喷嘴临界截面直径对喷射器性能影响实验研究

依据索科洛夫等学者提出的经验公式对喷射器进行优化设计,搭建了用于测量喷射器性能的实验台,以CO2为工质,分别研究当工作流体压力在8.0~9.6MPa、引射流体压力在2.4~2.8MPa以及工作流体温度在70~90℃时,喷嘴临界截面直径对喷射系数的变化规律。实验结果表明：当喷射器背压为3.9MPa、工作流体温度为90℃、引射流体压力为2.4MPa、工作流体压力在8.0~9.6MPa时,喷射器的喷射系数随喷嘴临界截面直径的增大而减小;当喷射器背压为3.9MPa、工作流体温度为90℃、工作流体压力为10.0MPa、引射流体压力在2.4~2.8MPa时,喷射器的喷射系数也随喷嘴临界截面直径的增大而减小;且喷射系数理论值与实验值吻合度较好,误差在±3.75%范围内。当喷射器工作流体压力为10.0MPa、引射流体压力为2.7MPa、喷射器背压为3.9MPa、工作流体温度在70~90℃时,喷射系数随着喷嘴临界截面直径的增大而逐渐减小。另外,在保持喷射器的基本工作参数不变时,工作流体压力及引射流体压力的提高对喷射器喷射系数均有提升作用。     

喷嘴临界截面直径对喷射器性能影响实验研究

依据索科洛夫等学者提出的经验公式对喷射器进行优化设计,搭建了用于测量喷射器性能的实验台,以CO_2为工质,分别研究当工作流体压力在8.0～9.6 MPa、引射流体压力在2.4～2.8 MPa以及工作流体温度在70～90℃时,喷嘴临界截面直径对喷射系数的变化规律。实验结果表明:当喷射器背压为3.9 MPa、工作流体温度为90℃、引射流体压力为2.4 MPa、工作流体压力在8.0～9.6 MPa时,喷射器的喷射系数随喷嘴临界截面直径的增大而减小;当喷射器背压为3.9 MPa、工作流体温度为90℃、工作流体压力为10.0 MPa、引射流体压力在2.4～2.8 MPa时,喷射器的喷射系数也随喷嘴临界截面直径的增大而减小;且喷射系数理论值与实验值吻合度较好,误差在±3.75%范围内。当喷射器工作流体压力为10.0 MPa、引射流体压力为2.7 MPa、喷射器背压为3.9 MPa、工作流体温度在70～90℃时,喷射系数随着喷嘴临界截面直径的增大而逐渐减小。另外,在保持喷射器的基本工作参数不变时,工作流体压力及引射流体压力的提高对喷射器喷射系数均有提升作用。     

基于CFD数值模拟下的蒸汽喷射器性能预测

建立了蒸汽喷射器热力学模型,并验证了该模型性能及结构计算的可靠性。并针对实际情况中,对该模型进行了动态模拟。结果显示：当工作流体的温度升高时,工质流体的质量流量都会增加,引射系数存在峰值,峰值所对应温度为热力学模型设定温度值;当引射流体的温度升高时,其质量流量也会随之增大,而工作流体的质量流量则较稳定,因此引射流体温度与压力的升高可以改善喷射器的性能;当背压升高时,在一定压力范围内,工质流体的质量流量都趋于稳定,而当背压超过热力学模型设定背压值时,引射流体的质量流量便随背压的升高而急剧下降,喷射器性能严重恶化,故认为该压力值为喷射器的临界背压。本文研究结果对喷射器的设计计算具有一定的指导作用。 关键词：蒸汽喷射器;热力学模型;数值模拟;引射系数     

蒸气喷射准双级压缩制冷系统的实验研究

实验探究了蒸气喷射准双级制冷系统中,气体喷射器进出口参数对喷射器喷射系数、COP和制冷量的影响,并与单级蒸气压缩制冷系统进行对比。实验数据显示:随着混合流体出口压力的增加,喷射系数和系统制冷量逐渐减小,而COP则先增加后减小;喷射系数、COP和制冷量随着工作流体压力的增加均呈现先增加后降低的趋势;随着引射流体压力的增加,喷射系数和制冷量均增加,COP先增加后减小;当蒸发温度到-31.4℃时(t_k=35.0℃),单级蒸气压缩式制冷系统将不再产生冷量,而蒸气喷射准双级制冷系统可达到的最低蒸发温度为-36.5℃。     

PEMFC发动机系统氢气喷射器流场模拟及性能分析

运用建立的初始几何模型模拟了PEMFC发动机系统氢气喷射器各工况的工作流体压力,每个工况保持引射流体压力和混合流体压力不变,分析工作流体压力对喷射器性能的影响规律。选取部分工况模拟了喷射系数随引射流体压力和混合流体压力的变化规律。     

