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Radiational cooling

  1. Nov 11, 2014 #1
    1. The problem statement, all variables and given/known data
    On a clear night, the loss of infrared radiation to space causes the loses 10 m of the atmosphere to cool by 5 K over 10 Hrs. Assuming a density of 1.25 kg^-3 for the air, what is the net rate of heat loss by radiational cooling, in Wm^-2 (Answer: 1.74 W m^-2)


    2. Relevant equations
    I know the first law of thermodynamics plays a role: dq = du + pda


    3. The attempt at a solution
    I believe the area is fixed so it will eliminate the second term leaving dq = du and du = CpdT leaving dq = CpdT. Since the net rate of heat loss is what we are looking for, it would be a change in hear over a change in time. So I have:

    Cp(dT/dt) = dq/dt

    then I tried to multiply the latent heat value by the (dT/dt) value to get dq but it did not provide the correct answer.
     
    Last edited by a moderator: Nov 11, 2014
  2. jcsd
  3. Nov 12, 2014 #2

    Bystander

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    "Latent heat value"? You mean CP? What value? "pda"? Check your units.
     
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