A novel type of angle plate inserts (APIs) was designed to improve the convection heat transfer in a circular pipe. In the present work characteristics of heat transfer, flow resistance, and overall thermo-hydraulic performance of turbulent airflow in a circular tube fitted with APIs were investigated at the Reynolds numbers range of 6000-18000 through numerical simulation. Our main attention was paid to the effects of the APIs with forward or backward arrangements, and the angle plates with various inclined angles (q = 30°, 45° and 60°) inserted in the circular tube for a constant pitch of 0.03 m. The results show that the Nusselt number is augmented by 2.39-4.63 times (Nu= 124.25-239.76) as that of the smooth tube. The value of performance index (PI) lies in the range of 1.34-1.63, which demonstrates that the angle plate insert has a very good overall thermo-hydraulic performance. The numerical results obtained were compared with those from plain tubes of published data and empirical relations. The maximum increases in Nusselt number for the inclined forward angle plate insert were 1.34 to 1.5 times and, while those for the backward angle plate insert were 1.46 to 1.63 over the plain tube, respectively. The friction factor ( f ) resulted in an increase of 4.28-23.12 times in case of forward arrangement and 8.09-31.76 times in case of backward arrangement. In addition, the use of the angle plate insert strip with backward arrangement leads to better overall enhancement ratio than that with forwarding arrangement around 8% to 9%.

angle plate inserts, backward/forward arrangements, friction factor, Nusselt number, thermo-hydraulic performance.