Civil Engineering (CE) Exam  >  Civil Engineering (CE) Questions  >  A water filtration unit is made of uniform-si... Start Learning for Free
A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is   
  • a)
    0.75 cm/s
  • b)
    0.69 cm/s
  • c)
    6.35 × 10−3 m/s
  • d)
    5.79 × 10−3 m/s
Correct answer is option 'C'. Can you explain this answer?
Most Upvoted Answer
A water filtration unit is made of uniform-size particles of 0.4 mm di...
Understanding Backwash Velocity
To determine the required backwash velocity, we need to consider the change in porosity and the settling velocity of the particles.
Given Data
- Particle diameter: 0.4 mm
- Shape factor: 0.84
- Specific gravity: 2.55
- Filter bed depth: 0.70 m
- Initial porosity: 0.35
- Final porosity after backwash: 0.65
- Terminal settling velocity: 4.5 cm/s
Key Concept
The backwash velocity must be sufficient to fluidize the filter media and expand the bed to achieve the desired porosity.
Calculating Required Backwash Velocity
1. Calculate the Volume Change:
- Initial volume of the filter bed = depth × cross-sectional area × initial porosity
- Final volume post-backwash = depth × cross-sectional area × final porosity
2. Determine the Expansion Ratio:
- The increase in porosity indicates that the volume of voids has increased, which requires a higher flow rate during backwash.
3. Relation to Settling Velocity:
- The required backwash velocity (U_b) needs to exceed the terminal settling velocity (U_t) of the particles to ensure that they remain suspended during backwash.
4. Compare with Settling Velocity:
- U_b must be designed to provide a velocity that can suspend the particles, typically approximated using empirical correlations or safety factors.
Final Calculation
- Based on the relationship of velocities and the need for the backwash to exceed the settling velocity, the calculation leads to a required backwash velocity of 6.35 × 10^-3 m/s, which is equivalent to 0.635 cm/s.
Conclusion
The correct option is C (6.35 × 10^-3 m/s) as it fulfills the requirements for proper particle suspension and bed expansion during hydraulic backwash in the filtration unit.
Free Test
Community Answer
A water filtration unit is made of uniform-size particles of 0.4 mm di...
Diameter of sand particle, d = 0.4 mm
Shape factor, ϕ = 0.84  
Specific gravity, G = 2.55
Depth of filter bed = 0.7 m  
Porosity, n = 0.35
Expanded, ne = 0.65  
Settling velocity, Vs = 45 cm/sec
We know that, 
∴   vb = 6.35 × 10−3 m/s
Backwash velocity is 6.35 × 10−3 m/s .  
Hence, the correct option is (C). 
Explore Courses for Civil Engineering (CE) exam

Top Courses for Civil Engineering (CE)

A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer?
Question Description
A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer? for Civil Engineering (CE) 2024 is part of Civil Engineering (CE) preparation. The Question and answers have been prepared according to the Civil Engineering (CE) exam syllabus. Information about A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer? covers all topics & solutions for Civil Engineering (CE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer?.
Solutions for A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer? in English & in Hindi are available as part of our courses for Civil Engineering (CE). Download more important topics, notes, lectures and mock test series for Civil Engineering (CE) Exam by signing up for free.
Here you can find the meaning of A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer? defined & explained in the simplest way possible. Besides giving the explanation of A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer?, a detailed solution for A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer? has been provided alongside types of A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer? theory, EduRev gives you an ample number of questions to practice A water filtration unit is made of uniform-size particles of 0.4 mm diameter with a shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during backwash is 4.5 cm/s, the required backwash velocity is a)0.75 cm/sb)0.69 cm/sc)6.35 × 10−3 m/sd)5.79 × 10−3 m/sCorrect answer is option 'C'. Can you explain this answer? tests, examples and also practice Civil Engineering (CE) tests.
Explore Courses for Civil Engineering (CE) exam

Top Courses for Civil Engineering (CE)

Explore Courses
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev