An explicit and continuous friction factor correlation for helical tubes with arbitrary roughness

Abstract

Convergence of numerical schemes for pipe network analysis requires continuous modelling of pressure losses in the transition region between laminar and turbulent regions. Several existing correlations for the friction factor of straight pipes and helical tubes are presented. Based on these correlations a new explicit correlation for helical tubes with arbitrary surface roughness is derived. The friction factor is expressed as a continuous function of the Reynolds number covering laminar, transitional, and turbulent flow regions. Potential sources of error are also discussed, including the effects of tube deformation caused by the bending process.