[wjchoi]

hello, i am beginner of openfoam!

when i studied the heat source problem related to fvOptions, i had a question.

there are two options to inject heat in fvOptions,
one is "specific", the other is "absolute"

as i know, the "specific" options can give heat to domain by power per unit volume (W/m^3) and the absolute options give heat to domain by power as itself (W).

in this situation, i had a question.

As i know, the heat equation consists of the unit, "per volume" [/m^3].
so, if we selected the "absolute option", how the heat eqution deals with the absolute option?

they divide the absolute power by volume of domain and then put it in the heat equation?

is there anyone to explain this for me?
thank you for reading my thread

[Pappelau]

Good Morning,
you are right.
if you want to find the threatment of absolute option(Q) you find it here :
https://cpp.openfoam.org/v9/heatSource_8C_source.html

void Foam::fv::heatSource::readCoeffs()


TLDR: foam converts your absolute source directly in a volumetric

[wjchoi]

Originally Posted by Pappelau

Good Morning,
you are right.
if you want to find the threatment of absolute option(Q) you find it here :
https://cpp.openfoam.org/v9/heatSource_8C_source.html

void Foam::fv::heatSource::readCoeffs()


TLDR: foam converts your absolute source directly in a volumetric

thank you very much!
if you don't mind, can i ask one more question?

when i saw the source code "thermophysicalproperties", the unit of Enthalpy was j/kg.

however, in fvoptions, the unit of heat source is W(watt, J/s).

so i wonder how the unit conversion (j/kg [enthalpy] <-> j/s (or j/s m^3) [specific or absolute power using fvOptions]) is conducted in calculation including fvoptions.

thank you very much!

[Pappelau]

Good morning again,
I don't exactly know what you mean by conversion - as each computational cell has a volume and a weight, you just have a enthalpy in joule per cell there you can add your heat of fvoptions.

[wjchoi]

Originally Posted by Pappelau

Good morning again,
I don't exactly know what you mean by conversion - as each computational cell has a volume and a weight, you just have a enthalpy in joule per cell there you can add your heat of fvoptions.

thank you very much for your kind explanation!


what i told you is that the unit of enthalpy in thermophysicalProperties is j/kg but, the unit of heat source is W (absolute) or W/m^3 (specific) in fvOptions. [as you know, W=j/s]

i think that when we calculate the heat problem, the differences of unit will make heat calculation difficult.

so, my additional question is below.

"how openfoam deals with the difference of unit between enthalpy in thermophysicalProperties and heat source in fvOptions about heat calculation?"

in openfoam, the unit conversion is automatically conducted?

for example, when i put the heat source in the domain using absolute option[W=j/s] of fvOptions, it consider the calculation time, so multiply calculation time by heat power [W * s] and then, divided by cell weight ? [W*s/kg -->same as the unit of enthalpy in thermophysicalProperties (j/kg)]

i found the source code related to this, but i could not..

can you explain this? or can you show the source code about this?
thank you for reading my thread!
and sorry for my a lack of knowledge