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  1. #1
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    best way to design condensor, evaporator and compressor sizes


    Hello again,

    My refrigeration project is coming along but I need some guidance on the best way to mathematically model the size of the condenser, evaporator and compressor.

    I originally thought that using the thermal load that I needed to move out of the milk ( roughly 80W), along with the type of condenser cooling I would plan on using (forced air), would be enough to determine the condenser and evaporator sizes. I have not found that to be true so far.

    Are there any obvious resources that I have missed? I would really like to calculate everything mathematically and circumvent previously obtained models but I would like to see the models for comparison to my numbers.

    Thanks again for your help. I look forward to the comments.



  2. #2
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    Re: best way to design condensor, evaporator and compressor sizes

    *condenser

  3. #3
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    Re: best way to design condensor, evaporator and compressor sizes

    you could give us more info, like u deduced 80 W for what quantity ,how stored and what temperature
    if your evap is air cooled it mens it is stored in a storing facility, what is it built of and so on

  4. #4
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    Re: best way to design condensor, evaporator and compressor sizes

    sorry about the lack of details.

    - i planned on having the condenser air cooled
    - the evap will sit inside milk (with a fan to prevent freezing and to promote better heat transfer)
    - milk is to be held at 38F
    - the thermal load was calculated and can be seen in the mathcad file below
    - i planned on using a Danfoss BD50F compressor because its manuf. specs. claimed that it can handle 120W of cooling...a good safety factor i thought.
    - planned on using R-134a but this is only because the compressor runs on this and i was familiar with the refrigerant due to thermodynamics (any help here would be greatly appreciated)
    - elevation is roughly 1500m
    - average ambient temp is 60F

    Tell me if this is correct:

    1. find the ambient temp and create a safety factor for the condensation temperature. (i want to be outside the dome (liquid side, subcooled)) leaving the condenser
    Ex. ambient temp: 95F
    condensation temp: 110F (safety factor of 1.15)

    The safety factor here is to allow for adequate flow through the expansion valve. Without it, the refrigerant will lose too much pressure and there will not be a big enough pressure drop across the expansion valve.

    2. a. determine the pressure drop across the condenser due to the cooling and then;
    b. determine the temperature i need the evaporator to be in order to cool the milk to 38F.
    c. determine the pressure drop needed across the expansion valve to get the required temp along with vaporization of the refrigerant

    these values should be able to be found in refrigerant tables.

    3. from this information i should be able to start sizing the condenser and evaporator.

    Thanks and I hope I didn't confuse anyone.
    Attached Images Attached Images

  5. #5
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    Re: best way to design condensor, evaporator and compressor sizes

    Safety Factor?
    I refrigeration system is a circular reference.
    You have stated a load 80w and a compressor of 120w, which by the way means nothing unless it is at some form of rated condition.
    What you are trying to achieve is an equalibrium which is with in comp specs and possibly efficiency.
    You have to draw a line in the sand as a starting point.
    Do base design best guess (choose cond and evap) then balance, change evap or cond to achieve desired results. each part effects the other.
    When you think you have found a balance, simulate at other working conditions (if in spec then all good)

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