recoveringEngineer
Mechanical
- Sep 17, 2004
- 17
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
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
