A
m/ρ . Vp
23
Q
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
24
Q
In washing type plate and frame filter press, the ratio of washing rate to the final filtrate rate is
A
1/4
25
Ball mills and tube mills with flint or porcelain balls are used for size reduction of
non-metallic ores
26
Size reduction of ____ is accomplished in steam heated rollers and roll crushers.
hard rubber
27
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
28
Which of the following is not a part of the Blake jaw crusher?
Hanger
29
If a force greater than that of gravity is used to separate solids & fluids of different densities, the process is termed as the
centrifugation
30
Filter aid is used to
increase the porosity of the cake.
31
Which of the following mineral dressing operations is termed as 'comminution'?
a. Panning
b. Spiralling'
c. Tabling
None of these
32
The capacity of a pneumatic conveying system depends upon the
a. bulk density of materials.
b. pressure of the conveying air.
c. diameter of the conveying line.
all (a), (b) and (c)
33
Pick out the wrong statement.
The equipment used for the removal of traces of solids from a liquid is called a classifier
34
Gravity settling process is not involved in the working of a
hydrocyclone
35
Froth floatation is the most suitable for treating
sulphide ores
36
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/to
37
Which of the following is the most suitable for cleaning of fine coal dust (<0.5 mm)?
Froth floatation
38
Pick out the correct statement:
The operating cost of shaking screen is more than that of a vibrating screen
39
Range of compressibility co-efficient of the commercial compressible cake obtained in filtration operation is
0.2 to 0.8
40
Highly viscous liquids & pastes are agitated by
multiple blade paddles
41
The value of 'angle of nip' is generally about
32°
42
Size reduction of the ____ can be suitably done by ball mills, crushing rolls and rod mills.
metalliferrous ores
43
Sulphuric acid mist is arrested by using a ____ scrubber.
venturi
44
The main size reduction operation in ultrafine grinders is
attrition
45
In case of a hammer crusher,
a. crushing takes place by impact breaking.
b. maximum acceptable feed size is 30 cms.
c. reduction ratio can be varied by adjusting the distance from cage to hammers.
all (a), (b) and (c).
46
Jigging is a technique by which different particles can be
separated by particle size.
47
Crushing of mineral particles is accomplished in a 'cage mill', when one or more alloy steel bars are revolved in opposite directions. It is a type of ____ mill.
impact
48
Balls for ball mills are never made of
lead
49
200 mesh screen means 200 openings per
inch
50
____ is the most commonly used 'filter aid'.
Diatomaceous earth
51
Energy consumed for crushing one ton of material ranges from ____ kWh.
0.5 to 1.5
52
For transporting pasty material, one will use a/an
screw colaveyor
53
Where the density difference of the two liquid phase to be separated is very small (as in milk cream separator), the most suitable separator is a
disc bowl centrifuge.
54
A tube mill compared to a ball mill
has a higher length/diameter ratio.
55
Trommels separate a mixture of particles depending on their
size
56
Basic slag is not ground in
jaw crushers
57
Grindability of a material does not depend upon its
size
58
Shape factor for a cylinder whose length equals its diameter is
1.5
59
In case of a hammer crusher, the
rotor shaft carrying hammers can be vertical or horizontal.
60
Dust laden air can be purified using a
cyclone separator
61
Rittinger's number designates the new surface created per unit mechanical energy absorbed by the material being crushed. Larger value of Rittinger's number of a material indicates its
easier grindability
62
Capacity (in tons/hr) of jaw/gyratory crusher is equal to (where, L = length of the receiving opening, cm S = greater width of the discharge opening, cm)
0.087 L.S
63
Vacuum is applied in ____ zone, in case of a general type continuous rotary drum vacuum filter.
a. filtering
b. washing
c. drying
all (a), (b) & (c)
64
General crushing equation is given by https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/122-368-1.png . Bond's crushing law isobtained by solving this equation for n = ____ and feed of infinite size.
1.5
65
Which of the follwoing mechanical conveyors does not come under the division 'scrapers' ?
Bucket elevators
66
____ mixer is used for devulcanisation of rubber scrap & making water dispersion & rubber solution.
Banbery
67
Which of the following mechanical conveyors does not come under the division 'carriers'?
Screw conveyor
68
Screen capacity is not a function of
atmospheric humidity
69
Which of the following is a vacuum filter?
Rotary disc filter
70
Pine oil used in froth floatation technique acts as a/an
frother
71
Length/diameter ratio of a ball mill is
< 1
72
Feed size of ≥ 25 cms can be accepted by
jaw crusher
73
Which is the most suitable conveyor for transportation of sticky material?
