FEA vs CFD for heat transfer analysis
FEA vs CFD for heat transfer analysis
(OP)
Can anyone provide facts on which method is best for problems including convection heat transfer? Please no opinions!
Tunalover
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FEA vs CFD for heat transfer analysis
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RE: FEA vs CFD for heat transfer analysis
RE: FEA vs CFD for heat transfer analysis
Tunalover
RE: FEA vs CFD for heat transfer analysis
RE: FEA vs CFD for heat transfer analysis
I admit that I was "fishing" for a particular answer. Is it not true that with FEA codes one must provide the heat transfer coefficients? Doesn't the user usually have to calculate these coefficients from handcalculations?
It seems that an accurate mesh isn't worth much if the boundary conditions are "a leap of faith" from the get-go.
Isn't it true that Finite Difference Method (traditional CFD) codes simply have no need for convection coefficients because they get deeper into the physics of the problem where such simplifications are unecessary?
The reason I ask these questions is that my boss uses FEA to solve thermal problems and I've been arguing that we go with a FDM code that is designed specifically for heat transfer problems.
Are there any heat xfer experts out there who can confirm these beliefs with a theoretical backbone?
Tunalover
RE: FEA vs CFD for heat transfer analysis
RE: FEA vs CFD for heat transfer analysis
I spoke purely in context of heat transfer analysis. Are you saying that an FEA code will give just as good results as an FDM code for heat transfer problems involving convection?
Tunalover
RE: FEA vs CFD for heat transfer analysis
OTOH, if your geometry or flow does not follow the restrictions on the hand-calc equations, then CFD _may_ be the way to go.
I've done things both ways, and positively demonstrated both of these principles.
RE: FEA vs CFD for heat transfer analysis
The thing I am trying to hammer home is that you keep saying FEA code..there are FEA codes for fluid dynamics as well as structural mechanics. FEA is just a discretization method. What you should be saying are structural mechanics code vs fluid dynamics code.
RE: FEA vs CFD for heat transfer analysis
Tunalover
RE: FEA vs CFD for heat transfer analysis
corus
RE: FEA vs CFD for heat transfer analysis
The Reynolds Number, film coefficients, etc. are all conveniences created to express the behavior of fluids and heat on a piece of paper. Based on my limited exposure to them, true CFD codes utilizing FDM (or FVM) have no need for these terms; instead they discretize and solve select PDEs from the Navier-Stokes equations. These codes use more realistic boundary conditions (temperatures, heat loads, adiabatic walls, etc.). You won't find inputs in CFD codes for convection coefficients or Reynold's Numbers! Of course real problems sometimes mean even THESE boundary conditions are rough at best!
Tunalover
RE: FEA vs CFD for heat transfer analysis
It may be a limitation for finite element analysis (FEA) codes which solve problems in solid mechanics but not for finite element analysis (FEA) codes which solve problems in fluid mechanics...I'm going to keep bugging you until you stop associating the word FEA with solid mechanics..grrrrrrrr!!!
RE: FEA vs CFD for heat transfer analysis
On the rare occasions I have used CFD codes the only boundary conditions I was permitted to use were either fixed temperatures or a fixed heat flux. These were thus assumptions made about heat reansfer into the solid body. As you say they are a rough estimate of reality.
Likewise the heat transfer coefficients derived empirically can also be an estimate but I've always found good agreement with measurements where taken to validate models, even though I think measurements are equally erroneous and are at best an estimate too.
corus
RE: FEA vs CFD for heat transfer analysis
My answer is that if your geometry is close to the conditions under which the heat transfer coefficients are applicable, then you only need to model the solid. Other, you should model both the solid and the fluid together.
RE: FEA vs CFD for heat transfer analysis
Perhaps you can explain how I am associating FEA with solid mechanics. Did I mention stress, strain, or deflection? CFD codes usually discretize solids and fluids in the same model. What am I missing?
Tunalover
RE: FEA vs CFD for heat transfer analysis
RE: FEA vs CFD for heat transfer analysis
The near-wall modeling of flow fields requires certain assumptions be made regarding turbulence. The methods (e.g. kappa-epsilon models) typically provide an averaged or equivalent viscosity, and are "tuned" to provide the best results for flow field simulation, not for heat transfer. Further, the scaling of grids in near-wall zones to acheive the best resolution of flow parameters is not the same scaling as should be used to obtain the best resolution of thermal transfer. If you really want to hurt your brain on this topic, suggest you look at NASA and AIAA archives using "combustion" and "aero heating" in your search terms.
Most heat transfer models that are anywhere near succesful at prediction use some method of empirical "anchoring"; I would trust a CFD model heat transfer number much less than its flow numbers, and that is not very much without some test data and/or good old-fashioned engineering judgement and hand-calc's. to back it up.