Mechanical Operations Part 1 Flashcards by Chris Wilfred Estrada

Short distance transportation of grain, gravel, sand, ash, asphalt etc. is done by using a __________ conveyor.
flight
slat or drag
ribbon
screw

screw

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Equivalent diameter of a particle is the diameter of the sphere having the same
ratio of surface to volume as the actual volume
ratio of volume to surface as the particle
volume as the particle
none of these

ratio of surface to volume as the actual volume

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If dp is the equivalent diameter of a non-spherical particle, Vp its volume and sp its surface area, then its sphericity is phi-s is defined by
phi-s = 6 Vp/dp sp
phi-s = Vp/dp sp
phi-s = 6 dp Sp/Vp
phi-s = dp Sp/Vp

phi-s = 6 Vp/dp sp

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Power required to drive a ball mill with a particular ball load is proportional to (where, D = diameter of ball mill )
D
1/D
D2.5
1/D2.5

D2.5

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Pick out the wrong statement.
Recycled coarse material to the grinder by a classifier is termed as circulating load
Wear and tear in wet crushing is more than that in dry crushing of materials
Size enlargement (opposite of size reduction) is not a mechanical operation
A ‘dust catcher’ is simply an enlargement in a pipeline which permits the solids to settle down due to reduction in velocity of the dust laden gas

Size enlargement (opposite of size reduction) is not a mechanical operation

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In continuous filtration (at a constant pressure drop), filtrate flow rate varies inversely as the
square root of the velocity
square of the viscosity
filtration time only
washing time only

square root of the velocity

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For sizing of fine materials, the most suitable equipment is a
trommel
grizzly
shaking screen
vibrating screen

vibrating screen

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Which of the following is not categorised as a “mechanical operation” ?
Agitation
Filtration
Size enlargement
Humidification

Humidification

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Which of the following is a pressure filter?
Leaf filter (Moore filter)
Plate and flame filter
Rotary drum filter
Sand filter

Plate and flame filter

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Tabular bowl centrifuges as compared to disk bowl centrifuges
operate at higher speed
employ bowl of larger diameter
can not be operated under pressure/vacuum
can’t be used for separation of fine suspended solids from a liquid

operate at higher speed

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Pebble mills are tumbling mills widely used for grinding in the manufacture of paints & pigments and cosmetic industries, where iron contamination in the product is highly objectionable. Pebbles used in pebble mill are made of
bronze
stainless steel
flint or porcelain
concrete

flint or porcelain

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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
added to the feed slurry
precoated on the filter medium prior to filtration
separated from the cake by dissolving solids or by burning it off
all ‘a’, ‘b’&’c’

all ‘a’, ‘b’&’c’

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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 σ
μ ≥ tan σ
μ > tan 2σ
μ ≤ tan σ

μ ≥ tan σ

≥ co-efficienct rock&roll

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Pick out the wrong statement pertaining to the roll crushers.
Maximum feed size determines the required roll diameter
For hard material’s crushing, the reduction ratio should not exceed 4
Both the rolls run necessarily at the same speed
Reduction ratio and differential roll speed affect production rate & energy consumed per unit of surface produced

Both the rolls run necessarily at the same speed

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Which of the following is not an ultrafine grinder (colloid mill)?
Micronizers
Agitated mills and fluid energy mills
Toothed roll crusher
Hammer mills with internal classification

Toothed roll crusher

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Two particles are called to be equal settling, if they are having the same.
size
specific gravity
terminal velocities in the same fluid & in the same field of force
none of these

terminal velocities in the same fluid & in the same field of force

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Which of the following is the most suitable for handling fibrous and dense slurries?
Propeller agitator
Cone type agitator
Turbine agitator
Radial propeller agitator

Cone type agitator

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__________ centrifuge is normally used in sugar mills.
Tubular bowl
Disc-bowl
Suspended batch basket
Perforated horizontal basket continuous

Suspended batch basket

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Solid particles separation based on the difference in their flow velocities through fluids is termed as the
clarification
classification
elutriation
sedimentation

classification

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Diatomaceous earth is a/an
explosive
filter aid
filter medium
catalyst

filter aid

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The distribution given by microscopic analysis of powder is
number
length
area
volume

number

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Number of particles in a crushed solid sample is given by (where, m = mass of particles in a sample, Vp = volume of one particle, rho= density of particles)
m/rho . Vp
m. rho/Vp
m . Vp/rho
Vp/m . rho

m/rho . Vp

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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
has the dimension of length
is always less than 1
is the ratio of volume of a sphere having the same surface area as the particle to the actual volume of the particle

is defined as the ratio of surface area of a sphere having the same volume as the particle to the actual surface area of the particle

