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  1. #1
    rohit_k's Avatar
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    Question Air Cooler -40°C



    I want to generate a cool air of temperature -40°C continuously at a rate of 1000L/min. Please suggest me the system to use for this purpose.



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    Re: Air Cooler -40°C

    use R -507 a

    Boiling point: -47.1

  3. #3
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    Re: Air Cooler -40°C

    Some more information would be useful.

    What is the entering air temperature, for example.
    Brian - Newton Abbot, Devon, UK
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  4. #4
    rohit_k's Avatar
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    Re: Air Cooler -40°C

    I'm from India. So the entering air temperature will be a room temperature from 25°C to 40°C.

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    Re: Air Cooler -40°C

    What are you trying to cool?

    If it is a space/room, can the air not be recirculated to save energy?
    Brian - Newton Abbot, Devon, UK
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  6. #6
    rohit_k's Avatar
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    Re: Air Cooler -40°C

    Actually I want to cool a laser head of a machine. So the air cannot be recirculated. Can you suggest me how to generate the cool air & what will be the setup?

  7. #7
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    Re: Air Cooler -40°C

    Quote Originally Posted by rohit_k View Post
    I want to generate a cool air of temperature -40°C continuously at a rate of 1000L/min. Please suggest me the system to use for this purpose.
    Kindly inform about the load factor. Air to be recirculated and inlet temp of air.

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    Re: Air Cooler -40°C

    load is approx 3Kw
    You need a very deep evap coil.

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    Re: Air Cooler -40°C

    I'm afraid a 80K cooling in one pass is some sort of a challenge.
    dry air has got a specific heat of 1 kJ/Kg K.
    Density varies considerably across the temperature range, from 1.1 to 1.5 Kg/m3, with an average of 1.3Kg/m3 or 1.3x10E-3Kg/l

    80k x 16.6 l/s x 1.3x10E-3 = 1.7 kJ/s that is 1.7kW, which is away from the 3kW you say, if my calculation is right.

    The point is that in India air is very moisty and you would end up with a frosted coil in minutes or seconds.

    I would suggest to buy liquid nitrogen and evaporate it on your laser.

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    Re: Air Cooler -40°C

    Quote Originally Posted by NoNickName View Post
    I'm afraid a 80K cooling in one pass is some sort of a challenge.
    dry air has got a specific heat of 1 kJ/Kg K.
    Density varies considerably across the temperature range, from 1.1 to 1.5 Kg/m3, with an average of 1.3Kg/m3 or 1.3x10E-3Kg/l

    80k x 16.6 l/s x 1.3x10E-3 = 1.7 kJ/s that is 1.7kW, which is away from the 3kW you say, if my calculation is right.

    The point is that in India air is very moisty and you would end up with a frosted coil in minutes or seconds.

    I would suggest to buy liquid nitrogen and evaporate it on your laser.
    80C single pass is not an issue1
    Yes your calculation is right, apart from the air is not dry, you must include humidity, water and ice then load is approx 3KW (of course depends upon original RH, for this calc 40Cdb 70%RH)
    If the coil was at one low temp then you would have a frost loading of aprox 2.1Kg/hr.
    With one pass air systems with big TD you should have at least two coils , 1st stage SST just above 0C and low face velocity (no water carry over) this reduces frost loading
    Second stage needs to be around -48C (care has to be taken on evap(refrigeration) pressure drop.
    The arrangement needs to be reapeated twice to allow for defrosting along with appropriate air dampers
    Last edited by mad fridgie; 19-06-2010 at 11:38 AM.

  11. #11
    rohit_k's Avatar
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    Re: Air Cooler -40°C

    Can you guide me about the system setup?
    Which compressor & refrigerant to use?
    Compressor capacity?

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    Re: Air Cooler -40°C

    Quote Originally Posted by rohit_k View Post
    Can you guide me about the system setup?
    Which compressor & refrigerant to use?
    Compressor capacity?
    May I suggest you employ an expert in refrigeration, this type of project even though is small, still needs a high level of knowledge.

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    Re: Air Cooler -40°C

    Definitely. Multipass refrigeration is quite a challenge for anyone, let alone rookies.

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