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Critical Pressure For Choke Valve Sizing

critical pressure choke valve multiphase flow

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#1 Sherif Morsi

Sherif Morsi

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Posted 07 November 2017 - 12:37 PM



I am currently filling out the datasheet for a choke valve to be sent to the vendor. I am using HYSYS to provide the data.


For 2 phase flow, the critical pressure is 330 bara (the inlet HYSYS stream to the valve) and when I copy the stream and flash it, the liquid HC critical pressure is 280 bara. Please note that the datasheet requires the liquid HC critical pressure. Which value should I use (note that there is some flashing across the valve)?


Another question, does the valve Cv increase with increasing Pc or decrease?




#2 serra


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Posted 07 November 2017 - 01:42 PM

critical pressure depends only from composition (not from vapor, liquid, two phases... states),

you need to define the composition (which do not change across the valve) to calculate the critical pressure,

to identify your operating point a good idea could be to calculate a phase diagram which shows you

two phase area, Cricondenbar and Cricondentherm , for these definitions see for example


These valves are (normally) designed to operate with critical flow through holes and flow depends from fluid density (not from position of critical point), but depending from the procedure adopted by vendor to select the valve several parameters can influence the selection, for example a manufacturers can require pseudo critical pressure (not the true critical pressure) and adopt correlations not too different from ISA correlations, you may contact the vendor to clarify these points.

Edited by serra, 07 November 2017 - 01:53 PM.

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