大温度滑移三元非共沸工质流动沸腾传热传质机理研究

Based on the characteristic of temperature variation of the high temperature glide zeotropic working fluid during the evaporation process, the temperature-enthalpy relationship of the binary working fluid can be improved by adding the third component. Then, an excellent temperature match can be obtained between the working fluid and the heat source/sink. Consequently, the heat transfer irreversibility can be significantly reduced and the efficiency of the thermodynamic cycle can be improved. Whereas, different from the phase change heat and mass transfer process of traditional zeotropic working fluid, remarkable sensible heating is transferred during the phase change of high temperature glide ternary working fluid, and the composition shift is obvious. Thus, the classical heat and mass transfer theory is incomplete. Therefore, the following research work will be conducted:.(1) Observing the phase interface morphology of flow boiling and analyzing the characteristics of flow pattern transition, measuring the two-phase pressure drop and developing the prediction model of two-phase friction pressure drop based on the flow pattern and separated-phase model;.(2) Experimentally and theoretically exploring the heat and mass transfer coupling mechanism, considering the influence of the additional sensible heat transfer resistance to the interface mass transfer resistance and phase change behavior for the high temperature glide working fluid. Then, developing the theoretical model for the flow boiling heat transfer coefficient;.(3) Studying the composition shift characteristic and temperature-enthalpy relationship for the ternary mixture during the evaporation process, on the base of non-equilibrium film theory and experimental results, and by taking a full consideration of the momentum, heat and mass transfer process near the gas-liquid interface and multi-component mass transfer interaction effects..The research can deepen the fields of gas-liquid two-phase flow and heat and mass transfer, and provide the theoretical basis for developing novel thermodynamic cycle.

基于大温度滑移非共沸工质蒸发变温特性，引入第三组元可明显改善二元工质温焓关系，实现与大温度变化的冷热源形成良好的温度匹配，可显著减小换热不可逆损失，提高热力循环效率。与常规非共沸工质相变传热传质规律不同，大温度滑移三元非共沸工质相变过程伴随显著的显热换热，并且存在明显的组分迁移，传统相变传热传质理论不尽完善。本项目将开展以下研究：（1）观测流动沸腾相界面形态，分析流型过渡规律，测试两相压降，基于流型及分相模型建立两相摩擦压降的预测模型；（2）实验和理论探索大温度滑移非共沸工质附加显热换热阻力对相界面传质阻力，以及相变行为影响的热质传递耦合机理，构建流动沸腾换热的理论模型；（3）根据非平衡薄膜理论和实验结果，充分考虑气液相界面动量、热量、质量传递过程及多元传质交互作用，探究三元非共沸工质相变过程的组分迁移规律及温焓特性。该研究将深化气液两相流和传热传质领域，为构建新型热力循环提供理论依据。

大温度滑移非共沸工质可与大温度变化的冷热源形成良好的温度匹配，提高热力循环效率。本项目以大温度滑移非共沸工质为研究对象，对工质对进行筛选，并对其流动沸腾换热过程的传热传质机理进行基础理论研究。.对过冷系统的非共沸工质进行筛选。相对于纯质和小温度滑移工质，大温度滑移工质可显著提高系统能效，较大的温度滑移以及合理的温焓曲线凹凸性是非共沸工质选取的两个重要原则。相对于二元工质，三元工质显示出更优良的温度匹配性能。.搭建了大温度滑移非共沸工质相变换热实验台，对大温度滑移非共沸工质相变过程的两相流型、摩擦压降梯度、对流换热系数的变化特性进行了观测和测试。发现大温度滑移非共沸工质流型有泡状流、塞状流、波状流、环状流以及雾状流，且随着质量流速的增加，环状流发生时的干度减小。采用灰度图像处理方法对两相流型进行定量研究，发现泡状流的灰度值在50~100之间，干涸流、环状流以及雾状流的灰度值相对泡状流和弹状流的变化幅度较小。在干度小于干涸干度时核态沸腾为换热的主导机制，干度大于干涸干度后气相流动换热占主导。考虑核态沸腾和对流换热的贡献，以及传质阻力对核态沸腾成核的影响，开发了大温度滑移非共沸工质流动沸腾换热系数的预测模型，平均绝对偏差为22.05%。.构建了非共沸工质相变换热的非平衡热质传递膜模型，揭示了大温度滑移非共沸工质组分迁移机理。传质阻力的存在削弱了相变换热强度，且传热削弱因子随干度的增加而降低。易挥发组分在气相的扩散通量随质量流量和干度的增加而增加。随着干度增加，气相中对流对传质的贡献减增加，扩散对传质的贡献减小。使用非平衡膜模型可以准确预测流动沸腾换热系数，平均偏差小于20%。.本项目所揭示的大温度滑移非共沸混合工质管内流动沸腾传热传质机理，为构建和发展新型热力循环、研发新型换热装置提供必要的理论支撑，并进一步深化和完善气液两相流传热传质理论体系。