| 摘要: |
| 结合湍流射流发展规律，本文提出一个两相喷射器喷嘴距的设计方法：在给定引射流量下，当射流外边界的半径增长至混合段半径时，射流行进的距离为最优喷嘴距。利用数值模拟对比喷嘴距分别为3、5、7.5、10、15 mm时两相CO2喷射器性能。结果表明：喷嘴距为5 mm时射流发展正好符合上述设计条件，此时喷射器升压性能最优，为0.69 MPa，相对15 mm时提升46.8%。对比引射腔内不同截面上的射流速度分布可知：当喷嘴距大于最优值时，引射腔内的射流外边界将超过混合段半径，一部分射流无法进入混合段，引射腔的壁面附近形成涡流区，导致射流动能耗散，升压性能下降；当喷嘴距小于最优值时，引射过程在混合段内完成，混合段有效长度减小，升压性能比最优时下降1.5%。根据射流速度分布特性，结合本文案例拟合了最优喷嘴距的关联式，预测结果与CFD相差4.2%，可用于优化设计时预估最优喷嘴距。 |
| 关键词: 喷射器 喷嘴距 优化 射流 |
| DOI： |
| Received:August 23, 2021Revised:November 02, 2021 |
| 基金项目:国家自然科学基金（51776119） |
|
| Optimization and CFD Analysis on Nozzle Exit Position of Two-phase Ejector |
|
Long Jun'an1, Song Xia1, Shi Junye1,2, Chen Jiangping1,2
|
| (1.Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University;2.Shanghai High Efficient Cooling System Research Center) |
| Abstract: |
| This study proposes an optimization guideline for a two-phase ejector's nozzle exit position (NXP) based on the turbulent jet mixing mechanism. Under a given suction mass flow rate, the optimal NXP is the distance that the jet travels when the external boundary of the jet increases to the mixer radius. The performances of two-phase CO2 ejectors with NXP values of 3, 5, 7.5, 10, and 15 mm were studied by numerical simulations. The results show that when the NXP is 5 mm, the jet mixing pattern can exactly satisfy the above guidelines. In this case, the ejector has a maximum pressure-lift of 0.69 MPa, 46.8% higher than that of the 15 mm case. By analyzing the jet velocity profiles on different cross-sections in the suction chamber, we show that if the NXP is greater than the optimum value, the external jet boundary will exceed the mixer radius, preventing part of the jet flow from entering the mixer. In addition, a vortex region appears near the suction chamber wall, resulting in jet energy dissipation and thus degrades pressure recovery. When the NXP is less than the optimal value, the entrainment process is completed in the mixer, and the effective length is reduced, causing a 1.5% decrease in pressure recovery. This study is enlightened by the jet velocity characteristic and proposes a correlation for the initial guess of the optimal NXP, which shows a 4.2% deviation from the CFD result. |
| Key words: ejector nozzle exit position optimization jet |
