Mechanical Operations Flashcards
Concepts and heuristics necessary for unit operations and processes involving solids (or with fluids) requiring mechanical operations.
Short distance transportation of grain, gravel, sand, ash, asphalt etc. is done by using a ____ conveyor.
screw
Equivalent diameter of a particle is the diameter of the sphere having the same
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
Power required to drive a ball mill with a particular ball load is proportional to (where, D = diameter of ball mill )
D2.5
Pick out the wrong statement.
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
For sizing of fine materials, the most suitable equipment is a
vibrating screen
Which of the following is not categorised as a “mechanical operation” ?
Humidification
Which of the following is a pressure filter?
Plate and flame filter
Tabular bowl centrifuges as compared to disk bowl centrifuges
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
flint or porcelain
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.
all ‘a’, ‘b’&’c’
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
Pick out the wrong statement pertaining to the roll crushers.
Both the rolls run necessarily at the same speed
Which of the following is not an ultrafine grinder (colloid mill)?
Toothed roll crusher
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
Which of the following is the most suitable for handling fibrous and dense slurries?
Cone type agitator
____ centrifuge is normally used in sugar mills.
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
filter aid
The distribution given by microscopic analysis of powder is
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
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
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
non-metallic ores
Size reduction of ____ is accomplished in steam heated rollers and roll crushers.
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’?
a. Panning
b. Spiralling’
c. Tabling
None of these
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)
Pick out the wrong statement.
The equipment used for the removal of traces of solids from a liquid is called a classifier
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/to
Which of the following is the most suitable for cleaning of fine coal dust (<0.5 mm)?
Froth floatation
Pick out the correct statement:
The operating cost of shaking screen is more than that of a vibrating screen
Range of compressibility co-efficient of the commercial compressible cake obtained in filtration operation is
0.2 to 0.8
Highly viscous liquids & pastes are agitated by
multiple blade paddles
The value of ‘angle of nip’ is generally about
32°
Size reduction of the ____ can be suitably done by ball mills, crushing rolls and rod mills.
metalliferrous ores
Sulphuric acid mist is arrested by using a ____ scrubber.
venturi
The main size reduction operation in ultrafine grinders is
attrition
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).
Jigging is a technique by which different particles can be
separated by particle size.
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
Balls for ball mills are never made of
lead
200 mesh screen means 200 openings per
inch
____ is the most commonly used ‘filter aid’.
Diatomaceous earth
Energy consumed for crushing one ton of material ranges from ____ kWh.
0.5 to 1.5
For transporting pasty material, one will use a/an
screw colaveyor
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.
A tube mill compared to a ball mill
has a higher length/diameter ratio.
Trommels separate a mixture of particles depending on their
size
Basic slag is not ground in
jaw crushers
Grindability of a material does not depend upon its
size
Shape factor for a cylinder whose length equals its diameter is
1.5
In case of a hammer crusher, the
rotor shaft carrying hammers can be vertical or horizontal.
Dust laden air can be purified using a
cyclone separator
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
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
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)
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
Which of the follwoing mechanical conveyors does not come under the division ‘scrapers’ ?
Bucket elevators
____ mixer is used for devulcanisation of rubber scrap & making water dispersion & rubber solution.
Banbery
Which of the following mechanical conveyors does not come under the division ‘carriers’?
Screw conveyor
Screen capacity is not a function of
atmospheric humidity
Which of the following is a vacuum filter?
Rotary disc filter
Pine oil used in froth floatation technique acts as a/an
frother
Length/diameter ratio of a ball mill is
< 1
Feed size of ≥ 25 cms can be accepted by
jaw crusher
Which is the most suitable conveyor for transportation of sticky material?
Screw conveyor
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
Laminar flow region is said to exist during agitation of a liquid in an agitator, when the value of Reynolds number is
<10
Filtration of water in a paper mill is done by a/an ____ filter.
open sand
Moore filter is a ____ filter.
leaf
Sphericity of a cubical particle, when its equivalent diameter is taken as the height of the cube, is
1
Ball mill is used for
fine grinding
In case of a ball mill,
coarse feed requires a larger ball
Maximum size reduction in a ball mill is done by the, ____ action.
impact
Increasing the capacity of a screen ____ the screen effectiveness.
decreases.
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
Bond crushing law
calls for relatively less energy for the smaller product particles, than does the Rittinger law.
Flow of filtrate through the cake in a plate and frame filter press is best described by the ____ equation.