Screw conveyor
74
The most suitable equipment for removing the fine dust particle (< 1 micron dia.) from air below its dew point will be a/an
electrostatic precipitator
75
Laminar flow region is said to exist during agitation of a liquid in an agitator, when the value of Reynolds number is
<10
76
Filtration of water in a paper mill is done by a/an ____ filter.
open sand
77
Moore filter is a ____ filter.
leaf
78
Sphericity of a cubical particle, when its equivalent diameter is taken as the height of the cube, is
1
79
Ball mill is used for
fine grinding
80
In case of a ball mill,
coarse feed requires a larger ball
81
Maximum size reduction in a ball mill is done by the, ____ action.
impact
82
Increasing the capacity of a screen ____ the screen effectiveness.
decreases.
83
The power number for a stirred tank becomes constant at high Reynolds number. In this limit, the variation of power input with impeller rotational speed (N) is proportional to
N2
84
Bond crushing law
calls for relatively less energy for the smaller product particles, than does the Rittinger law.
85
Flow of filtrate through the cake in a plate and frame filter press is best described by the ____ equation.
Kozney-Karman
86
The controlling resistance in a rotary drum vacuum filter is the ____ resistance.
cake
87
Which of the following is used for primary crushing of very hard lumpy materials?
Gyratory crusher
88
Coal is finally pulverised to 200 mesh size for burning in boilers by a
ball mill
89
Crushing efficiency is the ratio of the
surface energy created by crushing to the energy absorbed by the solid.
90
The resistance offered by the filter used in a bag filter is proportional to (where, c = dust concentration, and s = particle size )
c/s
91
Cement clinker is reduced to fine size by a
tube mill
92
The crushed material received for separation is called feed or
heading
93
For spheres, volume shape factor is given by
π/6(=V/D3)
94
Which of the following agitators having a large blade area, rotating at slow speed is used for mixing high viscosity liquids ( > 50000 centipoise)?
Helical screw
95
____ is defined as the geometric mean of the relative rejections and the relative recoveries of two minerals.
Selectivity index
96
The operating speed of a ball mill should be ____ the critical speed.
less than
97
Use of baffles in agitators help in minimising the ____ tendency.
a. swirling
b. vortexing
both (a) & (b)
98
____ are used for the separation of coarse particles from a slurry of fine particles.
Classifiers
99
Fibrous material is broken by a
squirrel-cage disintegrator
100
____ is the most suitable for compounding rubber and plastic solids.
Banbery mixer
101
Out of the following size reduction equipments, the maximum feed size can be accepted by the
jaw crusher
102
Bucket elevators are not suitable for the vertical lifting of ____ materials.
sticky (e.g. clay paste)
103
The most common filter aid is
diatomaceous earth
104
For removal of very small amounts of precipitate from large volume of water, the most suitable filter is the ____ filter.
sand
105
For separation of sugar solution from settled out mud, we use a ____ filter.
centrifugal
106
The sphericity of a cylinder of 1 mm diameter and length 3 mm is
0.9
107
Pulverised coal passing through 200 mesh screen has a diameter of 0.074 mm (74 micron). The same passing through 50 mesh screen will have a dia of ____ mm.
0.3
108
What is the selectivity index, if the grade of tailings & concentrate is the same?
1
109
The most suitable equipment used to devulcanise rubber scrap and to make water dispersion & rubber solution is a
boundary mixer.
110
Traces of solids are removed from, liquid in a
clarifier
111
_________ balls capable of grinding the feed in a ball mill gives the maximum efficiency.
Minimum size
112
The speed of a rotary drum vacuum filter may be about ____ rpm.
1
113
Colloid mills achieve size reduction mainly by
attrition
114
Mesh indicates the number of holes per
linear inch
115
For achieving maximum capacity of the ball mill, the ball charge should be equal to about ____ percent of the ball mill volume.
50
116
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).
sqrt(S/V)p
117
Which of the following gives the work required for size reduction of coal to -200 mesh in a ball mill most accurately ?
Rittinger's law
118
Electrical energy consumed by a jaw crusher is not a function of the
none of these
119
Size reduction mechanism used in Jaw crushers is
compression
120
Trommels employ ____ for screening of materials.
punched plate
121
A widely used size reduction equipment for ____ is Bradford breaker.
coal
122
Ultra centrifuges are used for the separation of ____ solid particles.
colloidal
123
Specific surface area is the surface area of a unit ____ of materials.
either (a) or (b)
124
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.
compartment
125
The constants (Kb, Kr and Kk) used in the laws of crushing (i.e., Bond's law, Rittinger's law and Kick's law) depend upon the
a. feed material.
b. type of crushing machine.
both (a) & (b).
126
Size reduction does not occur due to compression in case of
rod mills
127
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
0.0184
128
Which of the following represents the plot of filtrate volume versus time for constant pressure filtration?
Parabola
129
Driving force in case of filtration by a centrifuge is the
centrifugal pressure exerted by the liquid.
130
Rod mills employed for grinding
a. employ a steel shell having L/D ratio of 1.5 to 3.0.
b. is useful for handling sticky materials.
c. employ steel rods of 2-12 cms diameter extending over full length of the mill.
all 'a', 'b' & 'c'.
