how chtMultiRegionFoam calculates the convective heat transfer coefficient
 

dear FOAMers,

I was wondering about something and I thought of posting it here, in case somebody already knows and wants to share.

I use the solver chtMultiRegionFoam and I would like to discuss in my report how the solver (or the BC?) calculates the convective heat transfer coefficient (h or α). My problem is strongly defined by this parameter and since the calculation is based on empirical relations ( and there are a few), it would be good to know.

thanks a lot
giorgos

convective heat transfer coeffiecient
 

Hi Giorgos,

i think it calculates it from nusselt number specified in one of case system files and conduction coefficient K specified in thermoproperties file.

BR,
Ahmed

hello Ahmed,

thanks a lot for your answer! do you know where exactly we specify the Nusselt number?

all the best

convective heat transfer coefficient
 

Hi giorgos,

prantle number is specified in file thermoPhysicalProrerties file in path:

chtMultiRegionFoam/multiRegionHeater/constant/bottomAir


and in same file in topAir.

then nu=a Re^b Pr^c.

then nu= h/K.l,

K: is specified in same file belong heater and solid areas.

in this way h could be calculated.

Best Regards,
Ahmed :)

you are awesome
thank you very much!

Sorry to intervene, just a question: Do you know where h is calculated or used in the code?

The multiRegionHeater tutorial for example uses "compressible::turbulentTemperatureCoupledBaffleMi xed" as BC.
Checking the code in src/turbulenceModels/compressible/turbulenceModel/derivedFvPatchFields/turbulentTemperatureCoupledBaffleMixed, I see that the only thing happening is to impose continuity of temperature and conductive heat flux on the boundary.

But I may be wrong, I have been wrong plenty of times before :-)

very interesting. Can you elaborate a bit more please? where exactly is the temperature continuity imposed?

Hi giorgos and dear Foamers,

sorry giorgos it was along time from your post, i reviewed your post again and recently, i began with chtMultRegionFoam so i reviewed the tutorial case and boundary condition.

firstly, about heat convective coefficient, if you want to put it as input in your case there is no need to do this. if you reviewed the energy equation (which solver uses) you will find that only temperature, velocity, properties of solid and fluid are required. heat transfer coefficient in required as input if solver uses correlations which isn't applied in over solver.

secondly, if you want to get the overall coefficient based on temperature distribution gotten from your solver, i think there is a command you can use (you may have to search to get it).

finally, I'd like from you and anon_a to discuss this post with me. it was useful for me last time to get your feed back to re-review the case.

good luck, :)

ahmed

I am very grateful for your explanation about chtMultiRegionFoam and the heat transfer coefficient; but can you or anyone of the foamers tell which command to use to get the overall heat transfer coefficient (OpenFoam2.2.0 Solver chtMultiRegionfoam)?

Hi gruenertee,

i looked in OpenFoam file in order to try answering your question. i reached to a result may give a clue to this issue. i didn't test it but i think it will make use.

if you go to this directory
/opt/openfoam210/platforms/linuxGccDPOpt/bin

you will find a list of all executables in openFOAM among it you will find wallHeatFlux

if you go to source file in this directory

/opt/openfoam210/utilities/postProcessing/wall/wallHeatFlux.

you will find wallHeatFlux.c which contains file description as
i think we can get overall heat transfer coefficient by using wall heat flux and temp. difference.

i wish it will bee helpful :)