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# Mechanical Operations MCQ’s – Screening Equipments

What does the below equation represent?

a) Theoretical diameter

b) Theoretical speed

c) Minimum force

d) Minimum feed

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Answer: a

Explanation: The theoretical minimum diameter particle to be separated in a cyclone is given by the relation as mentioned above, where W is the width of cone and N is no. of turns.

For a good design, entrance velocities should be between ____

a) 500 to 1500 ft. /min

b) 1000 to 4000 ft. /min

c) 10 to 200 ft. /min

d) 500 to 800 ft. /min

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Answer: b

Explanation: Entrance velocities ranges from 1000 to 4000 ft. /min, 3000 ft. /min is good average although velocities up to 6000 ft. /min are used in special cases.

The larger the diameter, the _____ is pressure drop.

a) Large

b) Less

c) Same as

d) Constant

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Answer: b

Explanation: Small diameter has higher collection efficiency for the same entrance condition and pressure drop.

The efficiency for cyclone increases as

a) Pressure drop decreases

b) Pressure drop increases

c) Pressure drop is constant

d) No relation

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Answer: b

Explanation: The efficiency increases as the pressure drop increases that is a smaller separator might have higher efficiency due to higher gas velocity.

What is the pressure drop range of a cyclone?

a) 0.5 to 8.0 inches

b) 1.0 to 5.0 inches

c) 5.0 to 6.0 inches

d) 5.0 to 8.0 inches

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Answer: a

Explanation: The pressure drop in a cyclone usually is between 0.5 to 8.0 inches of water, it can be large but rarely exceeds 10 inches of water.

What does the following represents?

h_{ui} = 0.003ρ V_{c}^{2}

a) Inlet area

b) Inlet Velocity

c) Inlet head

d) Inlet pressure drop

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Answer: c

Explanation: Inlet velocity head on inlet area is given by the above relation, where p is the density of water and V is the velocity.

What does the below equation represent?

a) Pressure drop

b) Friction loss

c) Head loss

d) Depth loss

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Answer: a

Explanation: This equation represents the pressure drop, where De ¬and Dc is the cyclone gas exit and cyclone diameter in feet’s, K is a constant at 3.2.

Calculate inlet head, if density of fluid is 12.3 kg/m3 and critical velocity is 58 m/s?

a) 123.13

b) 2.145

c) 15.22

d) 58

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Answer: a

Explanation: As we know that inlet head is 0.003*12.3*582 = 123.13 m.

Calculate pressure drop for a cyclone with De to Dc ratio of 3/4?

a) 2.333

b) 1.8

c) 9.6

d) 2.4

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Answer: b

Explanation: As we know that dP = K (De/ Dc)2 = 3.2 (3/4)2 = 1.8.

The overflow ratio is defined as ___

a) D/E

b) F/E

c) E/F

d) D/F

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Answer: d

Explanation: The overflow ratio is defined as the ratio of mass flow rate F and the mass flow rate of overflow i.e. D, so D/F.