Experimental study on convective heat transfer characteristics of supercritical pressure RP-3 kerosene in serpentine tubes

Kerosene is used as coolant to cool airborne equipment and aero-engine, indicating the heat transfer performance of kerosene determines the security of aircraft. Serpentine tubes are widely utilized to conserve aircraft space and enhance heat transfer. In this study, RP-3 kerosene is electrically heated to the fixed outlet temperature of 800 K in horizontal serpentine tubes under supercritical pressure. The effects of the number of bending sections (2–4), mass flow rate (0.5–1.5 g/s), and system pressure (3–5 MPa) on heat transfer performance are analyzed. Results indicate that serpentine tubes significantly enhance heat transfer at a small cost of pressure drop increase, and heat transfer coefficient (HTC) increases with the number of bending sections. The average HTC increases by 56.7 % in 4-Bend serpentine tube compared with that in straight tube, but the pressure drop only increases by 135 kPa. Serpentine tubes significantly suppress the heat transfer deterioration in inlet region (260 < L/d_i < 600) and supercritical temperature range (700–775 K). The HTC increases as mass flow rate increases or system pressure decreases. The strong centrifugal force not only reduces the HTC differences in bending sections, but also induces a local decrease in heat transfer near the inlet of bending section. The integrated effects of drastic thermophysical property variations and centrifugal force improve heat transfer performance of RP-3 kerosene. This study reveals the action range of heat transfer enhancement of serpentine tubes, and provides necessary fundamental guidance to optimize serpentine tubes for its application in aircraft.