蒸汽喷射式热泵变工况性能分析

采用数值模拟的方法对低压蒸汽增压利用系统中的蒸汽喷射式热泵在非设计工况下的操作性能进行研究，计算并分析了工作蒸汽压力和温度、引射流体压力及混合流体压力等热力参数对热泵操作性能的影响。数值结果表明：当混合流体的压力低于一定的数值时，喷射系数维持一定值；而热泵对引射流体压力的变化极为敏感，引射压力的微小变化可能导致热泵操作性能的急剧下降；提高工作蒸汽的压力并不一定能改善喷射泵的工作性能，这是因为提高工作蒸汽压力会增加额外的蒸汽量所致；喷射系数随工作蒸汽温度的升高而略有增大，并近似呈线性率。     

圆柱形混合室截面直径对喷射系数影响的实验研究

依据索科洛夫等学者提出喷射器计算的经验公式对喷射器进行优化设计加工,并自行搭建测量喷射器性能实验台。采用N_2、CO_2、R290 3种自然工质,研究了当扩压室直径为定值,实验压力为高压(10 MPa≤P≤100MPa)状态时圆柱形混合室截面直径变化对喷射器性能的影响规律。实验结果表明:当喷射器背压为3.9 MPa、工作流体温度为90℃、工作流体压力变化范围为8.0～10.0 MPa或引射流体压力变化范围为2.4～2.9 MPa、混合室截面直径在1.7～2.1 mm范围变化时,喷射器的喷射系数均随圆柱形混合室截面直径的增大而升高,且在实验工况范围内,以N_2为工质的喷射系数随圆柱形混合室截面直径变化趋势相对平缓。     

二维流动模型的喷射器性能分析研究

采用二维轴对称流动模型，计算分析了吸入通道内回流现象、喷射器“恒能力”现象与静压力在轴线上分布情况之间的关系；探讨了工作压力对喷射器性能的影响。结果表明：持续降低出口压力会在混合室内形成激波，喷射因数保持不变；工作压力过高会在混合室内产生壅塞，反而降低喷射因数；吸入压力过低会在喷射器吸入通道内产生回流现象，影响喷射式制冷系统运行的安全性。     

氨水液-汽型喷射器性能分析与结构优化

建立氨水液-汽型喷射器的一维稳态热力学模型,对喷射器的热力学性能与结构进行研究,包括工作喷嘴、扩散段中的工作流体与引射流体的压力及速度的变化,以及不同扩散角对喷射器性能的影响。将氨水液-汽型喷射器应用于Kalina循环,以降低膨胀机的背压来提高循环输出功与效率。在对喷射器性能,如:引射系数、引射压力及混合出口压力等相互关系分析基础上,以得到Kalina循环更高的循环输出功为目的,对喷射器的性能与结构进行研究。结果表明,喷射器的扩散角越小,越有利于喷射器的压力回收,扩散角越大,越有利于汽、液两相的混合。给定喷射器混合出口压力时,引射系数越小,引射压力越小。引射系数对提高Kalina循环性能起关键作用。最终优化得到的喷射器设计工况为:扩散角为1°、引射系数0.1、引射压力656 k Pa。     

制冷用蒸汽喷射器的运行参数分析

蒸汽喷射制冷系统运行时,喷射器参数的变化将会对喷射器的工作性能造成很大影响。通过单因素分析法对喷射器的工作蒸汽压力、引射蒸汽压力和混合蒸汽出口压力进行分析,得到对喷射器内部流场和喷射系数影响的一般规律。     

气-液喷射器工作参数的数值模拟

建立了气-液喷射器工作过程的一维稳态模型。运用数值计算方法对模型进行求解,采用Nabil Beithou等中的定解条件,计算了水为工质时的气-液喷射器内轴向压力分布。计算结果表明,本模型得到的气-液喷射器轴向压力分布与相同条件下Cattadori的实验值吻合较好；以实验结果为基准,本模型蒸汽喷嘴数值模拟结果比Nabil Beithou等的结果大为改善。对太阳能双喷射式制冷系统中的气-液喷射器进行了模拟,得到轴向压力分布和速度分布,结果表明,喷射系数随工作压力的升高而降低。     

Numerical Investigation of Two-Phase Flow in Natural Gas Ejector

Increasing production and recovery from the mature oil and gas fields often requires a boosting system when the gas pressure is lower than that demanded by the transportation or process system. The supersonic ejector, considered to be a cost-effective way to boost the production of a low-pressure gas well, was introduced into the industrial field. However, the exploitation of natural gas often accompanies with water. The computational fluid dynamics (CFD) technique was employed to investigate the two-phase effect (water droplets) on the performance of natural gas ejector for the motive pressure ranging from 11.0 MPa to 13.0 MPa, induced pressure from 3.0 MPa to 5.0 MPa, and backpressure from 5.1 MPa to 5.6 MPa, while the injected water flow rate was less than 0.03 kg s^?1. The numerical results show that the entrainment ratio of the two-phase operation was higher than that of the single-phase operation with the variation of backpressure. Meanwhile, the entrainment ratio increased with the increase of injected water flow rate into the primary flow. When the water was injected into the secondary flow, the entrainment ratio decreased as the injected water flow rate increased, but the critical backpressure remained unchanged.     

