Do you have Crane #410 (Flow of Fluids)?  Page 2-8 discusses how to figure pressure drop in straight runs of pipe..

Patricia Lougheed

I do not have this document.

Is this publicly available or something that must be purchased?

You have to buy Crane - it's about $30 and can be ordered over the web at:  http://www.vervante.com/crane/ .  I highly recommend getting a copy of this if you're going to be doing any work with fluid flow.

I'll try to condense the basics here, but I need to warn you I may be leading you astray...I'm a nuclear engineer and picked up my fluid flow knowledge over the years.  Also I've only worked with water systems so don't know how two-phase flow affects the pressure drop and what limitations you have on it.

Basically the head loss (h) (or pressure drop) is a function of the (1) roughness of the pipe (f) , (2) length of pipe (L), (3) diameter of pipe (D) and (4) velocity of the fluid through the pipe (v).

formula is h=f*L/D*(v^2)/2g for non-compressible fluids

For compressible fluids (such as air and vapor), the formulae change with the amount of pressure drop expected.  If the pressure drop is fairly small (you're not adding a whole lot of piping), you can use the above formula.  If it's large, then the formulas get complicated.

If you're looking for more than a rough answer, it might be worthwhile to hire someone who knows about this.

Patricia Lougheed