Two-phase expansion waves at nozzle outlet using CO2
Two-phase expansion waves at nozzle outlet using CO2
复制标题
使用 CO2 在喷嘴出口处产生两相膨胀波
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
A. Harada
中科院分区：
文献类型：
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作者：
M. Nakagawa;Hiroyuki Chino;A. Harada
二氧化碳因其环保、无毒、不易燃等特性，作为制冷和空调系统的制冷剂得到了广泛的研究。为了提高CO2制冷系统的COP，需要一种利用两相流喷射器回收膨胀阀膨胀能量的新型制冷系统。了解两相流中这两种波的特性对喷射器的设计具有重要意义。本研究的目的是阐明实验确定的两相流喷嘴出口处的CO2膨胀波的特性。进行了CO2高压放空实验。通过改变入口温度、入口压力和喷嘴背压，得到了膨胀波的实测减压曲线。实验的减压后的喷嘴更迅速地减少比使用等熵均匀平衡预测。随着入口温度的降低，喷管内的压力分布和喷管后膨胀波的压力分布与预测的压力分布相差甚远。在喷嘴之后也出现了几乎平坦的压力分布，其长度随着入口温度的降低而增加。由于流动是超音速的，膨胀波可以在这些平坦轮廓之后到达相对的壁。随着入口温度的降低，喷管后膨胀区的有效长度也明显变长。CO2膨胀区的延长低入口温度是相同的蒸汽膨胀波的实验压力分布中观察到的。
CO2 has been extensively researched as a refrigerant for refrigeration and air conditioning systems because of its environment-friendly, nontoxic and nonflammable characteristics. In order to increase the COP in using CO2, a new refrigeration system that uses the two-phase flow ejector to recover the expansion energy at the expansion valve is needed. Understanding the characteristics of both waves in two-phase flow is very important in designing the ejector. The purpose of the present study is to elucidate the experimentally determined characteristics of expansion waves of CO2 at the outlet of the two-phase flow nozzle. High-pressure blowdown experiment of CO2 had been carried out. The measured decompression curves of the expansion waves were varied by changing the inlet temperature and pressure and the back pressure of the nozzle. The experimental decompression profiles after the nozzle were more rapidly decreasing than those predicted using Isentropic Homogenous Equilibrium. As the inlet temperature became low, the pressure profiles inside the nozzle and of expansion waves after the nozzle decreased far from the predicted profiles. Almost flat pressure profiles, which were increasing in length with decreasing inlet temperature, also appeared right after the nozzle. Expansion waves could reach the opposite wall after those flat profiles because the flow was supersonic. Considerably, the effective length of expansion region after the nozzle was also becoming longer with decreasing inlet temperature. The lengthening of the expansion region of CO2 for low inlet temperature was the same as that observed in the experimental pressure profiles of steam expansion waves.