The ratio of convective to conductive heat transfer across (normal to) the boundary:
{\rm Nu} = \frac{\rm Convective \ heat \ transfer}{\rm Conductive \ heat \
transfer} = \frac{U}{\lambda / L} =\frac{U \cdot L}{\lambda } |
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 Nusselt number is a constant number (OEIS sequence A282581):
{\rm Nu}=3.66 |
For transient and turbulent flow in pipelines the Nusselt number can be estimated through empirical correlation (Gnielinski):
{\rm Nu}=\frac{ (f/8) \, ({\rm Re} - 1000) {\rm Pr} }{ 1 + 12.7 \, (f/8)^{1/2} \, ({\rm Pr}^{2/3} -1) } |
where is Parndtl number.
Physics / Thermodynamics / Heat Transfer