Purpose

Two-phase R-744 ejectors are critical components enabling energy recovery in R-744 heat pump and refrigeration systems, but despite their simple geometry, the flow physics involve complex multiphase mixing phenomena that need to be well-quantified for component and overall system improvement. This study aims to report on multiphase mixture simulations for a specific two-phase R-744 ejector with supercritical inlet conditions at the motive inlet side.

Design/methodology/approach

Four different operating conditions, which have motive inlet pressure range of 90.1 bar–101.1 bar, are selected from an existing experimental data set. A two-phase thermodynamic equilibrium (TPTE) model is used, where the fluid properties are described by a thermodynamic look-up table.

Findings

The results show that the TPTE model overpredicts mass flow rates at the motive inlet, resulting in a relative error ranging from 15.6% to 21.7%. For the mass flow rate at the suction inlet, the relative errors are found less than 1.5% for three cases, while the last case has an error of 12.4%. The maximum deviation of the mass entrainment ratio is found to be 8.0% between the TPTE model and the experimental data. Ejector efficiency ranges from 25.4% to 28.0%. A higher pressure difference between the ejector outlet and the diverging nozzle exit provides greater pressure lift.

Research limitations/implications

Based on the results, near future efforts will be to optimize estimation errors while enabling more detailed field analysis of pressure, density, temperature and enthalpy in the computational domain.

Originality/value

The authors have two main original contributions: 1) the presented thermodynamic look-up table is unique and provides unique computation for the real-scale ejector domain. It was created by the authors and has not been applied before as far as we know. 2) To the best of the authors’ knowledge, this study is the first study that applies the STAR-CCM+ multiphase mixture model for R-744 mixture phenomena in heat pumps and refrigeration systems.

中文翻译：

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跨临界 R-744 热泵应用中两相 R-744 喷射器几何形状的计算多相混合物模拟

 目的

两相 R-744 喷射器是实现 R-744 热泵和制冷系统中能量回收的关键组件，但尽管其几何结构简单，但流动物理场涉及复杂的多相混合现象，需要很好地量化这些现象以改进组件和整体系统。本研究旨在报告特定两相 R-744 喷射器的多相混合物模拟，该喷射器在动力入口侧具有超临界入口条件。

设计/方法/方法

从现有的实验数据集中选择四种不同的工作条件，其动力入口压力范围为 90.1 bar–101.1 bar。使用两相热力学平衡 （TPTE） 模型，其中流体属性由热力学查找表描述。

 发现

结果表明，TPTE 模型高估了动力入口处的质量流速，导致相对误差范围为 15.6% 至 21.7%。对于吸入入口处的质量流速，三种情况的相对误差小于 1.5%，而最后一种情况的误差为 12.4%。发现 TPTE 模型与实验数据之间的质量夹带比的最大偏差为 8.0%。喷射器效率范围为 25.4% 至 28.0%。喷射器出口和发散喷嘴出口之间的压差越大，压力提升就越大。

研究局限性/影响

基于这些结果，不久的将来将努力优化估计误差，同时在计算域中实现对压力、密度、温度和焓的更详细的场分析。

 原创性/价值

作者有两个主要的原始贡献：1） 所提出的热力学查找表是唯一的，并为实际尺度的喷射器域提供了独特的计算。它是由作者创建的，据我们所知，以前从未应用过。2） 据作者所知，这项研究是第一项将 STAR-CCM+ 多相混合物模型应用于热泵和制冷系统中 R-744 混合物现象的研究。