An experimental study was carried out to investigate the influence of double twisted-tape inserts (DTs) in micro-fin tubes (MFs) on heat transfer, friction factor and thermal performance factor characteristics of the compound devices in the following configurations: (1) twisted tapes acted in the same direction (for co-swirl) while MF and twisted tapes acted in the same (parallel) direction (MF-CoDTs:P), (2) twisted tapes acted in the same direction (for co-swirl) while micro-fin tube and twisted tapes acted in opposite directions (MF-CoDTs:O) and (3) twisted tapes acted in opposite directions for counter swirl (MF-CDTs). The MF alone and the MF equipped with a single twisted tape in parallel/opposite arrangement were also considered for comparison. The experiments were conducted for the flows with the Reynolds numbers between 5 650 and 17 000, under uniform heat flux condition. The experimental results indicate that MF-CDTs induce stronger swirl/turbulence flow, resulting in higher heat transfer rate, friction factor and thermal performance factor than other combined devices. The thermal performance factors associated with the use of MF-CDTs were found to be higher than those associated with the uses of MF-CoDTs:P, MF-CoDTs:O and MF alone up to 9.3%, 6.5% and 56.4%, respectively. The empirical correlations developed using the present experimental data for the Nusselt number, friction factor and thermal performance factor are also reported. An experimental study was carried out to investigate the influence of double twisted-tape inserts (DTs) in micro-fin tubes (MFs) on heat transfer, friction factor and thermal performance factor characteristics of the compound devices in the following configurations: (1) twisted tapes acted in the same direction (for co-swirl) while MF and twisted tapes acted in the same (parallel) direction (MF-CoDTs: P), (2) twisted tapes acted in the same direction while MF-CoDTs: O) and (3) twisted tapes acted in opposite directions for counter swirl (MF-CDTs). The MF alone and the MF equipped with a single twisted tape The experiments were conducted for the flows with the Reynolds numbers between 5 650 and 17 000, under uniform heat flux condition. The experimental results indicate that MF-CDTs induce more swirl / turbulence flow, resulting in higher he The thermal performance factors associated with the use of MF-CDTs were found to be higher than those associated with the uses of MF-CoDTs: P, MF-CoDTs: O The empirical correlations developed using the present experimental data for the Nusselt number, friction factor and thermal performance factors are also reported.