# Nusselt Number

on . Posted in Dimensionless Numbers

Nusselt number, abbreviated as Nu, a dimensionless number, describes the ratio of convective heat transfer to conductive heat across a boundary.

## Nusselt number formula

$$\large{ Nu = \frac{h \; l_c}{k} }$$
Symbol English Metric
$$\large{ Nu }$$ = Nusselt number $$\large{dimensionless}$$
$$\large{ l_c }$$ = characteristic length $$\large{ft}$$ $$\large{m}$$
$$\large{ h }$$ = heat transfer coefficient $$\large{\frac{Btu}{hr-ft^2-F}}$$  $$\large{\frac{W}{m^2-K}}$$
$$\large{ k }$$ = thermal conductivity $$\large{\frac{Btu-ft}{hr-ft^2-F}}$$ $$\large{\frac{W}{m-K}}$$