131
Production rate ____ with increased fineness, with a given energy input to the size reduction machine.
decreases
132
Gold ore concentration is mostly done using
tabling
133
Mixing of light fine powder such as insecticides is done by
impact wheels
134
Run of mine (ROM) coal is crushed by a ____ for use in domestic ovens.
hammer crusher
135
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?
Sphere
136
The unit of specific cake resistance is
gm/cm2
137
Size reduction of asbestos and mica is done by
hammer mills
138
A pebble mill
a. is a ball mill.
b. employs flints or ceramic pebbles as the grinding medium
c. is a tube mill lined with ceramic or other non-metallic liner.
both (b) and (c).
139
The study on washability of coal is done by using the ____ technique.
heavy media separation
140
Horsepower required for a roll crusher is directly proportional to its
both (a) & (b).
141
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
0.6
142
____ conveyor is the most suitable for long distance transportation of cold, non-abrasive granular/irregular shape/fine materials.
Belt
143
The specific cake resistance for compressible sludges is a function of the pressure drop
over cake
144
Moisture can be removed from lubricating oil using
tubular centrifuge
145
Tabling process used for separating two materials of different densities by passing the dilute pulp over a table/deck, which is inclined from the horizontal surface at an angle of about
2 to 5
146
Pick out the wrong statement.
Crushing efficiency is the ratio of the energy absorbed by the solid to the surfaces energy created by crushing.
147
Addition of filter aid to the slurry before filtration is done to ...... of the cake.
increase the porosity
148
Which of the following terminology is not used for size reduction of materials to fine sizes or powders?
Compression
149
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).
all (a), (b) and (c).
150
Kick's law assumes that the energy required for size reduction is proportional to the logarithm of the ratio between the initial and the final diameters. The unit of Kick's constant is
kW. sec/kg
151
Which of the following gives the crushing energy required to create new surface?
Rittinger's law
152
In filtration, the use of 'filter aid' helps in
deplugging the filter medium.
153
Critical Speed (Nc) of a ball mill is given by (where R1 and R2 are radii of ball mill and the ball respectively).
Nc = (1/2π)`*`sqrt(g/(R1-R2))
154
Gizzlies are used for separating ____ solids.
fine
155
Which of the following clay mixing devices is vacuum operated for deairation of clay?
Pug mil
156
Pick out the material having minimum Rittinger's number.
Quartz
157
____ mills are termed as impactors.
Hammer
158
In case of a revolving mill, wet grinding compared to dry grinding
none of these.
159
To get a fine talc powder from its granules, the equipment used is
ball mill
160
For a cyclone of diameter 0.2 m with a tangential velocity of 15 m/s at the wall, the separation factor is
230
161
Width and speed of a conveyor belt depends upon the ____ of the material.
both (a) & (b)
162
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
all (a), (b) and (c).
163
Pick out the wrong statement.
Capacity of crusher in choke feeding is increased.
164
Which of the following size reduction equipments employs mainly attrition for ultrafine grinding?
all (a), (b) and (c)
165
Tank filter (e.g., Nutsch filter) is
used for small scale filtration work.
166
In bag filters, filter fabrics are never made of
metallic wire woven mesh
167
Use of 'grinding aids' is done in ____ grinding.
dry
168
Height of liquid in agitation tank is normally maintained equal to the tank diameter. However, if the tank is too tall and a large liquid hold up is desired, then two or more impellers mounted on the same shaft may be used. The clearance between the tank bottom and the bottom most impeller should be about (where, D = impeller diameter)
D
169
Which of the following is the most suitable filter for separation of abrasive solids suspended in a corrosive liquid?
Vacuum filter
170
All resistances during washing of cake
remain constant
171
A ____ mixer resembles a ball mill without balls.
tumbling
172
____ conveyor is the most suitable for short distance transportation of non-abrasive loose materials like garbage, grain, food wastes etc.
Flight
173
As the product becomes finer, the energy required for grinding
icreases
174
Gyratory crushers compared to the reciprocating jaw crushers
have greater capacity per unit of discharge area.
175
The important dimensional group involved in the power requirement calculation in mixing operation is the ____ number.
both (a) & (b)
176
At low Reynold's number, the power (P) required for agitating a fluid in a stirred tank becomes independent of inertial forces. In this limit, indicate which of the following relations is satisfied:
Po = ρ/ρN3 D5 : Power number
Re = ρ N D2/μ: Reynold's number
N is the impeller rotational speed, and D is the impeller diameter.
Po ∝ Re-1.0
177
Which of the following grinding mills has the horizontally arranged rods as the grinding elements thereby delivering more uniform granular products with minimum fines?
Rod mill
178
Rittinger's crushing law states that
work required in crushing is proportional to the new surface created.
179
Mechanical conveyors which push the material along an endless trough or tube are called scrappers. Which of the following conveying equipments comes under the category of 'scrappers'?
Both (b) and (c)
180
Sphericity of pulverised coal is
<1
181
The reduction ratio for fine grinders is
as high as 100
182
Which of the following is the hardest material?
