Engineering Questions with Answers - Multiple Choice Questions
Mechanical Operations MCQ’s – Screens
______ are used on the bottom of the blades.
c) Doctor knife
d) Both spikes and serration
Explanation: Spikes or serrations are used on the bottom of the blades, when the material handled tends to compact and become hard.
_____ is defined as peripheral speed or arm tip speed.
a) Critical speed
b) Rake speed
c) Elevation speed
d) Enhanced speed
Explanation: The rake speed defined as the peripheral speed or arm tip speed varies with the type of material handled, it usually ranges from 20 to 25 ft./min.
For a cyclone separator, the separating force is ____
a) 5 times gravity
b) 10 times gravity
c) 50 times gravity
d) 2 times gravity
Explanation: The centrifugal separating speed or force may range from five times the gravity in every large diameter, to 2500 times gravity in very small cyclones.
Cyclones can be employed for _______
a) Solid, liquid from gas
b) Solids from liquid
c) Liquid from solid
d) Interphase separation
Explanation: Cyclones have been employed to remove solid and liquid from gases and solid from gases, these units offers a least expensive separation.
Cyclones can be operated at temperature as high as ____
b) 50o C
c) 2000o C
d) 1500o C
Explanation: They can be operated at a temperature as high as 1000o C and pressure up to 5 atmospheres.
Cyclone can separate particles as small as ___
a) 100 microns
b) 5 microns
c) 50 microns
d) 20 microns
Explanation: Cyclones removing solids from gases are generally applicable when particles of over 5 microns (0.0002) inches diameter are involved.
When the gas enters the cyclone, velocity increases with decrease in ____
b) Flow rate
Explanation: As gas enters the velocity goes redistribution so that the tangential component of the velocity increases and radius decreases.
What does the following called?
Vct ~ r-n
a) Decreasing radius
b) Increasing radius
c) Decreasing vector
d) Increasing vector
Explanation: Decreasing radius is expressed by the above equation, where n=1 in the absence of wall friction.
For the decreasing radius, the value of n ranges from ____
a) 0.2 to 0.3
b) 0.5 to 0.7
c) 0.6 to 1.0
d) 1.0 to 2.0
Explanation: However, n will take the value in the range of 0.5 to 0.7 over a large portion of the cylinder radius, n is usually 0.52.
For a good cyclone design, velocity should not be ____
a) > 600 ft./min
b) < 600 ft./min
c) < 1000 ft./min
d) > 1000 ft./min
Explanation: Select an outlet diameter to give a gas velocity not exceeding 600 ft. /min, only special design can have higher velocities.