Flow and heat transfer in obstacled twisted tubes

The thermal and hydraulic performance of a twisted circular tube with an obstacle attached to the internal surface along the tube length (L = 1000 mm) is numerically analyzed in this work. The considered configuration is investigated by varying obstacle height ratio (OHR = h/D) which is the obstacle height (h) to the tube diameter (D = 20 mm) while obstacle thickness is kept constant under turbulent flow regime, i.e. Reynolds number 4000 <= Re <= 10,000 for air as working fluid. Various cases of OHR are triggered 0.0, 0.125, 0.25, 0.375, 0.5 and 0.625 respectively. The results show that the larger OHR gives a higher Nusselt number and vice versa due to increasing swirling power to the air in the tube. However, a higher friction factor is the penalty associated with this large obstacle. Recorded thermal performance factor TPF is beyond unity for all cases. The optimal value of TPF is observed at OHR = 0.625 which is recommended for high heat transfer rate requirement. Corresponding TPF = 2.07 at Re = 4000 and TPF = 1.69 at Re = 10,000. The results are validated against the findings of the previous works and the comparisons show good agreements.