Corundum
183
General mechanism of size reduction in intermediate and fine grinder is by
impact and attrition.
184
A straight line is obtained on plotting reciprocal of filtration rate vs. the volume of filtrate for ____ flow of filtrate.
incompressible cake and laminar
185
The work index in Bond's law for crushing of solids has the following dimensions
kWh/ton
186
Ore concentration by jigging is based on the difference in the ____ of the particles.
specific gravities
187
Size measurement of ultrafine particles can be best expressed in terms of
surace area per unit mass
188
Reduction ratio of crushers is the
ratio of feed opening to discharge opening.
189
Which is a secondary crusher for a hard & tough stone?
Cone crusher
190
Which of the following equations is Rittinger's crushing law ? (where P = power required by the machine, m = feed rate, k = a constant = volume surface mean diameter of feed & product respectively.)
P/m = K . (1-Dsb - 1-Dsa)
191
Cyclones are used primarily for separating
solids from fluids
192
There is practically no alternative/competitor to ____ in the beneficiation treatment of sulphide ores.
froth floatatio
193
Separation of isotopes is generally done using a/an ____ centrifuge.
ultra
194
Temperature of the product during ultrafine grinding
increases
195
Reciprocating screens are normally inclined at an angle of 5° with the horizontal and employ gyratory motion at feed end & reciprocating motion at the discharge end. They are not suitable for the screening of the
heavy tonnages of rocks or gravel.
196
In a ball mill, the volume occupied by the balls (when the mill is stopped) is about ____ percent of the volume of the mill.
50
197
Separation of materials of the same density based on their sizes by using then-different rates of flow is called
sizing
198
Molten ammonium nitrate is mixed with ground limestone in fertilizer plant in a
pug mill
199
Agglomeration of individual particles into clusters (flocs) is called flocculation. To prevent flocculation, the most commonly used dispersing agents are
silicates & phosphates
200
For a sphere falling in the constant drag co-efficient regime, its terminal velocity depends on its diameter (d) as
d2
201
With increase in the capacity of screens, the screen effectiveness
decreases
202
As particle size is reduced
screening becomes progressively more difficult.
203
Rittinger number which designates the new surface prduced per unit of mechanical energy absorbed by the material being crushed, depends on the
all (a), (b) and (c).
204
Dust collection efficiency of electrostatic precipitator can be as high as 99.9%. Maximum temperature and pressure of dust laden gas that can be cleaned in an electrostatic precipitator is respectively.
1000°C and 10 atm.
205
For efficient grinding, ball mills must be operated
at a speed less than the critical speed.
206
In a size reduction crushing operation, the feed size is 10 to 50 mm, while the product size is 2 to 10 mm. This is a case of ____ crushing.
fine
207
For spheres, the surface shape factor is given by (where, A = area, V = volume, and D = diameter)
π(=A/D2)
208
The reduction ratio for grinders is defined as(where, Df and Dp are average diameters of feed and product respectively).
Df/Dp
209
Pick out the wrong statement pertaining to the turbine agitator.
Pitched blade turbine agitator gives only radial flow with complete absence of the axial flow.
210
A fluid energy mill is used for
ultra grinding
211
Which of the following is the softest material ?
Talc
212
Dry powdery solid materials are transported by a ____ conveyor.
screw
213
Fluid energy mill comes in the category of
ultrafine grinder
214
Filtration capacity of a rotary drum vacuum filter depends upon the
both (a) & (b).
215
About 2-3 hp, power per gallon of a thin liquid provides vigrous agitation in an agitator. 'Power number' in agitation is given by
https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/118-323-1.png
216
____ conveyors are also called scrapers.
both (b) & (c)
217
For laminar flow of filtrate through the cake deposited on septum, which of the following will be valid
Kozney-Karman equation
218
Which of the following is a continuous filter?
None of these
219
During washing of filter at the end of constant pressure filtration, the rate of washing equals the rate of filtration
at the end of filtration.
220
In screen analysis, the notation +5 mm/-10 mm means particles passing through
10 mm screen and retained on 5 mm screen.
221
rpm of a trommel at critical speed is given by (where, D = Diameter of trommel in ft)
https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/123-387-2.png
222
Optimum ratio of operating speed to critical speed of a trommel is
0.33-0.45
223
The process opposite to 'dispersion' is termed as the
flocculation
224
The cake resistance increases steadily with the time of filtration in a plate and frame filter employing constant ____ filtration.
both (a) & (b)
225
Grinding efficiency of a ball mill is of the order of ____ percent
45296
226
Solid particles of different densities are separated by
sorting classifier
227
During agitation of liquids, power consumption during laminar flow is not proportional to the
density of the liquid
228
Trommels are revolving screens which normally operate in the range of ____ rpm
15 - 20
229
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
1.34 Wi
230
Maximum size reduction in a fluid energy mill is achieved by
interparticle attritio
231
Filtration rate through a filter cake is proportional to (where, S = filtering surface R= specific cake resistance μ = viscosity of the filtrate)
all (a), (b) & (c)
232
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
1-2 w2 . δρL (2R + δ)
233
Which one is a filter aid ?
