can you post screenshots of each of your inputs
and a picture of the mesh
and a picture of the study properties
Hi Marco: Try steady-state, first, to make sure it will run through and provide a reasonable temperature distribution at time t=infinity.
(then later you can do the "on" and "off" transient analyses).
Perhaps just apply convection on one or two of the fins to see if that works - the "all surfaces" may not solve realistically (i.e., where the LED is mounted you can remove convection from there).
As one check, I recall there is a list result or probe tool so you can check that power out = power in. I believe you will need to manually select all surfaces on which convection is defined, and right-click on the results icon and look for a list function - and it will provide a total power going out of those surfaces.
First of all thank you for your replay's.
I have made a screenshot of all the inputs and I tried first the stready state simulation.
Here we go:
Okay that's nice!
Lets try to put convection at all the fins!
Okay looks good. The Temperature also looks very realistic.
Lets try a tranient simulation!
What I'm a doing wrong?
I like the results of the steady state simulation, but i need the results for the transient simulation.
The temperature is minus degrees?
I hope this is enough information
apply initial temperature to the body instead of the faces
yes do what Jared indicated. There should be a 'entire body' option, or 'whole body'. it will apply temperatures to nodes inside the volume. You may have to select a feature in the tree that represents the whole body.
For trouble-shooting, set the element type to be the Tetra4 (the opposite of the 'high quality' mesh). The Tetra4's run very, very fast so you can obtain quick turnarounds and trouble-shoot. Also, I don't believe the first time step will be anywhere near accurate due to the large delta-t, so you could try a 300 second integration at 10 second intervals and see if that gives you something a little better, plots starting at time step number > 1.
Also you can probe the 3D plot to generate a 2D graph of the temperature at a node on the fin as a function of time and see if that looks reasonable.
Hope that helps.