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Simulating a Solar Greenhouse
Posted 12.08.2012, 01:44 GMT-4 Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD), Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.4 2 Replies
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I am very new to Comsol and I am trying to simulate heat transfer inside a solar greenhouse. I would greatly appreciate any help or advice. I am using Comsol 4.3 Class Kit License (CKL).
My first question is: how do I incorporate solar radiation in the simulation?
I found this on the web: www.comsol.com/blogs/heat-transfer-accounting-for-the-radiation-of-the-sun/
However, I couldn't find External Radiation Source anywhere in the program.
So far I have added Conjugate Heat Transfer (Low Re k-e Flow) physics (Transient Study) to the model, specified the domains for solid wall and fluid as well as the initial temperature and inlet velocity. I could not find the External Radiation Source mentioned above under Conjugate Heat Transfer.
Is it possible to use Inflow Heat Flux on all the walls to simulate solar radiation?
Again, I would greatly appreciate your help. Thanks in advance.
Amar
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it depends on your version and how you intend to model your input heat flux, in V4.3 you can get COSMOL to calculate the nominal solar heat flux for a given location (latitude) and time of the day/year, for earlier versions you must provide the solar heat flux value as a scalar, or a look-up table interpolation function, or by some other equation.
If you ignore the "air" absorption you can say your solid surface receives a heat influx from the sun, and probably is "cooled" by a natural convection, either one of the pre-cooked formulas, or by some h [W/m^2/K] that you know.
If you want to exchange via radiative exchanges, you need to turn that physics "on" by adding a check in the main HT physics node, then you can use these highly non linear formulas, but you also need to carefully define manually how the radiation bounces off the different surfaces, which are participating etc, quite a job, I suggest you start without, then when you are happy with your model, you can add radiation, step by step
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Good luck
Ivar
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External Radiation Source is an option as a part of the surface-to-surface radiation physics. It is included in the physics called "Surface-to-surface Radiation" and "Heat Transfer in Solids with Surface-to-surface Radiation". The other option is to use a Conjugate Heat Transfer physics and tick the box for "surface-to-surface" radiation.
One thing that is irking me right now is that I have discovered that the option to set it as "Solar and Ambient" seems to be missing when you put it in as part of conjugate heat transfer, as opposed to using a proper "Surface-to-surface" physics. It seems that the only way to have "Solar and Ambient" and volume force (and hence natural convection) in the same model is to use both "Conjugate Heat transfer" and "Heat Transfer with Surface-to-Surface" physics together in a multiphyics model.
Has anyone come up with a more elegant method of having natural convection and solar radiation in the same model?
Thanks!