Editing Heat transfer coefficient (section)

=== External flow, vertical cylinders ===
For cylinders with their axes vertical, the expressions for plane surfaces can be used provided the curvature effect is not too significant. This represents the limit where boundary layer thickness is small relative to cylinder diameter <math>D</math>. For fluids with Pr ≤ 0.72, the correlations for vertical plane walls can be used when<ref>{{cite journal | url=http://doi.org/10.1080/01457630801891557 | doi=10.1080/01457630801891557 | title=Free Convection Heat Transfer from Vertical Slender Cylinders: A Review | date=2008 | last1=Popiel | first1=Czeslaw O. | journal=Heat Transfer Engineering | volume=29 | issue=6 | pages=521–536 | bibcode=2008HTrEn..29..521P | url-access=subscription }}</ref>
   
:<math>\frac{D}{L}\ge \frac{35}{\mathrm{Gr}_{L}^{\frac{1}{4}}}</math>

where <math>\mathrm{Gr}_L</math> is the [[Grashof number]].

And in fluids of Pr ≤ 6 when

:<math>\frac{D}{L}\ge \frac{25.1}{\mathrm{Gr}_{L}^{\frac{1}{4}}}</math>

Under these circumstances, the error is limited to up to 5.5%.