Kozney-Karman
The controlling resistance in a rotary drum vacuum filter is the ____ resistance.
cake
Which of the following is used for primary crushing of very hard lumpy materials?
Gyratory crusher
Coal is finally pulverised to 200 mesh size for burning in boilers by a
ball mill
Crushing efficiency is the ratio of the
surface energy created by crushing to the energy absorbed by the solid.
The resistance offered by the filter used in a bag filter is proportional to (where, c = dust concentration, and s = particle size )
c/s
Cement clinker is reduced to fine size by a
tube mill
The crushed material received for separation is called feed or
heading
For spheres, volume shape factor is given by
π/6(=V/D3)
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
____ is defined as the geometric mean of the relative rejections and the relative recoveries of two minerals.
Selectivity index
The operating speed of a ball mill should be ____ the critical speed.
less than
Use of baffles in agitators help in minimising the ____ tendency.
a. swirling
b. vortexing
both (a) & (b)
____ are used for the separation of coarse particles from a slurry of fine particles.
Classifiers
Fibrous material is broken by a
squirrel-cage disintegrator
____ is the most suitable for compounding rubber and plastic solids.
Banbery mixer
Out of the following size reduction equipments, the maximum feed size can be accepted by the
jaw crusher
Bucket elevators are not suitable for the vertical lifting of ____ materials.
sticky (e.g. clay paste)
The most common filter aid is
diatomaceous earth
For removal of very small amounts of precipitate from large volume of water, the most suitable filter is the ____ filter.
sand
For separation of sugar solution from settled out mud, we use a ____ filter.
centrifugal
The sphericity of a cylinder of 1 mm diameter and length 3 mm is
0.9
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
What is the selectivity index, if the grade of tailings & concentrate is the same?
1
The most suitable equipment used to devulcanise rubber scrap and to make water dispersion & rubber solution is a
boundary mixer.
Traces of solids are removed from, liquid in a
clarifier
_________ balls capable of grinding the feed in a ball mill gives the maximum efficiency.
Minimum size
The speed of a rotary drum vacuum filter may be about ____ rpm.
1
Colloid mills achieve size reduction mainly by
attrition
Mesh indicates the number of holes per
linear inch
For achieving maximum capacity of the ball mill, the ball charge should be equal to about ____ percent of the ball mill volume.
50
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
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
Electrical energy consumed by a jaw crusher is not a function of the
none of these
Size reduction mechanism used in Jaw crushers is
compression
Trommels employ ____ for screening of materials.
punched plate
A widely used size reduction equipment for ____ is Bradford breaker.
coal
Ultra centrifuges are used for the separation of ____ solid particles.
colloidal
Specific surface area is the surface area of a unit ____ of materials.
either (a) or (b)
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
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).
Size reduction does not occur due to compression in case of
rod mills
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
Which of the following represents the plot of filtrate volume versus time for constant pressure filtration?
Parabola
Driving force in case of filtration by a centrifuge is the
centrifugal pressure exerted by the liquid.
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’.
Production rate ____ with increased fineness, with a given energy input to the size reduction machine.
decreases
Gold ore concentration is mostly done using
tabling
Mixing of light fine powder such as insecticides is done by
impact wheels
Run of mine (ROM) coal is crushed by a ____ for use in domestic ovens.
hammer crusher
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
The unit of specific cake resistance is
gm/cm2
Size reduction of asbestos and mica is done by
hammer mills
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).
The study on washability of coal is done by using the ____ technique.
heavy media separation
Horsepower required for a roll crusher is directly proportional to its
both (a) & (b).
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
____ conveyor is the most suitable for long distance transportation of cold, non-abrasive granular/irregular shape/fine materials.
Belt
The specific cake resistance for compressible sludges is a function of the pressure drop
over cake
Moisture can be removed from lubricating oil using
tubular centrifuge
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
Pick out the wrong statement.
Crushing efficiency is the ratio of the energy absorbed by the solid to the surfaces energy created by crushing.
Addition of filter aid to the slurry before filtration is done to …… of the cake.
increase the porosity
Which of the following terminology is not used for size reduction of materials to fine sizes or powders?
Compression
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).
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
Which of the following gives the crushing energy required to create new surface?
Rittinger’s law
In filtration, the use of ‘filter aid’ helps in
deplugging the filter medium.
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))
Gizzlies are used for separating ____ solids.
fine
Which of the following clay mixing devices is vacuum operated for deairation of clay?
Pug mil
Pick out the material having minimum Rittinger’s number.
