1. When a fluid is passed downwards through a bed of solids, then __
a) No movement takes place
b) Laminar flow occurs
c) Turbulent flow occurs
d) Mixing occurs
Answer: a [Reason:] When a fluid is passed downwards through a bed of solids, no relative movement between the particles takes place, unless the initial orientation of the particles is unstable.
2. The pressure drop across the bed is directly proportional to ____
a) Rate of mixing
b) Rate of sedimentation
c) Rate of flow
d) Rate of Velocity
Answer: c [Reason:] The pressure drop across the bed is directly proportional to the rate of flow, although at higher rates the pressure drop rises more rapidly.
3. When the frictional drag on the particles becomes equal to their apparent weight, then ____
a) High resistance is seen
b) Less resistance is seen
c) No resistance is seen
d) No changes occurs
Answer: b [Reason:] However, the frictional drag on the particles becomes equal to their apparent weight, the particles become rearranged thus offering less resistance to the flow of fluid and the bed starts to expand.
4. In the plot of height and concentration, the settling zone can be seen between ____
a) Compression and clarification zone
b) Compression and Flowing zone
c) Maximum height and lowest concentration
d) Flowing and maximum height
Answer: a [Reason:] In a batch settling, conditions and zone boundaries vary with time, in a continuous settling steady state is set up, but concentration and positions are constant.
5. What does the following equation represents?
b) Charge of feed
c) Volumetric rate
d) Magnetic field
Answer: c [Reason:] In the settling zone of the tank of area A, the volumetric rate of sedimentation of solids q is given by the above equation where uc is sedimentation velocity.
6. ____ will be a function of the depth of tank.
a) Viscosity of solid
b) Volume of solid
c) Concentration of solids
d) Feed of solid
Answer: c [Reason:] The concentration of solids in the underflow will be a function of the depth of tank below the feed point and time of residence of solid in thickener.
7. The below equation represents the ___
a) Height of thickening
b) Height of limit
c) Dewaxing height
d) Crane height
Answer: a [Reason:] The following equation represents the height of the required depth of thickening where, tr is required retention time of solid as determined experimentally in hours and seconds.
8. The concentration of a suspension is increased by sedimentation in ______
Answer: b [Reason:] The thickener is an industrial plant in which the concentration of a suspension is increased by the process of sedimentation.
9. After sedimentation, the thickened liquor is withdrawn from ___
d) Blow off
Answer: a [Reason:] A thickener usually consists of the cylindrical tank with the conical bottom, the thickened liquor is obtained from bottom and clear liquid from an adjustable pipe.
10. The liquor is fed at a depth of ____
a) 0.1 to 5 m
b) 5 to 10 m
c) 10 to 20 m
d) 0.3 to 1 m
Answer: d [Reason:] The continuous thickener, such as a dorr thickener, consists of a large diameter shallow tank with a flat bottom, a feed is at center depth of 0.3 to 1 m.