Heat solve with phase change - additive enthalpy and capacity?

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NJank
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Joined: 05 Dec 2009, 00:05
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Heat solve with phase change - additive enthalpy and capacity?

Post by NJank »

I for the first time took note of a statement in the Heat Equation docs stating:

"Note that for the current implementation of the heat equation heat capacity and enthalpy are additive. So if heat capacity is present in the command file it should not be incorporated to enthalpy as an integral."

I have been specifying Enthalpy and Effective Heat Capacity as required by the Transient Phase Change model, as per this discussion: viewtopic.php?f=3&t=2345

Using this, where enthalpy is the full enthalpy definition including solid and liquid sensible heating plus the latent heat approximation, and effective heat capacity it its full derivative, my test simulations have matched an analytical proof Neumann model, and I have been using this since.

Is this an exception? Is the additive property exclusive to the Heat Capacity and not the Effective Heat Capacity keyword?

I'm suddenly very worried that I have years of simulations with this error.
raback
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Re: Heat solve with phase change - additive enthalpy and capacity?

Post by raback »

Hi

Looking at the code it seems that a) "effective heat capacity" and b) "enthalpy" are never added but are rather alternative ways to give the same thing. If both are given then "spatial 1" (default) uses a) and "spatial 2" and "temporal" always require b).

Why is "enthalpy" sometimes needed? It is because some formulations require dE/dx where dx does not go to zero but is finite.

Now "heat capacity" is really additive. The idea is that you could more easily separate the heat release associated to phase change.

-Peter
NJank
Posts: 99
Joined: 05 Dec 2009, 00:05
Location: Baltimore, MD, USA

Re: Heat solve with phase change - additive enthalpy and capacity?

Post by NJank »

OK, thanks for the clarification. At least I know I didn’t screw up all of the other simulations. Just to clarify, if I had some reason to want to separately prescribe heat capacity and enthalpy to capture phase change, enthalpy would just be the excess energy profile In the melting zone above that which would come from simply integrating the heat capacity profile. But if I’m doing the temporal simulation that looks for an effective heat capacity term to get started (I forget if it also would look for regular heat capacity), the effective heat capacity would still need to be the full profile including both solid, liquid, and melting zone heat profiles, correct?

I think maybe I’m one of the next updates we should make example graphs for the manual
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