In 5.2 Heat transfer, it is said that the mean increase in Nusselt number was 40.6 – 43.9 % in comparison with that for the plain tube with circular-ring (CR), when d/D0 = 0.1 were performed, I cannot find these increases in Fig. 5 (a) in comparison between circle symbols and triangle symbols. Circle symbols which show results of the plain tube with circular-ring (CR) are very close to triangle symbols which show A-CR, DR=0.1. It is clearly seen in Fig. 5 (a) that their differences are less than 40 %. You also say that results of Nusselt number values for A-CR with annulus diameter ratios of d/D0 = 0.1, 0.15, and 0.2 is enhanced up to 210%, 244% and 303% compared to that the plain tube alone, those values are not read from Fig. 5 (b). Even Nu/Nup’s of d/D0 = 0.1 are round 3. Those are more than 210%. Those values described in 5.2 should be checked again.