Editing Heat transfer coefficient (section)

==Combining convective heat transfer coefficients==
For two or more heat transfer processes acting in parallel, convective heat  transfer coefficients simply add:

:<math>h = h_1 + h_2 + \cdots</math>

For two or more heat transfer processes connected in series, convective heat transfer coefficients add inversely:<ref>This relationship is similar to the [[harmonic mean]]; however, it is not multiplied with the number ''n'' of terms.</ref>

:<math>{1\over h} = {1\over h_1} + {1\over h_2} + \dots</math>

For example, consider a pipe with a fluid flowing inside. The approximate rate of heat transfer between the bulk of the fluid inside the pipe and the pipe external surface is:<ref>{{cite web |url=http://physics.stackexchange.com/questions/153434/heat-transfer-between-the-bulk-of-the-fluid-inside-the-pipe-and-the-pipe-externa |date=Dec 15, 2014 |title= Heat transfer between the bulk of the fluid inside the pipe and the pipe external surface|website=Physics Stack Exchange  |access-date = 15 December 2014}}</ref>

:<math>q=\left( {1\over{{1 \over h}+{t \over k}}} \right) \cdot A \cdot \Delta T</math>
where
:<math>q</math> = heat transfer rate (W)
:<math>h</math> = convective heat transfer coefficient (W/(m<sup>2</sup>·K))
:<math>t</math> = wall thickness (m)
:<math>k</math> = wall thermal conductivity (W/m·K)
:<math>A</math> = area (m<sup>2</sup>)
:<math>\Delta T</math> = difference in temperature (K)