【作者】 安青松；

【导师】 马一太；

【作者基本信息】 天津大学 ， 工程热物理， 2009， 博士

【摘要】 本文针对CO₂带膨胀机制冷热泵循环中的关键问题,重点研究了该工质在膨胀机中的内部相变膨胀过程的理论分析和试验观察。论文首先从“基团贡献法”的研究思路出发,将常规复杂的GWP值计算方法进行了简化,进而对一些复杂结构的工质的GWP进行了估算,计算结果与给出的参考数据基本一致。说明宏观性质GWP是物质微观各部分基团性质的综合表现,有利于对未来合成的新制冷剂的GWP性质作出预测性判断。基于对制冷剂各种性能评价标准的对比分析,论文对制冷剂提出了“自然度”评价标准的概念,并从可持续发展的观点,对未来制冷剂发展方向进行了分析预测,明确了未来制冷剂主要的发展方向应该是CO₂等自然工质。论文认为CO₂膨胀机是提高CO₂热泵系统性能的关键部件之一,膨胀机内部膨胀过程涉及从超临界到亚临界并有相变,有复杂的机理。本文从理论分析的角度,对膨胀机内部相变过程进行了探讨。根据调研的相关理论,从不同模型中进行分析对比,提出了一种新的综合理论和模型。论文根据提出的综合模型对膨胀机的相变膨胀过程进行了模拟计算,从参数变化以及汽泡驱动力将膨胀过程进行了简化,划分为三个阶段,分别为初始核化、自由膨胀和有限膨胀阶段,计算结果表明与观测数据能够吻合保持一致。为直接观察到CO₂膨胀机内部快速降压的全过程,本文设计了两种可视化的实验装置。第一个装置是高压CO₂快速降压试验试块,为区分汽泡和油滴,在润滑油中添加荧光示踪剂,采用高速摄影仪对CO₂与润滑油混合物的快速降压过程进行试验观测。研究发现:降压速率越大,产生的汽化核心数越多,形成的稳定汽泡直径越小。第二个装置是对原CO₂滚动活塞膨胀机进行了改造,添加了内部LED光源,并在汽缸上加工安装耐压石英视窗,对膨胀机端盖及活塞进行了精加工研磨目的为了增加其反光性,实现了膨胀机内部相变膨胀过程高速摄影观测,拍摄了大量膨胀机内部CO₂相变过程的连续图片,通过图像处理可跟踪单个汽泡的行踪,为膨胀过程的理论分析提供实测数据。最后,根据相变成核理论和增加分子聚集度的可能,考虑跨临界循环不存在制冷剂凝结过程,在系统中注入“不凝性气体”,对压缩过程和放热过程没有负面影响,对膨胀过程和蒸发过程增加体相内的汽化核心数,起到正面作用。通过分别添加适当比例两种“不凝性气体”试验结果来看,都对膨胀机的膨胀功回收性能有所提升。更多还原

【Abstract】 Based on the key issues of CO₂ heat pump cycle system with expander, paper focuses on researching the theoretical analysis and experimental observation of internal phase change and expansion process in expander.The conventional complex calculation approach of GWP value had been simplified on basis of“group contribution method”, and the GWP value of complex structure refrigerants were estimated by use of this method. The results are consistent with reference datum. The analysis approach, some macro nature is comprehensive contribution performance of group characters, was conducive to predict and judge the future uncertain nature of the new refrigerant. According to the evaluation standards comparative analysis of refrigerants various performance, paper suggested the“nature”evaluation criteria concept for refrigerants. And based on the view of sustainable development point, the future development direction of refrigerant was analyzed and predicted. It is established that CO₂ etc natural refrigerants should be the main development direction of the refrigerant.Paper regards as CO₂ expander is one of the key components for improving the performance of CO₂ heat pump system, internal expansion in expander involves the transformation from the supercritical to subcritical, so it has the complex mechanism. Therefore, paper discussed phase transition process in expander, firstly from the view of theoretical analysis. a new integrated suitable theory andmodel was put forward based on the relevant theories and different models. According to the integrated model, Papers simulated and caculated the phase transition and expanding process of expender, the expanding process had been divided into three stages according to parameters change and bubble-driven force: initial nucleation, free expansion and limited expansion; each stage could been analyzed by use of their own models, and thereby the whole research process of expansion could be simplied. The results show that the theoretical calculations value was anastomotic consistant with the visual observational datum.In order to directly observing the whole rapid decompression process in expander, paper designed two visual experimental devices. One is high-pressure CO₂ test block. To distinguish between lubricant drip and bubble, the fluorescent tracer is added to the mixture. The decompression process of CO₂ and PAG lubricant mixture solution was experimental observed using high speed camera. The research results found that greater decompression rate, more nucleation rate, and smaller diameter of the stability bubble. The other is the rebuilded CO₂ rolling piston. The LED light source were added in expander, and the internal high-pressure quartz windows was installed on cylinder, and the cover and piston of expander were processed and grinding in order to increase those reflectance. The high-speed photographic observation of internal phase change and expansion process was carried out. A lot of continuous picture of internal phase change process in expander were obtained, and the track a singe bubble could be caught through image processing. It provided the measured datum for the theoretical analysis of expansion processFinally, considering that there is not refrigerant condensation process in transcritical cycle,“non condensable gas”is appended CO₂ expander on the view of phase change and nucleation theory. It has no negative impact on compression and heat process, and plays a positive role as increasing nucleation of bulk phase in expansion and evaporation process. From the experimental test results of adding the appropriate ratio of two“no condensable gas”, the methods had improved the performance of expander.更多还原