Thermal Transient Analysis

Cheeraxe1999

As I'm trying to wrap my head around this software, I've come across a conundrum in regards to Transient Thermal Analysis. The subject to be analyzed is a metal duct wrapped in fiberglass with a thermal resistance element on the inside. For some reason, whenever I attempt to solve the problem, the result is always impossibly low - I'm working in Fahrenheit, and I always get a uniform temperature of -459 F or so throughout the pipe after the program has run its course. Is there any fix for this? Something I missed? Attached is the file.

Victor

You may be only looking at the first time step which shows the initial state. Dragging the slider on the timeline at the bottom of the screen shows higher temperatures.

You may also want to set an initial temperature on all elements instead of the default which is 0 K (-460 F). Select all elements, then right click Initial Conditions in the outline tree, and pick New temperature.

Cheeraxe1999

That's it! So the default is what my problem is. Thank you! Wasn't entirely certain I needed that - but thank you for confirming.

Cheeraxe1999

I'm still having issues with this - the temperature range is still way off. I changed the initial temperature on everything I could - still have no idea where the -880 F is coming from.

Victor

The initial temperatures don't cover the entire model (all nodes) so some parts, especially the interior, are still at the default 0 K and the extreme temperature change between 20°F on the surface and a uniform -460°F on the interior causes error.

Use elements instead of faces and preferably give them all (Ctrl-A for select all) the same temperature.

If you do need a non-uniform initial temperature, a safer way is to do a steady state analysis to obtain a realistic smooth temperature field between all the fixed temperature surfaces, then transfer that solution to the initial temperature for transient analysis. That way, there won't be abrupt changes in temperature that can cause the large errors.

Cheeraxe1999

Excellent! I shall proceed with the second option. Thank you for taking the time to answer my questions.

jbmag

Hi Victor,

Is it still possible to add an initial temperature? I seem to be either missing the option or more likely I have missed something.

jbmag

Okay - the solution in case someone else comes looking is to select the elements then right click the initial conditions in the left panel and then you can add in the initial temperature.

Personally I think would be good to also have the initial conditions section in the right click menu but glad I got it working!