How this calculator works
Nusselt number is the dimensionless convection coefficient hL/kf, where kf is the fluid conductivity. The length convention, property evaluation temperature and whether h is local or averaged must match the reference correlation. Natural and forced convection modes evaluate power-law forms using your own coefficient and exponents; the defaults are illustrative, not a recommended correlation or a validity check for a flow regime.
Formula
Nu = hL/kf; natural power law: Nu = C Ra^n; forced power law: Nu = C Re^m Pr^n.
Worked example
For h = 10 W/(m² K), L = 0.1 m and kf = 0.025 W/(m K), Nu = 40. A supplied natural-convection law with C = 0.1, Ra = 1e8 and n = 0.25 gives Nu = 10.
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Frequently asked questions
Which conductivity belongs here?
Use the fluid conductivity. Solid conductivity belongs in a Biot number.
Can I use any characteristic length?
No. Use the length defined by the selected correlation, such as pipe diameter or plate length.
Are the correlation defaults validated for my flow?
No. Supply parameters and applicability limits from a reference for your geometry and regime.