Free convection BCs
 

Hello, let's say I would like to model an object that is heated that is exposed to the air around it. Heat transfer is in the form of free convection off the object. If one were to model the air volume surrounding this object what are some general guidelines? For example if the object were 1 x 1 x 1 m how big would the air volume around it typically be? Also, what type of BCs would one use on the extremities of the air volume? If anyone knows of some public tutorials similar to this I am all ears.

Currently I have casting that I modeling in CFX (I need CFX since air is present inside the casting). Right now I have heat transfer coefficient BCs on the casting fins or boundary. These were confirmed with some lab test data and calculated the standard way with Nusselt nos., etc., but I would like to actually see the airflow coming off the casting someday to see if all the fins are effective. Thus the desire to model the surrounding air.

Thanks,

Craig Hildreth

Re: Free convection BCs
 

Hi,

The required size for the surrounding domain is problem dependant so you need to do a sensitivity check to establish the necessary size.

If you are looking for the details of flow in small cooling fins on the body then I would guess it could be fairly small (maybe extending 1m each side from the body based on a 1m body). You would need to check that - this is only a starting point.

Glenn Horrocks