Editing Heat transfer coefficient (section)

==Heat transfer coefficient of pipe wall==
The resistance to the flow of heat by the material of pipe wall can be expressed as a "heat transfer coefficient of the pipe wall". However, one needs to select if the heat flux is based on the pipe inner or the outer diameter.
If the [[heat flux]] is based on the inner diameter of the pipe, and if the pipe wall is thin compared to this diameter, the curvature of the wall has a negligible effect on heat transfer. In this case, the pipe wall can be approximated as a flat plane, which simplifies calculations. This assumption allows the heat transfer coefficient for the pipe wall to be calculated as:
:<math>h_{\rm wall} = {2 k \over x}</math>
where 
:<math>k</math> is the effective [[thermal conductivity]] of the wall material 
:<math>x</math> is the difference between the outer and inner diameter.

However, when the wall thickness is significant enough that curvature cannot be ignored, the heat transfer coefficient needs to account for the cylindrical shape.<ref name="Heat Conduction in Cylinderical Shell">{{cite web |last1=Aggarwal |first1=Nikita |title=Heat Conduction in Cylindrical Systems – Online Calculator & Python Code |url=https://chemenggcalc.com/heat-conduction-in-cylindrical-system/ |website=ChemEnggCalc |date=27 October 2024 |access-date=11 November 2024}}</ref> Under this condition, the heat transfer coefficient can be more accurately calculated using :

:<math>h_{\rm wall}  = {2k \over {d_{\rm i}\ln(d_{\rm o}/d_{\rm i})}}</math>

where 
:<math>d_i</math> = inner diameter of the pipe [m]
:<math>d_o</math> = outer diameter of the pipe [m]

The thermal conductivity of the tube material usually depends on temperature; the mean thermal conductivity is often used.