Application of profiled ejector in chemical lasers

Recently, the use of profiled ejectors based on constant rate of momentum change [I.W. Eames, Applied Thermal Engineering 22 (2002) 121] along the mixing chamber has been proposed for enhancing the recovery ratio across an ejector stage by minimizing shock losses for application in ejector based refrigeration system. Such ejectors can achieve pressure recovery ratio in excess of 150, thus making the system a compact one. Chemical lasers in general and chemical oxygen-iodine laser (COIL) in particular fall in the high power lasers category and find numerous applications in defense and industry. However, these lasers have not been exploited fully because these require pressure recovery systems for their operation and as such the practical systems are extremely voluminous and bulky. The profiled ejectors find direct applications in these lasers and thus can make the system extremely compact. The conventional supersonic COIL systems operate at a typical stagnation pressure of nearly 20 torr and a cavity static pressure of approximately 3 torr, which are amongst the lowest in the class of chemical lasers. Thus, a low-pressure operation of the laser system demands a high capacity vacuum system. Alternatively, efficient ejector based pressure recovery system has been utilized for achieving direct atmospheric exhaust of the lasing medium. However, a minimum of two-stage conventional supersonic ejectors need to be employed for the operation of the laser system. Multiple stages of the ejector are essential on account of the stagnation pressure loss occurring across a normal shock at the exit of the mixing chamber in each ejector stage. The present study presents a general treatment on the design of a profiled ejector for the case of dissimilar motive and suction fluids that are typical of these lasers. Also, determinations for the increase in recovery ratio for various conditions of entrainment ratio over the conventional ejectors have also been presented. Finally, a computational study using McCormack’s method for Euler system of equations has been carried out to numerically validate the analytical studies for a peripheral air ejector system suitable for a 500 W class COIL employing a flow rate of 3 gm/s with an entrainment ratio of 0.025. It has been concluded that a single-stage profiled ejector is sufficient to achieve atmospheric pressure recovery even in the low-pressure systems.     

Structural optimization and experimental investigation of supersonic ejectors for boosting low pressure natural gas

The supersonic ejector was introduced into boosting the production of low pressure natural gas wells. The energy of high pressure gas wells, which was usually wasted through choke valves, was used as its power supply to boost the low gas production. The operating performance of natural gas ejectors was determined not only by the operating parameters but also by the structural parameters. This study focused on the structural optimization and operating performance of natural gas ejectors. The optimal structural parameters were obtained by numerical simulation when the maximum pressure ratio was obtained, and the numerical results were validated by experimental investigation. The numerical results showed that the optimal diameter ratio of mixing tube to primary nozzle throat was 1.6, the optimal length to diameter ratio of mixing tube was 4.0 and the optimal inclination angle of mixing chamber was 28°. The entrainment ratios and pressure ratios from the numerical simulation agreed well with the field experimental data, with the maximum value of pressure ratio up to 60%. The operating performance of the supersonic ejector was also investigated by the field experiment, and the results showed that the induced gas flowrate and entrainment ratio showed nonlinear characteristics with peak values when the motive pressure ranged from 8 MPa to 13 MPa. These experimental results have proved the optimized structural parameters of the supersonic ejector. The investigation will help to the further application in boosting natural gas production of supersonic ejector.     

Phase change characteristics and their effect on the performance of hydrogen recirculation ejectors for PEMFC systems

The working fluid of the hydrogen recirculation ejector in proton exchange membrane fuel cell (PEMFC) systems is humid hydrogen containing water vapour. However, previous studies on the hydrogen recirculation ejector using computational fluid dynamics (CFD) were based on the single-phase flow model without considering the phase change of water vapour. In this study, the characteristics of the phase change and its effect on the ejector performance are analysed according to a two-phase CFD model. The model is established based on a non-equilibrium condensation phase change. The results show that the average deviation of the entrainment ratio predicted by a single-phase flow model is 25.8% compared with experiments involving a hydrogen recirculation ejector, which is higher than the 15.1% predicted by the two-phase flow model. It can be determined that droplet nucleation occurs at the junction of the primary and secondary flow, with the maximum nucleation rate reaching 4.0 × 10²⁰ m^?3s^?1 at a primary flow pressure of 5.0 bar. The higher temperature, lower velocity, and higher pressure of the gas phase can be found in the mixing region due to condensation, resulting in a lower entrainment performance. The nucleation rate, droplet number, and liquid mass fraction increase remarkably with an increasing primary flow pressure. This study provides a meaningful reference for understanding phase change characteristics and two-phase flow behaviour in hydrogen recirculation ejectors for PEMFC systems.     

