Environmental Engineering Questions for Campus interviews on “Minimum and Maximum Velocity of Flow”.
1. _______ is the velocity at which the solid matter in sewage remained in suspended form.
a) Settling velocity
b) Self cleansing velocity
c) Mean velocity
d) Non Scouring velocity
Answer: b
Clarification: Self cleansing velocity is the minimum velocity, which is required to keep the solid particles in suspended form otherwise they will settle and result in clogging.
2. The expression for the self cleansing velocity is given by ____________
a) (8*B* (G-1) *g*d/f)1/3
b) (8*B* (G-1) *g*d/f) 2
c) (8*B* (G-1) *g*d/f)
d) (8*B* (G-1) *g*d/f)1/2
Answer: d
Clarification: The self cleansing velocity V is given by V = (8*B* (G-1) *g*d/f) 1/2 Where, G is the specific gravity, g is the acceleration due to gravity, d is the diameter of sewer and f is the Darcy Weisbach friction factor.
3. The self cleansing velocity required for coarse sand is __________
a) 10cm/Sec
b) 20cm/Sec
c) 30cm/Sec
d) 40cm/Sec
Answer: b
Clarification: The self cleansing velocity required for coarse sand is 20cm/Sec which is higher than fine sand having 15cm/Sec.
4. In which of the following, the self cleansing velocity is maximum?
a) Angular stones
b) Fine sand
c) Fine clay
d) Fine gravel
Answer: a
Clarification: The self cleansing velocity for angular stones is 100cm/Sec while of fine sand, fine clay and fine gravel are 15cm/Sec, 7.5cm/Sec and 30cm/Sec respectively.
5. The diameter of the sewer is 23cm. What should be the self cleansing velocity?
a) 10cm/Sec
b) 40cm/Sec
c) 100cm/Sec
d) 130cm/Sec
Answer: c
Clarification: When the diameter of the sewer is between 15cm and 25cm, the self cleansing velocity is 100cm/Sec.
6. What should be the diameter of the sewer when the self cleansing velocity is 60cm/Sec?
a) 10cm
b) 20cm
c) >60cm
d) 100cm
Answer: c
Clarification: The self cleansing velocity varies inversely with the diameter of the sewer and when the diameter is above 60, the self cleansing velocity is 60cm/Sec whereas, for 15cm diameter of the sewer, it is 100cm/Sec.
7. The maximum velocity at which no abrasion takes place is called _______
a) Settling velocity
b) Self cleansing velocity
c) Mean velocity
d) Non Scouring velocity
Answer: d
Clarification: The non scouring velocity is the maximum velocity at which no scouring action takes place. It depends on the material used in the construction of sewers.
8. The non scouring velocity is 260cm/Sec. The type of material of the sewer is __________
a) Earth channels
b) Stone ware sewers
c) Brick lined sewer
d) Cement concrete sewer
Answer: d
Clarification: The non scouring velocity for cement concrete sewer lies between 250cm/Sec to 300 cm/Sec.
9. The non scouring velocity required for cast iron sewer pipes is __________
a) 50cm/Sec
b) 350cm/Sec
c) 160cm/Sec
d) 220cm/Sec
Answer: b
Clarification: The non scoring velocity depends on the material sewer and it is higher for cast iron sewer pipe with a range of 350-450cm/Sec.
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