Improvement of Nozzle Performance for Flashing Expansion of Initially Subcooled Hot Water

结果表明，喷管喉部附近的热不平衡程度影响喷管的性能特性，如临界流量、喷管轴向压力分布、推力和推力系数等。随着热不平衡程度的增加，闪蒸开始的延迟时间变长，喷嘴中的液滴没有得到充分加速，气液比滑移变大。因此，为了提高喷管的性能，有必要减小喷管喉部附近的热不平衡量。首先，采用传统的缩放式喷管，对喷管的性能特点和喷管效率降低的原因进行了实验研究。其次，将压力失调量(作为热不平衡程度之一)随减压率的降低而减小的关系应用于喷管设计。结果表明，采用这种方式可以提高喷管的推力系数。第三，众所周知，干扰刺激了闪光的开始。因此，在分流通道中安装细导线的喷嘴被设计成制造干扰，然后进行测试。细丝喷管的推力系数较大。提出了一种确定喷管出口截面积的方法。最后，从临界流模型的角度测量轴向含气率分布是很重要的。尝试用中子照相法测量喷管中轴向含气率分布。

It was made clear that the degree of thermal nonequilibrium near a nozzle throat affects the performance characteristics of nozzles, such as the critial flowrate, the pressure profile along the axis of the nozzle, the thrust, and the thrust coefficient. As the degree of the thermalnonequilibrium increases, the delay time of flashing inception becomes longer, and droplets in the nozzle are not accelerated fully and the slip between gas and liquid ratio becomes larger. Thus, it is necessary to decrease the magnitude of the thermal nonequilibrium near the nozzle throat for improving the nozzle performance.First of all, the performance characteristics and the reason why the nozzle efficiency de-creases were studied experimentally using conventional convergent-divergent nozzles. Second, the relationship that a pressure undershoot (as one of the degree of thermal nonequilibrium) decreases with decreasing a decompressive rate was applied to the nozzle design. It was found that the thrust coefficient of the nozzle is improved in this manner. Third, it is known that disturbance stimulates the flashing inception. Thus, the nozzle installed thin wires in the divergent passage was designed to make disturbance and then tested. The nozzles with the thin wires showed higher thrust coefficient. A methodof determining the cross-secectional area at the nozzle exit was also proposed. Last, it is important to measure axial void fraction profiles from the viewpoint of a critical flow modeling. Measurement of the axial void fraction profiles in the nozzle was tried by using neutron radio-graphy.