ANSYS Workbench 10, convection question

[mleka]

ANSYS Workbench 10
Hi everyone,
There is something unclear about the way coefficient of convection is applied in ansys. When you add convection as environment under "Details" you have the option to have constant or temperature dependent convection. When I choose constant have to enter ambient temperature. What does this mean? My model is enclosed space between two concentric cylinders and in such heat loss due to convection is calculated differently. In this case does Ambient temperature means Film temperature for which I used to calculate h for this particular set up?
For the case of temperature dependent h, what is the function of ambient temperature? In engineering data I specify different h for different film temperaures. Which value will the software pick from the graph supplied? Will it pick the value for Ambient temperature that I specify?
I have experimental data for h due to free convection and a theoretical model that is agreeing with them, am trying to make use of this data for Ansys use so my fellow FEA analysts can also use them for their similar models.
Another concern is the calculation of heat losses due to convection, Ansys values do not agree with my model. I think that Ansys assumes open space for every surface where convection is specified and fails to recognise the proximity to other or enclosed spaces(from which air can not escape. In these cases fluid viscosity and path of air movement play a major role in heat losses. Does Ansys in any way accounts for this? Your help or opinions on the matter are appreciated.

 

[Stringmaker]

I've never done this type of analysis in Ansys. My work is almost purely structural with some relatively simple thermal analysis every now and then. But I think what you need to do is a multiphysics analysis. This analysis type is a coupled analysis where two solvers work simultaneously to converge on a solution. For instance, the convectional effects of a surface have effects on how air flows around the model and vise versa.
I'm not positive that Ansys Workbench has this capability. I do however believe that Ansys Multiphysics does. Do you have access to this software? I'm not sure if CFX has this capability or not but if you have these options available to you I would certainly page through the documentation.
During my time as an application engineer at Algor, I had the opportunity to help customers with similar analyses using the Multiphysics solver. This analysis type can be temperamental and a good solution may be difficult to converge upon at times. I would recommend that you have a high quality mesh for this problem along with a robust fluid flow solver.

Hope this helps,
-Brian

 

[mleka]

Thanks,
CFD software definitely would be necessary for this type of analysis. i might have to settle for a representation of air as a solid body and represent the heat loss due to convection as conduction. It would be constant in all direction but that is ok.