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Fridge Thermodynamics

  1. Jan 8, 2015 #1
    Hi Guys

    I have a relatively simple question (I think!),

    I am trying to calculate the amount of time it takes for a fridge to cool 1m3 of air from 20°C to 3°C while running a fridge's compressor at 200 watts

    I have calculated this using T = E/P

    From this I am trying to work out the time this 1m3 of air will take to go through the piping system within the fridge using;

    Flow rate = Volume / Time

    I'm having trouble with putting all of this into practice, any help would be appreciated.

    Jim
     
  2. jcsd
  3. Jan 8, 2015 #2

    mfb

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    Without more data, this won't work.
    I guess the air is not going through the compressor, it gets cooled with a separate cooling cycle? Either way, you'll need data how efficient the fridge is, this will also depend on the temperature difference.
     
  4. Jan 8, 2015 #3

    Mech_Engineer

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    Gold Member

    Air doesn't have a very high specific heat capacity, so I'm thinking you'll find that a general refrigerator will be able to cool a cubic meter volume pretty fast. However, if you take ainto account a body of food in it (especially one with high water content, even a gallon of milk) it will take significantly longer to cool.

    If you make some assumptions about the typical efficiency of a fridge (maybe using the refrigeration coefficient of performance equations), you would be able to get a rough estimate of the time involved.
     
  5. Jan 8, 2015 #4
    You can't calculate it from thermodynamic principles - it depends on the design and efficiency of the particular fridge. (How fast does the fan move the air, what's the surface area of the cooling coils, what's the temperature of the room, etc.)

    If this is more in the nature of a test question, perhaps you can assume ideal efficiency, but you still need the room's temperature.
     
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