The method used by DIERS for two-phase, homogenous pipe flow is isenthalpic HEM numerical integration. For a constant-area pipe, pressure increments are made from the upstream pressure, P1, to the pressure at the exit of the pipe, P2 (which may or may not be the choked pressure), and then length...
Thanks for the replies and sorry for the late reply. There's no question in my mind that I should use an HEM approach, because it is easier and more conservative than other approaches, and recommended by DIERS and API. I was just wondering if I could implement HEM into the Resistance to Flow...
Does anybody know if the Resistance to Flow Method explained in Appendix E of API 520 Part 1 can be used to verify the capacity of rupture disk in two-phase flow service? The equations API uses are compressible flow equations from Crane Technical Paper No. 410.
I'm thinking that two-phase flow...
Thanks PaoloPemi. I didn't know what was meant by "constant energy flash operation" but I get it now after reading the description for the EPF() function.
>I see that for n-Heptane at 0 Psig (101327 Pa.a) Prode predicts a saturation temperature of 371.577 K or 209.168 F
Is there a Prode function that can be used in excel that outputs the saturation temperature for a given pressure?
>the ratio Pin/Pout in close to 1.0 which means that you are far...
...so I used the mass flux calculated for Pout=0 psig as my Gmax.
Pages 120-121 of the DIERS project manual show an example of this procedure.
Assuming I did everything right, then Prode must be using some different method or it's because of the difference in ANotine coefficients I mentioned...
First off, when I say Gmax, I mean the mass flux at choked conditions, or, if the flow is not choked (and it's not in this case), I mean the mass flux at the backpressure, 0 psig in this case.
I started my procedure by first assuming homogenous flow such that for a liquid full vessel, the...
Thanks apetri.
I spoke to an expert in the area of two-phase vent sizing and he suggested that when calculating the two-phase mass flow rate, I use the following equations, which can be derived from general principles:
Wv = Q/L
dVv/dt = Wv(1/ρv – 1/ρl)
Wtp = (dVv/dt)ρtp
Where...
Thanks for the reply apetri. I hadn't even realized there were all these excel sheets like nozzle.xls saved in the Prode installation folder until I read this post. It makes it much easier to use the program. Just to be sure, the Pout entered is the backpressure, right? I'm not sure because in...
apetri, I revisited API 521, namely section 5.15.3 for how to find flow rates in the fire case. For the all liquid case a hydraulic expansion equation is used and for the all vapor case the heat input is divided by the latent heat of vaporization (W=Q/L). However, as far as I can tell it is not...
I would preferably like to formulate a general procedure, but if you know a way for finding W in the fire case, I'd be glad to hear it, as that's often the worst case emergency. The information in the last thread I started indeed was very helpful. I've since been able to complete my excel sheet...
Hi all, I am trying to figure out how to size a PRV for two-phase flow. All the sizing calculations I've come across give methods like HEM or the Omega method in order to find the maximum two-phase mass flux, G. Then the formula A=W/(K*G) (where A is required orifice area, W is the mass flow...
Thanks for the post PaoloPemi. I've been trying to follow along with the thread you sent a link to before, http://eng-tips.com/viewthread.cfm?qid=329093. In the thread Latexman references a method in the FAQ section that he's based one of his own excel sheets off of...
@ Latexman, I believe the graph you're referring to is Figure I-B1 in the DIERS book. It is a graph of average void fraction vs. dimensionless superficial vapor velocity. There are also equations for the curves on the graph; I came across them when searching for a method of predicting when...
Yes, there are example problems for different models in Appendix II-E. It looks like they've done exactly what my excel sheet does, except that the fluid they consider is water so they just use steam tables to find properties for each individual phase (my excel sheet used the Peng-Robinson EOS...
Yes, I have looked at "Emergency Relief System Design Using DIERS Technology". Namely, section 3-2-2-2 of Chapter II gives analytical equations for solving mass flux (as opposed to just using numerical integration), but still, whether I use an analytical equation or numerical integration method...
Thanks apetri. I'll take a look at the Prode programs and the excel sheet on that thread as soon as I get a chance. I know I'm trying to reinvent the wheel but I really would like to be able to understand two-phase venting and the HEM method well enough to be able to make my own excel sheet...
Hi everyone,
I am a process engineer and I've been trying to find a method for sizing relief devices for two-phase vapor-liquid venting without the need for software/equipment like SuperChems, VSP2, or RSST (I know I would probably need these for reactive systems, but for now I am only...
