Prandtl Number
The Prandtl number is a parameter that relates the thicknesses of the
velocity and thermal boundary layers and is given by:
where n
is the kinematic viscosity, a
is the thermal diffusivity, r
is the fluid density, k is the
fluid thermal conductivity, and cp is the fluid heat capacity at constant
pressure.
The kinematic viscosity n
of a fluid reveals information about the rate at which momentum
may diffuse through the fluid because of molecular motion. Thermal diffusivity
a reveals
information about the diffusion of heat in the fluid. Thus the ratio of
these two quantities expresses the relative magnitudes of diffusion of
momentum and heat in the fluid.