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  1. #1
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    Ultra low temperature



    Dear All,
    Do friends have any experiences about ultra low temperature ?
    There is cascade system that using R404A in high temp. cycle and R23/R13/R508A/R508B in low temp. cycle.
    Also there is R290 in one stage cycle (ultra low temp. freezers) to reach to lower that -80.

    Are there any other ways and cycles ? Do you have any other experiences to share it with me and others ?



  2. #2
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    Re: Ultra low temperature

    .

    The most common way is to use a cascade system
    and mixing the refrigerants is the way to establish the
    correct pressures and temperatures.

    But one method I have seen on one ultra low temp system,
    down to about -120 C was to use one compressor and then
    blended refrigerants that evaporate at different stages inside
    the evaporator and the result is an evaporation temperature
    down to about -120 C.

    The refrigerants were blended by a consultant and it was used
    to dehumidify instrument lens and was critically charged.

    Rob

    .
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  3. #3
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    Re: Ultra low temperature

    Dear Rob,
    Thanks for your reply, It was interesting way ! I have not seen cycle like that !

  4. #4
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    Re: Ultra low temperature

    .

    I had not either until this.

    My company were asked to design and build an ultra low temperature machine
    and they worked with a very intelligent consultant who mixed his own blend
    of 3 refrigerants.

    It had a 30 or 40 kW compressor with an air cooled condenser, it had one receiver
    but a multiple pass evaporator and the refrigerant blend then boiled at different
    temperatures and the result was a final temperature of about -120 C.

    Very interesting, even from my limited knowledge of it, but they made about 8
    units and they were exported out.

    Rob

    .
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  5. #5
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    Re: Ultra low temperature

    ​Dear Rob,

    Would it be possible to explain with a sample, What actually happen when 2 or 3 refrigerant in a blend evaporates in different temperature and their boiling temperature be different ?
    As you know in Zeotropic refrigerants such as R407C or R410A , Refrigerant is blend but boiling point of elements in blend is near to each-other.
    Now what happen when boiling point of elements of blend be different ?

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