Diatomaceous earth
234
To remove dirt from the flowing fluid, we use a
strain
235
Which of the following crushers can be considered as a combination of a jaw crusher and a roller crusher ?
Gyratory crusher
236
Separation of solid suspended in liquid into a supernatant clear liquid and a denser slurry employs a process termed as the
sedimentation
237
Ultrafine grinders operate principally by
attrition
238
Half the angle of nip, (α), for a roll crusher is given by (where, dr, dp and df are diameters of crushing rolls, feed particles and rolls gap respectively).
https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/105-119-2.png
239
Which of the following comes in the category of primary crusher for hard and tough stone ?
Jaw crusher
240
Crushing efficiency of a machine ranges between ____ percent.
0.1 to 2
241
Screen capacity is expressed in terms of
tons/hr-ft
242
A screen is said to be blinded, when the
screen is plugged with solid particles.
243
What is the critical rotation speed in revolutions per second, for a ball mill of 1.2 m diameter charged with 70 mm dia balls
0.66
244
Percentage of drum submerged in the slurry in case of rotary drum filter is
30
245
Filter medium resistance is that offered by the
filter cloth and the embedded particle collectively.
246
In a roll crusher, both the rolls
all (a), (b) and (c).
247
Tube mill compared to ball mill
all (a), (b) & (c).
248
Critical speed of rotation, N (in rps - rotation per second) of a trammel is equal to (where, g = acceleration due to gravity = 9.81 m/sec2 and, r = radius of trammel, metre. )
https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/120-344-1.png
249
For the preliminary breaking of hard rock, we use a
gyratory crusher
250
Filtration operation carried out by continuous increase of the inlet pressure of slurry, is called the ____ filtration.
constant rate
251
Pick out the wrong statement.
Cake resistance is independent of the pressure drop.
252
Which of the following oxides is not present in hematite iron ore?
Cobalt oxid
253
Ribbon blenders are exclusively meant for
non-flowing powder and thin pastes.
254
In closed circuit grinding as compared to open circuit grinding, the
operation is economical.
255
Pick out the correct statement
A hopper is a small bin with a sloping bottom
256
Gelatinous solid (which plug the septum) can be filtered by a ____ filter.
precoat
257
During the washing of cak
all the resistances are constant.
258
The opening of a 200 mesh screen (Taylor series) i
0.0074 cm
259
A gravity decanter is meant for the separation of two ____ density.
immiscible liquids of different
260
The most suitable filter for the removal of very small amount of precipitate from very large volumes of water is the ____ filter.
sand
261
Separation of solid particles based on their densities is called
sorting
262
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?
Copper sulphate
263
____ are mixed using ribbon blenders.
Dry powders
264
During agitation of liquids, the
all (a), (b) and (c).
265
For crushing of solids, the Rittinger's law states that the work required for crushing is proportional to
the new surface created.
266
In a size reduction crushing operation, feed size is 300 to 1500 mm while the product size is 100 to 300 mm. This is a case of the ____ crushing
primary
267
As per Taggart's formula, the capacity (kg/hr) of Jaw & Gyratory crushers (for gapes of 10 to 60 cms) is equal to (where, L = Length of feed opening, cms S = Maximum width of discharge opening, cms )
93 LS
268
The process by which fine solids is removed from liquids is termed a
sedimentation
269
Which of the following crushing laws is most accurately applicable to the fine grinding of materials ?
Rittinger's law
270
Shell and leaf filter as compared to plate and frame filter
all (a), (b) & (c)
271
Metallic wire mesh is used as a filtering medium for the separation of dust from dust laden gas in case of a/an
air filter
272
Which of the following is a coarse crusher?
Gyratory crusher
273
Sorting classifiers employing differential settling methods for separation of particles make use of the differences in their
terminal velocities
274
Separation of particles of various sizes, shapes and densities by allowing them to settle in a fluid is called
classification
275
The specific cake resistance for incompressible sludges is (where ΔP = pressure drop over cake)
independent of ΔP
276
To produce talcum powder, use
ball mill
277
Angle of nip of the crushing rolls does not depend upon the
speed of the rolls
278
Paddle agitator
is suitable for mixing low viscosity liquids.
279
Pick out the wrong statement.
Cutting machines mainly employ 'attrition' for size reduction of solids.
280
Gummy & sticky materials like molasses, sugar etc. are best transported/handled by using a ____ conveyor.
ribbon
281
Soft & non-abrasive materials can be made into fines by
attrition
282
In constant pressure filtration,
#NAME?
283
The critical speed of a trommel (N) is related to its dia (D) as
N ∝ sqrt D
284
Which of the following minerals is not subjected to magnetic separation method?
Galena
285
Which of the following is not a revolving/tumbling mill used for size reduction?
