Editing Heat transfer coefficient (section)

=== External flow, horizontal plates ===
W. H. McAdams suggested the following correlations for horizontal plates.<ref>{{cite book |last=McAdams |first=William H. |title=Heat Transmission |date=1954 |publisher=McGraw-Hill |location=New York |page=180 |edition=Third}}</ref> The induced buoyancy will be different depending upon whether the hot surface is facing up or down.

For a hot surface facing up, or a cold surface facing down, for laminar flow:
   
:<math>h \ = \frac{k 0.54 \mathrm{Ra}_L^{1/4}} {L} \, \quad 10^5 < \mathrm{Ra}_L < 2\times 10^7</math>

and for turbulent flow:

:<math>h \ = \frac{k 0.14 \mathrm{Ra}_L^{1/3}} {L} \, \quad 2\times 10^7 < \mathrm{Ra}_L < 3\times 10^{10} .</math>

For a hot surface facing down, or a cold surface facing up, for laminar flow:

:<math>h \ = \frac{k 0.27 \mathrm{Ra}_L^{1/4}} {L} \, \quad 3\times 10^5 < \mathrm{Ra}_L < 3\times 10^{10}.</math>

The characteristic length is the ratio of the plate surface area to perimeter. If the surface is inclined at an angle ''θ'' with the vertical then the equations for a vertical plate by Churchill and Chu may be used for ''θ'' up to 60°; if the boundary layer flow is laminar, the gravitational constant ''g'' is replaced with ''g'' cos&nbsp;''θ'' when calculating the Ra term.