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In washing type plate and frame filter press, the ratio of washing rate to the final filtrate rate is
4
1/4
1
1/2

1/4

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Ball mills and tube mills with flint or porcelain balls are used for size reduction of asbestos rubber non-metallic ores limestone

non-metallic ores

Size reduction of __________ is accomplished in steam heated rollers and roll crushers. resins gums hard rubber waxes

hard rubber

The capacity of a belt conveyor depends upon two factors. If one is the cross-section of the load, the other is the __________ of the belt. speed thickness length none of these

speed

Which of the following is not a part of the Blake jaw crusher? Hanger Check plates Toggles Pitman

Hanger ## Footnote NOT part Blake Jaw Hanger

If a force greater than that of gravity is used to separate solids & fluids of different densities, the process is termed as the sedimentation flocculation dispersion centrifugation

centrifugation

Filter aid is used to increase the rate of filtration. decrease the pressure drop increase the porosity of the cake. act as a support base for the septum.

increase the porosity of the cake.

Which of the following mineral dressing operations is termed as 'comminution'? Panning Spiralling Tabling None of these

None of these

The capacity of a pneumatic conveying system depends upon the bulk density of materials pressure of the conveying air pressure of the conveying air all (a), (b) and (c)

all (a), (b) and (c)

Pick out the wrong statement. Close circuit grinding is more economical than open circuit grinding Cod oil, beef tallow or aluminium stearates are used as grinding aids in cement 'industries' The equipment used for the removal of traces of solids from a liquid is called a classifier Size enlargement is a mechanical operation exemplified by medicinal tablet making

The equipment used for the removal of traces of solids from a liquid is called a classifier ## Footnote wrong removal of traces - classifier

Gravity settling process is not involved in the working of a hydrocyclone classifier dorr-thickener sedimentation tank

hydrocyclone

Froth floatation is the most suitable for treating iron ores sulphide ores quartzite none of these

sulphide ores

The energy required per unit mass to grind limestone particles of very large size to 100 um 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 urn is 6.35 kWh/ton 9.0 kWh/ton 18 kWh/ton 25.4 kWh/ton

18 kWh/ton

Which of the following is the most suitable for cleaning of fine coal dust (<0.5 mm)? Trough washer Baum jig washer Spiral separator Froth floatation

Froth floatation

Pick out the correct statement: Removal of iron from ceramic material is necessitated (by magnetic separation method) so as to avoid discolouration of ceramic products The operating cost of shaking screen is more than that of a vibrating screen Screen capacity does not depend upon the specific gravity of the minerals Asphalt is best crushed using toothed roll crusher

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 0.01 to 0.1 0.1 to 0.3 0.2 to 0.8 0.2 to 0.4

0.2 to 0.8

Highly viscous liquids & pastes are agitated by propellers turbine agitators multiple blade paddles none of these

multiple blade paddles

The value of 'angle of nip' is generally about 16 degrees 32 degrees 52 degrees 64 degrees

32 degrees

Size reduction of the __________ can be suitably done by ball mills, crushing rolls and rod mills. metalliferrous ores non-metallic ores basic slags asbestos & mica

metalliferrous ores

Sulphuric acid mist is arrested by using a __________ scrubber. packed wet hollow wet venturi cocurrent

venturi ## Footnote SV sulphuric venturi

The main size reduction operation in ultrafine grinders is cutting attrition compression impact

attrition

In case of a hammer crusher, crushing takes place by impact breaking. maximum acceptable feed size is 30 cms. reduction ratio can be varied by adjusting the distance from cage to hammers. all (a), (b) and (c).

all (a), (b) and (c).

