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where
is the
convective heat transfer coefficient of the flow,
is the
characteristic length,
is the
thermal conductivity of the fluid.
For stagnant fluid and laminar flows the the Nusselt number is a constant number (OEIS sequence A282581):
| LaTeX Math Block |
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|
{\rm Nu}=3.6568 |
In moving fluids the convection component becomes contributing and the Nusselt number becomes dependant on Reynolds number
and Prandtl number .For laminar flows in pipeline the Nusselt number can be estimated through empirical correlation:
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|
{\rm Nu}=3.66 + \frac{ 0.065 \cdot {\rm Re} \cdot {\rm Pr} \cdot {D/L} }{ 1 + 0.04 \cdot ({\rm Re} \cdot {\rm Pr} \cdot {D/L})^{2/3} } |
For laminar-turbulent transition and turbulent flow in pipelines the Nusselt number can pipeline the Nusselt number becomes also depdedant on friction with wall, quantifiable by Darci friction factor
, and can be estimated through empirical correlation (Gnielinski):
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|
{\rm Nu}=\frac{ (f/8) \, ({\rm Re} - 1000) {\rm Pr} }{ 1 + 12.7 \, (f/8)^{1/2} \, ({\rm Pr}^{2/3} -1) } |
where
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See also
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Physics / Thermodynamics / Heat Transfer
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