I've been using this online calculator to work out the difference in pressure and flow between two ends of a pipe:

Pipe Friction Calculation for Fluid Flow in a Pipe

So far most of it makes sense, and I've managed to figure out the worst of it (pipe relative roughness >_<). The main problem is that we don't have the "Average fluid velocity in pipe $\mathrm{V}$", only the Flow at A in $\mathrm{l}/\mathrm{s}$.

Before you mock the next part I should explain that I'm a software developer, which apparently still qualifies me more for this sort of work than my water engineer brother-in-law...

Anyway, to convert from Flow to Velocity, I made up the following:

L: litres per second at A
D: diameter of pipe (m)
V: fluid velocity (in m/s)

$$V = \frac{ 1000L }{ \pi(D/2)^2 } $$

Is this the correct conversion, or have I missed something?


Volumetric flow $\Phi = A V$. Therefore the right expression would be

$$V = \frac{ L/1000 }{ \pi(D/2)^2 }.$$

To get volumetric flow in SI units $\mathrm{m}^3/\mathrm{s}$ you should DIVIDE $\mathrm{l}/\mathrm{s}$ by 1000.

  • $\begingroup$ I had a feeling I'd missed something vital. Thanks. $\endgroup$ – Stu Pegg Apr 9 '12 at 21:17
  • $\begingroup$ Marko: We have MathJax active on the site so you can typeset you mathematics using LaTeX alike notation. I'll do this one for you. $\endgroup$ – dmckee Apr 9 '12 at 21:20
  • $\begingroup$ @dmckee: Fancy. I've fixed my question using your edits as a template. $\endgroup$ – Stu Pegg Apr 9 '12 at 21:37
  • $\begingroup$ @dmckee cool. and some characters to obtain 15 $\endgroup$ – Pygmalion Apr 9 '12 at 22:07

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