F2 Heat Transfer by Free Convection: External Flows

1 Vertical Surfaces

The average dimensionless heat transfer coefficient [1, 2] for laminar and turbulent flows near a vertical surface in the range from Ra = 10⁻¹ to Ra = 10¹² is defined by [3]

$${\rm{Nu}} = \left\{ {0.825 + 0.387[{\rm{Ra}}f_1 ({\rm{Pr}})]^{1/6} } \right\}^2$$

((1))

The function f ₁(Pr) allows for the effect of the Prandtl number in the range 0.001 < Pr < ∞ [4]:

$$f_1 ({\rm{Pr}}) = \left[ {1 + \left( {{{0.492} \over {{\rm{Pr}}}}} \right)^{9/16} } \right]^{ - 16/9}$$

((2))

Its numerical values for some Prandtl numbers are presented in Table 1.

F2. Table1 Numerical values for the function f ₁ (Pr)