N. Koolnapadol, S. Sripattanapipat, S. Skullong, P. Wiriyavitsajjar, W. Thungwinyoo, and C. Suppasubsiri, “Numerical heat transfer study in a round tube with inclined rectangular rings”, J. Res. Appl. Mech. Eng., vol. 4, no. 2, pp. 183–191, Aug. 2018.