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# Two phase flow ejector

## Two phase flow ejector

(OP)
Hi all,

I'm trying to understand the Homogeneous Equilibrium Model (HEM) of a two phase flow nozzle as described here.

For critical mass velocity they write:

with

and

The part that puzzles me are the derivatives along the saturation line shown above. Another text writes these as partial derivatives AT the saturation line btw. Going through the refrigerant properties sheet, specific volume and enthalpy are given as function of temperature only, so these terms would vanish after taking the derivative. Or am I supposed to use the Clausius-Clapeyron relation here?

Could someone please explain how to deal with these terms and determine Gc?

Thx!

### RE: Two phase flow ejector

if I understand correctly it's a form of Delayed Equilibrium Model, the main problem with these models is the estimate of vaporizing liquid, of course equation 15 applies for all these models, you may need dH, dS, dV (from a EOS or similar method) for solving local equilibria,
I have not experience with this model but I use regularly HNE-DS (comparing results vs. rigorous HEM available in Prode Properties)
I must admit that with these models it is difficult to decide which gives the best results...

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