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

初始过冷热水闪蒸膨胀喷嘴性能的改进

基本信息

批准号：
62460100
负责人：
FUJII Terushige
金额：
$ 5.06万
依托单位：
Kobe University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

项目摘要

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.

结果表明，喷管喉部的热不平衡程度影响喷管的临界流量、沿喷管轴线沿着的压力分布、推力和推力系数等性能特性。随着热不平衡程度的增加，闪蒸起始的延迟时间变长，液滴在喷嘴内加速不充分，气液比滑移变大。因此，减小喷管喉部的热不平衡是提高喷管性能的必要措施。首先，采用常规收敛-扩张喷管，对喷管的性能特点和效率下降的原因进行了实验研究。其次，将压力下冲（作为热不平衡度之一）随减压率减小而减小的关系应用于喷管设计。发现以这种方式改善了喷管的推力系数。第三，已知扰动刺激闪光起始。为此，设计了一种在扩张通道内安装细丝的喷管来制造扰动，并进行了试验。细金属丝喷管具有更高的推力系数。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空隙率分布是很重要的。用中子射线照相法测量了喷管内轴向空隙率分布。