Cage mil
286
Which of the following achieves the least reduction ratio for a given feed size?
Roll crusher
287
A fluid energy mill is used for
ultragrinding
288
Filtration should be stopped in a filter press, if the
both(b)&(c)
289
For coarse reduction of hard solids, use
compression
290
In a size reduction crushing operation, feed size is 100 to 300 mm. while the product size is 10 to 50 mm. This is a case of the ____ crushing.
secondary
291
Traces of liquid tar fog present in coke oven gas is separated using
electrostatic precipitator
292
Close circuit grinding by a ball mill with air sweeping employs a
both (a) & (b).
293
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.
1.34
294
Choke crushing (in case of a Jaw crusher) compared to free crushing
consumes more power.
295
The specific surface of sherical particles is proportional to (where, Dp = diameter of particle).
1/Dp
296
Wheat is ground into flour in a
roller crusher
297
Gravity stamp mill is meant for the ____ crushing.
fine
298
Washability curve based on float and sink test enables an assessment to be made of the possibility of cleaning a coal fraction based on the
density separation.
299
Toothed roll crushers achieve size reduction by
both (a) & (b).
300
Pick out the wrong statement:
Reduction ratio in crushing operation is defined as the ratio of minimum feed size to the maximum product size.
301
To get ultrafine particles, the equipment used is a
fluid energy mill
302
Vacuum filter is most suitable for the
none of these.
303
The porosity of a compressible cake is
minimum at the filter medium.
304
Which of the following conveyors cannot be recommended for transportation of abrasive materials ?
Flight conveyor
305
Separation of materials into products based on the difference of their sizes is called
sizing
306
For classification of potable (drinking) water, we use a ____ filter.
gravity sand
307
Hot, lumpy & abrasive materials are best transported by using a/an ____ conveyor.
apron
308
Additives used for promoting the floccula-tion of particles is a/an
both (a) & (b)
309
In case of grinding in a ball mill
all (a), (b) and (c).
310
The capacity of a classifier in 'tons of solid/hr' is given by (where, A = cross-sectional area, m2 V = rising velocity of fluid, m/sec.S = percentage of solids in the suspension by volume.ρ = density of solids, kg/m3)
3.6 AVS.ρ
311
Kick's law relates to
energy consumption
312
____ mill is normally used for grinding of talc.
Ring-roll
313
Colloidal mills are used for ____ grinding.
ultrafine
314
Fluid medium used in the classification technique of mineral beneficiation is
either (a) or (b)
315
The maximum slope of a belt conveyor can be
30°
316
The filter medium resistance is controlled by
both pressure drop and flow rate
317
The unit of filter medium resistance is
cm-1
318
During size reduction by a jaw crusher, the energy consumed decreases with the
increasing size of feed at constant reduction ratio.
319
Which of the following can be most effectively used for clarification of lube oil and printing ink?
Sharpies supercentrifuge
320
Ultracentrifuges running at speeds upto 100000 rpm is normally used for the
separation of isotopes based on their density or molecular weights difference.
321
Sizing of very fine particles of the order of 5 to 10 microns is done by elutriation, which is a ____ operation.
classification
322
In the cyclone separator used for separation of dust from dust laden gas, the gas
both (b) and (c).
323
The basic filtration equation is given as where, https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/136-487-1.png V is volume of the filtrate ; A is the filtration area, a is specific cake resistance, μ is viscosity of the filtrate, and Cis the concentration of the solids in the feed slurry.
In a 20 minutes constant rate filtration, 5 m3 of filtrate was obtained. If this is followed by a constant pressure filtration, how much more time in minutes, it will take for another 5 m3 of filtrate to be produced ? Neglect filter medium resistance, Rm ; assume incompressible cake.
20
324
Size reduction of fibrous materials like wood, asbestos, mica etc. is done by a disintegrator exemplified by the
cage mill
325
The material is crushed in a gyratory crusher by the action of
compression
326
The equivalent diameter of channel of a constant non-circular cross-section of 3 cm by 6 cm will be ____ cms.
2
327
Which of the following may prove unsuitable for filtering volatile liquids ?
Vacuum filter
328
____ mean diameter of particles is given by
volume
329
Mass flow of granular solid (M) through a circular opening of dia, D follows
M ∝ D3
330
Sauter mean diameter is the same as the ____ mean diameter.
volume-surface
331
Cake resistance is
none of these.
332
In paint industries, blending of light paste is done by using a
charge can mixer
333
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
0.5
334
____ is used for producing a thick suspension from a thin slurry.
Pressure filter thickener
335
Wet seiving is employed, when the product contains ____ materials.
large quantity of very fine
336
Energy requirement (per unit mass of material crushed/ground) is highest for
fluid energy mill
337
The energy consumed by a ball mill depends on
all (a), (b) and (c).
338
Energy consumption in a crusher decreases with increase in the
all (a), (b) & (c).
