【作者】 李博；

【导师】 马一太；

【作者基本信息】 天津大学 ， 工程热物理， 2007， 硕士

【摘要】 随着国际上对自然工质CO₂跨临界循环研究的深入,提高CO₂跨临界制冷循环系统各部件的效率,加快其向实用化迈进是当前研究的关键问题。本文通过理论分析,实验研究相结合,重点对CO₂满液式蒸发器开展了研究。通过对CO₂管内和管外沸腾关联式的计算和对比,得出了CO₂池沸腾换热效果要好于管内沸腾换热,并为实验数据与关联式的对比提供了依据。论文对亚临界区CO₂与常规工质的物性进行了比较,研究了CO₂管内沸腾换热干涸问题和沸腾成核机理,提出了CO₂满液式蒸发器设计的设想。这些都有助于了解CO₂沸腾换热特性,可为设计高效、大型CO₂满液式蒸发器提供必要的理论基础。本文自行设计和制造了CO₂单管满液式蒸发器,并在原有CO₂热泵系统上进行改造,减少了实验成本。通过对CO₂单管满液式蒸发器进行实验研究,得出了满液式沸腾换热系数与热流密度、压力之间的变化关系,并与经验关联式进行了对比分析,发现实验结果与Cooper法吻合,平均偏差为9.85%。实验还对CO₂池沸腾进行了可视化研究,观察了CO₂沸腾气泡的变化情况。最后,总结出了二氧化碳单管池沸腾换热的实验关联式,和蒸发器换热系数表,为今后CO₂池沸腾蒸发器的研究和设计提供了实验基础和数据参考。更多还原

【Abstract】 As more and more international researches have concerned on natural working fluid CO₂ transcritical cycle, improvement of each refrigeration cycle’s part performance and the promotion of its practicality all become the key problems of current concerning research. Through theoretical analysis in the thesis, combined with experimental research, CO₂ pool-boiling evaporator was studied.Through calculation and comparison boiling correlations outside-tube with those of in-tube, it is found that CO₂ pool-boiling heat transfer coefficient is much higher than in-tube heat transfer coefficient. The analysis results also supply the basic data for the comparison with experimental data.The thermo-physical properties of carbon dioxide in the subcritical region are analyzed and compared with those of the conventional refrigerants in this thesis. Dry-up phenomena of CO₂ in-tube boiling heat transfer is analyzed, the characteristics CO₂ nucleation growth mechanism are investigated. The concept of CO₂ pool-boiling evaporator is presented. All the above studies can help to understand the theoretical for designing CO₂ pool-boiling evaporator in high efficiency and practicality.A CO₂ single tube pool-boiling evaporator was designed and made by ourselves. The primary CO₂ heat pump system was improved. Through experiment research on CO₂ single tube pool-boiling heat transfer, the relationship of heat transfer coefficient variety with heat flux and pressure was found, and compared with the experimental correlations. The experiment data are closed to theretical results of Cooper correlation, average error is 9.85%. The behaviors of bubbles in the experiment of CO₂ pool-boiling were observed. Finally, an experimental correlation of CO₂ single tube pool-boiling and a diagram of evaporator heat transfer coefficient is summarized in this thesis. All the results will give helps for study and design of CO₂ pool-boiling evaporator from experiments and data.更多还原