[Getdp] ... RadiativeHeatTransfer Wiki ...

Matt Koch mattkoch at scitex.us
Thu Oct 1 16:02:19 CEST 2009


Hello Bernhard,

thanks for your comments. I much appreciate them. See my replies below.

Best Regards,

Matt


Kubicek Bernhard wrote:
> As i did quite some things with radiation modelling, I have some remarks, that you might or might not find interessting:

> 1) It should be very easy to use P1 radiation model in getdp. Basically its just a heat-conduction equation with source terms prop T^4, adiabatic walls are flux zero, absorbing walls are value zero. I really think that P1 could give nice results in your case.
>   
When it comes to finite element analysis, I must admit, I do not know 
the first thing about its basics. I have learned GetDP entirely from the 
examples and the documentation and from comparing it with FreeFEM, and 
in most cases I still hope to "cheat" my way through. So, when you 
mention "P1 radiation model in GetDP", I am lost right off the bat. Do 
you have an explanation or an example of what you mean?


> 2) We did once a comparison of the heat transfer between opposed faces, where we, for each face, averaged Temperature and then used this Temperature for the radiation exchange using manually calculated view factors. This fails dramatically, if the temperature is un-evenly distributed over the surfaces. Of course, it would be better to average the T^4 for that.
> However, a full surface to surface (S2S) calculation was more physical in our cases:
> * W. Hribernik, G. Brauner, C. Faltin, B. Kubicek, F. Musai, A simulation-based methodology for high-current heat-run testing of distribution system components, 20 International Conference on Electricity Distribution, CIRED, Prage June 2009.
> * B. Kubicek, W. Hribernik, G. Brauner, C. Faltin, F. Musai, B. Semlitsch and M. Popovac, CFD analysis of the turbulent flow field and thermal behavior of high-current electric switchgear, 6th International Symposium on Turbulence, Heat and Mass Transfer, THMT Rome, 2009 
>   
Yes, this much I know. Radiative heat transfer is a matter of 
temperature AND geometry, and both must be in the integral. If you try 
to "cheat" your way out of that in the manner you describe, you are 
definitely on your own. And it may also not so much be a matter of 
averaging T or T^4, as far as I know, because depending on the geometry, 
the larger effect can be due to the configuration kernel or factor.


> 3) Maybe I misread your pro file, but it seems you also use this t^4 average. However, i think you to neglect the environmental temperature that is visible under a configuration factor (1-CfgKnl[]).
>   
I am not sure what you are referring to? Could you perhaps point me to 
the line? What I am trying to accomplish is Int(f,T^4), not 
Ave(T^4)*Int(f), f being the configuration kernel. As far as radiation 
to/from ambient is concerned, you are correct, I have neglected that 
completely. My intent was to demonstrate the radiative heat transfer 
interaction between two surfaces, not so much produce a completely 
physical model. For example, the edge of the sink is also not being 
considered (instead I am just cooling it with water here), and once you 
start doing this, shadows need to be included. All that would make the 
files even more complicated and would detract from the fundamental 
demonstration.

> 4) We are currently working on an spectral ray/pathtracing radiation model that is coupled with computational fluid dynamics.
>   
I presume this is outside of GetDP/GMsh? I thought you were in 
electrical power transfer research? Why are you working in CFD & 
Radiative Heat Transfer? Is this to model the components used in 
electrical power transfer? Are you a ME or an EE? Either way, you seem 
to have a tremendous grasp of the subject, and I am glad you are on the 
GetDP mailing list. Bouncing things off with folks in the know is 
priceless, especially when you are as clueless about finite elements as 
I am!

> nice greetings, 
>  bernhard
>
> -----------------------------------
> Bernhard Kubicek
> Energy Department
> Electric Energy Systems
>
> Bitte beachten Sie unsere neuen Kontaktdaten!
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>
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> bernhard.kubicek at ait.ac.at | http://www.ait.ac.at
> ________________________________________
> From: getdp-bounces at ace20.montefiore.ulg.ac.be [getdp-bounces at ace20.montefiore.ulg.ac.be] On Behalf Of Matt Koch [mattkoch at scitex.us]
> Sent: Wednesday, September 30, 2009 9:50 PM
> To: getdp at geuz.org
> Subject: [Getdp] ... RadiativeHeatTransfer Wiki ...
>
> Hi All,
>
> for those interested, I have just placed a radiative heat transfer on
> the Wiki: http://geuz.org/getdp/wiki/RadiativeHeatTransfer
>
> Regards,
>
> Matt Koch, Ph.D., P.E.
> Science & Technology Consultants (SciTeX)
> www.scitex.us
> mattkoch at scitex.us
> (830)-249-9499 (o)
> (830)-446-1839 (c)
>
>   


-- 
Matt Koch, Ph.D., P.E.
Science & Technology Consultants (SciTeX)
www.scitex.us
mattkoch at scitex.us
(830)-249-9499 (o)
(830)-446-1839 (c)

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