Investigation on thermo-hydraulic performance of supercritical CO2 in heated horizontal serpentine tubes

Serpentine tubes are one of the promising candidates for heat transfer channels of heat exchangers in supercritical CO 2 Brayton cycle system due to their compact structure. Compared with the horizontal straight tubes, the performance of supercritical CO 2 thermo-hydraulic in horizontal serpentine tubes is numerically researched in the current study. Furthermore, the effect of the curved sections number on the thermo-hydraulic performance of serpentine tubes is analyzed under a fixed heating length. In light of the hypothesis that supercritical CO 2 transforms between liquid-like and vapor-like states across the pseudo-critical temperature, the heat transfer mechanism of supercritical CO 2 is clarified. Numerical results reveal that periodic centrifugal force induces continuous reconstruction of the liquid-like and vapor-like phases distribution in serpentine tubes, which intensifies the turbulent disturbance and thermal diffusion of supercritical CO 2 . Therefore, serpentine tubes can greatly promote the supercritical heat transfer. Although flow resistance increases simultaneously, the overall thermo-hydraulic performance is significantly improved. Finally, the new heat transfer correlations are established separately for the curved and straight sections of serpentine tubes to improve prediction accuracy according to heat transfer mechanism of supercritical CO 2 . The reliability of the newly proposed heat transfer correlations, whose prediction error is only −0.57%, is remarkably superior to that of the typical correlations available in the literature. The present study can provide valuable theoretical references for the structural design of heat transfer components with serpentine tube.