Wizard,
My last post was interrupted, so consider this a continuation.
Yes, two phase flow calculations (liquid and vapor, in your case) are complex. The first step is to understand whether you have horizontal flow, upflow, downflow, or inclined flow. You may have some parts that are horizontal flow and some that are another type, like downflow for example. It would simplify matters *a lot* if your system could be represented by the predominant flow direction based on some criteria, like length of flow direction.
Despite the complexity and enormous research that has gone into two phase flow over the last 100 years, there is still substantial uncertainty in most of the correlations used today, so don’t feel that you are losing too much by characterizing your entire system by the predominant flow direction.
If you want the technical challenge, the next step is to determine the flow regime (wave, annular, spray, bubble, stratified, slug, plug) using the regime map for the flow direction you have. This will be trial and error since you have to assume a flow rate, calculate pressure drop, and see if it matches your problem. My 6th Edition of Perry’s has correlations for cocurrent horizontal flow (Lockhart and Martinelli) and vertical downflow for annular flow. For other flow directions and regimes, they point you to a reference document. This is not very convenient, huh? Again, it’s a complex matter.
It has become popular lately in the relief design area to use the conservative “homogeneous equilibrium model” method for two phase flow no matter what the flow direction or regime is. At least, that is my perception. My Perry’s doesn’t have this method in it, but I believe the 7th Edition does. If you google “homogeneous equilibrium model”, I got 214 hits.
You will have to decide how you will approach your problem. How accurate do you need to be? Do you just need to be conservative? Are you estimating a spill and release, and do you need to consider the amount evaporated after the spill occurs? These are all questions you need to consider. It’d help us help you if you could fill in some of the gaps. Like, what’s the chemical, why do you need the flow rate, what’s the flow direction, what’s the vapor density, liquid density, vapor viscosity, liquid viscosity, surface tension, change in elevation, number of velocity heads of the fittings, the flow area of the strainer, is the strainer submerged, if so, by how much, etc., etc., and etc. After you decide your approach, you can post your data and results from your calcs and someone will probably check it for you, or at least give you a ballpark gut check.
Good luck,
Latexman