13. Mixed Convection

When a surface is subjected to external flow, the problem involves both natural and forced convection. The relative importance of each mode of heat transfer is determined by the value of the coefficient Gr/Re\(^2\):

  • Natural convection effects are negligible if Gr/Re\(^2 \ll 1\).

  • Free convection dominates and the forced convection effects are negligible if Gr/Re\(^2 \gg 1\).

  • Both effects are significant and must be considered if Gr/Re\(^2 = 1\) (mixed convection).