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SeRGeiSarov May 4, 2009 11:57

How to calculate Nusselt number
 
Hello I need to calculate the Nusselt number for liquid sodium in a pipeline. Length of the pipeline is 3 meter. Diameter of the pipeline is 0.3 meter. Heat flux through outer surface of the pipeline is equal zero. Temperature on the right side and left side of the pipeline is 573 K and 773 K, respectively. Solution of the problem is free convective heat transfer.

Nu=\lambda_{eff}/\lambda

\lambda is heat flux coefficient for liquid sodium at 673 K (average temperature)
\lambda_{eff} is effective heat flux coefficient including effect of free convective heat transfer. \lambda_{eff}=Q\delta/S\DeltaT

Q is heat flux through surface
\delta is the length
S is cross sectional area of the pipe
\DeltaT is temperature difference (200 K)

Which the surface have be used for calculation of Q? (the right side, the left side, the outer surface) How to calculate Nusselt number?

TIA

Ahmed May 4, 2009 14:13

The Nu number, by definition, is a non dimensional heat transfer coefficient, in your case, you stated the outer surface of the pipe is adiabatic, so there is no heat transfer there.
Could you check your problem statement:confused:

SeRGeiSarov May 5, 2009 01:55

Quote:

Originally Posted by Ahmed (Post 215111)
The Nu number, by definition, is a non dimensional heat transfer coefficient, in your case, you stated the outer surface of the pipe is adiabatic, so there is no heat transfer there.
Could you check your problem statement:confused:

In problem statement it is written that Nu=\lambda_{eff}/\lambda

Ahmed May 5, 2009 21:38

Quote:

Originally Posted by SeRGeiSarov (Post 215101)
Heat flux through outer surface of the pipeline is equal zero. Temperature on the right side and left side of the pipeline is 573 K and 773 K, respectively. Solution of the problem is free convective heat transfer.

TIA


1- The sodium enters at 773K and leaves at 573K
2- Heat flux through outer surface is equal zero
This is your problem statement, so what causes this temperature drop :D

SeRGeiSarov May 6, 2009 01:57

Quote:

Originally Posted by Ahmed (Post 215256)
1- The sodium enters at 773K and leaves at 573K
2- Heat flux through outer surface is equal zero
This is your problem statement, so what causes this temperature drop :D

The pipe is insulated. There is boyuancy driven flow. On the left side and the right side only heat flux is set (temperature). Problem is solved into the pipe.


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