Experimental Investigation On Heat Transfer Of Supercritical Aviation Kerosene In A Mini Tube

Aircraft engines will produce enormous amount of heat while operating. As the rapid development of aviation technology, future aircraft will fly at higher Mach numbers, where aerodynamic heating becomes severer. Thus the cooling problem of engines will become a significant challenge for improving its performance in the future. At present, utilizing aviation fuel as the coolant to absorb the heat generated on aircraft is considered to be the most promising method to solve this problem. With the background of the thermal management for aero-engines, the heat transfer characteristics of supercritical aviation kerosene flows through a mini tube was studied by experimental method. The main purpose was to provide theoretical reference for design and optimization of fuel-air heat exchanger in the future.In the paper, a review of heat transfer and flow of supercritical fluid was completed. The heat transfer correlations for supercritical fluid were summarized and analyzed. Then an experimental investigation on heat transfer of supercritical aviation kerosene (China RP-3) flows through a mini tube was conducted. The experiment was conducted under pressure of3MPa and5MPa; the heat flux ranged from300to500kW/m2; the inlet temperature ranged from373.15K to573.15K; and the mass flow rate ranged from2g/s to2.5g/s.Firstly, the effects of heat flux, pressure, inlet temperature and mass flow rate on heat transfer were studied. Experiment results indicate that heat transfer coefficient increases with the increase of heat flux at5MPa; heat transfer deterioration appears at high heat flux condition at3MPa; the inner wall temperature was relatively high at the first1/3part of the tube when inlet temperature was relatively low, due to the incompletely developed thermal boundary layer; the inner wall temperature decreases with the increase of mass flow rate, and the heat transfer coefficient increases with the increase of mass flow rate.Secondly, the heat transfer and flow instabilities were described and analyzed briefly. The results indicate that instabilities are accompanied with the slight vibration of tube wall and sharp sound; instabilities all happened at low pressure, low inlet temperature and high heat flux conditions; the oscillation amplitude of outlet temperature was smaller than that of outer wall temperature, and the overall oscillation amplitude of outer wall temperature and outlet temperature decreases with the increase of mass flow rate. Thus, in the design of air- fuel heat exchanger for aeroengines, it is beneficial to raise the operating pressure of kerosene side to avoid the occurrence of heat transfer deterioration and improve the heat transfer effect. High pressure can also inhibit the occurrence of heat and flow instabilities and reduce the destructive effect of cyclical stress.Finally, the applicability of current heat transfer correlations on heat transfer of supercritical aviation kerosene was discussed. The Nusselt numbers were calculated with different correlations and then compared with the experimental results. The results indicate that the applicability of Krasnoshchekov, Dittus-Boelter and Sieder-Tate correlation is poor due to the large error; Hu and Gnielinski correlation showed good accuracy but could not describe the heat transfer deterioration, the applicability of these two correlation is limited; Jackson correlation showed similar trend with the experimental result, but the accuracy was not good enough, the applicability of Jackson correlation is also limited; all of the correlations could not precisely describe the occurrence of heat transfer deterioration.