Heat transfer characteristics of hydrocarbon fuel at supercritical pressure in vertical circular tubes

Experimental results of convection heat transfer to supercritical hydrocarbon fuel (RP-3) in heated vertical tubes were reported in this paper. The effects of heat flux, inlet temperature and flow direction (upward and downward) on heat transfer were studied. In the experiments, the pressure and mass flow rate were maintained at 5 MPa and 3 g/s the respectively; the heat flux changed from 300 kW/m ² to 600 kW/m ² and the inlet temperature ranged from 293 K to 673 K. Test results indicate that heat transfer deterioration appears firstly at the inlet of the heated test section and then increases after thermal boundary layer is developed totally. In addition, heat transfer is enhanced near the critical point of the fuel due to the significant changes of thermalphysics properties; when the inlet temperature of RP-3 exceeds its pseudo-critical temperature, heat transfer deterioration occurs again due to the heat capacity of RP-3 decreases rapidly, Furthermore, the heat transfer coefficient of RP-3 in downward flow is greater than that in upward flow due to the buoyancy effect even if the value of determining factor is lower than 10 ^-5. Based on the experimental data, correlations are developed for the local Nusselt number of convection heat transfer to supercritical hydrocarbon fuel in vertical miniature heated tubes.