# Calculation of heat transfer coefficients

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 October 25, 2005, 15:04 Hi, using wallHeatflux I ca #1 New Member   Ulrich Uphoff Join Date: Mar 2009 Posts: 9 Rep Power: 8 Hi, using wallHeatflux I can calculate the heatFlux over the wall patches. Has anybody found a solution to calculate the heat transfer coefficient? It is defined as q/(T_wall-T_fluid) where T_fluid is the temperature somewhere near the wall. I am not sure which temperature to use, a temperature somewhere in the boundary layer or the first temperature value outside the boundary layer. How can I realize this in openFoam in an elegant way? Regards Uli

 October 26, 2005, 06:05 I'm also interested in this pr #2 unoder Guest   Posts: n/a I'm also interested in this problem, but my view on this case is that this is problematic, based on what I've read earlier on this forum. As far as I understand, then you'll probably need two meshes, one for each material. This problem with the two meshes and the coupling between them has been discussed here before, but if anyone has any easy solutions for implementing the heat transfer coeffient in the interface for a temperature calculation for two different kinds of materials then I would also like to hear some hints on how to model this (since I'm a beginner with Foam). So far, I've only used laplacianFoam to calculate the temperatures for a uniform material and used setFields to make a small box with higher temperatures in the middle... In my opinion, Foam would become much more popular, if this kind of problem would become easy to deal with (but since I'm a beginner with Foam, perhaps there already exists an easy solution?). Actually I don't understand your question completely. Seems like you already have some simulation results but you don't know the heat transfer coefficient? I think the problem should be seen from this viewpoint: How to implement HTC in the interface with laplacianFoam for two different materials (different thermal diffusivity for each mesh) and then calculate the new temperatures based on this? (I don't know the answer).

 October 26, 2005, 13:01 Hi Martin, your point of vi #3 New Member   Ulrich Uphoff Join Date: Mar 2009 Posts: 9 Rep Power: 8 Hi Martin, your point of view is right, but I wanted to work on the problem step by step: First step: Assuming a fluid calculation with a constant wall temperature I just wanted to calculate the heat transfer coefficient. My problem is the estimation of a "near wall" gas-temperature. What temperature should I use and how do I calculate it with OpenFoam? Second step: Assuming a wall thickness distribution on the outer surface I would like to calculate the heat transfer coefficient in conjunction with the 1-D heat conduction in the wall. Third step: Using two meshes, fluid and solid and coupling them. I know that this has already been discussed... Best regards Uli

 October 26, 2005, 14:17 I think you have the problem b #4 Senior Member   Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 12 I think you have the problem backwards here. The heat transfer coefficient is a modeled quantity dependent on the local flow properties. The temperatures you use to calculate the heat flux are the wall temperature and the temperature in the first off-the-wall cell.

 October 27, 2005, 01:56 Actually, Ulrich is right. In #5 Senior Member   Håkan Nilsson Join Date: Mar 2009 Location: Gothenburg, Sweden Posts: 193 Rep Power: 8 Actually, Ulrich is right. In a CFD solver you compute the heat flux, which is determined by the temperature gradient close to the wall. The heat transfer *coefficient* on the other hand is a pure definition, and it can be defined as h=q/(T_wall-T_fluid). If q is computed with given T_wall, all that is needed to compute h is T_fluid. That is where the definition comes in. You have to define what T_fluid you want to use for your particular application. In free-stream flow it can be the free-stream temperature, and in internal flow it can be some average temperature. It is just a definition. Usually you determine T_fluid during post-prosessing, in the post-processor. I'm sure that you could write an application in OpenFoam for it also, but I'm not sure that it is worth the effort. Håkan.

 October 27, 2005, 05:09 Ah ok, I got it wrong, you wan #6 Senior Member   Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 12 Ah ok, I got it wrong, you want to calculate the overall heat transfer coefficient of an object or boundary. In that case I agree with Hakan. Specifically, I would use the temperature of the fluid at the inlet as T_fluid.

