Experimental And Numerical Study On Heat Transfer Of Aviation Kerosene At Supercritical Pressures

The thermo-physical properties of fluids at supercritical pressures vary significantly at pseudo-critical point. The viscosity drops dramatically, thus the fluid velocity increases and the turbulent intensity increases; the heat capacity also increases continually to a maxium value, which allows the fluid to absorb more heat for a given temperature. These variations of thermo-physical properties benefit the heat transfer of supercritical fluids and thus researchers focused on the heat transfer of supercritical fluids. However, early studies mainly focused on heat transfer performance of supercritical water and carbon dioxide. In recent years, with the development of advanced hypersonic aircraft, rocket and missile engines etc, the interest on heat transfer characteristics of hydrocarbon fuels at supercritical pressures is also increasing. In order to improve the cooling efficiency of heat transfer systems, the regenerative cooling system, where engine fuel (e.g. aviation kerosene) works as coolants and travels through the cooling tubes along the chamber wall, is developed as an effective thermal management technique.In this paper, the effects of important parameters (such as mass flow rate, heat flux, pressure, inlet temperature, tube diameter and flow direction) on heat transfer of aviation kerosene flowing in a vertical smooth tube were studied by expereimental and numerical methosds. The parametric effects were analyzed by experimental data and simulation results. The heat transfer deterioration was also numerically investigated. Then, the heat transfer of aviation kerosene flowing in enhanced tubes was studied, and the simulation results were compared with that flowing in smooth tubes at the same working condition.The experimental results show that heat transfer coefficient increases with increasing mass flow rate and inlet temperature. The effects of heat flux on heat transfer are complicated. The enhanced effects caused by fluid temperature compete with the deteriorated effects caused by wall temperature. The effect of pressure on heat transfer is rather small. The difference of fluid temperature, wall temperature and heat transfer coefficient under different pressures is small.The simulation results show that the heat transfer coefficient increases with decreasing tube diameter when the working condition is the same (e.g. the same inlet Reynolds number, the same heat flux, pressure and inlet temperature). The heat transfer in downward flow is better than that in upward flow in a 1.8 mm tube. However, there is no much difference in heat transfer coefficient between downward flow and upward flow in a 1 mm tube. Heat transfer deterioration was observed at low mass flow rates, high heat fluxes, low pressures and high inlet tempreratures. Two kinds of heat transfer deterioration were observed. The first kind of heat transfer deteorioration occurrs at where the inner wall temperature is higher than the pseudo-critical temperature, while the second kind of heat transfer deterioration occurrs at where the fluid temperature is higher than the pseudo-critical temperature. When the mass flow rate is high enough, or the heat flux is small enough or the pressure is high enough, the heat transfer deterioration would disappaear. With the existence of asymmetric fins, the heat transfer coefficient in the enhanced tubes is much higher that in the smooth tube.