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 0.052 W/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.