Enhanced thermal performance of mini-tube with chained-jet-chamber insert

Abstract

Significantly enhanced thermal performance of mini-tubes is of vital importance to achieve high efficiency of heat exchangers. While existed studies have comprehensively investigated various inserts with an aim to enhance heat exchange performance by disrupting the core flow of mini-tube, the limitation of strong fluid mixing within the boundary layer remains unresolved. Herein, a novel chained-jet-chamber insert was proposed to generate strong jetting flow in the vertical direction of fluid flow. Therefore, fluid flow boundary layer was substantially disturbed, leading to the significant enhancement of heat exchange. Numerical investigation was conducted to characterize heat transfer characteristics of this as-designed mini-tube inserted with a chained-jet-chamber for Reynolds number (Re) changing from 200 to 1200. Numerical results show that the overall Nusselt number (Nu) is substantially improved to about 180 at a Re of 1200 with a significant enhancement of 5.5-fold compared to the tube without insert owing to the intense spatial fluid mixing induced by the strong jetting flows. To evaluate the overall effectiveness of this proposed insert, the performance evaluation criteria (PEC) was calculated. A value of 2.6 is presented at a Re of 200. In contrast, the PECs of the twisted tape and helical screw tape are 1.6 and 1.9, respectively. To conclude, this novel chained-jet-chamber insert completely outperforms the twisted tape and helical screw tape inserts by generating spatial fluid mixing. This new solution can significantly increase the efficiency of compact heat exchangers in practical applications.