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For laminar flows thru the circular conduits, the average velocity can be estimated exactly as one half of the maximum flow at the centerline. How about for the turbulent flows, and for rectangular duct lines ? Will anyone guide me to a web site which provides a conversion table to estimate the average from the maximum ?
Thanks in advance.
sgk
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Average Velocity Estimation From Maximum Velocity
Started by Guest_sgk_*, May 14 2003 01:02 PM
2 replies to this topic
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#2
Guest_phex_*
Guest_phex_*
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Posted 15 May 2003 - 02:24 AM
an ideally turbulent flow should have the same fluid velocity at every point, except the "boundary layer". medium fluid velocity can be estimated as maximum flow at centerline, at least with a reasonable accuracy for preliminary calculations.
#3
siretb
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Posted 16 May 2003 - 05:13 AM
There is no easy answer.
For gazeous streams, It will depend so much from how far you are from an obstacle (bend, restriction, valve, ...) that there is no rule.
When accuracy is critical, one must comply fully with the standards, using log-tchebitchev located sampling points in a circular duct.
One rule I have seen is U mean=0.85 U max, when symmetrical. (Umax at center, this value at 0.379r from center. Unless you sample far enough (>10D from bend, do not assume symmetry
I have found that a reasonable accuracy is obtained in most cases (5%, no guarantee) by sampling in 5 points.
I strongly advise against any single point measurement in gaz streams. liquids are a bit easier.
The following paper may be of interest to you:
Comparison of Pitot Traverses taken at varying distances downstream of obstructions AIHA journal(60) march/april 1999 by S Guffey and D Booth
For gazeous streams, It will depend so much from how far you are from an obstacle (bend, restriction, valve, ...) that there is no rule.
When accuracy is critical, one must comply fully with the standards, using log-tchebitchev located sampling points in a circular duct.
One rule I have seen is U mean=0.85 U max, when symmetrical. (Umax at center, this value at 0.379r from center. Unless you sample far enough (>10D from bend, do not assume symmetry
I have found that a reasonable accuracy is obtained in most cases (5%, no guarantee) by sampling in 5 points.
I strongly advise against any single point measurement in gaz streams. liquids are a bit easier.
The following paper may be of interest to you:
Comparison of Pitot Traverses taken at varying distances downstream of obstructions AIHA journal(60) march/april 1999 by S Guffey and D Booth
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