An experimental study was carried out to investigate the transition from laminar to turbulent flow in helically coiled pipes. Twelve
coils have been tested, with ratios of coil diameter to tube diameter ranging from 6.9 to 369, and the interaction between turbulence
emergence and coil curvature has been analyzed from direct observation of the experimental friction factor profiles. The experimental
data compare favorably with existing results and reveal new features that apparently were not observed in previous research.
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