Experimental research on convective heat transfer of supercritical hydrocarbon fuel flowing through U-turn tubes

Convective heat transfer characteristics of hydrocarbon fuel RP-3 flowing through U-turn tubes at supercritical pressures were experimentally investigated. The inner diameter of U-turn tubes is 1.82 mm and bending diameters are 20 mm, 30 mm and 40 mm. Inner wall temperature and HTC variations were analyzed under different physical factors including heat flux, system pressure, bending diameter and flow direction. Test results indicate that centrifugal force strengthens the flow mixing at the bending section and HTC is averagely enhanced by 40% to twice compared with straight tube. In addition, HTC values increase with decrease of bend diameter and variation curves of all U-turn tubes are displayed as “Inverted U” type. Finally, Grq/Grth>2 is concluded as one criterion evaluating buoyancy effect for supercritical hydrocarbon fuel flowing in U-turn tubes.