Quote:
Originally posted by pHaestus
Anyway flow rate is useful because it can be measured anywhere in the loop (constant) much more easily than velocity at a lot of points. Plus I assume water velocity can be estimated at any point with cross sectional area.
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Only the average velocity through a plane surface through which the whole flow passes can be calculated easily.
Areas through which only a part of the flow passes can have dramatically different different average velocities. (Consider eddies.)
An interesting image to consider. (Provided by roscal in
this OCAU thread.)
Edit: Upon thinking about it more, I don't think it is necessarily easy to determine the average velocity even through an area which all the flow passes through. Considering the image above, it appears that it could be very difficult to predict.