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How to calculate Nusselt number

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Old   May 4, 2009, 11:57
Default How to calculate Nusselt number
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Sergey Malashenko
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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
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Old   May 4, 2009, 14:13
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Ahmed
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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
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Old   May 5, 2009, 01:55
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Quote:
Originally Posted by Ahmed View Post
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
In problem statement it is written that Nu=\lambda_{eff}/\lambda
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Old   May 5, 2009, 21:38
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Quote:
Originally Posted by SeRGeiSarov View Post
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
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Old   May 6, 2009, 01:57
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Quote:
Originally Posted by Ahmed View Post
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
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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