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how chtMultiRegionFoam calculates the convective heat transfer coefficient

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Old   August 25, 2012, 18:43
Default how chtMultiRegionFoam calculates the convective heat transfer coefficient
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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
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Old   August 26, 2012, 01:59
Default convective heat transfer coeffiecient
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Originally Posted by turbulencious View Post
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

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
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Old   August 26, 2012, 06:48
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hello Ahmed,

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

all the best
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Old   August 29, 2012, 04:19
Thumbs up convective heat transfer coefficient
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Quote:
Originally Posted by turbulencious View Post
hello Ahmed,

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

all the best
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
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Old   August 30, 2012, 20:37
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you are awesome
thank you very much!
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Old   August 31, 2012, 02:59
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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 :-)
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Old   October 4, 2012, 04:56
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very interesting. Can you elaborate a bit more please? where exactly is the temperature continuity imposed?
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Old   December 19, 2012, 09:47
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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
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Old   July 18, 2013, 15:26
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Originally Posted by rebel ahmed View Post

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).

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)?
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Old   September 9, 2013, 09:02
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Originally Posted by gruenertee View Post
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
PHP Code:
Description
    Calculates 
and writes the heat flux for all patches as the boundary field
    of a volScalarField 
and also prints the integrated flux for all wall
    patches

i think we can get overall heat transfer coefficient by using wall heat flux and temp. difference.

i wish it will bee helpful
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