Nusselt number may be characterised as:

Explanation:-

Nusselt number

It is the ratio of heat flow rate by convection process to the heat flow rate by the conduction process.

\(Nu = \frac{{{Q_{conv}}}}{{{Q_{cond}}}} = \frac{{hA{\rm{\Delta }}T}}{{\frac{{kA{\rm{\Delta }}T}}{L}}} = \frac{{hL}}{k}\)

\(Nu_x = (\frac{\delta \theta }{\delta y'})_{y'=\theta}\)

The above equation implies that the local Nusselt number is equal to the dimensionless temperature gradient at that point on the surface provided the temperature is normalized by the reference temperature difference

The Nusselt number is in

here Nu = Nusselt's Number

Re = Reynold's Number, Pr = Prandtl Number, Gr = Grashoff Number 

Other important dimensionless numbers are:

• Biot number  → Ratio of internal thermal resistance to boundary layer thermal resistance
• Grashof number  → Ratio of buoyancy to viscous force
• Prandtl number  → Ratio of momentum to thermal diffusivities
• Reynolds number  → Ratio of inertia force to viscous force