Researches On Thermal Cracking And Convection Heat Transfer Of Supercritical Pressure Endothermic Hydrocarbon Fuels

It is an important way that supercritical endothermic hydrocarbon fuels are used ascoolant in high temperature parts of modern hypersonic flight, which is one of the mostimportant thermal protection technologies. Along with the increasing of the Machnumber, the high temperature becomes a big problem, cooling technology isincreasingly important. The regenerative cooling technology for scramjet engine caneffectively reduce the weight of vehicle and has a good cooling effect. Furthermore, Itcan also improve the combustion performance. However, the coking phenomenon canalso make heat transfer deterioration or cause an accident. An obvious characteristic ofsupercritical fluid is the dramatic changes in property near critical point, which makesconvection heat transfer change obviously. At the same time, the pressure and massflow rate can bring a variouty of changes on convection heat transfer. Many studieshave shown that the buoyancy and thermal acceleration will cause a great impact onheat transfer. The thermal cracking happens when the temperature increases. With thedevelopment of the flight technology, the research of supercritical hydrocarbon fuelswill be more and more vital, including heat transfer, and characteristics of cracking anddeposition.In this article, an experiment research and a numerical simulation study of thesupercritical hydrocarbon fuels RP-3in2mm vertical tube has been carried out,including heat transfer and characteristics of cracking.For the convection heat transfer of supercritical RP-3kerosene in a vertical tubewith inner diameter of2mm, the experimental results show that, in the the2mm tubewithin a Reynolds number of2500, the buoyancy force decrease the heat transfer ofupward flow, but does not decrease the heat transfer of downward flow. Close to thecritical pressure, changes of the thermal properties are enhanced, which makes theconvection heat transfer more effective. High mass flow rate strengthen convection heattransfer and the changes of pressure make complex influences on heat transfer, becauseof the properties. When the gas conversion of RP-3thermal cracking reaction less than3%, it will be increased exponentially with the increasing temperature and theincreasing of residence time will also increase gas conversion. Through these reasons, the mass flow rate and pressure has a complex influence in gas production. For less than3%of the gas production rate, gas composition changes little. We conclude a one-stepreaction by the Proportional Product Distribution model, which plays well in numericalsimulation. As the numerical simulation of convective heat transfer been carried out, wecompared different models in different Reynolds number conditions, in which there aredeviations on the results of existing model. The speed radial gradient and the theturbulent kinetic energy decreases near the wall when buoyancy affecting heat transfer.