As somoeone who has done a ton of this type of analysis, on these very systems, I think I can make some comments.
The method you choose to do the analysis depends on how sharp you need your pencil to be, and how much $$$ depends on the quality of the answer.
If you need a 'reasonable' answer (insert your definition of reasonableness here) then you can use the incompressible assumption as a defensible starting point. You assume no density change and no heat trasnfer over the length of the line, and use the Darcy equation. Run the calc and if your calculated dP is about 10% or less than the inlet pressure, your answer should be OK, within 25% or so.
If you need a better answer, you can use a physical property generator, or the steam tables, to estimate the density change along the length of the line. You split the line into segments and calc the dP in that segment using the density in that segment, again using the Darcy equation. Obviously this means you have to know something about the state of the steam in the line. This is a lot of work; proceed with caution.
Most industrial steam systems do not approach the velocities where a rigorous compressible analysis would be used. The vast majority of systems I analyze are best handled by a correlation like BBM, in my experience.
If you want the best answer, again in my experience, use a simulator like PipePhase because it will do the rigorous heat transfer calcs and phase change calcs, and it will use a decent correlation for the dP, like BBM. This method will predict your condensate rates, vapor and liquid velocities, pressure drops, steam exit quality, blah blah blah. Since you have a piping network, this is the way I would go since it will VASTLY speed up the calculations and leaves you with a model you can run under varying conditions of p, T, and x. For the system you describe I can build the model and run it in a few hours, including properly accounting for all valves and fittings. If your system goes saturated, all bets are off unless you do use the simulator. Don't even waste your time using a correlation like Lockhart-Martinelli and the Baker two-phase plot for this (that particular one happens to be easy to program into Excel). I would hesitate to use the 'black box' terminology here, for these simulators. Pipephase has all its correlations fully documented, so you can run a hand calc to back-check it, if desired. There's just no other way to do this kind of work that gives this level of accuracy for this level of time/effort investment.
In my experience, a steam system that is assumed to be adiabatic can be anything but. I have field measurements of large, fuly-insulated steam distribution systems, currently online, that show a 20% or more heat loss across the system. If you have uninsulated valves and flanges, pipe shoes, pipe anchors, support hardware, damaged insulation, etc., you will in fact have a non-negligible heat loss/phase change to contend with, which, if not accounted for, will muck up your calculations to varying degrees. Been there, done that, got the bite marks on my arse to prove it. ;-)
If you decide to go this way, you should be able to find a consultant to do this for you for $4-6k, depending on the complexity of the system and to what level you need the analysis done. If you email me (pjchandl@prou.com) I can prolly hook you up with somebody in your area, if you want.
Just what I think I know. - Pete Thanks!
Pete
