Heat transmission problems among elements

[francesco_fasani]

Good Morning,

I keep running a Non linear heat transfer transient analysis on Inventor Nastran 2022. I have an assmebly model composed of multiple parts some of which are represented with shell elements (see picture) and the other are represented by solid elements. I applied a surface heat flux as load on 2 surfaces: the problem is that, from the resusts, it looks like the heat does not spread among the mesh elements (the only heated elements are near the heat flux). The model represents 1/16 of an insulated cylindrical vessel heated from the bottom with 2 resistances. I need to specify I put bonded contact with no separation between surfaces.

Do you have an Idea of where is the problem?

Inventor Nastran 2022 Version

HEAT FLUX LOAD

LOAD TABLE FACTOR VS. TIME

HEAT FLUX LOAD N2

INITIAL TEMPERATURE LOAD

CONTACTS

IDEALIZATION

RESULTS

[John_Holtz]

Hi @francesco_fasani . Welcome to the Inventor Nastran forum.

Did you check the material properties? In particular, the thermal conductivity (K) and specific heat (C). Whether the loads and contacts are right or wrong, the heat should still be conducting through the solid part with the heat flux. I do not see that happening which implies a problem with the material properties.

Other things that should be checked:

1. Seven time steps in 4500 seconds is a very large time step size. Did you try more time steps or smaller time step size?
2. Do all parts have contact defined with its neighbor?
3. What is the purpose of the shells? And where are they located relative to the solid? It looks like the mesh on the shell is different than the mesh on the solid which implies you created a separate surface for the shells. If the shell and solid are in contact, then the idealization for the shell should be using the surface of the solid, not a separate surface created in the CAD model. But if you do that, why even have the shells?

John

[francesco_fasani]

Good morning @John_Holtz ,

1. here follow the material properties related to 1) diatermic oil , 2) wax 3)rockwool 4)air 5) AISI 304 everything expressed in International system units C (J/kgk) ,K (W/mK). The values all look reasonable to me: do I miss something on this side?

1. I changed the time steps as follows but nothing seems to change in the results.

2. Yes, I did define contact between all parts. All the contacts are set to bonded.

3. The shell elements are put between the solid elements to simulate the thin layer of sheet metal (AISI 304) which constitutes the insulated cylindrical vessel. They were idealized by shells using the mid surface. In the picture the position of their surfaces is represented by the light blue dashed lines.

[John_Holtz]

The answer to question 3 is no -- the shells are not performing any function in the analysis. Shell elements have no temperature difference through the thickness. The heat is conducted from the solid through the contact to the shell through the contact to the next solid. You can remove all the shells from the analysis.

You should try the analysis with just the "green" part that has the two holes. It does not make sense that the part would heat up to 9000 K in one area but still be "cold" at whatever value cold is at another end (300 K, 800 K, somewhere in the blue region). Something is wrong: the dimensions, the heat load magnitude, something else? Hopefully you can determine what is wrong by analyzing that first part. (You can also do a hand calculation to approximate how quickly the first part will heat up. That will confirm whether the Nastran results are reasonable or not.)

If the analysis of the first part by itself (meaning opening the .ipt file and running the analysis on it) is still wrong and you do not know why, feel free to attach the .ipt file to the forum.

John