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## Main Question or Discussion Point

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=[tex]\lambda_{eff}[/tex]/[tex]\lambda[/tex]

[tex]\lambda[/tex] is heat flux coefficient for liquid sodium at 673 K (average temperature)

[tex]\lambda_{eff}[/tex] is effective heat flux coefficient including effect of free convective heat transfer. [tex]\lambda_{eff}[/tex]=Q[tex]\delta[/tex]/S[tex]\Delta[/tex]T

Q is heat flux through surface

[tex]\delta[/tex] is the length

S is cross sectional area of the pipe

[tex]\Delta[/tex]T 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

Nu=[tex]\lambda_{eff}[/tex]/[tex]\lambda[/tex]

[tex]\lambda[/tex] is heat flux coefficient for liquid sodium at 673 K (average temperature)

[tex]\lambda_{eff}[/tex] is effective heat flux coefficient including effect of free convective heat transfer. [tex]\lambda_{eff}[/tex]=Q[tex]\delta[/tex]/S[tex]\Delta[/tex]T

Q is heat flux through surface

[tex]\delta[/tex] is the length

S is cross sectional area of the pipe

[tex]\Delta[/tex]T 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