制冷系统两相喷射器失效机理及耦合调控策略研究

According to the malfunction of the two-phase ejector as the expansion device applied in vapor compression refrigeration systems, in-depth research with simulation and experimental methods will be carried out to investigate the malfunctional mechanism of the two-phase ejector and the coupled system control strategy in this project. The visualization method will be used to observe and reveal the jet-entrainment flow characteristics in the suction chamber when the ejector is malfunctional for pressure lift or fluid entrainment. The improper match conditions among the ejector structure parameters and the thermodynamic parameters at the inlets and outlet of the ejector will be verified. In this condition, we will get the macroscopic malfunctional mechanism of the two-phase ejector. The ejector structure optimization and performance investigation at different operation conditions will be conducted, and the equations describing the performance characteristics of the ejector will be established. Then the structure optimization principle and design criteria of the ejector will be obtained. Based on research platform of an ejector enhanced autocascade refrigeration system, the coupling characteristics between the ejector and the system in the dynamic operation including start-up，intermittent and variable heat loads processes will be investigated，and the method of the performance degradation and malfunction diagnoses for the ejector in dynamic operation will be obtained. The effect of the control method which is integrated with the ejector, compressor and expansion valve on the adjustment of the ejector performance will be revealed. And then the optimal control strategy and technical scheme of realizing the high operation efficient and reliability of the refrigeration system will be achieved. The prospective research results of this project will be helpful to improve the system operation reliability and operating performance of various types of vapor compression refrigeration systems using ejector as the expansion device. Furthermore, it is hoped to provide the theory basis for the development of the ejector enhanced technique by conducting this research project.

本项目针对液-气两相喷射器作为膨胀机构应用于蒸气压缩式制冷系统中出现的失效现象，拟采用计算模拟和实验对两相喷射器失效机理及调控策略进行深入的研究。通过可视化手段观测并揭示两相喷射器升压和引流失效状态下引射腔内射流卷吸特性，探明喷射器结构与进出口热力参数的不良匹配条件，阐明喷射器失效的宏观机理；进行喷射器的结构优化和变工况性能研究，建立两相喷射器特性曲线方程，掌握喷射器结构优化设计准则；依托喷射器增效自复叠制冷系统为实验研究平台，揭示系统启动，间歇和变负荷运行过程中喷射器性能与系统热力参数的动态耦合规律，获取动态运行过程中喷射器性能衰减预测和失效判定方法。探讨喷射器与压缩机、节流阀联合控制方法对喷射器性能的调控作用，获得实现系统高效稳定运行的控制策略与技术方案。预期研究结果将为增强采用喷射器的各类蒸气压缩式制冷系统的运行可靠性和整体性能提供技术支持，并为喷射器增效技术的发展奠定理论基础。

随着人们生活水平的提高和科技的不断进步，低温制冷的需的日益增加，混合工质低温制冷技术获得了广泛关注。喷射器增效技术在降低蒸气压缩式制冷系统能耗方面具有独特的优势。然而，两相喷射器失效问题成为困扰系统可靠性的关键因素。本文针对两相喷射器失效内在机理和调控机制开展了相关研究，获得的主要结论如下：.（1）研究了喷射器结构不同对降温性能的影响特性，发现喷嘴喉部直径和混合段直径以及喷嘴出口位置均对于喷射器运行稳定性有至关重要的作用，过大和过小均会导致喷射器的失效，存在最佳的结构匹配关系；研究还通过多参数分析发现喷射器二次流入口温度的波动情况对于分析喷射器失效及失效类型的积极的作用；.（2）研究了制冷剂浓度分布和迁移特性对喷射器性能和系统整机性能的影响特性，发现制冷剂的迁移也是引起喷射器失效的主要因素。在混合工质制冷系统中，浓度又与制冷剂迁移密切相关，当低沸点工质浓度过大时，容易导致引射失效现象的发生。.（3）针对系统启动，二次流流量过大导致喷射器失效的特点，本项目创新提出了喷射器失效控制旁路并搭建实验系统。对比研究显示二次流单向旁通可以一定程度上避免引射失效的发生；研究了不同喷射器结构与系统调控参数，如压缩机转速、节流阀开度的耦合作用对喷射器失效特性的影响，发现降低压缩机启动转速，降低节流阀开度可以避免喷射器引射失效。.（4）研究发现了液引射气液两相流体时容易诱发压力脉动，且与混合段直径和压缩机转速密切相关。增大混合段直接可以降低压力脉动幅度，减少二次流入口带液量可以避免压力脉动的发生。.（5）提出了多种节能效果显著的低温制冷与高温热泵循环，探讨了回热器位置对喷射器自复叠制冷循环性能的影响，研究了喷射器在两级自复叠循环和高温热泵循环中的节能机制，提出了2种适用于高温热泵和大温跨热泵的新喷射器增效循环。