The velocity distribution for the flow between two parallel plates, both at rest is parabolic in nature. The distance between the two plates is 0.3 m apart and the maximum velocity at the centre is 0.6 m/sec. The average velocity will be
- A0.4 m/secCorrect
- B0.5 m/sec
- C0.6 m/sec
- D0.7 m/sec
Solution
Concept
Average velocity in parallel-plate laminar flow
Formula
Vavg = (2/3) · umax
Step-by-step solution
1. Velocity distribution is parabolic. 2. Vavg = (2/3) × umax = (2/3) × 0.6 = 0.4 m/s.
Explanation
For laminar flow between fixed parallel plates the average velocity is two-thirds of the maximum velocity at the centre. The distance between the plates does not matter.
Shortcut
Parallel plates: avg = 2/3 max. Circular pipe: avg = 1/2 max.
Common mistake
Using ½ of the maximum velocity (circular pipe value).
Correct answer: A) 0.4 m/sec