Flow And Heat Transfer Characteristics Of Aviation Kerosene At Supercritical Pressure

With the increase of flight Mach number,the engine combustion chamber of hypersonic vehicle bears the extremely high heat flux generated by the fuel supersonic combustion,which greatly increases the thermal load of aircraft engine parts.Therefore,it is urgent to provide more effective thermal protection technology to prevent the damage of engine high-temperature components.Regenerative cooling technology can not only cool the combustion chamber wall of the engine and extend the service life of the engine,but also improve the thermal efficiency of fuel combustion for great economic benefits.An experimental study on the flow and heat transfer characteristics of RP-3 aviation kerosene flowing through a vertical pipe under supercritical pressure was carried out,and effect of the inlet temperature,mass flow rate and pressure on the thermal performance of the aviation kerosene were analyzed.It is found that under supercritical pressure,the heat transfer coefficient peaks near the pseudo critical temperature due to the small temperature gradient between the main fluid and the near-wall fluid.Moreover,the increase in the inlet temperature cannot significantly change the heat transfer capacity of the fluid in the tube,but it can determine the location of heat transfer distribution.With the increase in the system pressure,the change of the fluid’s physical property tends to be flat,and the peak value of the heat transfer coefficient near the pseudo critical temperature also decreases.The increase in mass flow rate can effectively improve the local convective heat transfer coefficient in the tube,and the increase in the heat transfer coefficient in the pseudo-critical temperature area is more obvious.Effects of the buoyancy lift and thermal acceleration induced by the inlet temperature and pressure can be ignored for the mini-tube,but for the low mass flow,the radial temperature gradient and density difference of fuel in the pipe are too large,and the effect of buoyancy lift is relatively obvious.According to the experimental results,numerical simulation was carried out to simulate the flow heat transfer in a smooth circular pipe,and the difference between the experimental results and the simulation results under the same working conditions was compared.Artificial rough elements were set to explore the influence of different positions,shapes and heights of rough elements on the heat transfer performance.The results show that the addition of rough element can significantly change the flow field distribution in the tube,and the backflow zone appears after the rough element on the wall surface,which destroys the viscous bottom layer.The laminar bottom layer becomes thinner,which reduces the thermal resistance between the fluid and the wall surface,and enhances the heat conduction.At the same time,the appearance of the backflow zone increases the turbulence intensity,makes the fluid mix more intense,reduces the radial density gradient and temperature gradient,and enhances the heat transfer.Compared with the rough element with other parts,shape and height ratio,the rough element structure with full pipe,trapezoid and height ratio of 4/5 has better heat exchange effect by comprehensive strengthening.