Calculate Control Valve Two Phase Flow

[Tonylmiller]

I have a Cv for a control valve, and the material flowing consists of 15% ammonia in the liquid phase and some inert gases. I am not concerned with flashing of the ammonia, since the pressure is 300 psia and ambient temperature. I need to calculate the flow rate at a given pressure differential across the control valve.

Does anyone know of a way to calculate the flow rate of this two phase flow through the control valve?

If not, what about some good engineering estimations?

Thanks in advance,

Tony

 

[davefitz]

I think the NH3 boiling is related to the partial pressure of teh NH3 in the downstream gas mixture, and not the total pressure. To be more specific, if the partial pressure of NH3 in the gases at the valve vena contracta is below the vapor pressure at ambient temp, then the liquid may boil at the vena contracta.

The ISA Handbook of Control valves gives a procedure for predicting 2 phase flow thru valves .

 

[Tonylmiller]

Thank you for your comments. 300 psi is the downstream pressure. I will see if I can find a copy of the ISA Handbook.

 

[khan101]

Look for ANSI/ISA S75.01 Standard "Flow Equations for sizing control valves", section 6.

 

[Tonylmiller]

Do you know if the referenced method uses the homogeneous flow theory approach? I have found a good discussion of that approach. Also, I am familiar with it because of my work with pressure relief valves.

Thank you for your responses.

 

[CARF]

thread698-95817

Control Valve Handbook

 

[Tonylmiller]

Thanks a bunch, CARF. That is a nice resource.

Tony