Your were right Mad and so we went to the sun deck and had a couple of Fiji Golds and the watched the world cup final and saw Brazil win 3 - 2. Exemplorary. Good input.

So the last test seems to be that h5-h3-x(h5+h4)+2xh3 must tend to zero to make

dh=d(S+pv) true.

But for this to happen it makes it an isochoric process and that then means that the gas portion at the outlet of the TXV already has the properties of the gas at the gas line. It is therefore only the liquid that holds the core thermodynamic properties. ie it does not matter what you do with the gas as it cannot affect the liquid except for normalising the mass if one removes it. Interesting!

How to calculate this on the fly and use it is a distant goal at the moment. But without it how can we go to stage 2.

Knickers, we are going back to the sun deck for some more Fiji Gold.

Chef