Quartz
____ mills are termed as impactors.
Hammer
In case of a revolving mill, wet grinding compared to dry grinding
none of these.
To get a fine talc powder from its granules, the equipment used is
ball mill
For a cyclone of diameter 0.2 m with a tangential velocity of 15 m/s at the wall, the separation factor is
230
Width and speed of a conveyor belt depends upon the ____ of the material.
both (a) & (b)
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).
Pick out the wrong statement.
Capacity of crusher in choke feeding is increased.
Which of the following size reduction equipments employs mainly attrition for ultrafine grinding?
all (a), (b) and (c)
Tank filter (e.g., Nutsch filter) is
used for small scale filtration work.
In bag filters, filter fabrics are never made of
metallic wire woven mesh
Use of ‘grinding aids’ is done in ____ grinding.
dry
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
Which of the following is the most suitable filter for separation of abrasive solids suspended in a corrosive liquid?
Vacuum filter
All resistances during washing of cake
remain constant
A ____ mixer resembles a ball mill without balls.
tumbling
____ conveyor is the most suitable for short distance transportation of non-abrasive loose materials like garbage, grain, food wastes etc.
Flight
As the product becomes finer, the energy required for grinding
icreases
Gyratory crushers compared to the reciprocating jaw crushers
have greater capacity per unit of discharge area.
The important dimensional group involved in the power requirement calculation in mixing operation is the ____ number.
both (a) & (b)
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
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
Rittinger’s crushing law states that
work required in crushing is proportional to the new surface created.
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)
Sphericity of pulverised coal is
<1
The reduction ratio for fine grinders is
as high as 100
Which of the following is the hardest material?
Corundum
General mechanism of size reduction in intermediate and fine grinder is by
impact and attrition.
A straight line is obtained on plotting reciprocal of filtration rate vs. the volume of filtrate for ____ flow of filtrate.
incompressible cake and laminar
The work index in Bond’s law for crushing of solids has the following dimensions
kWh/ton
Ore concentration by jigging is based on the difference in the ____ of the particles.
specific gravities
Size measurement of ultrafine particles can be best expressed in terms of
surace area per unit mass
Reduction ratio of crushers is the
ratio of feed opening to discharge opening.
Which is a secondary crusher for a hard & tough stone?
Cone crusher
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)
Cyclones are used primarily for separating
solids from fluids
There is practically no alternative/competitor to ____ in the beneficiation treatment of sulphide ores.
froth floatatio
Separation of isotopes is generally done using a/an ____ centrifuge.
ultra
Temperature of the product during ultrafine grinding
increases
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.
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
Separation of materials of the same density based on their sizes by using then-different rates of flow is called
sizing
Molten ammonium nitrate is mixed with ground limestone in fertilizer plant in a
pug mill
Agglomeration of individual particles into clusters (flocs) is called flocculation. To prevent flocculation, the most commonly used dispersing agents are
silicates & phosphates
For a sphere falling in the constant drag co-efficient regime, its terminal velocity depends on its diameter (d) as
d2
With increase in the capacity of screens, the screen effectiveness
decreases
As particle size is reduced
screening becomes progressively more difficult.
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).
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.
For efficient grinding, ball mills must be operated
at a speed less than the critical speed.
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
For spheres, the surface shape factor is given by (where, A = area, V = volume, and D = diameter)
π(=A/D2)
The reduction ratio for grinders is defined as(where, Df and Dp are average diameters of feed and product respectively).
Df/Dp
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.
A fluid energy mill is used for
ultra grinding
Which of the following is the softest material ?
Talc
Dry powdery solid materials are transported by a ____ conveyor.
screw
Fluid energy mill comes in the category of
ultrafine grinder
Filtration capacity of a rotary drum vacuum filter depends upon the
both (a) & (b).
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
____ conveyors are also called scrapers.
both (b) & (c)
For laminar flow of filtrate through the cake deposited on septum, which of the following will be valid
Kozney-Karman equation
Which of the following is a continuous filter?
None of these
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.
In screen analysis, the notation +5 mm/-10 mm means particles passing through
10 mm screen and retained on 5 mm screen.
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
Optimum ratio of operating speed to critical speed of a trommel is
0.33-0.45
The process opposite to ‘dispersion’ is termed as the
flocculation
The cake resistance increases steadily with the time of filtration in a plate and frame filter employing constant ____ filtration.
both (a) & (b)
Grinding efficiency of a ball mill is of the order of ____ percent
45296
Solid particles of different densities are separated by
sorting classifier
During agitation of liquids, power consumption during laminar flow is not proportional to the
density of the liquid
Trommels are revolving screens which normally operate in the range of ____ rpm
15 - 20
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
Maximum size reduction in a fluid energy mill is achieved by
interparticle attritio
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)
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)
Which one is a filter aid ?
