Negative Kelvin temperatures in solution

[rogmitch]

Hi

I used Nastran for the very first time yesterday in the hope I could model part of a cryogenic instrument.  To understand the software I decided to model heat flow through a 1 metre cube of stainless steel.  Using SI units I apply 300K to one face and a negative heat flux to the opposite face.  Provided the heat flux is within a certain limits the results are as I expect.  However, increasing the heat flux I can establish negative Kelvin results for the cooled face-which is  obviously non-physical.  

Is there a way to limit the cooled face to positive Kelvin temperatures only?

As a side question-if I input a temperature dependence for the thermal conductivity of the stainless steel this dependence does not seem to be saved when I save the material as a nasmat file.  Am I doing something wrong or do I need to input the temperature dependence each time I create a model?

Any help with these two question would be appreciated.

Roger Mitchell

[John_Holtz · Accepted solution]

Hi Roger,

The software knows very little about physical limits. Therefore, your input has to mimic physical reality.

For temperature dependent properties, I agree that saving the material does not save the Table. My suggestion would be to save all of your tables in a spreadsheet so that you can copy and paste the data into the temperature-dependent table when needed.

[rogmitch]

Thanks John. Your answers are most helpful.  It is a shame that the program does not know about zero Kelvin  especially as I heard it was initially developed by NASA where a lot of 'space' components must be subject to cryogenic temperatures.  

Roger