Visualization of the Carbon-dioxide Refrigerant in the Convergent-divergent Nozzle
Visualization of the Carbon-dioxide Refrigerant in the Convergent-divergent Nozzle
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收敛-扩散喷嘴中二氧化碳制冷剂的可视化
DOI：
10.11368/tse.27.77
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
中川 勝文
中科院分区：
文献类型：
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作者：
川村 洋介;藤沢 拓弥;中川 勝文
提高两相流喷嘴的性能对喷射式制冷系统的发展具有重要意义。在CO2临界点附近，小喷嘴中制冷剂的速度尚未被测量。利用阴影法对CO2制冷剂在短扩张段缩放喷管中的流动进行可视化，并验证能否从拍摄的视频中计算出液滴速度。本文对三种不同扩张长度和扩张角度的收敛扩张喷管进行了实验研究。在过冷液体和超临界进口条件下，对喷嘴内CO2制冷剂的流量和液滴速度进行了测量。对于喷嘴入口温度为20℃的情况，流量测量结果表明，与其它入口温度条件不同，在所有入口压力下，测量流量均比理论流量增加约5%。这主要是由于热力学非平衡现象引起的沸腾延迟对汽液两相流动的影响比其它入口温度情况下的影响大。此外，液滴速度测量的结果阐明，在喷嘴中的液滴几乎没有加速的路径从喉部到出口。在临界点附近，CO2制冷剂容易发生减压沸腾，因此，在喷嘴内的流动应处于均相平衡状态。而在入口温度为20℃时的实验结果表明，由于测量的液滴速度并没有比均质平衡流模型的理论平衡速度加速得更多，所以小喷嘴内的制冷剂流动偏离了均质平衡流。
To improve the performance of the two-phase flow nozzle is very important for the development of the ejector refrigeration system. The velocity of refrigerant in the small nozzle has not yet been measured at near the critical point of the CO 2. The purpose of this study is to visualize the CO 2 refrigerant flowing in a convergent-divergent nozzle with short divergent length using the shadowgraph method, and to verify whether the droplet velocity can be calculated from the captured video. In this study, three types of convergent-divergent nozzles with the same cross-sectional area at the inlet, throat and outlet and different divergent lengths and angles were tested. The measurements of the flow rate and the droplet velocity of CO 2 refrigerant in the nozzle were carried out at the subcooled liquid or supercritical inlet conditions. For the case of the nozzle inlet temperature of 20℃, the results of flow rate measurement showed that the measured flow rate increased by about 5% for all inlet pressure compared with the theoretical flow rate, unlike the other inlet temperature conditions. It is mainly because the influence of boiling delay according to thermodynamic non-equilibrium phenomena is larger than the other inlet temperature cases. Also, the results of the droplet velocity measurement elucidated that the droplets in the nozzle were scarcely accelerated in the path from the throat to the outlet. The CO 2 refrigerant flow in the nozzle is expected to be at the homogeneous equilibrium condition because the decompression boiling can start easily near at the critical point. However, the experimental results at the inlet temperature of 20℃ showed that the refrigerant flow in small nozzle deviated from the homogeneous equilibrium flow because the measured droplet velocity was not accelerated more than the theoretical equilibrium velocity of homogeneous equilibrium flow model.