In my fluid mechanics class, we did an experiment where we were asked to measure some values and then, using a Moody Diagram, estimate the roughness of the pipe. Briefly, each trial consisted of allowing water to flow down a thin tube (diameter D=9.5mm) and into a discharge cylinder. A manometer was connected to two points along the tube (separated by a distance of 1m) so that we could measure the pressure differential.(adsbygoogle = window.adsbygoogle || []).push({});

As an example, i will use the data from one of the trials we conducted:

Flow speed (V): 52.3 cm/s

This was measured by observing the rate at which the water level rose in the discharge cylinder and then using this, along with the tube geometry, to calculate a flow speed.

Head Loss (h) over 1m of tube: 4cm

Calculated by measuring the height differential of the manometer.

I then calculated the friction factor:

[tex]

f=\frac{2hDg}{LV^2}=0.027

[/tex]

and the Reynolds Number:

[tex]

Re=\frac{VD}{\upsilon}=4950

[/tex]

Now when i plot this on a Moody Diagram, it falls below the line for a smooth pipe, which as far as i thought, was impossible? This happened with all of our trials.

Does anybody know what could possibly have gone wrong? Have i made a mistake in my calculations?

Any help is greatly appreciated.

Thanks,

Dan.

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# Calculating Pipe Roughness

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