Numerical investigation of ejector transient characteristics for a 130-kW PEMFC system

Improvement of fuel utilization is an important issue for proton exchange membrane fuel cell (PEMFC) system. As a promising anode recirculation method, ejector has attracted great attention because it does not require additional power consumption. However, some transient processes such as the suck, diffusion, and mix of fluids are still not thoroughly revealed, which significantly influence ejector performances. In this study, a dynamic three-dimensional (3D) multicomponent ejector model for a 130-kW PEMFC system is developed. The model is validated against experimental data, including the entrainment ratio and mass flow rates. The effects of operating conditions (eg, pressure, water vapor, and nitrogen mass fraction) are investigated. The results show that the fuel supply can be controlled by the primary flow pressure. When the pressure difference between the primary and secondary flow is less than 10 kPa, the secondary flow cannot be sucked into the ejector. The transient response of ejector during stack power variations can be classified into two periods: the primary flow impact period and the mixed flow impact period. Under normal fuel cell system operating conditions, when the inlet relative humidity of the secondary flow is higher than 85%, the water vapor condensation is possible to happen at the ejector outlet region, leading to fuel supply instability. Besides, the hydrogen entrainment ratio decreases with the increase of nitrogen mass fraction. The effects of geometric parameters (eg, nozzle convergence angle, secondary flow tube diameter, mixing tube length, and diffuser angle) on ejector performances are also studied. It is found that the relatively short tube leads to pressure fluctuations in the vacuum region. Increasing the tube length is beneficial to creating a stable vacuum region. However, excessive tube length can increase the friction loss. Increasing the secondary flow inlet tube diameter is beneficial to the entrainment ratio. However, further enlarging the diameter contributes negligibly to the increase of entrainment ratio once the secondary flow mass rate depends on pressure.     

Determination of optimum ejector operating pressures for anodic recirculation in SOFC systems

In this study, a numerical analysis of an ejector for micro combined heat and power system based on 18 kW Solid Oxide Fuel Cell (SOFC) using methane as fuel is presented. An ejector design, which reflects the real system conditions in the view of the flow characteristics, is provided and the ejector performance is numerically investigated for various methane pressure to exhaust pressure ratios and methane inlet temperatures. The results show that the fuel inlet temperature and the pressure ratio of the methane to exhaust significantly affect the steam to carbon ratio (STCR) and entrainment ratio. The higher pressure ratio and methane temperature allow a high entrainment ratio and STCR, but as pressure ratio and methane temperature increase, STCR and entrainment ratio remain unchanged after a specific value. 1140 different scenarios related with the inlet and outlet pressures of the ejector and methane temperature are created to determine the optimum operating conditions. The simulations show that the optimum methane inlet pressure is 7 bar and exhaust pressure is 1.159 bar for the ejector geometry of the interest. The entrainment ratio and STCR are determined as 2.05 and 0.92, respectively at this optimum scenario.     

有机郎肯循环复合系统中喷射器能量分析

有机郎肯循环利用太阳能、地热能和余热驱动,是回收余热、实现能源可持续发展的一个很好途径。有机郎肯循环可与喷射制冷循环结合,可同时提供电能和冷量。喷射器内部流体的不可逆混合引起的能量损失,是该系统最大部分的能量损失。着眼喷射器内部流场分布和机理,分析工作参数和几何参数对其性能的影响,以优化喷射器设计,减小系统能量损失,提高带有喷射器的有机郎肯循环复合系统的效率和节能潜力。结果显示,提高引射压力和出口压力会导致喷射器内部更多能量损失,制约整体系统的性能;在给定工况下,可通过钝化喷嘴内壁面、喷嘴处于最佳位置使喷射器达到最大喷射系数、最优性能,和最小的能量损失。     

喷射制冷系统关键部件的数值分析

建立喷射制冷系统中可调喷嘴喷射器的数学模型,采用数值模拟方法对可调式喷射器与固定结构喷射器的流场进行对比分析,并计算调节锥在不同位置的可调式喷射器内部流场的变化。结果显示,可调式喷射器在喷嘴出口处的速度提高3.5%,真空度提高65.3%,喷射系数提高47.6%;调节锥进入喷嘴可达到更低的轴线压力,喷射器出口轴线流速降低8.9%。