Heat transfer characteristics and novel optimization of a supercritical N-decane-Cooling tube under gravity condition

To study the flow and heat transfer characteristics of supercritical n-decane in the actual regenerative cooling tube, the heat transfer characteristics in a horizontal square tube under a single-side heated condition with considering and ignoring gravity were numerically investigated. The k-ωSST turbulence model was used and tested against the experimental data. The heat transfer characteristics on circumferential walls were presented and the radial flow pattern in the main flow zone and the boundary layer zone was analyzed to explore the mechanism of the heat transfer under gravity conditions. It was found that the heat transfer was enhanced at the bottom wall and weakened at the remaining three walls because of the secondary flow caused by gravity effect. Furthermore, the heat transfer would be enhanced when the velocity component of the boundary layer along the normal direction of the wall is toward the wall. Besides, a brand-new structure constructed by ribs section and smooth section was proposed. The additional pressure drop caused by the enhanced heat transfer structure can be reduced by up to 95.4% with the same heat transfer performance compared with the traditional ribs-tube structure which ribs spread all over a tube.