The flow in a helical duct with rectangular cross-section is analyzed. A se
ries solution based on curvature and torsion is introduced. The components
of the series are determined analytically using appropriate eigenfunction e
xpansions. The resulting solution is limited to flows in the low Dean numbe
r, low Germano number regime. An analytical friction factor relation is est
ablished and compared with previous numerically determined correlations. (C
) 2001 Editions scientifiques et medicales Elsevier SAS.