Diatomaceous earth
To remove dirt from the flowing fluid, we use a
strain
Which of the following crushers can be considered as a combination of a jaw crusher and a roller crusher ?
Gyratory crusher
Separation of solid suspended in liquid into a supernatant clear liquid and a denser slurry employs a process termed as the
sedimentation
Ultrafine grinders operate principally by
attrition
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
Which of the following comes in the category of primary crusher for hard and tough stone ?
Jaw crusher
Crushing efficiency of a machine ranges between ____ percent.
0.1 to 2
Screen capacity is expressed in terms of
tons/hr-ft
A screen is said to be blinded, when the
screen is plugged with solid particles.
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
Percentage of drum submerged in the slurry in case of rotary drum filter is
30
Filter medium resistance is that offered by the
filter cloth and the embedded particle collectively.
In a roll crusher, both the rolls
all (a), (b) and (c).
Tube mill compared to ball mill
all (a), (b) & (c).
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
For the preliminary breaking of hard rock, we use a
gyratory crusher
Filtration operation carried out by continuous increase of the inlet pressure of slurry, is called the ____ filtration.
constant rate
Pick out the wrong statement.
Cake resistance is independent of the pressure drop.
Which of the following oxides is not present in hematite iron ore?
Cobalt oxid
Ribbon blenders are exclusively meant for
non-flowing powder and thin pastes.
In closed circuit grinding as compared to open circuit grinding, the
operation is economical.
Pick out the correct statement
A hopper is a small bin with a sloping bottom
Gelatinous solid (which plug the septum) can be filtered by a ____ filter.
precoat
During the washing of cak
all the resistances are constant.
The opening of a 200 mesh screen (Taylor series) i
0.0074 cm
A gravity decanter is meant for the separation of two ____ density.
immiscible liquids of different
The most suitable filter for the removal of very small amount of precipitate from very large volumes of water is the ____ filter.
sand
Separation of solid particles based on their densities is called
sorting
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
____ are mixed using ribbon blenders.
Dry powders
During agitation of liquids, the
all (a), (b) and (c).
For crushing of solids, the Rittinger’s law states that the work required for crushing is proportional to
the new surface created.
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
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
The process by which fine solids is removed from liquids is termed a
sedimentation
Which of the following crushing laws is most accurately applicable to the fine grinding of materials ?
Rittinger’s law
Shell and leaf filter as compared to plate and frame filter
all (a), (b) & (c)
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
Which of the following is a coarse crusher?
Gyratory crusher
Sorting classifiers employing differential settling methods for separation of particles make use of the differences in their
terminal velocities
Separation of particles of various sizes, shapes and densities by allowing them to settle in a fluid is called
classification
The specific cake resistance for incompressible sludges is (where ΔP = pressure drop over cake)
independent of ΔP
To produce talcum powder, use
ball mill
Angle of nip of the crushing rolls does not depend upon the
speed of the rolls
Paddle agitator
is suitable for mixing low viscosity liquids.
Pick out the wrong statement.
Cutting machines mainly employ ‘attrition’ for size reduction of solids.
Gummy & sticky materials like molasses, sugar etc. are best transported/handled by using a ____ conveyor.
ribbon
Soft & non-abrasive materials can be made into fines by
attrition
In constant pressure filtration,
NAME?
The critical speed of a trommel (N) is related to its dia (D) as
N ∝ sqrt D
Which of the following minerals is not subjected to magnetic separation method?
Galena
Which of the following is not a revolving/tumbling mill used for size reduction?
Cage mil
Which of the following achieves the least reduction ratio for a given feed size?
Roll crusher
A fluid energy mill is used for
ultragrinding
Filtration should be stopped in a filter press, if the
both(b)&(c)
For coarse reduction of hard solids, use
compression
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
Traces of liquid tar fog present in coke oven gas is separated using
electrostatic precipitator
Close circuit grinding by a ball mill with air sweeping employs a
both (a) & (b).
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
Choke crushing (in case of a Jaw crusher) compared to free crushing
consumes more power.
The specific surface of sherical particles is proportional to (where, Dp = diameter of particle).
1/Dp
Wheat is ground into flour in a
roller crusher
Gravity stamp mill is meant for the ____ crushing.
fine
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.
