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  1. #1
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    Right Pipe dimensioning



    Hello RE !!

    I am currently in the process of creating and dimensioning a AC unit, for the first time, and I have some questions regarding the pipes that are to be used.

    The AC unit is to be used to Telecom cooling, and are designed to deliver 0.2 kW cooling, since it is for telecom cooling our main focus at this point is too keep it very compact, and therefor we are using a SECOP compressor called BD1.4 VSD 24VDC, and we use R134a as refrigerant.
    The AC unit are to be deployed in deserts, jungles, and other harsh enviroments, so the ambient temperatures are pretty high (50 degree celsius), and the evaporator temperature has to be around 15 degree celsius, because this would deliver to optimal temperature to the electronics needed to be cooled.

    As of right know we have dimensioned most of the system, and are now in the process of trying to figure out what specific components that we need to source, but we still need the correct pipe size.

    We have a little trouble dimensioning the pipes of the system, we have used a program called CoolPack (made by the department of mechanical engineering, technical university of Denmark), and when plotting in the data, the only feasible pipes that we can use is as follows:
    Suction line: 3/16" gives a velocity of 7.5 m/s
    Discharge line: 1/8" gives a velocity of 8 m/s
    Liquid line : 1/8" gives a velocity of 0.5 m/s

    These pipes seem awfully small to us, but since we are new to this, we would like a second oppinion on it, hope you are able to help !! :-)

    Regards Woot



  2. #2
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    Re: Right Pipe dimensioning

    Use 1/4" throughout the system. The internal volume of such small tubing is small enough that oil issues are unlikely.

    You can also look into using R600a, which would decrease your operating pressures and make it even less likely for there to be any oil issues.

  3. #3
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    Re: Right Pipe dimensioning

    But would that not cause the velocity of the fluid to be even lower than the one i already specified, and wouldnt that have negative impact on the system?
    R600a is not an option, the customer will only accept R134a.

    Regards
    Woot

  4. #4
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    Re: Right Pipe dimensioning

    I forgot to say that the pipes given is the outer diameter, and with a thickness of 0.75mm for the 3/16" pipe, and 0.7mm for the 1/8" pipe.

    Regards

  5. #5
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    Re: Right Pipe dimensioning

    1/4" is simply too small for oil issues to be likely.

  6. #6
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    Re: Right Pipe dimensioning

    But according to CoolPack, the velocity with this pipe size, would be as follows:

    Suction line: 2.1 m/s
    Discharge line: 0.6 m/s
    And the liquid line is so small that the program cant even calculate it,

    I am sorry but i cant really understand how this would be sufficient?
    Is it just because the pipes are so small that the fluid dont really need any velocity to drag the oil around, and thereby we can just choose an standard pipe? or is this wrong?

    Regards
    If the facts don't fit the theory, change the facts.

  7. #7
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    Re: Right Pipe dimensioning

    The tubing is so small that it simply won't hold much oil. The liquid line is a complete non issue since the liquid refrigerant is a good solvent.

  8. #8
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    Re: Right Pipe dimensioning

    okay, so for small systems, you simply skip the math and just go with some standard solution because it will be sufficient?

    Wouldnt the there be any negative results of choosing pipes that are overdimensioned?

    Regards
    If the facts don't fit the theory, change the facts.

  9. #9
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    Re: Right Pipe dimensioning

    From solken program , suction line 8 mm , discharge line 6 mm, liquid 6 mm .......

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