# Mechanical Operations Questions and Answers – Screens

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This set of Mechanical Operations Multiple Choice Questions & Answers (MCQs) focuses on “Screens”.

1. ______ are used on the bottom of the blades.
a) Spikes
b) Serrations
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.

2. _____ 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.

3. 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.
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4. 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.

5. Cyclones can be operated at temperature as high as ____
a) 1000oC
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.

6. 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.

7. When the gas enters the cyclone, velocity increases with decrease in ____
b) Flow rate
c) Force
d) Mass

Explanation: As gas enters the velocity goes redistribution so that the tangential component of the velocity increases and radius decreases.

8. What does the following called?
Vct ~ r-n
c) Decreasing vector
d) Increasing vector

Explanation: Decreasing radius is expressed by the above equation, where n=1 in the absence of wall friction.

9. 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.

10. 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.

Sanfoundry Global Education & Learning Series – Mechanical Operations.

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