@wikipedia
Dimensionless quantity characterising the development of Natural Thermal Convection:
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\mbox{Ra}_L = \mbox{Gr} \cdot \mbox{Pr} = \frac{g \, \beta \, \Delta T \, L^3}{\nu \cdot a} |
where
For the Natural Thermal Convection in the annulus between two concentric pipes:
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\mbox{Ra}_D = \frac{8}{(D_o - D_i)^3} \cdot \frac{ \left[ \ln D_o/D_i \right]^4 }{D_i^{-3/5}+D_o^{-3/5}} \cdot \mbox{Ra}_L |
where
| outer pipe |
| inner pipe |
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body | L = 0.5 \cdot ( D_o - D_i) |
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| annulus gap |
See also
Physics / Thermodynamics / Heat Transfer
[ Dimensionless Heat Transfer Numbers ]