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Discussion on the Validity of Radiation Heat Transfer Modeling Under Cloudy and Clear-Sky Conditions

Posted 2025年3月20日 GMT-4 05:15 Heat Transfer 1 Reply

Ying Z
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Hello everyone,

I am using COMSOL to simulate radiative heat transfer and analyze the radiative performance of a sample under both cloudy and clear-sky conditions. I have obtained surface irradiance data for both cases and am conducting simulations using surface-to-surface radiation heat transfer to evaluate the effects of different atmospheric conditions.

In my model, I consider radiative counterpart temperature and external radiation source irradiance as the primary variables:

For clear-sky conditions: The radiative counterpart temperature is set to outer space at 3K. The external radiation source irradiance is taken from clear-sky surface irradiance data. For cloudy conditions: The radiative counterpart temperature is set to the cloud layer temperature. The external radiation source irradiance is taken from cloudy-sky surface irradiance data.

I have the following questions and would appreciate any insights:

  1. Are there similar application cases that I can refer to? If so, is my modeling setup reasonable?
  2. Since the surface irradiance already accounts for atmospheric absorption and scattering, is it appropriate to use surface-to-surface radiation heat transfer (which neglects the effects of the medium) for this simulation?
  3. In my model, I only vary the radiative counterpart temperature and assume both the cloud layer and outer space are at an infinite distance. However, clouds are much closer to the Earth's surface than outer space. Is this assumption valid, or should I consider the finite distance of the cloud layer in my model?

Thank you for your time—I look forward to your suggestions!

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1 Reply Last Post 2025年3月21日 GMT-4 15:49
Walter Frei COMSOL Employee

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Posted: 6 days ago 2025年3月21日 GMT-4 15:49

Hello Ying,

Your description is for the most part reasonable.

There are in the literature many correlations and equations for the diffuse irradiance from the sky and it is a surprisingly complex topic, but your approach is conceptually reasonable. Unless you are dealing with something quite out-of-the-ordinary, the clouds almost certainly can be treated as infinitely far away.

Keep also in mind that the surrounding air temperature also needs to be considered and here also there is much data, and even more variability to that data. The additional heating due to ambient radiation is most likely going to represent a small variation on top of the variability of the convective heat transfer with the surrounding air.

Happy Modeling!

Hello Ying, Your description is for the most part reasonable. There are in the literature many correlations and equations for the diffuse irradiance from the sky and it is a surprisingly complex topic, but your approach is conceptually reasonable. Unless you are dealing with something quite out-of-the-ordinary, the clouds almost certainly can be treated as infinitely far away. Keep also in mind that the surrounding air temperature also needs to be considered and here also there is much data, and even more variability to that data. The additional heating due to ambient radiation is most likely going to represent a small variation on top of the variability of the convective heat transfer with the surrounding air. Happy Modeling!

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