利用计算流体动力学模拟软件Fluent建立两相流CO2喷射器非均相模型，基于非均相模型对CO2喷射器的内部流场进行数值模拟，分析喷射器内部流场的相变、压力和速度变化情况，通过实验验证了模型精度；通过改变喷嘴段结构参数，探究了喷嘴设计对于喷射器性能的影响，并对喷射器结构进行优化.结果表明：喷射器喷射流量以及引射压力的模拟值与实测值的误差分别为 6.5% 和 5.0%，即所建模型具有较高的精度；当喷射器喷嘴段出口出现激波现象时，流体的压力和速度均出现波动，并且存在明显的边界层；喷嘴发散段的长度越长，喷射流量越小，喷射速度越高；通过优化喷嘴段结构参数，可使喷射器的效率提高 10.5%.
A CFD-based numerical analysis of a two-phase R744 ejector using heterogeneous mixture model is presented in this work. The flow patterns inside the ejector, such as the mass transfer rate, change of pressure and velocity alongside the ejector are analyzed. Based on the experimental work, the numerical model is validated. The effect of the ejector’s nozzle geometry on the ejector performance is discussed, and an optimization of the nozzle geometry is performed. Based on the experimental data, the numerical model predicts the motive mass flow rate and the suction pressure within an error margin of 6.5%. Shock wave phenomenon can be observed around the nozzle exit. The motive mass flow rate of the ejector decreases and the motive velocity increases with the increasing divergent length. The optimization of the nozzle geometry can increase the ejector efficiency by 10.5%.
［1］TISCHENDORF C. Investigation of an ejector in a R744 refrigeration systems with intermediate pressure evaporator ［D］. Braunschweig, Germany: Braunschweig University of Technology, 2014.
［2］LIU F, GROLL E A. Study of ejector efficiencies in refrigeration cycles ［J］. Applied Thermal Engineering, 2013, 52(2): 360-370.
［3］LUCAS C, KOEHLER J. Experimental investigation of the COP improvement of a refrigeration cycle by use of an ejector［J］. International Journal of Refrigeration, 2012, 35(6): 1595-1603.
［4］YAZDANI M, ALAHYARI A A, RADCLIFF T D. Numerical modeling of two-phase supersonic ejectors for work-recovery applications［J］. International Journal of Heat and Mass Transfer, 2012, 55(21/22): 5744-5753.
［5］PALACZ M, SMOLKA J, KUS W, et al. CFD-based shape optimisation of a CO2 two-phase ejector mixing section［J］. Applied Thermal Engineering, 2016, 95: 62-69.
［6］ANSYS Inc. ANSYS Fluent theory guide ［CP］. Canonsburg, PA: ANSYS Inc, 2011.
［7］SINGHAL A K, ATHAVALE M M, LI H, et al. Mathematical basis and validation of the full cavita-tion model［J］. Journal of Fluids Engineering, 2002, 124(3): 617-624.
［8］ELBEL S, HRNJAK P. Experimental validation of a prototype ejector designed to reduce throttling losses encountered in transcritical R744 system operation［J］. International Journal of Refrigeration, 2008, 31(3): 411-422.
［9］MATSUO K, MIYAZATO Y, KIM H D. Shock train and pseudo-shock phenomena in internal gas flows［J］. Progress in Aerospace Sciences, 1999, 35(1): 33-100.
［10］GNANI F, ZARE-BEHTASH H, KONTIS K. Pseudo-shock waves and their interactions in high-speed intakes［J］. Progress in Aerospace Sciences, 2016, 82: 36-56.
［11］LIEELE A B, GARIMELLA S. A critical review linking ejector flow phenomena with component- and system-level performance［J］. International Journal of Refrigeration, 2016, 70: 243-268.
［12］KAWAMOTO Y, OGATA G, SHAN Z. Ejector energy-saving technology for mobile air conditioning systems［J］. SAE Int J Passeng Cars-Mech Syst, 2017, 10(1): 102-110.
