topic Re: Solar Wall material issue in CFD Forum

Solar Wall material issue

Anonymous — Thu, 13 Apr 2017 00:19:58 GMT

Hello,

I'm having some problems running a solar heating simulation.

I've already reviewed the AEC tutorials, and I've been trying to get something similar to work.

The thing is, I have an internal natural convection problem due to solar heating with a window. However, when I input the transparent BC to the external surface of the window and I try to run the analysis, it terminates due to "having put a transparent BC on a material with a transmissivity = 0".

I don't know if I've been doing something wrong, because I have selected the "Solar Window" material from the Autodesk Default Material List.

I ran the simulation without the transparent BC, however, no radiation energy seemed to have been let through the window.

Also, I noticed that the value of Transmissivity for the Solar window condition, is shown to be 0 (when I click on the list of properties while assigning the material to a solid). Is that the reason why I'm getting this error?

For the rest of the model, I assigned a custom steel material with a solar wall transmissivity condition. This is supposed to be heated by the sun radiation.

Can you help me with that?

Thank you,

Roberto

Re: Solar Wall material issue

Jon.Wilde — Thu, 13 Apr 2017 07:50:33 GMT

It sounds like you are using strange boundary conditions.

Some questions:

Are you modelling any external air?
Do you have solar loading on?
Are any of your boundary conditions internal? By this, I mean internal to the outer walls of the entire analysis - this is not permitted. I am not sure why you would need one applied to a window, this does not really make sense
Solar Window transmissivity is not zero by default, it should have a SHGC and a U Factor assigned. If you have 'zero' I would guess you assigned the wrong material? Below is what it should look like, by default

I hope this helps,

Jon

Re: Solar Wall material issue

Anonymous — Thu, 13 Apr 2017 17:54:50 GMT

Thank you for your reply!

1. No I'm not.

2. Yes.

3. They aren't. The transparent condition BC was put on the outer wall of the window.

4. See attachment 🙂

I have also attached the model in question. I ran the entire model with another custom material - One with a user input transmissivity of 0.3 and the analysis actually ran. However, it didn't seem to let any heat from the sun through.

Can you guide me more in detail?

Roberto

Re: Solar Wall material issue

Jon.Wilde — Thu, 13 Apr 2017 19:42:33 GMT

I would think you just need to remove the transparent BC, the solar windows are already transparent 🙂

I suggest you also keep an eye on the mesh - you might need a couple of elements through the thickness of those copper pipes to allow for a thermal gradient. An easy way to do this is either a uniform mesh or split the part into two in CAD (so you have a smaller tube inside a larger one).

It runs OK for me without that BC 😉

(Although your mesh is definitely too coarse - this looks 'lumpy')

Hope that helps,

Jon