## Simulation Mechanical and Multiphysics

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# Heat Flow Calculation

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Hello!

I have a question and hope that you will help me.

While doing some of the tutorials I came across the "Heat Flow Calculation"-setting in *Edit - Element Data**.* today, but although I read the paragraph about it in the wiki I still do not completly understand what it means. Can someone give an understandable explanation on the difference between *Projected at Centroid**, Nonlinear Based on BC* and *Linear Based on BC*?

Kind regards,

Walter

Solved! Go to Solution.

# Re: Heat Flow Calculation

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The wiki already gives the information for the basic differences. Here I am trying to clarify and help to understand the options.

To answer your question, some basic knowledge of heat transfer and numerical approaches need to be reiterated here.

(a) Three basic heat transfers and how the thermal BCs applied

Heat conduction, convection and radiation are three kinds of heat transfer. As a general thermal analysis package, we cover all of them including the corresponding BCs.

(b) Relationship between temperature and heat flux/heat rate

Heat flux is the temperature derivative in space, i.e. Heat flux=constant*dT/dx(Fourier's law), here T is temperature, from this point of view, they are dependent.

(c) Primary variable and derived variable in heat transfer and numerical analysis

In numerical heat transfer in FEA, nodal temperature is the primary variable to be solved in solver (major effort here) , while heat flux is the derived variable from above space derivative relation. As one of thermal boundary conditions, the radiation effect is enforced from heat flux of part exterior surfaces.

Note the three "Heat Flow Calculation" options in element definition are used to handle the thermal boundary conditions from radiation and convection, which bring nonlinear effect.

Here are the differences for three kinds of heat flux.

(1) Projected at Centroid

Calculate heat flux by nodal temperature at element centroid from Heat flux=constant*dT/dx(Fourier's law), and use it to calculate element face heat rate by

Element face heat flux= normal projection component of element Centroid heat rate *element face area

This is the regular expression in numerical heat transfer, and is used in thermal post-processor.

(2) Nonlinear Based on BC

To count the thermal boundary condition from convection or radiation loads, the heat rate (integration from flux) of the part exterior surfaces is calculated from convection, radiation boundary conditions and contribution of nodal temperatures as in (1)

The name of nonlinear comes from the nonlinear nature of radiation loads.

(3) Linear Based on BC

This option is close to (2) except heat flux on surfaces with radiation loads is linearized.

Principal Engineer

MFG-Digital Simulation

# Re: Heat Flow Calculation

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Thumbs up! Thanks for the good explanation!

Maybe some of the details could be merged into the wiki

Do you know if there are other documents available (e. g. course material), beside the official user guide and the wiki, from which one can learn how to use Autodesk Simulation/Multiphysics ?

Kind regards,

Walter

# Re: Heat Flow Calculation

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I also would be interested in finding some more literature that covers the setup of thermal analysis as well as dynamic MES analysis. Some more tutorials or course materials of that nature, downloadable or for purchase.

Thank you.

# Re: Heat Flow Calculation

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Take a look at the following link for In-person training: Training

You can also go through the training manuals on your own time by purchasing the books from the following e-store

-Sualp