Jigging is a technique by which different particles can be separated by particle size. separated by particle density. separated by particle shape. mixed.

separated by particle size. ## Footnote jigging 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 roll vibratory none of these

impact

Balls for ball mills are never made of forged/cast steel lead cast iron alloy steel

lead

200 mesh screen means 200 openings per cm2 cm inch inch2

inch

__________ is the most commonly used 'filter aid'. Diatomaceous earth Fuller's earth Vermiculite Semi-plastic clay

Diatomaceous earth

Energy consumed for crushing one ton of material ranges from __________ kWh. 0.01 to 0.1 0.5 to 1.5 2 to 3.5 4 to 5.

0.5 to 1.5

For transporting pasty material, one will use a/an apron conveyor belt conveyor screw colaveyor bucket elevator

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. sharpies supercentrifuge. batch basket centrifuge. sparkler filter.

disc bowl centrifuge.

A tube mill compared to a ball mill has a higher length/diameter ratio. produces a coarser product. has a higher diameter/length ratio. uses much larger balls.

has a higher length/diameter ratio.

Trommels separate a mixture of particles depending on their size density wettability electrical & magnetic properties

size

Basic slag is not ground in jaw crushers ball mills compartment mills tube mills

jaw crushers

Grindability of a material does not depend upon its elasticity hardness toughness size

size

Shape factor for a cylinder whose length equals its diameter is 1.5 0.5 1 2

1.5 ## Footnote Cylinder...equals its diameter..1.5

In case of a hammer crusher, the feed may be highly abrasive (Moh's scale >5). minimum product size is 3 mm. maximum feed size may be 50 mm. rotor shaft carrying hammers can be vertical or horizontal.

rotor shaft carrying hammers can be vertical or horizontal.

Dust laden air can be purified using a cyclone separator bag filter gravity settler tubular centrifuge

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 poor grindabilit high power consumption in grindin high power consumption in grinding

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) 0.01 L.S 0.087 L.S L.S L.S/0.087

0.087 L.S

Vacuum is applied in __________ zone, in case of a general type continuous rotary drum vacuum filter. filtering washing drying all (a), (b) & (c)

all (a), (b) & (c)

General crushing equation is given by d(p/m) = -KdDs/Ds^n. Bond's crushing law isobtained by solving this equation for n = __________ and feed of infinite size. 1 1.5 2 2.5

1.5

Which of the follwoing mechanical conveyors does not come under the division 'scrapers' ? Ribbon conveyor Flight conveyor Bucket elevators Drag conveyor.

Bucket elevators

__________ mixer is used for devulcanisation of rubber scrap & making water dispersion & rubber solution. Tumbler Banbery Muller Rubbon blender

Banbery

Which of the following mechanical conveyors does not come under the division 'carriers'? Belt conveyor Bucket elevator Screw conveyor Apron conveyor.

Screw conveyor

Screen capacity is not a function of its openings size. screening mechanism. screening surface. atmospheric humidity

atmospheric humidity

Which of the following is a vacuum filter? Filter press Rotary disc filter Batch basket centrifuge Tank filter (Nutsch filter)

Rotary disc filter

Pine oil used in froth floatation technique acts as a/an collector modifier frother activator

frother

Length/diameter ratio of a ball mill is 1.5 1 < 1 > 1

< 1

Feed size of ≥ 25 cms can be accepted by ball mill rod mill fluid energy mill jaw crusher

jaw crusher

Which is the most suitable conveyor for transportation of sticky material? Apron conveyor Belt conveyor Screw conveyor Pneumatic conveyor

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 bag filter electrostatic precipitator cyclone separator wet scrubber

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 <10 >100 <100

<10

Filtration of water in a paper mill is done by a/an __________ filter. open sand plate and frame vauum leaf sparkle

open sand

Moore filter is a __________ filter. leaf press rotary sand

leaf ## Footnote ML Moore Leaf

Sphericity of a cubical particle, when its equivalent diameter is taken as the height of the cube, is 0.5 1 √2 √3

1 ## Footnote Cubical Height of Cube Sphericity 1

Ball mill is used for crushing coarse grinding fine grinding attrition

fine grinding

In case of a ball mill, coarse feed requires a larger ball fine feed requires a larger ball operating speed should be more than the critical speed none of these

coarse feed requires a larger ball

Maximum size reduction in a ball mill is done by the, __________ action. attrition compression impact cutting

impact

Increasing the capacity of a screen __________ the screen effectiveness. decreases. increases does not effect none of these

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 N N1 N2 N3

Bond crushing law calls for relatively less energy for the smaller product particles, than does the Rittinger law. is less realistic in estimating the power requirements of commercial crushers. states that the work required to form particle of any size from very large feed is proportional to the square root of the volume to surface ratio of the product. states that the work required for the crushing is proportional to the new surface created.

