Prandtl Number???

WHAT IS PRANDTL NUMBER???

The Prandtl number is a dimensionless number; the ratio of momentum diffusivity (kinematic viscosity) to thermal diffusivity. It is named after the German physicist Ludwig Prandtl.

 Defined as:

\mathrm{Pr} = \frac{\nu}{\alpha} = \frac{\mbox{viscous diffusion rate}}{\mbox{thermal diffusion rate}} = \frac{c_p \mu}{k}

where:

ν : kinematic viscosity, ν = μ / ρ, (SI units : m2/s)
α : thermal diffusivity, α = k / (ρcp), (SI units : m2/s)
μ : dynamic viscosity, (SI units : Pa s = (N s)/m2)
k: thermal conductivity, (SI units : W/(m K) )
cp : specific heat, (SI units : J/(kg K) )
ρ : density, (SI units : kg/m3 ).

Note that whereas the Reynolds number and Grashof number are subscripted with a length scale variable, Prandtl number contains no such length scale in its definition and is dependent only on the fluid and the fluid state. As such, Prandtl number is often found in property tables alongside other properties such as viscosity and thermal conductivity.