Mechanical Operations Multiple Choice Questions on “Flow”.
1. Which of the following velocity components are observed in an agitator?
a) Radial, Axial, Longitudinal
b) Radial, Inclined, Longitudinal
c) Inclined, Axial, Radial
d) Axial, Inclined, Longitudinal
Answer: a
Clarification: The velocity components observed in agitated tank are radial, axial and longitudinal where each of these components act in a particular direction.
2. The radial velocity component acts in the direction ____
a) Parallel with the shaft
b) Perpendicular to the shaft
c) Tangent o the circular path around the shaft
d) At an inclined angle with the shaft
Answer: b
Clarification: Radial velocity component always acts in a direction along a radius from the center of the impeller.
3. The tangential velocity component acts in the direction ____
a) Parallel with the shaft
b) Perpendicular to the shaft
c) Around the shaft
d) At an inclined angle with the shaft
Answer: c
Clarification: The tangential velocity component acts in the tangential direction to the circular motion of the fluid flow.
4. The axial velocity component acts in the direction ____
a) Parallel with the shaft
b) Perpendicular to the shaft
c) Tangent o the circular path around the shaft
d) At an inclined angle with the shaft
Answer: a
Clarification: Axial velocity component always acts in a direction perpendicular to the radius of the impeller and parallel to the shaft.
5. When the shaft is vertical and centrally located in the tank, the ____ component is generally disadvantageous.
a) Radial
b) Axial
c) Tangential
d) Rotational
Answer: c
Clarification: The tangential velocity component acts in the tangential direction to the circular motion of the fluid flow around the shaft and creates vortex, which is disadvantageous.
6. If solid particles are present in agitating tank then instead of mixing reverse concentration may occur.
a) True
b) False
Answer: a
Clarification: When solid particles are present, the circular motion of the impeller tends to throw the particles towards the wall of the tank and from there slide downwards to center of the tank at the bottom.
7. In small agitating tanks, impellers can be mounted off center in order to prevent swirling.
a) True
b) False
Answer: a
Clarification: In Unbaffled, centrally mounted agitator, circulatory motion of fluids leads to vortex formation. In order to avoid vortex impellers can be mounted off center.
8. Suspending settling solid particles and low viscosity bulk blending are examples of process that work well utilizing axial flow.
a) True
b) False
Answer: a
Clarification: Agitators that are responsible for axial flow movement are suitable for applications that require high product flow and low turbulent energy, which is beneficial for low viscous fluid.
9. Which of the following flow is ideal for de-agglomerating solids, dispersion and emulsion?
a) Axial
b) Radial
c) Longitudinal
d) Tangential
Answer: b
Clarification: Radial flow is velocity component acts in a direction along a radius from the center of the impeller which is beneficial for mixing of solid particles, de-agglomerating solids, dispersion, and emulsion.
10. Axial flow is preferred when solid particles are kept in suspension.
a) True
b) False
Answer: a
Clarification: Axial flow impellers like propellers drive the liquid down to the bottom of the tank, where the streams spread radially in all directions toward the wall, flow upward along the wall and returns to the suction of propeller from the top. This principle helps in keeping the solid particles in suspension.