# view factor to sky: how to calculate?

• posted

Hi all,

I am wondering how I can calculate the view factor for some easy applications. In this case, I am trying to calculate view factors between surfaces on earth and the sky.

In the literature I found that the view factor between a surface inclined at slope b and the sky is as follows: F1 = (1 + cos(b)) / 2

And between the same surface and the ground: F2 = (1 - cos(b)) / 2

My questions: (1) How are these view factors calculated? (2) How can I calculate more complex view factors? E.g. if there is some object between the inclined surface and the sky producing some shadow on it (so part of the sky is not visible).

Thanks a lot for your help & comments! Jens

• posted

Dear cool.bambus:

snipped-for-privacy@web.de wrote: ...

Google: calculate "view factor"

27,100 hits.

Same way.

David A. Smith

• posted

Look in any book on radiation heat transfer, or just about any book on general heat transfer.

book gives the formula and several worked examples.

It's rare to sit down and integrate to find a view factor. Books on heat transfer and handbooks list pages of view factors for different geometries, and there are some tricks you can use if the exact situation you need isn't in the table.

By the way, some people call them "configuration factors" instead of "view factors".

Olin Perry Norton

• posted

Olin,

thank you for the hints and for the link to the book. This was a really good source of information. I hadn't thought I'd gone into such a weird topic... So thanks a lot!

David: I had been googling for quite a while without getting a good answer to what I was looking for (not view factors in general, but to the sky). I usually do that before posting to the usenet ;-) I should have mentioned...

Jens

Ol> You can download a good heat transfer book

• posted

Dear cool.bambus:

If it was easy, they wouldn't call it "work". And they wouldn't pay you.

I assumed you had. But you can get very frustrated if you do not form a specific search phrase. I supplied one that could cut your search time down, maybe getting good hits on the first few pages of hits.

I miss AltaVista, where you had all the power of Google, and the keyword "NEAR", that would let you find one word NEAR another (say 10 words either direction). There are PC-based solutions that you can obtain to do this, but...

David A. Smith

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