Effect of conical cut-out turbulators with internal fins in a circular tube on heat transfer and friction factor

Heat transfer, friction factor and thermal performance factor characteristics in a circular tube fitted with conical cut-out turbulator integrated with internal fins are investigated for three pitch ratios (PR) 3, 4, 5 and tested with two different arrangements as convergent mode (C-turbulators) and divergent mode (D-turbulators). The experiments were conducted with air as the working fluid and with Reynolds number range between 6800 and 9700 under constant heat flux of 0.052W/m². The experimental results in the plain tube and the tube positioned with C-turbulators, D- turbulators are reported for comparison. It is found that the D-turbulators arrangement with PR=3 shows the maximum heat transfer rate of 315%, thermal performance factor of 2.4 and friction factor of 3.2 times than that of plain tube. These enhancements may lead to an increase in heat transfer rate in the humidification-dehumidification desalination system, which is currently in stage. Results of existing Nusselt numbers are compared to the new predicted Nusselt number. These results agree well within 5-9% of error. Results were also compared with previous researchers work.