Toothed roll crushers achieve size reduction by
both (a) & (b).
Pick out the wrong statement:
Reduction ratio in crushing operation is defined as the ratio of minimum feed size to the maximum product size.
To get ultrafine particles, the equipment used is a
fluid energy mill
Vacuum filter is most suitable for the
none of these.
The porosity of a compressible cake is
minimum at the filter medium.
Which of the following conveyors cannot be recommended for transportation of abrasive materials ?
Flight conveyor
Separation of materials into products based on the difference of their sizes is called
sizing
For classification of potable (drinking) water, we use a ____ filter.
gravity sand
Hot, lumpy & abrasive materials are best transported by using a/an ____ conveyor.
apron
Additives used for promoting the floccula-tion of particles is a/an
both (a) & (b)
In case of grinding in a ball mill
all (a), (b) and (c).
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
Kick’s law relates to
energy consumption
____ mill is normally used for grinding of talc.
Ring-roll
Colloidal mills are used for ____ grinding.
ultrafine
Fluid medium used in the classification technique of mineral beneficiation is
either (a) or (b)
The maximum slope of a belt conveyor can be
30°
The filter medium resistance is controlled by
both pressure drop and flow rate
The unit of filter medium resistance is
cm-1
During size reduction by a jaw crusher, the energy consumed decreases with the
increasing size of feed at constant reduction ratio.
Which of the following can be most effectively used for clarification of lube oil and printing ink?
Sharpies supercentrifuge
Ultracentrifuges running at speeds upto 100000 rpm is normally used for the
separation of isotopes based on their density or molecular weights difference.
Sizing of very fine particles of the order of 5 to 10 microns is done by elutriation, which is a ____ operation.
classification
In the cyclone separator used for separation of dust from dust laden gas, the gas
both (b) and (c).
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
Size reduction of fibrous materials like wood, asbestos, mica etc. is done by a disintegrator exemplified by the
cage mill
The material is crushed in a gyratory crusher by the action of
compression
The equivalent diameter of channel of a constant non-circular cross-section of 3 cm by 6 cm will be ____ cms.
2
Which of the following may prove unsuitable for filtering volatile liquids ?
Vacuum filter
____ mean diameter of particles is given by
volume
Mass flow of granular solid (M) through a circular opening of dia, D follows
M ∝ D3
Sauter mean diameter is the same as the ____ mean diameter.
volume-surface
Cake resistance is
none of these.
In paint industries, blending of light paste is done by using a
charge can mixer
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
____ is used for producing a thick suspension from a thin slurry.
Pressure filter thickener
Wet seiving is employed, when the product contains ____ materials.
large quantity of very fine
Energy requirement (per unit mass of material crushed/ground) is highest for
fluid energy mill
The energy consumed by a ball mill depends on
all (a), (b) and (c).
Energy consumption in a crusher decreases with increase in the
all (a), (b) & (c).
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
The term ‘angle of nip’ is concerned with the operation of the ____ crushers.
roll
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.
Vibrating screens have capacity in the range of ____ tons/ft2 .mm mesh size.
0.2 to 0.8
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.
To remove very small amount of tiny solid impurities from liquid, we use a
coagulant
Screw conveyors are
suitable for sticky materials.
____ mills fall in the category of tumbling mills,
all (a), (b) & (c)
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
Which of the following is not a cutting machine?
Tube mills
Weber number is significant and is concerned with the
dispersion of liquid in liquid.
Power consumption during turbulent flow in agitation tank is proportional to the ____ of the liquid.
density
Screen efficiency is
none of these
For grinding of cereals, grains, spices, pigments, saw dust, cork etc., the most extensively used size reduction equipment is a
Buhrstone mill
Handling of ashes and similar materials can be done best by a ____ conveyor.
drag or slat
Which of the following must be stored in silos and not in open yard ?
High V.M. bituminous coal
Apron conveyors are used for
heavy loads & short runs.
Sedimentation on commercial scale occurs in
rotary drum filters
With increase in drum speed, in a rotary drum filter, the filtration rate
increases
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
200 mesh seive size corresponds to ____ microns.
74
What is the usual value of angle of nip for crushing of ordinary rock in smooth steel crushing rolls ?
32°
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
Which of the following is not accomplished by agitation of liquids in agitators?
Blending of immiscible liquids.
Which of the following parts of a jaw crusher is subjected to maximum wear and tear during its operation ?
