【作者】 孙方田；

【导师】 马一太；

【作者基本信息】 天津大学 ， 工程热物理， 2007， 博士

【摘要】 采用自然工质CO₂的跨临界循环技术具有广阔的应用前景,而提高CO₂跨临界制冷循环系统性能是推广此技术应用的关键。本文通过理论分析和实验研究相结合,重点分析了CO₂专用润滑油PAG及CO₂/PAG混合物性能、超临界CO₂冷却换热的机理、新型气体冷却器换热性能及其对CO₂跨临界水-水热泵循环系统性能的影响。论文对润滑油基本参数的不同计算公式进行了分析,利用已知润滑油烷基苯的数据,提出了便于工程应用的合成润滑油基本参数的新通用计算公式。在少量已知的润滑油PAG物性数据基础上,通过修改润滑油物性经验公式,得出PAG物性的新计算公式。论文利用润滑油与制冷剂混合物物性计算公式对超临界CO₂/PAG混合物物性进行了计算分析;同时还利用聚集态理论和非平衡热力学对临界区物性的特殊性进行了分析,结果表明临界区分子聚集行为变化较为显著是临界区物性剧烈变化的主要原因。论文分析了润滑油对制冷系统的影响。利用连续性方程和动量方程计算分析了换热管内壁上的当量油膜厚度分布。并根据提出的气体冷却器的新换热模型,对气体冷却器的性能进行了计算分析。根据计算分析结果,提出了气体冷却器的优化结构,并设计加工出新型实验用气体冷却器。新型实验用气体冷却器不仅能够减小换热管内壁上的油膜厚度,减小热阻,而且还能强化了两侧流体的对流换热效果,在很大程度上,提高了气体冷却器的整体换热性能。论文通过实验研究对CO₂新型实验用气体冷却器性能进行了分析,发现新型实验用气体冷却器换热性能较好。同时还对带膨胀机或节流阀的CO₂跨临界水-水热泵循环系统进行了实验研究。结果表明,新型实验用气体冷却器在很大程度上提高了CO₂跨临界水-水热泵循环系统性能。气体冷却器出口处的CO₂温度越低,CO₂跨临界水-水热泵循环系统性能就越高,膨胀机可回收功也就越小。更多还原

【Abstract】 The natural refrigerant CO₂ transcritical cycle technology has a broad application foreground. Improvement of cycle system performance is the key for the CO₂ transcritical cycle technology popularization. Performance of lubricant oil special for CO₂ transcritical cycle and CO₂/PAG mixture were researched. The theoretical and experimental research was used to analyze heat transfer performance of gas cooler. The mechanics of supercritical CO₂ heat transfer under cooling condition was investigated. Heat transfer performance of the new type gas cooler was studied by means of simulated and experimented. And the effect of new type gas cooler on CO₂ transcritical water-to-water heat pump cycle system was researched.New general computing formulas of synthetic lubricant oil basic parameters were put forward by use of alkybenzene lubricant oil data, after different empiric formulas of lubricant oils basic parameter had been analyzed. The new computing formulas of lubricant oil PAG physical properties were presented on the base of existed empiric formulas and a few of PAG physical properties data.The properties of CO₂ and PAG mixture were calculated according to property empiric calculating formulas of refrigerant and lubricant oil mixture. The molecular aggregation theory and non-equilibrium thermodynamics were applied to study properties change in the critical region. The CO₂ properties severe change is resulted in severe change of CO₂ molecular aggregation behavior in the critical region.The effect of lubricant oil on refrigeration system was investigated. The equivalent oil film thickness distribution along length of tube was calculated by continuity equation and momentum equation. The new heat transfer model of gas cooler was proposed according to practical heat exchange process of gas cooler in the CO₂ transcritical refrigeration or heat pump cycle unit. The new heat transfer model was used to simulated heat transfer performance of the different structure gas cooler. And the new experimental gas cooler was designed and made by the simulated and analyzed results. The new experimental gas cooler not only reduces lubricant oil thickness and decreases heat resistance, but strengthens heat convection of heat exchanger fluids CO₂ and water. Thus the whole heat transfer performance of new experimental gas cooler was enhanced at a great degree.The experimental researches on new experimental gas cooler and new CO₂ transcritical water-to-water heat pump cycle were performed. It found that the heat transfer performance of the new experimental gas cooler was better than old one. And experimental research on performance of the CO₂ transcritical water-to-water heat pump cycle system with expander or throttling valve was executed. It was found that the new experimental gas cooler improved the cycle performance of the CO₂ transcritical water-to-water heat pump cycle, at a large degree. The lower the CO₂ outlet temperature of gas cooler is, the better the cycle performance of the CO₂ transcritical water-to-water heat pump system is. The lower the CO₂ outlet temperature of gas cooler is, the smaller the recovery work.更多还原