Thermal Conductance Value (Approriate Modeling?)

[Transient1]

Hi all,

I am modeling two aluminum plates (.125 in thick, 1.048 in tall,2.25 in long) connected at a right angle to each other along the short side. There are three fasteners spaced evenly (NAS 662 Flat Head Screws (100°)). I take the thermal resistance to be L/kA with its inverse being the thermal conductance. For L I use the thickness of the plate (.125"). However, the units of this formulation are (m)/((W/m/K)(m^2)) giving W/K. ANSYS requires thermal conductance in W/m^2/K. So if I leave out the Area, the units are correct but then it seems that ANSYS is always using a Wet Interface (i.e. all the area around the bolts) but I want to represent a lesser area (a circle around each bolt whose diameter is 2*bolt diameter). Any advice is appreciated.

 

[Stringmaker]

Wow! You've managed to confuse the heck out of me. Yes you're right that Ansys uses the "wet" area as you put it...or rather the area where it sees contact as the area where heat can transfer. I'm really confused about how a lesser area would have twice the diameter like you explain in your second to last sentence but I do have a couple suggestions to offer:

a) Scale your thermal conductance values to give you the desired result at the respective interfaces (ie. you may have to define more than one real constant set to apply to your contact elements). Or if you're using Ansys WB this is super easy.

b) Create custom contact or custom contact components so you have complete control over where conduction can and cannot occur.

-Brian

 

[Transient1]

Thanks for your help . I'm not sure what the confusion is. In one case the thermal conductance is considers the entire interface area and in the other case it is not. I conservatively consider twice the bolt diameter as the effective area around each bolt where heat transfer occurs. I had thought about just scaling it and I wanted some one else's input.