# Mechanical Operations Questions and Answers – Separation of Solid by Screening

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This set of Mechanical Operations test focuses on “Separation of Solid by Screening”.

1. In a continuous thickener, the area is determined by the _____
a) Commination layer
b) Newton layer
c) Plank layer
d) Concentration layer

Explanation: In case of a continuous layer, the area is determined by that concentration layer for which solids handling capacity is per unit time minimum.

2. What does the following equation represents?
Q (1 – C)
a) Feed rate
b) Evaporation rate
c) Drying rate
d) Pull over rate

Explanation: The liquid feed rate is given by the above equation for a thickener, where Q is the volumetric flow and C is the concentration.

3. Calculate the feed rate, if the volumetric flow is 55 m3/s and concentration is 0.5?
a) 27.5
b) 3.5
c) 55
d) 50

Explanation: As we know feed rate = Q (1 – C) = 55(1-0.5) = 27.5.

4. What does the following equation represents?
p (1-C)
a) Feed rate
b) Evaporation rate
c) Mass rate
d) Pull over rate

Explanation: The mass feed rate is given by the above equation for a thickener, where p is the density of fluid in kg/m3 and C is the concentration.

5. Calculate the feed rate, if the density of fluid is 78.9 kg/m3 and concentration is 0.03?
a) 76.53
b) 75.5
c) 50.2
d) 1.33

Explanation: As we know mass feed rate = p (1 – C) = 78.9 (1-0.03) = 76.533.

6. To obtain largest throughput, rate of sedimentation should be _____
a) Same
b) High
c) Low
d) Constant

Explanation: In order to obtain the highest throughput from a thickener, the rate of sedimentation should be as high as possible.

7. Cone scrapers are bolted to ______
a) Bottom End
b) Centre shaft
c) Back valve
d) Dirt separator

Explanation: Cone scrapers are bolted to the center shaft to prevent plugging of the bottom discharge cone.

8. What are the size of centered column thickener?
a) 75 ft. in diameter
b) 55 ft. in diameter
c) < or = 75 ft. in diameter
d) < or = 55 ft. in diameter

Explanation: They are usually 75 ft. in diameter and in special cases they may be smaller, Lifting devices will lift the raking arms 12 to 36 inches.

9. For a tray thickener, feed enters a ____
a) Exchanger
b) Splitter
c) Driver
d) Separator

Explanation: Feed enters a feed splitter box at the top of the tank which divides the flow amongst the compartments of the thickener.

10. ______ is defined as the distance from the liquid from top to bottom.
a) Extrapolation
b) Superposition
c) Superelevation
d) Evenpolation 