Abstract:

As an important energy-saving component of the CO₂ refrigeration/heat pump system, the working ability of the ejector has an important impact on the improvement of system performance. Despite the structural simplicity of the CO₂ ejector, its internal flow is intricate and encompasses physical phenomena like non-equilibrium phase transitions, transonic and Mach waves. To this end, a homogeneous relaxation model (HRM) for two-phase flow of CO₂ was developed in this study, and the reliability of the model was verified by experimental data, from which a numerical study of the adjustable ejector was conducted to analyze the effects absence or presence of needle, needle position, and operating condition variations on the performance and internal flow of the adjustable ejector. The results demonstrate that the needle increases the irreversible loss of the primary flow and also alters the expansion state of the primary flow at the nozzle outlet. By adjusting the nozzle throat area through the needle, it improves the ability of the ejector to adapt to different operating conditions, so that the ejector maintains the optimal running state under different conditions. Consequently, compared with fixed ejectors, adjustable ejectors exhibit an average efficiency improvement of 10.74%.

Key words: adjustable ejector, CO₂, homogeneous relaxation model, two-phase flow, computational fluid dynamics

摘要：

作为CO₂制冷/热泵系统重要的节能部件，喷射器的工作能力对系统性能的提升有着重要影响。尽管CO₂喷射器的结构简单，但其内部流动十分复杂，包含非平衡相变、跨声速和马赫波等物理现象。为此，本研究建立了用于CO₂两相流模拟的均相弛豫模型（HRM），通过实验数据验证了模型的可靠性，并以此开展了对可调式喷射器的数值研究，分析了有无探针、探针位置和工况变化对可调式喷射器性能和内部流动的影响。研究结果表明，探针增加了一次流的不可逆损失，同时也改变了喷嘴出口一次流的膨胀状态；通过探针调整喷嘴喉部面积，提高了喷射器适应不同工况运行的能力，使喷射器在不同工况下保持最佳的运行状态；与固定式喷射器相比，可调式喷射器效率平均提升10.74%。

关键词: 可调式喷射器, CO₂, 均相弛豫模型, 两相流, 计算流体力学