Experimental Research On Heat Transfer And Flow Resistance Characteristics Of Hydrocarbon Fuels At Supercritical Pressure

Hypersonic aircraft technology is developing rapidly.As the speed of the aircraft increases,the thermal load on the aircraft surface increases,resulting in excessive local engine temperature.With extremely high heat flux densities,traditional passive thermal protection is difficult to achieve the cooling target.At present,the most effective cooling technology is regenerative active cooling technology.The aircraft fuel flows through the heated engine surface to cool the engine before entering the combustion chamber.The key to regenerative active cooling design is to obtain the heat transfer and flow characteristics of hydrocarbon fuel under actual engineering conditions.In this paper,endothermic hydrocarbon fuel is used as the working medium.The experimental pressure is 3～5MPa;the mass flow rate is basically controlled at about1.26g/s;the heat flux density is 0～250kW/m~2;the fluid temperature is 280～875K;horizontal round tube with inner diameter 4mm;and the twist ratio is 12.63 and 6.31,respectively.The heat transfer characteristics and flow resistance characteristics under supercritical pressure were experimentally studied.The characteristics and mechanisms of heat transfer and flow under supercritical pressure were explored.And the effects of thermal parameters on them were analyzed.The results show that:(1)During the entire heat transfer process,the hydrocarbon fuel will undergo 5 heat transfer stages,which respectively are laminar,turbulent,pseudo-boiling,turbulent,and chemical reaction zone;system pressure and heat flow density affect the the thermophysical properties of hydrocarbon fuels to affect convective heat transfer;the effect of thermal acceleration is negligible,and the buoyancy effect is significant in the test range of this article;the average heat transfer coefficient of the twisted tube is greater than the ordinary smooth tube by about 6.0～9.0%.(2)The heat transfer test data of the ordinary smooth tube in this article fits the Gnielinski correlation well,but the predicted value of the Dittus-Boelter correlation is lower than the experimental value;the heat transfer test data of twisted tube has a large fitting error with Petukhov correlation and Hata–Masuzaki correlation.An improved heat transfer correlation of horizontal twisted tube is proposed,whose mean absolute error(MAE)is 12.57%,root mean square error(RMSE)14.88%.(3)For the frictional resistance coefficient of hydrocarbon fuel,at the same mass flow rate and temperature,the greater the pressure,the smaller the resistance;the heat flow density has a small effect on the frictional resistance coefficient;the frictional resistance coefficient of the twisted tube is higher than that of ordinary smooth tubes.And the smaller the twist ratio y,the larger the frictional resistance coefficient.(4)The experimental friction coefficient of the ordinary smooth pipe in this paper fits well with the Filonenko correlation,and the predicted f value of the Blasius correlation is lower than the experimental value.The experimental results of the frictional resistance coefficients of the twisted tube has large fitting errors with Jensen correlation and Manglik?Bergles correlation.An improved frictional resistance coefficient is proposed,with MAE of 4.75%and RMSE of 5.09%.