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Sonic velocity in Pipephase

Sonic velocity in Pipephase

Sonic velocity in Pipephase

(OP)
Hi, everybody!!!
I begin to work with the program Pipephase. And I have a some questions. What model in this program is used for calculation sonic velocity two phase flow? Why Pipephase calculated very high sonic velocity (250m/s)? On the Fortunati model the sonic velocity is lower (100m/s).

RE: Sonic velocity in Pipephase

for two-phase, critical flow, I prefer HEM (Homogeneous Equilibrium) or HNE (with velocity slip, see for example Fauske Contribution to the Theory of Two-Phase, One-Component Critical flow...)
Comparing results (HEM vs. HNE) with Prode Properties I see that for low vapor fractions (say < 10%) predicted sonic velocities can vary substantially (say 10-50%) while agreement is good for other cases (considering a limited slip),
also, small differences in physical model (say fluid properties, phase equilibria as calculated with a multiparameter model, for example GERG 2008 or a EOS as Peng Robinson) can introduce large variations...
Similar comments for the model proposed by Fortunati which considers a polytropic expansion and physical properties are calculated at downstream conditions...


RE: Sonic velocity in Pipephase

(OP)
In general it is necessary to calculate the vacuum transfer line for VDU.
The sonic velocity (or critical velocity) in two phases system is always lower than sonic velocity in a 100% vapor phase and 100% liquid phase. However in the Pipephase this rule isn't observed. The minimum of critical velocity in two phases system will be 0,5 at a liquid holdup. Calculation of sonic velocity in a 100% vapor phase is simple.

RE: Sonic velocity in Pipephase

I have verified sonic velocity calculated for a simple mixture with composition C1 0.7 C3 0.3 and GERG 2008 model, pressure 10 Bar.a, HEM model predicts a minimum immediately before bubble line (t 155.5 K liquid fraction 0.999) with 23.9 m/s (really low), below bubble line (all liquid phase) at 145 K HEM returns 1022 m/s, with liquid fraction 0.5 (with t 167 K) HEM predicts 158 m/s, immediately below dew line with liquid fraction 0.01 , t = 255 K it predicts 298.96 m/s while at 256 K , above dew line (all gas phase),it gives 311.69 m/s , values which seem to confirm what you said,
HNE model gives different values within the two phase area but main differences are in the area 0.0 .. 0.1 liquid fractions where HNE do not predict those low values calculated by HEM.

Different methods (as, for example, the formula given in Two-Phase Flow through Wellhead Chokes) can return different values which are however suitable for specific applications..

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