 March 1, 2006, 05:51 Hi, I want to model a experime #7 newbee Guest   Posts: n/a Hi, I want to model a experiment which has a incompressible fluid flow alongside bars with constant heat flux. The goal is to describe the spatial velocities, temperatures and presures. I was told on the message bord that rhoSimpleFoam would be a good solver for this problem if the density somehow was set to a fix value. Once I made rhoSimpleFoam visible in FoamX it seemed identical to buoyantSimpleFoam. Are there any differance between the solvers? I have reed on the message board that constant heat flux needs to be aranged thru fixed gradiant b.c on T. But I can only find fixed value och zero gradient as b.c alternatives. The big quesiton is: How do i modify rhoSimpleFoam so that it models a flow being heated with constant heat flux? Thanks /E

 October 15, 2007, 05:37 Dear Foamers, want to study #8 Member     Stefan Radl Join Date: Mar 2009 Location: Graz, Austria Posts: 82 Rep Power: 9 Dear Foamers, want to study mass/heat transfer in a simple pipe flow. I want to calculate the local heat flux from the wall and plot it against the pipe length. An idea would be to calculate the heat flow / the mean temperature in a certain slice perpenticular to the axis and then write to a file. Has anybody tried this ever or has an appropriate postProcessor? br Stefan Radl

 November 17, 2008, 12:09 HI, i would like to know th #9 Member   Pattyn Eric Join Date: Mar 2009 Posts: 61 Rep Power: 8 HI, i would like to know the wall heat flux of a flat plate at a constant temperature which is heating a fluid by forced convection. When using the function wallHeatflux, it complains about my thermophysical model: Selecting thermodynamics package hMixtureThermo>>>> cannot open file file: /net/ric_home/ep4/OpenFOAM/ep4-1.5/run/Channel_Flowinitialisation/920/Ydefault at line 0. From function regIOobject::readStream(const word&) in file db/regIOobject/regIOobjectRead.C at line 66. FOAM exiting The ones he proposes me are complicated and not necessary for my application. Is it possible, using a pureMixture model to know the heat flux, to get easely this quantity or the normal gradient ?

 November 18, 2008, 04:25 Hi, make a copy of the exis #10 Member   Ville Tossavainen Join Date: Mar 2009 Location: Helsinki, Finland Posts: 60 Rep Power: 8 Hi, make a copy of the existing "wallHeatFlux" utility and modify the code (and the make files) a little bit. At least you need to replace "hCombustionThermo" in createFields.H with something more appropriate (like basicThermo). Also you need to replace "hCombustionThermo.H" with something else (like hThermo.H). Just play with the code

 November 18, 2008, 04:42 Hi Ville, I am also interes #11 emilianyassenov Guest   Posts: n/a Hi Ville, I am also interested in wallHeatFlux utility from where can I get this? Thanks Emo

 November 18, 2008, 06:17 Before playing with any code, #12 Member   Pattyn Eric Join Date: Mar 2009 Posts: 61 Rep Power: 8 Before playing with any code, i have tried to recompile the wallHeatFlux application with an other name. However, after the wmake exe, i received the following error: ep4@wobwslx2:/net/ric_home/ep4/OpenFOAM/ep4-1.5/applications/wallHeatFluxpure\$ wmake exe SOURCE=wallHeatFluxpure.C ; g++ -m64 -Dlinux64 -DDP -Wall -Wno-strict-aliasing -Wextra -Wno-unused-parameter -Wold-style-cast -march=opteron -O3 -DNoRepository -ftemplate-depth-40 -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/finiteVolume/lnInclude -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/turbulenceModels/RAS -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/thermophysicalModels/specie/lnInclude -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/thermophysicalModels/combustion/lnIncl ude -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/thermophysicalModels/basic/lnInclude -IlnInclude -I. -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/OpenFOAM/lnInclude -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/OSspecific/Unix/lnInclude -fPIC -c \$SOURCE -o Make/linux64GccDPOpt/wallHeatFluxpure.o g++ -m64 -Dlinux64 -DDP -Wall -Wno-strict-aliasing -Wextra -Wno-unused-parameter -Wold-style-cast -march=opteron -O3 -DNoRepository -ftemplate-depth-40 -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/finiteVolume/lnInclude -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/turbulenceModels/RAS -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/thermophysicalModels/specie/lnInclude -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/thermophysicalModels/combustion/lnIncl ude -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/thermophysicalModels/basic/lnInclude -IlnInclude -I. -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/OpenFOAM/lnInclude -I/ric_home/ep4/OpenFOAM/OpenFOAM-1.5/src/OSspecific/Unix/lnInclude -fPIC Make/linux64GccDPOpt/wallHeatFluxpure.o -lcompressibleRASModels -lcombustionThermophysicalModels -lfiniteVolume -lspecie -lbasicThermophysicalModels \ -lm -o a.out /usr/local/bin/ld: cannot find -lcompressibleRASModels collect2: ld returned 1 exit status make: *** [a.out] Fehler 1 When installing OpenFoam, i had alredy have such errors with -l... and resolved it by recompiling the different libraries with the command wmake libso. In this case, they are already "up to date". I don't understand why i have this problem again. Thank you for any help, comments. Eric

 November 18, 2008, 16:55 Pattyn: type just "wmake" E #13 Member   Ville Tossavainen Join Date: Mar 2009 Location: Helsinki, Finland Posts: 60 Rep Power: 8 Pattyn: type just "wmake" Emo: "wallHeatFlux" utility is provided in the OpenFOAM distribution package. If you want to use it with non-combustible mixture, you need to make the small modification I described before.

