Film temperature

In heat transfer and fluid dynamics, the film temperature (${\displaystyle T_{f}}$) is an approximation to the temperature of a fluid inside a convection boundary layer. It is calculated as the arithmetic mean of the temperature at the surface of the solid boundary wall (${\displaystyle T_{w}}$) and the free-stream temperature (${\displaystyle T_{\infty }}$):

The film temperature is often used as the temperature at which fluid properties are calculated when using Prandtl number, Nusselt number, Reynolds number or Grashof number to calculate a heat transfer coefficient, because it is a reasonable first approximation to the temperature within the convection boundary layer.

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