Liquid metals differ from gases and other liquids in that their thermal diffusivity is considerably greater than their kinematic viscosity, that is, Pr << 1. Molecular heat transfer in laminar or turbulent flow of a liquid metal plays a significant part in both the boundary layer and turbulent core. The Nusselt number is a function of the Peclet number, Nu = f(Pe), where Pe is the Peclet number. Pe is the product of the Reynolds number and the Prandtl number (thus, Pe = Re Pr = u ℓ /κ where u is the fluid velocity, ℓ the characteristic length and κ the thermal diffusivity).

A. Flow in channels

(a) Tubes

The heat transfer between the wall of a duct and a fluid moving relative to the wall can be calculated at any position along the duct using a local heat transfer coefficient defined as

\[\label{eq1} \alpha_{x} = \frac{\dot{q}}{(T_w-T_b)_x} \tag{1}\]