339
In a mixer, the quantity, (v. L/D) is termed as ____ number(where, v = longitudinal velocity of material, L = length of the mixer, D = diffusivity in axial mixing).
Pclet
340
The term 'angle of nip' is concerned with the operation of the ____ crushers.
roll
341
Cartridge filters are termed as 'edge' filters, because of the fact that the
bulk of the solids are removed at the periphery of the disks.
342
Vibrating screens have capacity in the range of ____ tons/ft2 .mm mesh size.
0.2 to 0.8
343
Cumulative analysis for determining surface is more precise than differential analysis, because of the
assumption that all particles in a single fraction are equal in size, is not needed.
344
To remove very small amount of tiny solid impurities from liquid, we use a
coagulant
345
Screw conveyors are
suitable for sticky materials.
346
____ mills fall in the category of tumbling mills,
all (a), (b) & (c)
347
Capacity of flight conveyor in tons/hr is given by (where, W & D = width and depth of flight respectively in metre V = speed of the conveyor, metre/second ρ = bulk density of material, kg/m3)
3.6 W.D.V.ρ
348
Which of the following is not a cutting machine?
Tube mills
349
Weber number is significant and is concerned with the
dispersion of liquid in liquid.
350
Power consumption during turbulent flow in agitation tank is proportional to the ____ of the liquid.
density
351
Screen efficiency is
none of these
352
For grinding of cereals, grains, spices, pigments, saw dust, cork etc., the most extensively used size reduction equipment is a
Buhrstone mill
353
Handling of ashes and similar materials can be done best by a ____ conveyor.
drag or slat
354
Which of the following must be stored in silos and not in open yard ?
High V.M. bituminous coal
355
Apron conveyors are used for
heavy loads & short runs.
356
Sedimentation on commercial scale occurs in
rotary drum filters
357
With increase in drum speed, in a rotary drum filter, the filtration rate
increases
358
Arrange the following size reduction equipment in the decreasing order of the average particle size produced by each of them.
Jaw crusher, Ball mill, Fluid energy mill
359
200 mesh seive size corresponds to ____ microns.
74
360
What is the usual value of angle of nip for crushing of ordinary rock in smooth steel crushing rolls ?
32°
361
For a turbine agitated and baffled tank, operating at low Reynold's number (based on impeller diameter), the power number (Np) varies with NRe as
Np ∝ 1/NRe
362
Which of the following is not accomplished by agitation of liquids in agitators?
Blending of immiscible liquids.
363
Which of the following parts of a jaw crusher is subjected to maximum wear and tear during its operation ?
Jaw plates
364
A 30% (by volume) suspension of spherical sand particles in a viscous oil has a hindered settling velocity of 4.44 μm/s. If the Richardson Zaki hindered settling index is 4.5, then the terminal velocity of a sand grain is
1 μm/s
365
The specific surface of spherical particles is given by (where D and ρ are diameter and density of particle).
https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/106-134-1.png
366
Velocity of a small particle of diameter 'Dp' at a distance 'r' from the rotational axis of a cyclone rotating at an angular speed 'ω' is given by (the other symbols are as per standard notation)
https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/132-461-4.png
367
In froth floatation, chemical agent added to cause air adherence is called
collector
368
The sphericity of a solid particle of cubical shape is
(π/6)1/3
369
Vertical transportation of materials can be done by a/an
both(b)&(c)
370
In a roll crusher, the specific power consumption and the production rate is affected by the
both (a) and (b).
371
A cottrel precipitator makes use of the ____ for dusty air cleaning.
corrona discharge
372
Pick out the correct statement.
Kick's crushing law is, P/m = K . ln https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/122-367-2.png
373
If radius of a batch basket centrifuge is halved & the r.p.m. is doubled, then the
centrifugal force is doubled.
374
The ratio of the area of openings in one screen (Taylor series) to that of the openings in the next smaller screen is
none of these
375
Compressibility co-efficient for an absolutely compressible cake is
1
376
Mixing of plastic solids is generally facilitated by
kneading
377
grinding element & the housing.
both (a) and (b).
378
Which of the following is not an industrial screening equipment ?
Sharpies centrifuge
379
Which of the following is not a wet classifier ?
None of these
380
Helical screw agitator is used for
mixing highly viscous pastes.
381
For raschig rings, the sphericity is
<1
382
For Indian standard (IS) screens, the mesh number is equal to its aperture size expressed to the nearest deca-micron (0.01 mm). Aperture width of IS screen of mesh number 50 will be approximately ____ microns.
500
383
____ mills are termed as disintegrators.
Cage
384
Supporting legs of a plate and frame filter is normally made of
cast iron
385
The cummulative mass fraction of particles smaller than size dj for a collection of Ni particles of diameter di and mass mi (i = 1, 2, 3, ...... ∞) is given by
https://www.indiabix.com/_files/images/chemical-engineering/mechanical-operations/136-492-2.png
386
Wet grinding in a revolving mill ____ as compared to dry grinding.
increases capacity
387
The grinding in a hammer crusher takes place due to the
both (a) & (b)
388
A compressible cake has the
maximum porosity at the upstream side.
