竖直下降圆管内超临界压力RP-3航空煤油传热恶化实验研究

为理解空-油换热器中的冷却换热特性，对竖直下降圆管内超临界压力RP-3航空煤油的换热进行了实验研究。探究了稳态换热特征和换热机理，探讨了质量流量、热流密度、运行压力和进口温度对换热的影响；基于拟沸腾数提出了传热恶化的临界准则以及壁温最大飞升值的预测准则；通过浮升力和热加速判别准则分析了两者对换热的影响；实现了换热关联式预测。结果表明：浮升力和热加速对换热的影响可以忽略。拟沸腾换热机制，即近壁流体膨胀力相比惯性力占主导时，类气态流体层覆盖壁面是传热恶化的原因。当拟沸腾数高于2.5×10^-4时，拟沸腾换热机制起作用。最后，探究了泄压过程中的瞬态换热特征。泄压过程中拟沸腾数不断增大，传热恶化加剧，高泄压速率下甚至出现壁温波动。

Experimental Study on Heat Transfer Deterioration of Supercritical-Pressure RP-3 Aviation Kerosene in a Vertical Downward Round Tube

To understand the cooling heat transfer characteristics in the air-kerosene heat exchanger, an experimental investigation on heat transfer of supercritical-pressure RP-3 aviation kerosene in a vertical downward round tube was conducted. The steady-state heat transfer characteristic and mechanism were studied, and the effects of mass flux, heat flux, operating pressure and inlet fluid temperature on heat transfer were discussed. Based on the pseudo-boiling number, the critical criterion for heat transfer deterioration and the prediction criterion for maximum rise in inner-wall temperature were proposed. The influences of buoyancy and thermal acceleration on heat transfer were analyzed by the discriminate criteria. The prediction correlation of heat transfer was achieved. Results indicate that the effects of buoyancy and thermal acceleration on heat transfer can be ignored. When the expansion force of near-wall fluid is dominant compared to the inertial force, the vapor-like fluid film covering the inner-wall, and this pseudo-boiling heat transfer mechanism is the reason for deteriorated heat transfer. When the pseudo-boiling number is higher than 2.5×10-4, the pseudo-boiling heat transfer mechanism becomes significant. Finally, the transient heat transfer in the pressure relief process was investigated. The pseudo-boiling number continuously increases during the pressure relief process, thus the heat transfer deterioration become more enhanced. High pressure reduction rate even leads to the wall temperature fluctuation.