Heat flux across a face selection

DaveStupple

Hi, any steer on how to get a figure for, say, heat Flux X across a face selection? I can get a table of node or element values from the selection, but summing either of these and dividing by the area does not give sensible answers (way too high.

Cheers, D

Victor

The heat flux is already given in the solution and it doesn't have a single value for a surface. Do you mean average heat flux? Or heat flow rate, with units of power? In the latter case, you need to integrate the heat flux X values. There's currently no simple tool for that but here are a couple of ways:

A ) If it's a uniform mesh, especially with linear elements, you might get away with averaging the heat flux X values of the nodes to get average heat flux. Multiply that by the area of the surface to get heat flow rate. The disadvantage with this way is that it weights each node equally in the average so a varying mesh density over the surface will cause error.

B ) More accurate, especially for complex geometry:
1. Extrude a thin layer of elements from the surface
2. Create a new component for the extruded layer.
3. Move the boundary conditions to the new surface.
4. After solving, use Tools -> Mean to get the average heat flux in this thin layer. Again, multiply that by the surface area to get heat flow rate.

DaveStupple

Thanks Victor. It is heat flow rate I am after, and I should have been averagiing rather than summing. Doh! I blame too many hours sitting in front of a screen in a hot office.

DaveStupple

Method A: I have a uniform mesh but with quadratic elements. This method overestimated the total power by a factor of about 2. This seems quite a big error. I might have made a mistake in the calculation, or it might have something to do with the number of nodes at edges that are shared between faces. 'Heat flux X' in my original question was an oversimplification, as each surface that I am interested in is made up of several faces in different orientations.

Method B: This estimated the total power to within 0.001%, so perfectly happy with that.