Numerical investigation of tube-side fully developed turbulent flow and heat transfer in outward corrugated tubes

A numerical study was conducted to investigate the mechanism of turbulent flow dynamics and heat transfer enhancement in novel outward corrugated tubes with a Reynolds number ranging from 3800 to 43,800 and a constant wall temperature condition. Experiments were conducted for one case of a transversely corrugated tube and five cases of a helical corrugated tube to determine the relationship between the geometric structure and flow dynamics, and the effect of the detached vortex and spiral wake on the heat transfer and pressure drop. The results show that the reasons for the heat transfer enhancement are the convective heat transfer into a jet impingement heat transfer at windward side of the corrugation and the severely turbulent fluctuation with the boundary-layer redevelopment. The rotational flow has little effect on the heat transfer enhancement; however, it inhibits the secondary flow and fluid pulsation, thereby reducing flow resistance. Moreover, the maximum values of the average Nusselt number improvement and overall heat transfer performance were 1.77 and 1.40, with Hl/D = 0.10, pl/D = 0.5 at Re = 6260 and Hl/D = 0.15, pl/D = 1.0 at Re = 3800, respectively. With the variation in Re, the performance evaluation criterion presents the interval optimum principle for various structure parameters, which is superior for coarse and dense corrugation under a low Re and more suitable for small and sparse corrugation under a high Re. For the whole range of Re, the cases of Hl/D = 0.10, pl/D = 1.5 and Hl/D = 0.1, pl/D = 1.0 are the better design of geometrical parameters.