external wall heat transfer
Hello,
I am actually trying to implement a boundary condition with heat transfer through the external wall. The equation is Code:
Has anybody got any idea on how to implement this BC using groovy? with alphain and Tair generating from the solver. Till now I have tried something like this: Code:
which does'nt work and gives me an error like this Code:
--> FOAM FATAL ERROR: I am using buoyantSimpleFoam Solver. I have no idea on how to generate the Tair and heat transfer coefficient from the solver. I hope somebody here has an idea about it. Regards Ashwin |
Hi Ashwin,
hmmm your problem seems "easy". First - the solver calculates Alpha (in the air Domain) and you will get the temperature of the wall. You want to extend the wall with an thickness of "l" to simulate a pipe or sth like that and the heat Transfer from the pipe to the outer fluid (i think air). So you will do a fluid - solid - fluid Simulation. a) you can do it with chtMultiRegion b) you can build your own BC - as you tried In your case (b) you made some mistakes. 1. you do not calculate the heat Transfer from fluid to solid surface - that do the solver. Therefor you do not Need alphain. 2. Tair is not a OpenFOAM variable. I think you have to use "T" or "T()" instead. 3. I did not get your Point with Tw, Tair, Tinf. What do you want to achive? In my opinion you Need: - conductivity - Tinf - Thickness Any questions? Regards Tobi |
Hello Tobias,
First of All, Thank you for the reply. Yeah I need conductivity, Thickness, The outside wall temperature = Tinf and the heat transfer coefficient on the outside = alphaout as a user input to calculate the Tw= wall temperature on the inside. I am applying this to a Normal wall(with a thickness d) in a room, to calculate the inside wall temperature. Regards Ashwin |
I think you're trying to apply a mixedBC / Robin boundary condition: http://www.cfd-online.com/Forums/ope...acianfoam.html
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Quote:
I am trying to do something similar to the external wall heat flux. Regards Ashwin |
Hi Ashwin,
ähm ... hmmm i am a bit confused :) Just to clear my mind. You want to bring heat energy into your system ? :) Well alphaout you have to define yourself :) |
Hello Tobias,
Yes I am bringing the heat Energy from outside the system and yeah I give alphaout, conductivity, thickness and outside temperature as a user input. The alphain and Tair are derived from the solver. So when I use a Value expression like Code:
Tw=(T-(alpha+(l/d)+alphaout)(T-Tinf))/alpha http://www.flickr.com/photos/115947529@N08/12211738076/ |
Quote:
Hi you have a logical mistake. You do not need Tw ... Tw is calculated from the solver! Regards Tobi |
Quote:
Now I am using this piece of code Code:
wand2 Code:
#0 Foam::error::printStack(Foam::Ostream&) at ??:? Regards Ashwin |
hello,
Why you don't use the "externalWallHeatFluxTemperature" BC ? regards, olivier |
Quote:
I tried to use that, but I am not getting good heat balance. The HeatFlux's seem to be bad. Regards Ashwin |
hello,
If something is wrong with "externealWallHeatFluxTemperature", you may report as a bug. This will help all OF user, including you. If you use use groovyBC, you may follow the advice from Akidess: Code:
type groovyBC; regards, olivier |
Hello Oliver,
I have a question from your code. Why do we need DT and K ? Since l is the thermal conductivity provided. Regards Ashwin |
Hello,
Check and read the link from Akidess for more info. DT, rho , Cp are for the bulk properties. regards, olivier |
Hello Tobias, Akidess and Oliver,
I have another question regarding external wall heat flux temperature. Can I input Q in [W/m³] instead of [W/m²] making it as a volumetric source term? Regards Ashwin |
Hello,
My Expression is working when I use h instead of alpha. Is it correct? I took it as h w.r.t to convective heat transfer coefficient notation. Please leme know if I am wrong. Code:
valueExpression "(T-(h+(l/d)+alphaout)*(T-Tinf))/h"; Code:
Parser Error for driver PatchValueExpressionDriver at "1.5-9" :"field alpha not existing or of wrong type" Ashwin |
Hello,
I am currently trying to model a solar volumetric receiver, i have conducted optical ray tracing analysis and have value for the heat flux at the aperture of the receiver. i have the data for the heat flux in 3 formats, grid form, matrix form, and table form. the heat flux represents a spot focus area (3cm radius) with energy density values in the formats mentioned. if you can shed some light on this issue it would be really helpful. thanks |
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