Comsol Transient Heat 3-D, Data does not make sense

[zer0c123]

I'm working on a project to study the heat transfer of a connecting rod using comsol. Basically starting at a temperature above melting point of AISI steel 4340 and then cooling to room temperature. I'm using temperature dependent equations in my simulation; however, simulations show that it takes maybe 1*10^7 seconds for the model to cool.


As a check to make sure I'm using the software correctly, I modeled a simple cube 1x1x1 dimensions. Inserted constant properties for AISI 4340 material. Boundary conditions of convective heat transfer coefficient of 100 W/m^2*K. Surrounding temperature is room temperature. I ran the simulation for a time of 7200 seconds with steps of 1. I set an initial temperature of 1800 K.

A sliced plot shows that the interior of the cube is at ~1466K, while the exterior is at 900 K. I must be doing something fundamentally wrong with the software if a simple case does not work.....

 

[jhardy1]

This could be an issue of appropriate units. It would take a 1 m x 1 m x 1 m cube of steel an AWFULLY long time to cool down to ambient temperature by convective cooling alone. Try using a 100 mm x 100 mm x 100 mm cube, and see how it goes.

 

[zer0c123]

Hey thanks for the tip. I ran the simulation again as a 100mm x100mm x 100mm cube and the results totally make sense now.

Now I have to go back to the connecting rod model. If units are indeed the case for the long cool time, then something must have went wrong when I imported my solidworks CAD model into Comsol.

 

[jhardy1]

Check your units on the CAD import - e.g. if the SolidWorks CAD model uses mm as the dimension unit, but your FEA assumes metres, you are modelling a truly HUGE con-rod, and its cooling time would indeed be very long.

Hope this helps.

 

[zer0c123]

Yea it makes total sense. I won't have access to solidworks until tomorrow, but I already know the units are wrong in Comsol. The scale on the side of my model in comsol is from 0-216 m! I really wish it was labeled visually with units, but other programs, such as, Ansys and Abaqus don't do it either.

Thanks

 

[FeX32]

That's a common hickup with Comsol. Use mm in Solidworks.


Fe