Jaw plates
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
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
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
In froth floatation, chemical agent added to cause air adherence is called
collector
The sphericity of a solid particle of cubical shape is
(π/6)1/3
Vertical transportation of materials can be done by a/an
both(b)&(c)
In a roll crusher, the specific power consumption and the production rate is affected by the
both (a) and (b).
A cottrel precipitator makes use of the ____ for dusty air cleaning.
corrona discharge
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
If radius of a batch basket centrifuge is halved & the r.p.m. is doubled, then the
centrifugal force is doubled.
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
Compressibility co-efficient for an absolutely compressible cake is
1
Mixing of plastic solids is generally facilitated by
kneading
grinding element & the housing.
both (a) and (b).
Which of the following is not an industrial screening equipment ?
Sharpies centrifuge
Which of the following is not a wet classifier ?
None of these
Helical screw agitator is used for
mixing highly viscous pastes.
For raschig rings, the sphericity is
<1
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
____ mills are termed as disintegrators.
Cage
Supporting legs of a plate and frame filter is normally made of
cast iron
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
Wet grinding in a revolving mill ____ as compared to dry grinding.
increases capacity
The grinding in a hammer crusher takes place due to the
both (a) & (b)
A compressible cake has the
maximum porosity at the upstream side.
Which of the following is not used as a filter medium in case of corrosive liquids ?
Cotton fabric
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
Pine oil and cresylic acid are used as ____ in the froth floatation process.
frother
Grinding characteristic of a material is given by its
HGI
Which of the following is not a non-metalliferous mineral?
Cassiterrite
Filter medium resistance is important during the ____ of filtration.
early stages.
Float and sink test determines the possibility of cleaning of coal by a process based on the
gravity separation
____ baffles are provided in ball mills.
Horizontal
Mixer used for rubber compounding is
banbury internal mixer
For spheres, the specific surface shape factor is given by
AD/V
____ mill is not used for grinding wheat into flour and for milling of cereals & other vegetable products.
Pebble
In case of a hammer crusher, the final product size depends on the
all (a), (b) and (c).
Sphericity of raschig ring (whose length and diameter are equal) is
1
Mixing mechanism employed in a pan mixer is by
mulling
Chance process is used for the
cleaning of coal.
Which of the following screens has the maximum capacity ?
Vibrating screen
Stamp mills are generally used for crushing
gold ores
In case of a plate and frame filter press, filtrate flow through the cake follows ____ flow.
laminar
Which of the following is a batch sedimentation equipment ?
Filter thickener
The most suitable equipment for the transportation of 200 mesh size particles is a
pneumatic conveyor
Which of the following is not used as filter aid?
Rice husk
Raw materials are charged in the iron blast furnace using
skip hoist
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
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’.
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
Pick out the wrong statement pertaining to the roll crushers.
Both the rolls run necessarily at the same speed.
Which of the following is not an ultrafine grinder (colloid mill)?
Toothed roll crusher
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.
Which of the following is the most suitable for handling fibrous and dense slurries ?
Cone type agitator
____ centrifuge is normally used in sugar mills.
Turbine agitator
Solid particles separation based on the difference in their flow velocities through fluids is termed as the
classification
Diatomaceous earth is a/an
filter aid
The distribution given by microscopic analysis of powder is
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
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.
In washing type plate and frame filter press, the ratio of washing rate to the final filtrate rate is
45295
Ball mills and tube mills with flint or porcelain balls are used for size reduction of
non-metallic ores
Size reduction of ____ is accomplished in steam heated rollers and roll crushers.
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’?
None of these
The capacity of a pneumatic conveying system depends upon the
all (a), (b) and (c).
Pick out the wrong statement.
The equipment used for the removal of traces of solids from a liquid is called a classifier.
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.
Range of compressibility co-efficient of the commercial compressible cake obtained in filtration operation is
0.2 to 0.8
Highly viscous liquids & pastes are agitated by
multiple blade paddles
The value of ‘angle of nip’ is generally about
32°
Size reduction of the ____ can be suitably done by ball mills, crushing rolls and rod mills.
metalliferrous ores
Sulphuric acid mist is arrested by using a ____ scrubber
venturi
The main size reduction operation in ultrafine grinders is
attrition
In case of a hammer crusher,
all (a), (b) and (c).
Jigging is a technique by which different particles can be
separated by particle size.
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
Balls for ball mills are never made of
lead
200 mesh screen means 200 openings per
inch
____ is the most commonly used ‘filter aid’.
Diatomaceous earth
