Difference OF7 to OF8 - hconst to econst

PSander · December 8, 2020, 13:46

I recently tried to switch from OF7 to OF8. When I tried to run my chtMultiRegionFoam case I got the error messages of "Unknown solidThermo Type", so I had to change in thermophysicalProperties from "hConst" to "eConst", from "sensibleEnthalpy" to "sensibleInternalEnergy" and in fvSolution as well from h to e.

With this changes the case ran.

Checking here: https://cfd.direct/openfoam/user-gui...hermophysical/
the Thermodynamic models gives this explanation:

hConst
assumes a constant cp and a heat of fusion Hf which is simply specified by a two values cp Hf, given by keywords Cp and Hf.

eConst
assumes a constant cv and a heat of fusion Hf which is simply specified by a two values cv Hf, given by keywords Cv and Hf.

Running the case for 1000 seconds, gives me a tiny difference in results, but there is a difference. I know that OF6 and OF7 did not produce the same results either, but since I had to change from "hconst" to "econst", I would like to know, if there is any physical difference between cp and cv.
So is the difference in results just "normal", as I changed from OF7 to OF8, or is it a difference produced by different physical setting?

dlahaye · December 8, 2020, 14:11

Heat capacity of solid at constant volume (cv) or constant pressure (cp) can (and typically are) different. Tabular data will typically list both.

PSander · December 9, 2020, 04:40

Thank you for your help!
Since liquids and solids can practically assumed to be incompressible, Cp and Cv for them have almost same values at least at moderate temperatures?

keitaro7_14 · January 21, 2021, 08:32

I noticed the same. Cp and Cv are practically the same for solid, so I guess the developers thought that for a solid it makes more sense eConst.

For the change of sensibleInternalEnergy, it seems to be for numerical reasons

https://github.com/OpenFOAM/OpenFOAM...25ab9817b3ec62

source: When choose sensibleInternalEnergy or sensibleEnthalpy in thermophysicalProperties

keitaro7_14 · February 4, 2021, 10:17

I noticed the same problem. I am solving a heat transfer model with two solids of different diffusivities and I get differences. I am still investigating where the trick is.

December 8, 2020, 13:46	Difference OF7 to OF8 - hconst to econst	#1
PSander New Member Join Date: Jan 2020 Posts: 26 Rep Power: 6	I recently tried to switch from OF7 to OF8. When I tried to run my chtMultiRegionFoam case I got the error messages of "Unknown solidThermo Type", so I had to change in thermophysicalProperties from "hConst" to "eConst", from "sensibleEnthalpy" to "sensibleInternalEnergy" and in fvSolution as well from h to e. With this changes the case ran. Checking here: https://cfd.direct/openfoam/user-gui...hermophysical/ the Thermodynamic models gives this explanation: hConst assumes a constant cp and a heat of fusion Hf which is simply specified by a two values cp Hf, given by keywords Cp and Hf. eConst assumes a constant cv and a heat of fusion Hf which is simply specified by a two values cv Hf, given by keywords Cv and Hf. Running the case for 1000 seconds, gives me a tiny difference in results, but there is a difference. I know that OF6 and OF7 did not produce the same results either, but since I had to change from "hconst" to "econst", I would like to know, if there is any physical difference between cp and cv. So is the difference in results just "normal", as I changed from OF7 to OF8, or is it a difference produced by different physical setting?

December 8, 2020, 14:11		#2
dlahaye Senior Member Domenico Lahaye Join Date: Dec 2013 Posts: 802 Blog Entries: 1 Rep Power: 18	Heat capacity of solid at constant volume (cv) or constant pressure (cp) can (and typically are) different. Tabular data will typically list both. PSander likes this.

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December 9, 2020, 04:40		#3
PSander New Member Join Date: Jan 2020 Posts: 26 Rep Power: 6	Thank you for your help! Since liquids and solids can practically assumed to be incompressible, Cp and Cv for them have almost same values at least at moderate temperatures?

January 21, 2021, 08:32		#4
keitaro7_14 Member JuanMi Join Date: Nov 2017 Posts: 41 Rep Power: 9	I noticed the same. Cp and Cv are practically the same for solid, so I guess the developers thought that for a solid it makes more sense eConst. For the change of sensibleInternalEnergy, it seems to be for numerical reasons https://github.com/OpenFOAM/OpenFOAM...25ab9817b3ec62 source: When choose sensibleInternalEnergy or sensibleEnthalpy in thermophysicalProperties

February 4, 2021, 10:17		#5
keitaro7_14 Member JuanMi Join Date: Nov 2017 Posts: 41 Rep Power: 9	I noticed the same problem. I am solving a heat transfer model with two solids of different diffusivities and I get differences. I am still investigating where the trick is.