Mechanical Operations Flashcards
Sphericity of raschig ring (whose length and diameter are equal) is
1
Mixing mechanism employed in a pan mixer is by
mulling
The filtrate flow rate in constant pressure filtration
continuously decreases.
Theoretical capacity of crushing rolls in tons/hr is given by (where,V= peripherial velocity, m/sec.W= width of rolls, m Dr= distance between rolls ρ = density of material to be crushed, kg/m^3 here,V=πN.Dwhere,N= speed of the rolls in rotation per second (rps)D= diameter of rolls, m)
3.6 V.W.Dr.ρ
The inlet pressure in a constant rate filtration
increases continuously
Particle size range in which dust catcher (gravity settling chamber) works most effectively and efficiently is __________ microns.
< 74
Screen capacity is proportional to (where,S= screen aperture)
S
Separation of a suspension or slurry into a supernatant clear liquid (free from particles) and a thick sludge containing a high concentration of solid is called
sedimentation
With increase in the pressure drop across the cake, the specific cake resistance for the compressible sludge
increases
200 mesh screen has 200 openings per linear cm.
Wrongggg
Xanthates are used in the froth floatation process as a/an
collector
Limestone is normally crushed in a
hammer crusher
Filtrate flow rate in case of a rotary drum vacuum filter (in whichRm< <Rc) is proportional to __________ and the cycle time (where, μ = filtrate viscosityRm= filter medium resistanceRc= cake resistance ).
1/√μ
The main differentiation factor between tube mill and ball mill is the
length to diameter ratio
The optimum moisture content in solids to be crushed/ground ranges from __________ percent.
3 to 4
The capacity of a gyratory crusher is __________ that of a jaw crusher with the same gape, handling the same feed & for the same product size range.
2.5 times
gross energy (kWh/ton of feed) needed to reduce very large feed to such a size that 80% of the product passes through a 100 micron screen.
Work Index
Removal of activated carbon from glycerine is done by
plate and frame filter
What is the reduction ratio in a fine crushing operation having following feed and product sizes?

2
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
With increase in drum speed, in a rotary drum filter, the filtration rate
increases
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°
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
In froth floatation, chemical agent added to cause air adherence is called
collector
The sphericity of a solid particle of cubical shape
(π/6)^1/3
Kick’s crushing law is,P/m=K. ln(Dsa/Dsb)
Correctuee
Compressibility co-efficient for an absolutely compressible cake is
1
Mixing of plastic solids is generally facilitated by
kneading
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
Wet grinding in a revolving mill __________ as compared to dry grinding.
increases capacity
In ball mill operation, the feed size (Dfin meters) and the ball diameter (Dbin metres) are related as ( where,K= grindability constant (varying from 0.9 to 1.4 in increasing order of hard ness))
Db^2=K.Df
Pine oil and cresylic acid are used as __________ in the froth floatation process.
frother
Filter medium resistance is important during the __________ of filtration.
early stages
__________ baffles are provided in ball mills.
Horizontal
__________ mill is not used for grinding wheat into flour and for milling of cereals & other vegetable products.
Pebble
Conveyor that is not recommended for transportation of abrasive materials.
Flight conveyor
Hot, lumpy & abrasive materials are best transported by using a/an __________ conveyor.
apron
Kick’s law relates to
energy consumption
The maximum slope of a belt conveyor can be
30°
The filter medium resistance is controlled by
both pressure drop and flowrate
Most effectively used equipment for clarification of lube oil and printing ink?
Sharpies Centrifuge
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
Mass flow of granular solid (M) through a circular opening of dia,D follows
M∝D^3
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
0.50
__________ is used for producing a thick suspension from a thin slurry.
Pressure filter thickener
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).
Peclet
The term ‘angle of nip’ is concerned with the operation of the __________ crushers.
roll
Vibrating screens have capacity in the range of __________ tons/ft2.mm mesh size.
0.2 to 0.8
Power consumption during turbulent flow in agitation tank is proportional to the __________ of the liquid.
density
Cake resistance is independent of the pressure drop.
Wrongggg
A hopper is a small bin with a sloping bottom.
Correctuee
