“…All the three models under predict the experimental data, which implies that the conventional correlations for circular channel using the concepts of mean velocity and hydraulic diameter as the characteristic length do not well describe the frictional coefficient for rod bundles. Lee et al (2012) reported that the McAdams and Blasius correlations showed good agreements with experimental frictional coefficient for a rod bundle (P/D ¼ 1.35) in the region of Re > 40,000, but the experimental data for low Reynolds number were not investigated. Therefore, the calculated method for frictional coefficient need to be further studied.…”