制冷剂在工质泵轴承微隙内高速剪切流动与传热特性研究

Flow and heat transfer characteristics of refrigerant under high shear-rate within limited space are the bases of oil-free refrigerant hydrodynamic lubrication which are crucial for the stability and reliability of self-lubricated refrigerant pump/compressor in free cooling system with evaporation. In this project, the flow pattern transition and heat balance characteristic of refrigerant confined within rotational periodic micro-scale convergent-divergent channel of journal bearing in refrigerant pump will be highlighted, especially focusing on phase transition with cavitation and non-equilibrium thermodynamic process under high shear-rate near saturated liquidus curve. Through combination of theoretical analysis and experimental research, the basic coupling mechanism between flow and heat transfer characteristics of refrigerant film with phase transition under high shear-rate within limited space will be studied in search of the formation condition and evolution features of pressurized refrigerant film under pulsed excitation. In order to clarify the principal influencing factors and acting mechanism on the formation of non-equilibrium thermodynamic refrigerant transient interface within limited space, the theoretical visco-elastic hydrodynamic lubrication model of refrigerant with phase change will be established by considering the nonlinear thermal physical properties of meta-stable fluid and rheological characteristics induced by cavitations. Based on above, load capacity and dynamic stability experiments of pressurized refrigerant film with phase change will be carried out to analyze the fluid-structure coupling mechanism between refrigerant film and high speed rotor aiming at establishing the basic design criteria of hydrodynamic lubrication with phase change for oil-free refrigerant pump.

受限空间高速剪切条件下制冷剂的空化相变流动与传热特性是无油制冷剂动压润滑的基础，也是蒸发相变自然冷却系统自润滑制冷剂泵/压缩机稳定性与可靠性的关键。本项目重点关注工质泵径向轴承旋转周期缩-扩微小间隙内制冷剂的流态转捩特征和热平衡特性，尤其是近饱和液相区制冷剂高速剪切受迫流动的空化相变规律和非平衡热力学过程；拟采用理论分析与实验研究相结合的方式研究受限空间高速剪切制冷剂液膜相变流动与传热的基本耦合规律，探寻脉动激励下制冷剂相变压力膜的形成条件和演化规律；考虑相态转变过程中亚稳态流体非线性热物性和空泡诱发的流变特征，构建制冷剂相变粘弹性流体动压润滑理论模型，阐明影响受限空间制冷剂非平衡热力学瞬态界面形成与发展的主要因素和影响机理；在此基础上，进行制冷剂相变压力膜承载特性与动力学稳定性实验，获得制冷剂自润滑压力膜与高速转子的流-固耦合特性，最终确立工质泵无油制冷剂相变动压润滑的基本设计准则。

在工质泵驱动自然冷却系统中，制冷剂工质泵采用贯流式设计，制冷剂不仅是润滑剂，而且也充当了冷却剂的角色，其中蒸汽型汽蚀是影响制冷剂自润滑轴承承载特性的关键核心问题。本研究针对自然冷却系统的工作环境设计了高速制冷剂自润滑工质泵，实现了制冷剂润滑工质泵的高速运转，探索了饱和液相线附近动压的形成机理，考虑了蒸汽型汽蚀的影响，结合雷诺边界条件分析了轴承内的压力分布和轴承的承载特性，比较了不同环境温度、压力、偏心率和运转速度对轴承性能的影响，另外比较了蒸汽型空化发生时轴承的动态参数和稳定性参数，揭示了制冷剂空化相变流体动压润滑形成与发展过程中流动与传热特性及耦合机理，建立空化相变流体动压润滑的数理模型，实现相变流体动压润滑承载特性和热稳定性的预测与评估；明确了制冷剂剪切空化相变压力膜形成的非平衡热力学过程；获得了流体热物性参数、通流截面变化率、环境温度和压力等参数对压力膜承载特性和稳定性的影响规律；解决了高速旋转工质泵/压缩机中制冷剂自润滑热平衡和动力学平衡的基础性问题，确立制冷剂相变自润滑的基本设计准则；此外，分析了柔性轴承在高速旋转机械中的应用，包括止推轴承瓦块分区对压力分布的影响和全动压柔性支承技术，进而建立了高速转子的动力学模型，分析了影响高速旋转机械可靠性的主要影响因素和影响机理，为制冷剂自润滑高速轴承-转子系统的优化设计提供了更全面的理论支撑。