×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Formula to determine Temperature after EEV (electronic expansion valve)

Formula to determine Temperature after EEV (electronic expansion valve)

Formula to determine Temperature after EEV (electronic expansion valve)

(OP)
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: CALCULATING TEMPERATURE DECREASE IN EXPANSION VALVE: CALCULATING TEMPERATURE DECREASE IN EXPANSION VALVE", or "thread378-301968: Formula for temperature change of liquid through a valve: Formula for temperature change of liquid through a valve".
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!

RE: Formula to determine Temperature after EEV (electronic expansion valve)

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.

RE: Formula to determine Temperature after EEV (electronic expansion valve)

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.

RE: Formula to determine Temperature after EEV (electronic expansion valve)

(OP)
@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!

RE: Formula to determine Temperature after EEV (electronic expansion valve)

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources