Pneumatic Piping

pipe size for compressed air for a given line velocity, and flow rate at a particular pressure.

Unfortunately the link that you have given would not take the line velocity into consideration.

It is the dp calculator for a given flow, length and pressure (of compressible fluid)

Of course in real world the averaging of the flow does not exist nor does laminar flow (with profile of paraboloid of revolution)

Whether one wants or not there are bound to be eddies/turbulence at the boundaries.

And just for information the link given provides an equation, please check the derivation of it how the Q and D are related into that. Also it may be noted that in the case of compressible fluids (air) the only effect that pressure has is in the ρ and from there into the viscosity.

To end it what the OP asked?

UD15

The engineering toolbox should really clean up their website.. it is so cluttered with ads all over the place, its almost impossible to navigate sometimes..

Don't know what browser you're using, but of late I've been using Mozilla Firefox, with Adblock Plus as an add-on.

Here's an example of what I see:

Doesn't look too bad to me.

oh.. i gotta check out this adblock plus you are referring too.. i use firefox too.. i tend to avoid some websites with too many ads, and eng. tool bx is one of them