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 nic July 21, 2009 09:01

heat trasnfer coefficient

Hi everyone,

I am looking for any equation to calculate the heat transfer coefficient for the following case:

A cuvette made of metal and inside there is water (in a batch system). Outside of the cuvette there is water flowing for heating the inside content of the cuvette.

I think this case corresponde to forced convection, and for this case I could use the Nusselt number for external flows:

Nu = 0,66*Re^(1/2) * Pr^(1/3).

then: heat transfer coefficient = Nu*k / L

But I don't know what equivalent length (L) I shoul use for it. The corresponing one to where the external fluid is moving or the cuvette wall thickness?
And also for calculating the Reynolds number, I don't know either, since inside the cuvette the water is not moving.

Thank you very much!.

nic

 mettler July 21, 2009 09:49

you might want to look into flow over a cylinder. You might be able to find a lot of the answers there.

 Ahmed July 21, 2009 22:53

Quote:
 Originally Posted by nic (Post 223468) Hi everyone, I am looking for any equation to calculate the heat transfer coefficient for the following case: A cuvette made of metal and inside there is water (in a batch system). Outside of the cuvette there is water flowing for heating the inside content of the cuvette. I think this case corresponde to forced convection, and for this case I could use the Nusselt number for external flows: Nu = 0,66*Re^(1/2) * Pr^(1/3). then: heat transfer coefficient = Nu*k / L But I don't know what equivalent length (L) I shoul use for it. The corresponing one to where the external fluid is moving or the cuvette wall thickness? And also for calculating the Reynolds number, I don't know either, since inside the cuvette the water is not moving. Thank you very much!. nic
finding a convection correlation is not difficult, for example, look this link (the internet is full of such pages) http://www.cheresources.com/convection.shtml#annular
It seems to me the geometry is confusing you, attach a picture, may be we could help

Good luck

 augusto_bassan August 19, 2009 22:07

Convection Heat Transfer

hi someone have or know where I can found the solution manual of book Convection Heat Transfer, third edition of author Adrian Bejan, because I need very much in my pos- graduate , thanks.
my e mail is augusto_bassan@yahoo.com.br

 shefali August 22, 2009 13:39

Hello Nic
The correlation which you are using is for the case when fluid is attached (or in direct contact) with (long) flat plate. However as far as I understood your problem the correlation shall give you overestimate of the heat transfer. The fluid which is flowing shall create a recirulation in the cavity and the Nu relationship shall notconvey the physics. I will suggest you to look at the literature on OPEN LID CAVITY PROBLEM.

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