Transient thermal analysis with cooling curve and custom materials failing

[vailo973]

Hello all,
I am trying to model the transient thermal response of a system being cooled with a cryocooler. I've simplified the model to a cylinder with one end being connected to the "cryocooler face".

First, I created a Custom Material and applied temperature-dependent curves for Thermal Conductivity and Specific Heat. Then I create a mesh and use a steady-state study so that the initial temperature at all elements to be 300K. I copy that study and change the properties so that it is a transient thermal analysis, set it for 200sec at 20sec intervals.

Whenever I run the simulation past a certain time step, the simulation either 1) gets stuck on a step or 2) returns an error. When I look into the data set, in the last two time steps the lowest temperature jumps from ~40-50K to the negative thousands of Kelvin.

Any help would be greatly appreciated!

 

[academix]

Hello:

What about the boundary conditions? If no convective boundary conditions are provided, then it is fully insulated.

Possible reasons for the issues could be:

1. Boundary conditions
2. Material property curve with points of tangent changes
3. Flux input
4. Time steps required to achieve stability

Hope this helps,

Best regards
Nat


Natarajan Ramamoorthy
Design Engineering Consultant

http://www.egsindia.com