The article presents an experimental study of turbulent heat transfer and friction characteristics in a circular tube equipped with single spiral ladder rotor (SLR)-assembled strand, single low flow resistance rotor (LFR)-assembled strand and rotor-assembled strands mixed by spiral ladder rotor (SLR) and low flow resistance rotor (LFR). Seven different mixed-rotor-assembled strands are tested in the current work; they included the mixed-rotor-assemble strand with five different number ratios, Y = 3, 2, 1, 0.5 and 0.33, and three total numbers, H = 2,4 and 6, of rotors in each group at Y = I. The obtained results reveal that mixed-rotor-assembled strand with number ratio, Y = 1, yields higher mean thermal performance factor than those with other number ratios, Y = 3, 2, 0.5 and 0.33 around 3.9%, 8.3%, 18.9% and 15.1%, respectively and the highest thermal performance factor of mixed-rotor-assembled strands at Y = 1 with H = 2, 4 and 6, are found to be 2.04, 1.96 and 1.85. In addition, the empirical correlations of the heat transfer, friction factor and thermal performance factor are also reported. (C) 2015 Elsevier Ltd. All rights reserved.