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 Hagen-Poiseulle's Fanning's Kremser

Kozney-Karman

The controlling resistance in a rotary drum vacuum filter is the __________ resistance. piping cake filter medium none of these

cake

Which of the following is used for primary crushing of very hard lumpy materials? Toothed roll crusher Gyratory crusher Ball mill Tube mill

Gyratory crusher

Coal is finally pulverised to 200 mesh size for burning in boilers by a hammer crusher ball mill roll crusher gyratory crusher

ball mill

Crushing efficiency is the ratio of the surface energy created by crushing to the energy absorbed by the solid. energy absorbed by the solid to that fed to the machine. energy fed to the machine to the surface energy created by crushing. energy absorbed by the solid to the surface energy created by crushing.

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 s/c s . c 1/s . c

c/s

Cement clinker is reduced to fine size by a roll crusher ball mill tube mill hammer mil

tube mill

The crushed material received for separation is called feed or tailing heading concentrate middling

heading

For spheres, volume shape factor is given by π(=A/D²) 2π(=2A/D²) π/6(=V/D³) AD/V

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)? Propeller Helical screw Flat blade turbine Curved blade turbine

Helical screw

__________ is defined as the geometric mean of the relative rejections and the relative recoveries of two minerals. Separation efficiency Selectivity index Concentration ratio none of these

Selectivity index

The operating speed of a ball mill should be __________ the critical speed. less than much more than at least equal to slightly more than

less than

Use of baffles in agitators help in minimising the __________ tendency. swirling vortexing both (a) & (b) neither (a) nor (b)

both (a) & (b)

__________ are used for the separation of coarse particles from a slurry of fine particles. Thickeners Classifiers Hydrocyclones Decanters

Classifiers

Fibrous material is broken by a rollcrusher squirrel-cage disintegrator ball mill tube mill

squirrel-cage disintegrator

__________ is the most suitable for compounding rubber and plastic solids. Banbery mixer Pan mixer Pug mill Charge can mixer

Banbery mixer

Out of the following size reduction equipments, the maximum feed size can be accepted by the tube mill ball mill jaw crusher jet pulveriser

jaw crusher

Bucket elevators are not suitable for the vertical lifting of __________ materials. fine (e.g. - 200 mesh size coal) sticky (e.g. clay paste) small lumpy (e.g. grains and sand) free flowing

sticky (e.g. clay paste)

The most common filter aid is diatomaceous earth calcium silicate sodium carbonate silica gel

diatomaceous earth

For removal of very small amounts of precipitate from large volume of water, the most suitable filter is the __________ filter. plate & frame shell & leaf sand rotary vacuum

sand

For separation of sugar solution from settled out mud, we use a __________ filter. sparkler plate and frame centrifugal rotary drum vaccum

centrifugal

The sphericity of a cylinder of 1 mm diameter and length 3 mm is 0.9 0.78 0.6 0.5

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. 0.007 0.3 5 0.014

0.3

What is the selectivity index, if the grade of tailings & concentrate is the same? 0 infinite 1 0

The most suitable equipment used to devulcanise rubber scrap and to make water dispersion & rubber solution is a boundary mixer. propeller agitator. sharpies centrifuge. none of these.

boundary mixer.

Traces of solids are removed from, liquid in a classifier clarifier sparkler filter rotary vacuum filter

clarifier ## Footnote CRRT ClaRifieR Traces of solids

_________ balls capable of grinding the feed in a ball mill gives the maximum efficiency. Cast iron Minimum size Maximum size Elliptical

Minimum size

The speed of a rotary drum vacuum filter may be about __________ rpm. 1 50 100 500

Colloid mills achieve size reduction mainly by impact attrition cutting compression

attrition ## Footnote colloid reduction attrition

Mesh indicates the number of holes per square inch linear inch square foot linear foot

linear inch

For achieving maximum capacity of the ball mill, the ball charge should be equal to about __________ percent of the ball mill volume. 10 25 50 75

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). (S/V)p √(S/V)p (S/V)2p (S/V)f

√(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 Kick's law Bond's law none of these