389
Which of the following is not used as a filter medium in case of corrosive liquids ?
Cotton fabric
390
In ball mill operation, the feed size (Df in meters) and the ball diameter (Db in metres) are related as ( where, K = grindability constant (varying from 0.9 to 1.4 in increasing order of hard ness))
Db2 = K.Df
391
Pine oil and cresylic acid are used as ____ in the froth floatation process.
frother
392
Grinding characteristic of a material is given by its
HGI
393
Which of the following is not a non-metalliferous mineral?
Cassiterrite
394
Filter medium resistance is important during the ____ of filtration.
early stages.
395
Float and sink test determines the possibility of cleaning of coal by a process based on the
gravity separation
396
____ baffles are provided in ball mills.
Horizontal
397
Mixer used for rubber compounding is
banbury internal mixer
398
For spheres, the specific surface shape factor is given by
AD/V
399
____ mill is not used for grinding wheat into flour and for milling of cereals & other vegetable products.
Pebble
400
In case of a hammer crusher, the final product size depends on the
all (a), (b) and (c).
401
Sphericity of raschig ring (whose length and diameter are equal) is
1
402
Mixing mechanism employed in a pan mixer is by
mulling
403
Chance process is used for the
cleaning of coal.
404
Which of the following screens has the maximum capacity ?
Vibrating screen
405
Stamp mills are generally used for crushing
gold ores
406
In case of a plate and frame filter press, filtrate flow through the cake follows ____ flow.
laminar
407
Which of the following is a batch sedimentation equipment ?
Filter thickener
408
The most suitable equipment for the transportation of 200 mesh size particles is a
pneumatic conveyor
409
Which of the following is not used as filter aid?
Rice husk
410
Raw materials are charged in the iron blast furnace using
skip hoist
411
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
flint or porcelain
412
Filter aids like asbestos, kieselguhr, diatomaceous earth etc. are used to increase the porosity of the final filter cake & reducing the cake resistance during filtration. Filter aid is
all 'a', 'b'&'c'.
413
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
414
Pick out the wrong statement pertaining to the roll crushers.
Both the rolls run necessarily at the same speed.
415
Which of the following is not an ultrafine grinder (colloid mill)?
Toothed roll crusher
416
Two particles are called to be equal settling, if they are having the same.
terminal velocities in the same fluid & in the same field of force.
417
Which of the following is the most suitable for handling fibrous and dense slurries ?
Cone type agitator
418
____ centrifuge is normally used in sugar mills.
Turbine agitator
419
Solid particles separation based on the difference in their flow velocities through fluids is termed as the
classification
420
Diatomaceous earth is a/an
filter aid
421
The distribution given by microscopic analysis of powder is
number
422
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
423
For a non-spherical particle, the sphericity
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.
424
In washing type plate and frame filter press, the ratio of washing rate to the final filtrate rate is
45295
425
Ball mills and tube mills with flint or porcelain balls are used for size reduction of
non-metallic ores
426
Size reduction of ____ is accomplished in steam heated rollers and roll crushers.
hard rubber
427
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
428
Which of the following is not a part of the Blake jaw crusher?
Hanger
429
If a force greater than that of gravity is used to separate solids & fluids of different densities, the process is termed as the
centrifugation
430
Filter aid is used to
increase the porosity of the cake.
431
Which of the following mineral dressing operations is termed as 'comminution'?
None of these
432
The capacity of a pneumatic conveying system depends upon the
all (a), (b) and (c).
433
Pick out the wrong statement.
The equipment used for the removal of traces of solids from a liquid is called a classifier.
434
Gravity settling process is not involved in the working of a
hydrocyclone
435
Froth floatation is the most suitable for treating
sulphide ores
436
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
437
Which of the following is the most suitable for cleaning of fine coal dust (<0.5 mm) ?
Froth floatation
438
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.
439
Range of compressibility co-efficient of the commercial compressible cake obtained in filtration operation is
0.2 to 0.8
440
Highly viscous liquids & pastes are agitated by
multiple blade paddles
441
The value of 'angle of nip' is generally about
32°
442
Size reduction of the ____ can be suitably done by ball mills, crushing rolls and rod mills.
metalliferrous ores
443
Sulphuric acid mist is arrested by using a ____ scrubber
venturi
444
The main size reduction operation in ultrafine grinders is
attrition
445
In case of a hammer crusher,
all (a), (b) and (c).
446
Jigging is a technique by which different particles can be
separated by particle size.
447
Crushing of mineral particles is accomplished in a 'cage mill', when one or more alloy steel bars are revolved in opposite directions. It is a type of ____ mill.
impact
448
Balls for ball mills are never made of
lead
449
200 mesh screen means 200 openings per
inch
450
____ is the most commonly used 'filter aid'.
Diatomaceous earth
