| In the process of hypersonic flight,the high speed airflow brings significant aerodynamic load to the structures of the aircraft,which is far beyond the bearing capacity of the existing materials.Therefore,it is necessary to cool the structures down.The regenerative cooling is the most frequently used method in the cooling schemes.For this method,it is necessary to study the flow and heat transfer characteristics of the endothermic hydrocarbon fuels.Density as an important thermophysical parameter is essential,which is important for the calculation of other physical quantities.In order to realize the online density measurement of the endothermic hydrocarbon fuels,two online density measuring systems were designed and constructed based on the attenuation theory of gamma-ray using an account rate model for high temperature and high pressure and negative temperature and high pressure.The temperature measurement ranges were 290-730 K and233-323 K,respectively.The highest pressure reached 10 MPa and the synthetic relative standard uncertainties were 0.17%-1.38% and 0.13%-1.46% respectively.On the basis of experimental tests to verify the accuracy of the two measurement systems by pure fluids and mixtures of different density ranges,the density of hydrocarbon fuels A and B for high temperature and high pressure and the density of hydrocarbon fuel C for negative temperature and high pressure were tested,and the density curves of each of the different working conditions were plotted.At the same time,the changes of the density of hydrocarbon fuels A,B and C with temperature and pressure were analyzed.On this basis,the isothermal diffusion coefficient of these three hydrocarbon fuels under different pressures were deduced,which will be helpful to understand the heattransfer mechanism of fuels.The construction of the gamma-ray density measurement system makes it possible for the on-line measurement of the densities of hydrocarbons and their mixtures under supercritical conditions. |
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