pressure drop of two phase flow in valves

[Hansss]

Who can help me with the correct formulas for calculating the pressure drop in wet return suction lines (two -phase flow).
The Hansen and the Danfoss program are doing this completelly different, same Kv value and double the pressure drop.....................?

[Andy]

Who can help me with the correct formulas for calculating the pressure drop in wet return suction lines (two -phase flow).
The Hansen and the Danfoss program are doing this completelly different, same Kv value and double the pressure drop.....................?

Hansss:)
welcome:)

in my experience the Danfoss program comes out with practical solutions that work:)

I am still waiting for a copy of the Hansen program, I think they are in the process of upgrading it.

Stick to DIRCAL it will be as close as required.

Kind Regards Andy:)

[US Iceman]

Hi Hansss,

Welcome to the RE site.

It seems you have asked two questions.


Who can help me with the correct formulas for calculating the pressure drop in wet return suction lines (two -phase flow).

and your title was...


pressure drop of two phase flow in valves

Two phase flow is one of those things an academic professor will discuss. If you get an honest answer it will be something like, who knows?

I have not seen anything solid yet although a lot of research is starting to be done I think.

From a traditional point of view a practical approach would be to calculate the pressure drop with single phase flow for the operating conditions. For vapor only and not include the effects of the overfeed or circulation rate.

This sets the minimum pipe size for the vapor volume flow at a 1:1 rate. The liquid that does overfeed is such a small amount by volume that it remains a small puddle in the bottom of the pipe.

Of more concern (at least in my opinion) is the vapor velocity in the line and the chance for liquid hammer induced by high velocity liquid slugs.

If the pipe is sized for single phase flow for the pressure drop, that will establish the minimum pressure drop the pipe will create and also allow the compressors to be selected for this pressure loss. Then... up size the wet suction line one diameter.

This lowers the vapor velocity and probability of vapor propelled liquid slugs that can do damage to the pipeline and valves.

For the valve capacities this is a little more tricky. But I think based on similar logic I have described above. If the valve capacity requirement is for say 75 kW cooling (single phase vapor only) the valve capacity will be reduced (at the same pressure drop) if the overfeed liquid also flows through the valve.

I have not used the Hansen or Danfoss programs too much, since I usually hand select any valve I would use.

On any liquid valves in the overfeed liquid supply the mass flow is of course the multiple of the circulation rate used for single phase (non-overfeed). These valves are very easy to select since they are single phase only (just higher liquid mass flows to account for).

Not very scientific I know, but it works well.:D