Rittinger's law

Electrical energy consumed by a jaw crusher is not a function of the average feed size average product size machine capacity none of these

none of these

Size reduction mechanism used in Jaw crushers is attrition compression cutting impact

compression

Trommels employ __________ for screening of materials. fibrous cloth woven wire screen punched plate none of these

punched plate

A widely used size reduction equipment for __________ is Bradford breaker. talc coal iron core wheat

coal ## Footnote coal Bradford

Ultra centrifuges are used for the separation of __________ solid particles. coarse fine colloidal dissolved

colloidal

Specific surface area is the surface area of a unit __________ of materials. dissolved volume either (a) or (b) neither (a) nor (b)

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 tube rod pebble.

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 feed material. type of crushing machine. both (a) & (b). neither (a) nor (b)

both (a) & (b).

Size reduction does not occur due to compression in case of rod mills gyratory crushers jaw crushers smooth roll crushers

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 0.00184 0.0184 0.184 1.84

0.0184

Which of the following represents the plot of filtrate volume versus time for constant pressure filtration? Parabola Straight line Hyperbola Exponential curve

Parabola

Driving force in case of filtration by a centrifuge is the speed of the centrifuge. centrifugal pressure exerted by the liquid. narrow diameter of the vessel. formation of highly porous cake.

centrifugal pressure exerted by the liquid.

Rod mills employed for grinding employ a steel shell having L/D ratio of 1.5 to 3.0. is useful for handling sticky materials. employ steel rods of 2-12 cms diameter extending over full length of the mill. all 'a', 'b' & 'c'.

all 'a', 'b' & 'c'.

Production rate __________ with increased fineness, with a given energy input to the size reduction machine. decreases increases remains unchanged may increase or decrease; depends on the machine

decreases

Gold ore concentration is mostly done using jigging tabling froth floatation elutriation

tabling ## Footnote TG Tabling Gold

Mixing of light fine powder such as insecticides is done by banbery mixer pug mill impact wheels kneader

impact wheels

Run of mine (ROM) coal is crushed by a __________ for use in domestic ovens. jaw crusher hammer crusher ball mill tube mill

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 Cube Cylinder (L/D = 1) Raschig rings

Sphere

The unit of specific cake resistance is gm/cm2 cm/gm cm/gm2 gm/gm

gm/cm2

Size reduction of asbestos and mica is done by hammer mills rod mills gyratory crushers crushing rolls

hammer mills ## Footnote HAM hammer asbestos mica

A pebble mill is a ball mill. employs flints or ceramic pebbles as the grinding medium is a tube mill lined with ceramic or other non-metallic liner. both (b) and (c).

both (b) and (c).

The study on washability of coal is done by using the __________ technique. tabling elutriation heavy media separation none of these

heavy media separation

Horsepower required for a roll crusher is directly proportional to its reduction ratio. capacity. both (a) & (b). neither (a) nor (b).

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 0.1 0.4 0.6 none of these

0.6

__________ conveyor is the most suitable for long distance transportation of cold, non-abrasive granular/irregular shape/fine materials. Bucket Belt Screw Apron

Belt

The specific cake resistance for compressible sludges is a function of the pressure drop over cake over medium overall none of these

over cake

Moisture can be removed from lubricating oil using tubular centrifuge clarifier sparkler filter vacuum leaf filter

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 1 to 2 2 to 5 5 to 10 10 to 15

2 to 5

Pick out the wrong statement. Gape is the greatest distance between the crushing surfaces or the jaws. The angle of nip (2o) is the angle between roll faces at the level where they will j ust take hold of a particle and draw it in the crushing zone. Crushing efficiency is the ratio of the energy absorbed by the solid to the surfaces energy created by crushing. Reduction ratio is the ratio of the maximum size of the particles in the feed to that in the product.

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 increase the compressibility co-efficient decrease the porosity decrease the compressibility co-efficient

increase the porosity

Which of the following terminology is not used for size reduction of materials to fine sizes or powders? Comminution Dispersion Pulverisation Compression

Compression

A tube mill as compared to a ball mill employs smaller balls. gives finer size reduction but consumes more power. has larger length/diameter ratio (>2 as compared to 1 for ball mill). all (a), (b) and (c).

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 kWh/kg kWh/sec. kg kg/sec.

kW. sec/kg