From: i0c0256@rigel.tamu.edu (IGOR)
Newsgroups: sci.physics.fusion
Subject: Re: Fluid mechanics question.. how crude is the heat estimate?
Date: 13 Dec 1992 18:20 CST
Organization: Texas A&M University, Academic Computing Services
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In article <1992Dec12.004233.13433@murdoch.acc.Virginia.EDU>, crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes...
>In article <11DEC199218025457@zeus.tamu.edu> i0c0256@zeus.tamu.edu (IGOR) writes:
>>
>>I am kinda of puzzled by this cold fusion thing but I have an open mind
>>about it. The question I have is a question from a fluid mechanics
>>person and not that of a (nuclear) engineer :
>>
>>How can one so precisely determine the amount of heat generated?
>>have they been fluid flow studies about this ? that is computer generated
>>calculation proving that what the sensor gets  is linked to a certain amount
>>a heat on the cell side.
>>I am working in two-phase flow ( I DO NOT use correlation) solving the 
>>Navier-Stokes equation and I know that even phase change problem 
>>(such as the one occuring in the boiling) is a bitch... how can people be
>>so sure of the heat generated ? My reasoning comes from my total distrust
>>of heat transfer coeficient used in nuclear engineering that are there
>>to give an estimate and not a TRUE value ( since they are mainly used 
>>for design purposes)...
> 
>     Energy balances are much easier than detailed flow calculations,
>     especially when you aren't venting to the atmosphere. A seemingly
>     good example of how to do so fairly accurately has been posted
>     by Tom Droege regularly (in various incarnations).  Any more adverbs
>     in the previous sentence, and I'll have to barf on my own prose.
> 
>     By the way, how do you do two-phase flow without correlations
>     or constitutive relations based on correlations?

 The only constitutive relations I use are the NS equations and 
jump conditions for the interface...Even though those are still mass-averaged
solutions of the true flow of particles...


> 
>     Where do you get your computer?  Mine won't go that fast.

	Cray and other Maspars help.. but they are indeed very slow :-))

>     People have difficulty computationally accounting for a single
>     bubble interface, to say nothing of the generic interspersed
>     turbulent two-phase flow.

	Nothing indeed.  

> 
>     If you do have some magic approach, please tell me soon.  I'm finishing
>     a dissertation on boiling two-phase flow calculations in cryogens
>     using all sorts of averaging and jury-rigged constitutive relations.

Yes I know I used to work on the same kind of problem, but I prefered
to be purer :-))) seriously, I just cannot picture being able to give an
information on a system ( two-phase flow) when the topology is given adhoc
( when do you know when to apply inverted annular config. or the annular
config.) and also when one looks at an ideal case, the phase space
is 7 times bigger than a comparable single phase flow. Since the correlation
were adopted from monophasic flow methodology 
how can one accept that this success story
would apply to more complex flows ????

>     A more elegant approach would sure be appreciated.

		Indeed again.

I would not like to attract the wrath of thermodynamicians, but I am not 
extremely
 comfortable with those energy balances.. since they are themselves valid
in media where the flow is averaged (in time and physically),
 at rest and is most probably overlooked.
 Thermodynamics works, it is just a question of 'can we apply it here '.
Shouldn't we be looking at the
exact flow close to the cell (streamlines....)to make damm sure that we have
excess heat supply....?. I have the underlying feeling that this excess heat
COULD be the result of what is happening when one tries to compute heat fluxes
in traditional nuclear engineering with correlations! The overestimation is
due to the tools used.
This idea came last year when a guy from some japanese university came to
Texas A&M and showed us his results which where based on pulsing the cells
which is to me far from a steady process. Then again I listened very well
since my job may not exist if it reveals to be true:-)))).
Can somebody dissipate my surely erroneous beliefs :-)?   



Igor Carron
PhD Student in Nuclear Engineering
Texas A&M University
Newsgroups: sci.physics.fusion