跨临界CO2两相流可调式喷射器的流动模拟和性能分析

doi:10.11949/0438-1157.20230985

摘要/Abstract

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

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

中图分类号:

TK 123

陈壮, 刘光弟, 曾宏轩, 赵红霞. 跨临界CO₂两相流可调式喷射器的流动模拟和性能分析[J]. 化工学报, 2023, 74(11): 4515-4526.

Zhuang CHEN, Guangdi LI, Hongxuan ZENG, Hongxia ZHAO. Flow simulation and performance analysis of adjustable ejector for trans-critical CO₂ two-phase flow[J]. CIESC Journal, 2023, 74(11): 4515-4526.

图/表 18

图1 喷射器内部流动示意图

Fig.1 Schematic of the flow inside the ejector

图2 可调式喷射器结构尺寸示意图

Fig.2 Schematic of adjustable ejector structure

表1 可调喷射器的几何参数

Table 1 Geometrical parameters of the adjustable ejector

几何参数	数值
探针直径D_ne/mm	1.78
喷嘴入口直径D_in/mm	4.99
喷嘴喉部直径D_th/mm	1.76
混合室直径D_mix/mm	3.46
扩散室出口直径D_ej,out/mm	8.35
探针长度L_ne/mm	2.40
喷嘴收敛段长度L_con/mm	9.16
喷嘴扩散段长度L_dif/mm	6.32
喷嘴出口位置NXP/mm	6.00
混合室长度L_mix/mm	15.00
扩散室长度L_ej,dif/mm	70.00
探针位置L_p/mm	0~2.40

图3 可调式喷射器3D流道剖视图

Fig.3 Adjustable ejector 3D flow channel cutaway view

图4 跨临界一次流喷嘴工况下饱和压力的确定

Fig.4 Saturation pressure determination of the trans-critical primary flow nozzle operation conditions

表2 Fluent的设置方案

Table 2 Setup program for Fluent

名称		设置
求解算法		pressure-based coupled algorithm
空间离散方式	梯度	least squares cell-based
	压力项	PRESTO!
	其他项	second order upwind
喷射器入口边界		pressure-inlet
喷射器出口边界		pressure-outlet
湍流边界		turbulent intensity and hydraulic diameter

图5 喷射器网格划分示意图

Fig.5 Schematic diagram of the mesh division of the ejector

图6 网格独立性验证

Fig.6 Grid independence verification

表3 模型可靠性验证所用实验数据［30］

Table 3 Experimental data for model reliability validation［30］

组别	一次流入口		二次流入口		压力升程	质量流量/(kg/s)
组别	P_p/MPa	T_p/℃	P_s/MPa	T_s/℃	P_lift/MPa	m_p	m_s
1	7.70	32.10	4.35	23.60	0.43	0.0273	0.0131
2	7.78	32.40	4.34	23.50	0.43	0.0279	0.0150
3	7.93	33.30	4.36	23.20	0.44	0.0278	0.0167
4	8.07	34.20	4.35	23.0	0.45	0.0277	0.0183
5	8.21	35.20	4.34	22.70	0.47	0.0276	0.0193
6	8.29	35.60	4.21	22.0	0.46	0.0274	0.0225
7	8.30	35.70	4.22	22.20	0.49	0.0273	0.0195
8	8.38	36.50	4.32	22.70	0.48	0.0273	0.0206
9	8.65	39.0	4.29	22.50	0.51	0.0265	0.0217
10	8.80	41.0	4.28	22.60	0.53	0.0264	0.0225
11	8.96	43.40	4.28	22.50	0.55	0.0258	0.0231

图7 模型可靠性验证结果

Fig.7 Results of model reliability validation

图8 探针对喷射器的影响

Fig.8 Effect of needle on ejector

图9 不同工况下可调式和对照组喷射器速度云图

Fig.9 Velocity distribution of adjustable and comparison group ejectors under different operating conditions

图10 探针位置对喷射器性能的影响

Fig.10 Effect of needle position on ejector performance under different inlet conditions

图11 不同压力升程下探针位置对喷射器性能的影响

Fig.11 Effect of needle position on ejector performance at different pressure lifts

图12 不同探针位置下可调式喷射器沿轴向压力分布

Fig.12 Axial pressure distribution of adjustable ejector with different needle positions

图13 不同探针位置下可调式喷射器速度云图

Fig.13 Velocity distribution of adjustable ejector at different needle positions

图14 可调式喷射器与固定式喷射器性能比较

Fig.14 Performance comparison of adjustable and fixed ejectors

图15 不同压力升程下可调式喷射器与固定式喷射器性能变化

Fig.15 Performance variation of adjustable and fixed ejectors at different pressure lifts

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跨临界CO₂两相流可调式喷射器的流动模拟和性能分析

Flow simulation and performance analysis of adjustable ejector for trans-critical CO₂ two-phase flow

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