Formula to determine Temperature after EEV (electronic expansion valve)

[DavidMi]

Good morning all together,

I have an issue with determining the temperature after an EEV (electronic expansion valve). I am trying to build a modell of a refrigerant circuit for simulation purposes, the information I have so far are:

- Temperature (Input)
- Pressure (Input)
- Mass flow (Input)

- Pressure (Output)
- Mass flow (Output)

I have already read a lot in this forum but haven't found a solution, that is suitable for my case. For example: "thread124-86992", or "thread378-301968".
I think the simplification to think of the valve throttling as an isenthalpic process is legitimate but it does not help me because the spec. heat c is dependent upon the temperature, so correctly it is c(T). Therefore there are still two unknown values.

I hope that I made my question clear enough and I'm looking forward for your help.
Thanks in advance!

 

[Compositepro]

The temperature in the evaporator of a refrigerator is controlled by the pressure in the evaporator (the boiling point of the liquid changes with pressure). The expansion valve controls this.

 

[georgeverghese]

Take a look at expression 4-34 in Perry Chem Engg Handbook, 7th edition, and you'll realise that for an non ideal gas, the compressibility factor variation is part of the difficulty in manually computng this. I've been in this mess before, trying to get a stable mathematical expression for the isenthalpic temp drop for a high pressure multicomponent natural gas stream to be input into DCS - a real nightmare. Vaguely recall I had to work out what (dz/dp) at const T (or some variant of this).

As suggested, you may need to lower your expectations and provide this temp drop manually by referring to established mollier curves, else you may need medication to recover from this trauma.

 

[DavidMi]

@georgeverghese:

Thanks a lot for your detailed answer. I see that this problem is well known, good to know that others had their problems here as well
Btw, I've seen people quoting the Perry Chem Engg Handbook a lot of times here.. is there a digital version available?

Thanks in advance!

 

[georgeverghese]

Yes, the 7th edn is on CD-ROM, and so would the later 8th.