Quote Originally Posted by desA View Post
Chef will know it well. It represents a bifurcation curve generated for a particular case of this same evap. The two branches you see represent two 'stable' modes of evap operation, as a function of the heat-transfer governing equations. The test points are always found to be on one of the branches, even though, in practice, the curves morph slightly with change in evap conditions.

Evaps are non-linear in their nature & hence present some quite extraordinary complications in their control.

If the process ends up on the 'wrong' branch, bad things happen - unstable process (stable evap). If it ends up on the 'other' branch, the process (& evap) is/are stable.

The dTlm='0/0' point is at the bifurcation point i.e. where the single line splits into two (a fork).

It is now fairly clear for 'one' (not all) of the underlying reasons for TXV hunting - the system tries to jump between the two branches on offer...

(A lot of this is pretty much 'hot-off-the-press' as I've been burning the midnight oil developing the theory - in order to best understand the system dynamics).
desA your coming up with some dramatic new revelations in heat transfer and fluid flow!

First is it possible you can explain the two axis on your graph, as they are calculated you should also include the original formulae. You have previously introduced the alpha and beta coefficients but are they the same in the plot you have posted.

I have not come across a curve like this but have seen heat transfer coefficients change during changes in the flow regime, these are almost parrallel but offset and can cause jumps in the evap condition. These curves are always sloping in the same direction leading to stabliity assuming all alse is industry standard. The flow can jump from one line to another but they always have a positive slope.

Many years ago there was a paper that purported a mythical negative pressure slope where an increase in flow reduced the pressure drop, an interesting concept but it has never been shown in experimental data.

You also mention that evaps are non linear in their behaviour, well condensers, compressors, pressure drops in pipes and TXV's are all non linear but it does not mean they can't be modelled or understood.

Looking forward to graph details.

Chef