Help with Transient Thermal Analysis

[dan240]

Hello,

I am using Simulation for a transient thermal analysis for the first time.

To start I am simply modeling a solid copper rod with a heat load attached at the end. The heat load (watts) varies as a function of temperature. The heat load is actually a cooling curve taken from one of our cryogenic cold-heads.

The question I have I believe is pretty basic but I am unable to figure out what I am doing wrong here.

I have applied an initial condition to all faces of the rod and set them to 293 Kelvin. My total time (just to start) is 100 s with 10 s intervals.

The part meshes and I am able to run the analysis. The results are not believable. The rod cools much, much to fast. At first I thought I may have the cooling curve improperly set up or possibly the material properties. So far I do not believe that is the problem.

I went ahead and suppressed the heat load altogether. The part should then sit at 293 K indefinetly. After running the analysis again I find out that it does not. After only a few seconds the part cools itself down to ~5 K.

Is there something in the initial conditions I am not setting up properly? I see that I am able to select faces, but really I need the entire volume to be set to the initial temperature. Is this the problem? Is the problem that I am not setting the entire mesh to the initial temperature? How do I do that?

Thanks,
Dan

 

[corus]

I suspect that the inernal nodes are initially set at 0 K with the nodes on the outer face at 293 K. With your large time step I'd imagine that the results would not be stable over the transient and that temperatures would oscillate as temperatures tried to balance between 293 and 0 K, and hence go negative. Use a smaller time step in your original analysis.

corus

 

[dan240]

Thanks Corus,

How do I set the internal node temperatures? I seem to only be able to select faces when I set up the initial conditions.

 

[dan240]

EDIT: I had to create an assembly and insert my single part. This allowed me to select entire components and not just faces/edges.

Problem solved, on to next problem.

Thanks