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Two-phase (water-steam) flow across an orifice

Two-phase (water-steam) flow across an orifice

Two-phase (water-steam) flow across an orifice

(OP)
Does anyone have experience applying Figure U-10, Choking Mass Flow Rate (for isentropic process and equilibrium conditions) of the ASME Steam Tables For Industrial Use. The Figure assumes an isentropic enthalpy drop.  

I have read many of the postings concerning the lack of choking across a thin orifice.  I must admit, this concept went against my grain, initially.   However, I am coming to a greater understanding.  I have ordered R. W. Millers book and await its arrival. Having said that, I am attempting to APPROXIMATE two phase steam flow for the following conditions.

Consider
A short piping run ( 50 feet) of 12 " ID
with a 6 inch orifice (A2 = 28.3 in^2)
consider it thin at 1/4 " thick.
discharging to atmosphere

h0, stagnation enthalpy = 600 BTU/lbm (i.e., upstream condition)
po, stagnation pressure = 115 psia

I like to perform my approximations by bounding problems.  

Certainly, my process in not isentropic (I will assume adiabatic) and entahlpy should be considered constant across a throttle (choke). However applying Figure U-10, Choking Mass Flow Rate, yields 81 lbm/hr per square inch (of based on diameter 2) per psia (of upstream pressure) for a total flow rate of 81 * 115 * 28.3= 260 kph (thousands of lbm per hour).  

I have also used a program I wrote for two-phase pressure drops in piping systems using Martinelli-Lockhart.  I have considerable confidence in this program for horizontal piping and pressure drops less than P0 - Pcritical (no choking conditions).  Relating the orifice to 1290 feet of 12 inch pipe based on Crane Technical Paper 410 for two-phase pressure drop through piping.  That solution (no choking, all the pressure drop results in accelerating the fluid) yields a flow of 380 kph.

Can figure U-10 be applied as I have in the case above?

recoveringEngineer



RE: Two-phase (water-steam) flow across an orifice

I'm curious.  What is the pressure DROP in the upstream piping to the orifice?

RE: Two-phase (water-steam) flow across an orifice

(OP)
The wellhead pressure is about 3 psi higher than just upstream of the orifice.  

recoveringEngineer


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