This set of Environmental Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Chemical Clarification”.
Figure: Flash mixer
Answer the following questions based on the above diagram.
1. Which of the following represents the coagulant pipe?
Explanation: ‘A’ represents the coagulant pipe which is used for discharging the coagulant into the flash mixer.
2. Which of the following represents the device which is used for sludge removal?
Explanation: ‘D’ represents the drain valve which is used for the removal of sludge from the mixer.
3. _________ is the average of velocities at a point over a definite period of time.
a) Mean velocity
b) Relative velocity
c) Velocity gradient
d) Temporal mean velocity
Explanation: Temporal mean velocity is the average of velocities at a point over a definite period of time. It is represented by G.
4. Which of the following goes to the flocculation tank?
Explanation: ‘B’ represents the outlet of the mixer which goes to the flocculation tank.
5. Which of the following is the correct expression regarding temporal mean velocity?
a) G = (P/μV) 1/2
b) G = (P/μV)
c) G = (P/μV) 2
d) G = (Pμ/V) 1/2
Explanation: Temporal mean velocity G = (P/μV) 1/2, where P is the power, μ is the dynamic viscosity and V is the volume of the tank. It is measured in per second.
6. Which of the following is correctly paired?
a) C – Impeller
b) D – Outlet
c) F – Deflecting wall
d) E – Impeller
Explanation: E represents the Impeller which is driven by the electric motor to revolve in the tank.
7. The speed of impeller in a flash mixer is
Explanation: The speed of impeller in a flash mixer is between 100 to 120 rpm and the propeller type impeller is used.
8. ‘C’ in the following figure represents the ________
b) Impeller shaft
c) Deflecting wall
d) Flash mixer wall
Explanation: ‘C’ represents the deflecting wall, whereas the boundary below the inlet and outlet of the tank is the flash mixer wall.
9. The detention period of a flash mixer is
a) 2 minutes
b) 30 minutes
c) 1 hour
d) 2 hours
Explanation: The detention period of flash mixer lies between 30 seconds to 2 minutes.
10. Which of the following represents the impeller shaft?
Explanation: Impeller is connected to impeller shaft which is further connected to electric motor so as to drive the impeller and mixing of coagulant in water takes place.
Sanfoundry Global Education & Learning Series – Environmental Engineering.
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