 November 19, 2008, 02:52 Hi, i'm not sure to have un #14 Member   Pattyn Eric Join Date: Mar 2009 Posts: 61 Rep Power: 8 Hi, i'm not sure to have understood. Should i make wmake in my new application directory in place of wmake exe or a wmake for the compressibleRASModels in place of wmake libso? The first option gives me this: /ric_home/ep4/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libcompressibleRASModels .so: undefined reference to `Foam::cellDistFuncs::correctBoundaryPointCells(Fo am::HashSet > const&, Foam::Field&, Foam::Map&) const' /ric_home/ep4/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libfiniteVolume.so: undefined reference to `Foam::triSurface::triSurface()' /ric_home/ep4/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libfiniteVolume.so: undefined reference to `Foam::triSurfaceTools::delaunay2D(Foam::List > const&)' /ric_home/ep4/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libfiniteVolume.so: undefined reference to `Foam::cellDistFuncs::maxPatchSize(Foam::HashSet > const&) const' /ric_home/ep4/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libOpenFOAM.so: undefined reference to `Foam::Pstream::init(int&, char**&)' /ric_home/ep4/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libfiniteVolume.so: undefined reference to `Foam::directMappedPolyPatch::calcMapping() const' /ric_home/ep4/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libcompressibleRASModels .so: undefined reference to `Foam::cellDistFuncs::sumPatchSize(Foam::HashSet > const&) const' /ric_home/ep4/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libOpenFOAM.so: undefined reference to `Foam::Pstream::addValidParOptions(Foam::HashTable &)' collect2: ld returned 1 exit status make: *** [/ric_home/ep4/OpenFOAM/ep4-1.5/applications/bin/linux64GccDPOpt/wallHeatFluxpur e] Fehler 1 Thank you for any help Eric

 November 19, 2008, 04:51 I meant the first thing, "wmak #15 Member   Ville Tossavainen Join Date: Mar 2009 Location: Helsinki, Finland Posts: 60 Rep Power: 8 I meant the first thing, "wmake" to make executables and "wmake libso" for libraries. I have got the same error if I tried "wmake exe" (never used it before though) to build an executable. Did you run "wclean" before "wmake" in your new utility directory? I have no clues what could be wrong..

November 25, 2009, 08:43
#16
New Member

Join Date: Nov 2009
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Rep Power: 7
Quote:
 Originally Posted by unoder I'm also interested in this problem, but my view on this case is that this is problematic, based on what I've read earlier on this forum. As far as I understand, then you'll probably need two meshes, one for each material. This problem with the two meshes and the coupling between them has been discussed here before, but if anyone has any easy solutions for implementing the heat transfer coeffient in the interface for a temperature calculation for two different kinds of materials then I would also like to hear some hints on how to model this (since I'm a beginner with Foam). So far, I've only used laplacianFoam to calculate the temperatures for a uniform material and used setFields to make a small box with higher temperatures in the middle... In my opinion, Foam would become much more popular, if this kind of problem would become easy to deal with (but since I'm a beginner with Foam, perhaps there already exists an easy solution?). Actually I don't understand your question completely. Seems like you already have some simulation results but you don't know the heat transfer coefficient? I think the problem should be seen from this viewpoint: How to implement HTC in the interface with laplacianFoam for two different materials (different thermal diffusivity for each mesh) and then calculate the new temperatures based on this? (I don't know the answer).
for laplacianFoam i found a solution as shown in this thread: http://www.cfd-online.com/Forums/ope...roperties.html
Maybe not the best way, but it works fine in my opinion

 November 25, 2009, 11:41 #17 Senior Member   Eelco van Vliet Join Date: Mar 2009 Location: The Netherlands Posts: 122 Rep Power: 9 Hi Ulrich, I used wallHeatFlux as well and found some strange behaviour with it after a restart of a parallel run (heatflux will be reset to zero) My solution was using groovyBC (available on the openfoam contributions), a flexible way of settings boundary conditions. With groovyBc you can impose both a constant heat flux as well as a heat transfer coefficient. Have a look at the thread below to see what I did. Regards, Eelco wallHeatFlux BC not constant after restart

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