The friction in the tube is significantly varied to the values of Reynolds number as shown in Fig. 7(a-b). It is found that the frictions obtained from both of the axial flow (plain tube) and the re-circulating flow (tube with annulus circular-ring) is in the similar trend. The values of the friction increasingly go up relatively according to the increasing values of the Reynolds number. It can be noticeable that the friction of the A-CR insert is higher than that in the plain tube. This is because of the dissipation of dynamic pressure of the fluid due to the very high viscosity loss near the tube wall and the act caused by the re-circulating flow. Moreover, the friction has the high possibility to occur by the interaction of the pressure forces with inertial forces in the boundary layer. The results also showed that the A-CR performs to the higher friction than those the typical circular-ring. It can be observed that the friction factors of the A-CR with annulus diameter ratios of d/Do = 0.1, 0.15, and 0.2, are, respectively, around 47.9%, 69% and 82.9% of those the typical circular-ring.