Nusselt number

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The Nusselt number is a nondimensionalization of the convective heat transfer coefficient. Like the heat transfer coefficient, the Nusselt number may be defined locally, at a single position on a surface, or as an average value that represents the heat flow from the entire surface. The Nusselt number is named in honor of Wilhelm Nusselt, who first identified this dimensionless group in 1915. Analytical results and empirical correlations allow the Nusselt number to be estimated in many situations. For forced convection, these expressions depend on the Reynolds number and the Prandtl number. For natural convection (or "free" convection) the predictions use the Grashof number or Rayleigh number along with the Prandtl number. The mass transfer analog of the Nusselt number is the Sherwood number.

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