The
critical speed of the ball mill of radius R, which contains balls of radius r,
is proportional to
(A)
(R-r)-0.5
(B)
(R-r)-1
(C)
(R-r)
(D)
(R-r)2
GATE 2005
Answer: (A)
A centrifuge of
diameter 0.2 m in a pilot plant rotates at a speed of 50 Hz in order to achieve
effective separation. If this centrifuge is scaled up to a diameter of 1 m in
the chemical plant, and the same separation factor is to be achieved, what is
the rotational speed of the scaled up centrifuge?
(A)
15 Hz
(B)
22.36 Hz
(C)
30 Hz
(D)
44.72 Hz
GATE 2005
Answer: (B)
For a cyclone of
diameter 0.2 m with a tangential velocity of 15 m/s at the wall. The separation
factor is
(A)
2250
(B)
1125
(C)
460
(D)
230
GATE 2004
Answer: (D)
Match the system
in Group I with equipment used to separate them in Group II
Group I Group II
P. gas-solid 1. filter press
Q. Liquid-Liquid 2. Cyclone
3. decanter
4. thickner
(A)
P – 1, Q – 2
(B)
P – 2, Q – 3
(C)
P – 3, Q – 4
(D)
P –4, Q – 1
GATE 2004
Answer: (B)
The cumulative
mass fractions 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
GATE 2004
Answer: (A)
The
Kozney-Carman equation, rewritten in terms of non-dimensional numbers, gives (ΔP/ρu2)
proportional to
GATE 2004
Answer: (A)
Umf
is the minimum fluidization velocity for a bed of particles. An increase in the
superficial gas velocity from 2Umf to 2.5Umf results in
(all velocities are smaller than the entertainment velocity of the particles)
no change in
(A)
Drag on particles
(B)
Drag on column walls
(C)
The bed height
(D)
The bed voidage
GATE
2004
Answer: (B)
To keep the
power input constant for a stirred vessel operating under fully developed
turbulent flow conditions (constant power number), if the impeller diameter is increased
by 20%, the impeller speed should be decreased by a factor of
(A)
(1.2)3/2
(B)
(1.2)3/5
(C)
(1.2)2/3
(D)
(1.2)5/3
GATE 2004
Answer: (D)
A centrifugal
filtration unit operating at a rotational speed ω 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
Answer: (C)
In constant
pressure filtration
(A)
Resistance decreases with time
(B)
Rate of filtration is constant
(C)
Rate of filtration increases with time
(D)
Rate of filtration decreases with time
GATE 2004
Answer: (D)
Energy
requirement (per unit mass of material crushed/ground) is highest for
(A) Jaw crusher
(B) Rod mill
(C) Ball mill
(D) Fluid energy mill
GATE 2003
Answer: (D)
The basic
filtration equation is given as
Where, V is
volume of the filtrate; A is the filtration area; a is specific cake
resistance, μ is viscosity of the filtrate, and C is the concentration of
solids in the feed slurry. In a 20 mm. constant rate filtration, 5 m3
of filtrate was obtained. If this is followed by a constant pressure
filtration, how much more time in minutes will it take for another 5 m3
of filtrate to be produced? Neglect filter medium resistance, Rm;
assume incompressible cake
(A) 10
(B) 20
(C) 25
(D) 30
GATE
2003
Answer: (A)
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
(A) N0
(B) N1
(C) N2
(D) N3
GATE 2001
Answer: D
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 µm is
(A)
6.35 KWh/Ton
(B)
9.0 KWh/Ton
(C)
18 KWh/Ton
(D)
25.4 KWh/Ton
GATE 2001
Answer: C
The volumetric
flow rate during constant pressure filtration is given by
dV/dt = 1/(KcV
+ Q0) Where Q0 = 1/q0
and
V is the total volume of filtrate collected in time t, and Kc and Q0
are constant
Given
V = 1.0 lit at t = 41.3 sec and V = 2.0 lit at t = 108.3 sec. Find KC.
(A)
26 S/lit2
(B)
28 S/lit2
(C)
30 S/lit2
(D)
32 S/lit2
GATE 2001
Answer: A
A 30% (by
volume) suspension of spherical sand particles in a viscous oil has a hindered
settling velocity of 4.4 µm/s. If the Richardson-Zaki index is 4.5, then the
terminal settling velocity of sand grain is
(A)
0.9 µm/s
(B)
1 µm/s
(C)
22.1 µm/s
(D)
0.02 µm/s
GATE 2000
Answer: A
For
a sphere falling in a constant drag coefficient regime, its terminal velocity
depends on its diameter ‘d’ as
(A) d
(B) d0.5
(C) d2
(D) 1/d
GATE 2000
Answer: B
During washing
of filter at the end of constant pressure filtration, the rate of washing
equals the
(A) Rate
of filtration at time zero
(B) Rate
of filtration at the end of filtration
(C) Rate
of filtration when half the filtration has been obtained
(D) Rate
of filtration at the end of filtration but decreases with time subsequently
GATE 1999
Answer: B
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