# Mechanical Operations Questions and Answers – Open Turbine

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

1. Which of the following impellers is not an example of axial flow impeller?
a) Propeller
b) Hydrofoils
c) Pitched turbines
d) Ruston

Explanation: Ruston is a radial flow impeller. The classification of impeller depends on the angle that the blade makes with the plane of impeller rotation.

2. The range of mixing operation of the turbine based on viscosity in a batch process is _____ (centipoise)
a) 105
b) 104
c) 103
d) 102

Explanation:

```Turbine - 105 centipoise
Air agitator - 103 centipoise ```

Turbines are the equipment that are used for the mixing of highly viscous materials, which is not the case with paddles and air agitators. These are the equipment used for the mixing operation of relatively less viscous materials having viscosity ranging from 102 to 104.

3. Which of the following combination of the flow pattern can be observed in an open turbine?
b) Axial only
d) Mixed

Explanation: In an open turbine both radial and axial flow can be observed, whereas in propellers only axial type of flow pattern can be observed. And in equipment like shrouded turbines and paddles axial flow pattern can be observed. The presence of both the flow patterns in an open turbine makes it advantageous over other equipment.

4. Which of the following impeller works best in low viscous system?
a) Shrouded turbine
b) Propeller
c) Anchor

Explanation: Shrouded turbine, anchor and paddle are suitable for high viscous system. High viscosity liquids don’t mix into a homogeneous liquid quite as readily. Also, you can’t force two or more high viscosity liquids into mixing well by increasing the speed of rotation of your mixer impellers. So, heavy duty equipment like shrouded turbines, anchors and paddles or pitched turbines are used.
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5. Which of the following impeller is best suited in mixing operation in lead, rubber and plastics?
a) Propeller – marine
c) Anchor

Explanation: In case of lead, rubber and plastics they require high intensity solid scrubbing which is primarily provided by flat blade turbines. These are used for blending when high shear is required.

6. Open turbines works on which of the following principle?
a) Electrostatic
b) Centrifugal force
c) Frictional force
d) Static force

Explanation: Fresh air enters the compressor at suitable temperature where its pressure and temperature are increased. The high temperature (and pressure) gas enters the turbine where the centrifugal force acts and produces work.

7. The factors on which curved blade turbines are selected?
a) Low shear required and high pumping capacity
b) High shear required and low pumping capacity
c) High shear required and high pumping capacity
d) Low shear required and low pumping capacity

Explanation: Curved blade turbine creates a dual suction flow pattern which is same as flat blade turbine. This design helps in relatively low shear required when relatively low shear required when abrasion must be considered.

8. Agitation and Mixing are synonymous.
a) True
b) False

Explanation: Mixing is a physical process of distribution of particles which can be performed in any desired manner that is randomly, whereas agitation is a physical process of distribution of particles involving a particular circular motion. Also generally mixing is used for creating a homogenous phase whereas agitation is usually used for the purpose of separation.

9. Baffles are often used to reduce tangential motion of fluid.
a) True
b) False

Explanation: The impeller causes the liquid to circulate through the vessel and eventually return to the impeller, which leads to vortex formation. In order to avoid the vortex formation baffles are used.

10. In Propeller the angle that the blade makes with the plane of impeller rotation is _____
a) Greater than 180
b) Between 90 to 180
c) Less than 90
d) Between 145 to 200

Explanation: The design of propeller is constructed such that the angle that the blade makes with the plane of impeller rotation is less than 90. The proper angle of impellers allows for effective pumping and bulk mixing with strong axial velocities and low power consumption.

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