This paper presents the effect of the circular-ring turbulator (CRT) on the heat transfer and fluid friction
characteristics in a heat exchanger tube. The experiments were conducted by insertion of CRTs with various
geometries, including three different diameter ratios (DR=d/D=0.5, 0.6 and 0.7) and three different pitch
ratios (PR=p/D=6, 8 and 12). During the test air at 27 °C was passed through the test tube which was
controlled under uniform wall heat flux condition. The Reynolds number was varied from 4000 to 20,000.
According to the experimental results, heat transfer rates in the tube fitted with CRTs are augmented around
57% to 195% compared to that in the plain tube, depending upon operating conditions. In addition, the results
also reveal the CRT with the smallest pitch and diameter ratios offers the highest heat transfer rate in
accompany with the largest pressure loss.