Is the loss coefficient (K), used in the determination of head losses, is independent of size of the piping and the material type?
I have looked in multiple textbooks and online resources but this answer is not clear.
Well, the head loss coefficient is only an approximation.
Normally the validity is specified by assuming fully developed turbulent flow. Hence you cannot use them for low Reynolds numbers (e.g. low speed compared to diameter). So indirectly the diameter determines if the approximation is applicable
Another approximation is that they neglect surface roughness. Normally it is assumed that the surface roughness correction for the straight part is sufficient an no additional correction for the bends has to be used.
A good place to start is Crane's Technical Paper 410, "Flow of Fluids Through Valves, Fittings, and Pipe," which is available free online as a pdf.
The answer is NO. K depends on Reynolds number (size, fluid and velocity) and surface roughness (material).
However, for most practical engineering calculations (eg pipe flow) taking K as a constant is adequate.
However, some manufacturers will give K values for different diameter values.
For air flow calculations in ducts, we usually consider these K variations with flow rate and diameter.
google " F34 Duct Design - UFPR"
and see the data given in last few pages.
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