Results 1 to 5 of 5
  1. #1
    Join Date
    Mar 2016
    Location
    IRAN
    Posts
    182
    Rep Power
    9

    Pressure = Function of (T)



    Dear Friends,
    By some application such as refrigerant slider [photo at below] we can obtain pressure of refrigerant when we have temperature of it (and vice versa) in saturation area.
    Also same as this, In drive of electronic expansion valves we have same as this matter and drive by measuring suction pressure can realize evp. Temperature and finally obtain superheat.

    Definitely these applications and devices use a formula and function such as :
    Pressure = Function of (T).

    Suppose I want to program a SIMENS MINI PLC that measure pressure of suction and suction temp. then by using a function can understand evp. Temperature and then obtain superheat to open or close electronic expansion valve.

    Definitely these devices or softwares do not use table, They use a formula to obtain temperature or pressure on saturation area.

    I need this formula or function for different refrigerants. Have you ever seen these formulas on any sources ?

    photo_2018-05-12_21-47-23.jpg



    Sincerely yours.
    Last edited by A.Mortezania; 12-05-2018 at 06:25 PM.



  2. #2
    Join Date
    Dec 2007
    Location
    australia
    Posts
    3,356
    Rep Power
    39

    Re: Pressure = Function of (T)

    I doubt anyone has a formula or algorithm to pass on that would be deadly accurate.
    The ones I know of have a PT entered for that type of refrigerant, which Danfoss have made pretty easy for us to memory accurate than ever before.
    If someone did work it out, I would expect they would keep it to themselves.
    Why not just buy a Danfoss or whatever brand controller?

  3. #3
    Brian_UK's Avatar
    Brian_UK is offline Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
    Join Date
    Mar 2001
    Location
    Dorset
    Age
    76
    Posts
    11,192
    Rep Power
    60

    Re: Pressure = Function of (T)

    This is a question often asked over the years by people who want program PLCs etc without having to pay the big bucks for the data handling.

    As yet I haven't found anyone who has done it.

    One old thread found by searching this forum gives a formula which may be good enough for you.

    http://www.refrigeration-engineer.co...hp/t-9731.html

    You could, of course, purchase NISTs Refprop for $325 and have the work done for you.

    https://www.nist.gov/srd/refprop

    Download the user guide and you may begin to understand the complexities of the subject.
    Last edited by Brian_UK; 12-05-2018 at 11:18 PM.
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

  4. #4
    Join Date
    Feb 2015
    Location
    Lithuania
    Age
    33
    Posts
    20
    Rep Power
    0

    Re: Pressure = Function of (T)

    Different refrigerant p/T dependencies you can find in internet (mostly they are presented in tables) or you can download software like Solkane that presents quite long list of refrigerants where you can check it graphs.

    https://i.ytimg.com/vi/JZkFzVvHEZk/maxresdefault.jpg

    What you said about programming - it's not worth. The market is quite full of controllers. Like CAREL controllers, got own algorithms between refrigeration circuit and electronic expansion valve openings where you set SH value and so on.

  5. #5
    Join Date
    Mar 2012
    Location
    denmark
    Age
    46
    Posts
    4
    Rep Power
    0

    Re: Pressure = Function of (T)

    Just a note on the RefProp option, try check out what ILK Dresden has available in the form of ASEREP.
    It's for free, and derived from the RefProp.
    - But I guess it does not make the programming much easier, though.
    What we mostly use in Refrigerant Slider is just the simple Antoine equation, which requires three constants, that we have derived from RefProp (licensed, of course)
    When I say "mostly" it's, as some of you may have noticed, because for the transcritical range in CO2 we had to work a bit differently.
    But again, try check out the Aserep stuff:
    https://www.ilkdresden.de/en/project/software-modules/
    Last edited by deulengame; 18-05-2018 at 11:39 AM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •