Results 1 to 8 of 8
  1. #1
    fedri's Avatar
    fedri Guest

    pressure and temperature drops in R22 evaporator



    Hi, i want to know about formulas to calculate pressure and temperature drops in evaporator.



  2. #2
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,302
    Rep Power
    25

    Re: pressure and temperature drops in R22 evaporator

    The temperature drop is based on the differences in pressures due to the saturation temperatures of the specific refrigerant.

    The pressure drop is very complex as it is a two phase (liquid and vapor) flow problem. The pressure losses are normally limited to reduce the temperature penalty to a minimum so the heat exchanger performance is not drastically affected.

    The design value changes for the operating evaporating temperature and liquid feed type (DX, flooded, or liquid overfeed).

  3. #3
    Join Date
    Dec 2004
    Location
    Weihai,China
    Posts
    800
    Rep Power
    20

    Re: pressure and temperature drops in R22 evaporator

    It's too general question.
    The pressure drop affect directly the temp drop across the evaporator. It's needed to optimize the heat exchanger size and the pressure drop. I think you can get the formula based on the specified type of HX. There is no universal formula for it.

    rgds
    LC
    I hear...I forget;I see...I remember;I do...I understand

  4. #4
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,302
    Rep Power
    25

    Re: pressure and temperature drops in R22 evaporator

    If you want an estimated value without too much trouble do this....

    Figure the mass flow through the evaporator as all vapor.

    Find the refrigerant velocity through a single tube circuit.

    Find the Reynolds number of the flow through the circuit tube.

    Find the friction factor for the tube and inside surface of the circuit tube. You can find the friction factor by using the Moody diagram or the Colebrook equation.
    http://www.cheresources.com/colebrook1.shtml

    Find the pressure loss using the Darcy-Weisbach equation.

    http://arash.dejkam.com/software/pre...ss/methods.php


    To find the temperature loss find the saturation temperature for the entering pressure to the circuit.

    Also find the saturation temperature for the outlet pressure of the circuit.

    The difference in saturation temperatures is the temperature loss due to flow.
    Last edited by US Iceman; 11-05-2006 at 09:37 PM.

  5. #5
    Join Date
    May 2006
    Location
    Xi an, China
    Age
    51
    Posts
    65
    Rep Power
    19

    Re: pressure and temperature drops in R22 evaporator

    Hi guys,

    There is not only friction factor, but also a acceleration caused pressure drop, which is produced by gas velocity increasing. see this file
    http://fire.nist.gov/bfrlpubs/build01/PDF/b01078.pdf

    Then two phase outlet temperature got by its corresponding saturated pressure.
    Last edited by autt; 16-05-2006 at 02:23 PM.

  6. #6
    md.tanwir's Avatar
    md.tanwir Guest

    Re: pressure and temperature drops in R22 evaporator

    Hello. I am new to this site and I want to know how and where to write your messages. Plz. provide complete information.

    Thanks.

  7. #7
    md.tanwir's Avatar
    md.tanwir Guest

    Question Pump Head Calculation

    Any body who can clear my doubts in NPSH calculation for the pumps in reverse return system. Plz. see the attachment.

    Tanwir
    Attached Files Attached Files

  8. #8
    Join Date
    May 2006
    Location
    Xi an, China
    Age
    51
    Posts
    65
    Rep Power
    19

    Re: pressure and temperature drops in R22 evaporator

    Quote Originally Posted by md.tanwir
    Hello. I am new to this site and I want to know how and where to write your messages. Plz. provide complete information.

    Thanks.
    From this page,
    http://www.refrigeration-engineer.com/forums/index.php
    Select a forum, when new page appears press "New thread" on top left of list table to post you messages.

    I have seen your file, may be you can calculate every duct loss by its design flow and diameter, include fittings as bends, tee branches, valves and equipments etc, select the maximal loss for each parallel flows, so that to get the total loss, finally plus spare capacity to determine the pump head.

Similar Threads

  1. Pressure to Temperature Conversion
    By cryptojoe in forum Technical Speculations
    Replies: 5
    Last Post: 13-04-2010, 12:42 PM
  2. CARE refigerants by BOC
    By dogma in forum Refrigerants
    Replies: 8
    Last Post: 23-03-2010, 12:39 PM
  3. This a long one - AKV
    By Peter_1 in forum Industrial
    Replies: 6
    Last Post: 26-12-2008, 11:47 AM
  4. Q=? h1=? mechanical schematics
    By fridg in forum Technical Speculations
    Replies: 22
    Last Post: 19-03-2006, 01:43 PM

Posting Permissions

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