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| \mbox{Nu}= \left[ 0.825 + \frac{0.387 \, \mbox{Ra}^{1/6}}{ \left[ 1+ (0.492/\mbox{Pr})^{9/16} \right]^{8/27}} \right]^2 |
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| \mbox{Nu}= 0.68 + \frac{0.663 \, \mbox{Ra}^{1/4}}{ \left[ 1+ (0.492/\mbox{Pr})^{9/16} \right]^{4/9}} |
| | Laminar flows
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body | --uriencoded--\mbox%7BRa%7D \leq 10%5e9 |
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In Forced Fluid Convection the Nusselt number becomes dependant on Reynolds number
and Prandtl number :
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body | --uriencoded--\mbox%7BNu%7D = f (\mbox%7BRe%7D, \mbox%7BPr%7D) |
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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} } |
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Laminar flow in pipeline |
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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) } |
| | laminar-turbulent transition and turbulent flow in pipeline the Nusselt number (Nu) becomes also dependant on friction with wall, quantifiable by Darcy friction factor , and can be estimated through empirical correlation (Gnielinski
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body | --uriencoded--0.5\leq \mathrm %7BPr%7D \leq 2000 |
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body | --uriencoded--%7B\displaystyle 3000\leq \mathrm %7BRe%7D\leq 5\cdot 10%5e%7B6%7D%7D |
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Image Modified | Churchill–Bernstein correlation
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See also
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Physics / Thermodynamics / Heat Transfer
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