ANSYS Icepak - radiation from a wall shared by a sold block and a hollow block

[ReneZ]

Hi,

I have a question regarding the way Icepak calculates the radiation and heat transfer by convection on a shared wall.

I am interested in specifying a certain heat transfer coefficient and radiation for two walls of a solid block. This solid block is surrounded by another block, which can be either a fluid or hollow block. This means the solid block shares certain walls with the fluid or hollow block. My plan was to specify the individual sides of the solid block as having certain external conditions, in this case, a heat transfer coefficient at a reference temperature, and radiating to a reference temperature and a specific view factor. However, I am noticing something unexpected. When the surrounding block is a hollow, only the external conditions specification seems to be working, while the radiation seems to be completely off. On the other hand, when the surrounding block is a fluid, the external conditions specification stops working (apparently replaced by the convection effect of the fluid block), while the radiation specification starts to work.

I have to add that the solid block has a higher priority than either the fluid block or hollow block, thus the shared walls should have the specified conditions of the individual sides of the solid block (or at least this is what I would expect).

Could you explain to me why is this issue happening? Ideally, I would like to use a solid block surrounded by a hollow block. Nonetheless, I cannot simulate the radiation effect of the solid block, even when radiating to a reference Temperature.

FYI, I am using Icepak 17.2.

Thank You!
-René

 

[hendersdc]

A picture of your model would be helpful to understand what you are trying to do.

I don't have Icepak in front of me right now so I can't test anything out but I think what might be happening is that your hollow block is meshing on the shared surface regardless of your assigned priority because of the built in preferences in Icepak, you would run into the same thing with network blocks or other 2D objects. You can check this by reviewing the surface mesh of each component and see if there is a cutout in the hollow block surface on the shared face or not.

 

[ReneZ]

Hi hendersdc,

I just checked and I do have a surface mesh at the walls where I would expect to have radiation coming from or going in (see Fig 1).

(Fig1)

After further testing, I have noticed that the radiation at the walls looks to be slightly affecting my surface temperatures. However, the effect looks to be constant. This is, even when changing the reference temperatures or view factors (fig 2), the temperatures remain the same. In addition, a measurement of the radiative heat flow in that surface results in 0.0 W.

(Fig 2)

Looks to me like the presence of a hollow block in the model dominates the radiation calculation, regardless of the priorities set on the rest of your objects.

Any thoughts on this?

 

[IRstuff]

Some other views would be helpful; you know what is what in your figure, but not everyone else can read your mind.

Assuming that your verbal description is correct, two solids sharing the same wall cannot have a net radiation transfer, unless one of the solids is infrared transmissive or transparent. That's because physical contact implies they're at the same temperature, and the only mechanism at work is purely conduction. I can't tell if your "fluid" is air or liquid. If air, then there convection, and the surface temperature is different than the air temperature and the far walls, so a net radiation is possible. If the fluid is a liquid, then you still get convection, but net radiation is unlikely, since most liquids do not transmit in the infrared, and the intimate surface contact again makes the liquid contact temperature the same as the surface temperature.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm