Defect and Diffusion Forum Vol. 429

Abstract: For LOX/LCH4 variable thrust rocket engine, the propellant methane is traditionally selected as the coolant in regenerative cooling channel (RCC). With the decrease of engine thrust, the mass flow rate of coolant methane decreases gradually. At low engine thrust, the coolant methane is usually in a subcritical state. The heat transfer deterioration of subcritical methane occurs in RCC, which may cause thrust chamber wall ablation. The two-phase pressure drop data of methane are crucial parameters for the design and optimization of RCC. But it is rarely to find such measured frictional pressure drop data of methane in open published literature. The two-phase pressure drop of methane during flow boiling in the single mini channels with the diameters of 2.0 mm are investigated systematically. Effects of the mass flux (582.19~1755.48 kg/m²·s), inlet pressure (0.56~3.55 MPa), heat flux (53.25~318.68 kW/m²) on the frictional pressure drop of methane are discussed. The results show that the frictional pressure drop of methane during flow boiling increases with mass flux and inlet pressure at the experimental conditions, and heat flux shows weak effect on the frictional pressure drop. The comparisons of the experimental data with the predicted value by existing six correlations are analyzed. Contrary to the conventional channels, homogeneous model yields better prediction than five separated flow models. Present experimental results can provide reference for the design and optimization of RCC in LOX/LCH4 rocket engine.

Abstract: LOX/LCH4 rocket engine has been recognized as the ideal power choice for future space vehicles due to the merits of low cost, non-toxic and pollution-free, convenient maintenance, suitable for reuse and high specific impulse. In the process of wide range variable thrust of LOX/LCH4 rocket engine, the coolant methane is in a subcritical state due to the low combustor pressure under low operation conditions. The instability of two-phase flow is easy to occur in regenerative cooling channel (RCC), and it is urgent to investigate the heat transfer performance of methane with phase change in RCC. Experiments have been conducted to investigate the flow boiling characteristics of liquid methane in the single mini channels with the diameters of 1.0, 1.5 and 2.0 mm. Effects of the mass flux (266.75~1781.26 kg/m²·s), inlet pressure (0.56~4.24 MPa), heat flux (53.25~800.07 kW/m²) and channel diameter (1.0~2.0 mm) on the flow boiling heat transfer coefficients are tested. Results show that there are two regions with different heat transfer mechanism, one is the nucleate boiling dominated region for low mass quality and the other is the convection evaporation dominated region for high mass quality. A new correlation expressed by Bo, We, Kp, X, Co, Ftg is proposed, which yields good fitting for 355 experimental data with a mean absolute error (MAE) of 10.9%. Present experimental results can provide reference for the thermal protection prediction and optimal design of RCC in LOX/LCH4 rocket engine.