非共沸混合物在不同润湿性表面水平管降膜蒸发的蒸汽压缩制冷系统特性研究

Due to the global warming potential (GWP) limit of refrigerants in the world, the researches about mixtures working fluids with low GWP and good environmental features and technologies to decrease the charging amount of refrigerants are big challenges faced by refrigeration industries. This project is to study the system characteristics of vapor compression refrigeration with various wettability surface horizontal tubes fall film evaporation. This project is to use non-azeotropic mixtures as working fluids, and focus on the improvement of heat transfer of fall film evaporation which has the advantage of decreasing the charging amount of refrigerants. This study will solve the following problems.(1) It is investigated the effect of the non-azeotropic mixture concentration in the liquid film on the thickness of the liquid film. (2) The various wettability surfaces are developed by machining methods and the influence of these surfaces on the fall film of non-azeotropic mixtures are studied. (3) Based on the theoretical and experimental studies , the influence of the mass transfer resistance on the non-azeotropic mixture fall film evaporation heat transfer is analyzed in order to improve the heat transfer of mixture and the efficiency of system . (4) The performance stability of non-azeotropic mixture vapor compression refrigeration system with a fall film evaporator is investigated. The influence of non-azeotropic mixture on the system is analyzed. The performance regulation of whole system under changed conditions is summarized and the changing fraction of mixture in the system is discussed as well. All these study will supply the theoretical basis and basic data for the improvement of non-azeotropic mixture application in the vapor compression system with a fall film heat transfer evaporator. This project has significant meaning of environmental protection and save energy.

随着国际上对制冷剂温室效应势（GWP）的限制，研究环保低GWP的混合工质和降低工质使用量是当前制冷界面临的重要课题。本项目以低GWP非共沸混合物为工质，结合可降低制冷剂使用量的降膜蒸发换热技术，并以提高水平管降膜换热为核心，拟开展非共沸混合物在不同润湿性表面水平管降膜蒸发的蒸汽压缩制冷系统特性的研究。此研究将要解决（1）揭示非共沸工质液膜浓度对管外液膜厚度的影响；（2）通过机械方法开发不同润湿性管表面，分析此表面对非共沸工质降膜的影响；（3）为提高换热和系统效率，通过理论和实验的方法分析非共沸工质液膜中传质阻力对降膜换热的影响；（4）研究非共沸工质对系统运行稳定性的影响，以及在变工条件下的系统运行规律和组分的迁移情况。这些研究为低GWP非共沸混合物在有降膜换热蒸发器的蒸汽压缩制冷系统中的应用提供重要的基础数据与理论基础，具有重要的环保和节能的意义。

以低GWP非共沸制冷剂为工质，结合可降低制冷剂使用量的降膜蒸发换热技术，并以提高水平管降膜换热为核心，采用理论分析、数值模拟和实验研究相结合的方法开展研究。通过研究制冷剂在不同改性铜表面的润湿特性，揭示了表面微结构改变对润湿性增强和润滑油添加对润湿性减弱的作用机制，掌握了激光加工表面稳定性变化的一般规律。通过激光加工对定向运输表面做出进一步的表面微结构优化与性能提升，制备出无液体损失的定向运输功能表面。分析了液体定向运输过程中的受力状况，阐明了不同方向的运动阻力对定向运输过程的影响，并对微结构对运输过程的影响进行机理解释。为进一步探索不同改性铜表面对换热的影响，进行了池沸腾换热实验，研究结果揭示了表面微结构和表面润湿性对传热增强和临界热流密度的影响机制。进行了蒸汽压缩式制冷系统水平管降膜蒸发换热研究，探索了热流密度、喷淋密度、含油率、蒸发温度、不同润湿性表面等变化对降膜蒸发换热的影响，分析了非共沸混合工质传质阻力、表面润湿性对换热过程中传热系数和临界热流密度的影响，明确了非共沸混合物在变工况条件下的组分迁移导致系统运行压力产生波动的特性。对管外混合工质降膜蒸发进行了液膜厚度测量及数值模拟，构建了管外液膜临界液膜厚度模型，揭示了液膜浓度和润湿性对液膜分布和传热系数分布的影响。研究结果为非共沸工质水平管降膜蒸发制冷系统的设计和运行以及换热表面改性设计提供理论与实践基础。