The experimental results of the present investigation are shown in Figs. 5–17, which depict the experimental friction factor profiles for the coils tested. The friction factor profile obtained for the straight tube has been added to the coils friction factor profiles for comparison. The measured results are compared in the plots with Itos laminar and turbulent resistance formulas, Eqs. (11) and (12), respectively [11]. It is worth emphasizing that Itos resistance formulas have been extended in the plots beyond their quoted limits of validity. When plotted in a log–log scale, Eq. (11) results in a curve with a mild upward oriented curvature while Eq. (12) results in a straight line. These characteristics are referred to in the discussion of the results and might be difficult to catch from visual observation of the plots. The results are discussed in the following subsections, dealing
respectively with strong curvature coils, intermediate
curvature coils and mild curvature coils.