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How to calculate thermal exchange rate of Air?

  1. Feb 15, 2013 #1
    How would I calculate thermal exchange rate of Air for different amounts of humidity?

    I'd like to create a graph to show how much radiant heat air would absorb, (at some temperature (10°C) changes depending on the humidity amount, 0 - 100%
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  3. Feb 15, 2013 #2


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    Air in which setup?
    Heat capacity changes as function of humidity, you can find formulas somewhere in the internet.
  4. Feb 15, 2013 #3


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    The difference is not significant for most ambient temperatures/humidities. In English units, it is about 1.082 BTU/CFM-F
  5. Feb 16, 2013 #4
    For air at SAP at MSL ?

    I've looked in the internet and haven't found it yet...
  6. Feb 16, 2013 #5


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    Are you looking for the Specific Heat Capacity of humid air?...

    See reply 4...


  7. Feb 18, 2013 #6
    As I understand it, dry air is heated by radiation by some small amount and 100% humid air by a greater amount?
    So I should be able to find or create a formula to make a graph showing the change from 0 to 100% humidity (or find a graph)?
  8. Feb 18, 2013 #7
    You are forgetting about other, more important, heat transfer mechanisms like conduction and convection. In most practical situations, these will dominate over radiation.
  9. Mar 26, 2013 #8
    If there are measurements or calculations to show how much they change (if any) depending on the amount of water vapor in the air? I'd take that as well.

    But I was looking for how much the air would be warmed by IR radiation, and then that heat would be transferred by conduction and convection.

    Seems as tho if I knew what amount of IR radiation would be absorbed by a sample of air that was 1% water vapor, that I would just double that to estimate it for 2% water vapor?
  10. Mar 26, 2013 #9
    Sorry. I was confused about what you were asking for. For what you are asking, Google
    Water Vapor Infrared Absorption Spectrum. Of course, this is just the basic property data. You still need to know how to apply the data in modeling atmospheric heating.

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