蒸汽喷射器流动参数与性能的数值分析

通过二维流动数值计算，分析了以水蒸气为工质的喷射器内工作流体压力、引射流体压力及出口压力对喷射系数的影响；探讨了各工作参数变化对喷射系数产生影响的原因，以及激波产生的条件、激波的位置、强度，产生引射流体雍塞的条件等。结果表明：喷射器存在临界的出口压力pd，当喷射器出口压力大于pd时，喷射器的喷射系数随出口压力升高而降低；当喷射器出口压力小于pd时，喷射器的喷射系数将保持不变。在计算模拟的制冷工况范围内，工作流体压力升高，引起喷射系数降低，pd升高；而引射流体压力升高时，喷射系数与pd都升高。     

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。     

蒸汽喷射压缩器性能的三维数值模拟

通过对蒸汽喷射压缩器内流场进行三维数值模拟,对初步设计的蒸汽喷射压缩器进行结构优化,并研究了结构参数、工况参数和调节锥对喷射器工作性能的影响.结果 表明:混合室直径和喷嘴出口到混合室入口间距是影响喷射器性能的两个关键参数;降低工作蒸汽压力、提高引射蒸汽压力和降低背压都能够使喷射系数升高;使用调节锥能够在一定程度上提高喷...     

太阳能喷射式制冷系统喷射器性能的三维数值模拟

利用FLUENT软件对太阳能喷射式制冷系统中的喷射器进行三维数值模拟,从影响喷射器性能的主要工作参数和喷射器的主要尺寸、结构等方面进行了数值计算。从数值模拟的研究中得出：流线型结构的喷射器能减弱混合过程中的回流现象;在超过某一值时继续增加工作流体的压力对喷射器性能没有改善;喷嘴出口和扩压管入口存在一定的距离会提高喷射器的性能;收缩段采用流线型的喷射器性能很接近四段都采用流线型的喷射器的性能,并且都能提高喷射器的性能。     

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。     

激光诱导荧光法研究柴油机新概念燃烧中的喷雾混合过程

建立了一套基于激光诱导荧光法的光学试验装置，用高压共轨式电控喷射器喷射燃油，其喷射压力达120MPa。此喷射器能在微机控制下实现预喷射和分段喷射。定容燃烧弹预先充上气体，其主要成分是氮气，还有一部分是乙炔和氧的混合气。在燃油喷射之前，点燃乙炔和氧的混合气，使燃烧室内的压力上升至6MPa，温度上升至1000K。试验结果与前期的气体射流模型结果吻合，在燃烧室壁面设置限流沿后，所产生的二次射流可以形成稀薄的混合气区。因此，使用限流沿的新概念混合气形成过程有望用于降低柴油机的碳烟和NOx排放。     

多喷嘴汽-液两相喷射性能的实验研究

提出了一种多喷嘴结构的汽-液两相喷射器,该装置由7个蒸汽喷嘴、吸入室、7个混合室和扩散室组成.通过实验研究了不同蒸汽干度下多喷嘴汽-液两相喷射器的工作特性.结果表明:由于汽羽的特性和蒸汽喷嘴与混合室的距离对喷射性能的共同影响,喷射器存在一个最佳蒸汽压力,且其数值随低温水温度的升高而减小;蒸汽干度未明显影响低温水质量流量的分布规律;喷射系数随蒸汽干度的增大而增大,随低温水温度的升高而减小.     

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℃。     

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。     

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。     

Experimental investigation on starting process of supersonic single-stage air ejector

This paper deals with experimental study of flow field of starting process in two-dimensional, single-stage supersonic ejector on different air total pressure. Schlieren pictures of flow field were taken, static pressure distribu-tions on side wall were measured. The obtained results show that, on critical pressure, the starting main shock waves in ejector oscillated back and forth between the second throat and the middle section of the mixing chamber, it causes the pressure in the second half of the mixing chamber acutely fluctuated .When the working pressure of the active flow is higher than the critical starting pressure, ejector starts normally and the inner flow-field of the mixing chamber keeps stable and the shock waves in the second throat have a certain degree of oscillation . After ejector starts, the operating pressure of the active flow may be lower than the starting pressure .     

Weight analysis on geometric parameters of ejector under high back pressure condition of SOFC recirculation system

With advantages of no parasitic energy consumption, small size, and low noise, ejector is a promising choice for the solid oxide fuel cell (SOFC) anode gas recirculation system. However, it is difficult to design an ejector with good performance under the high back pressure condition of the SOFC system. In this paper, weight analysis on key geometric parameters of ejector is carried out based on the result of an experimentally validated ejector simulation model. Four main geometric parameters that have the most significant effect on ejector performance, namely the ejector diameter ratio (D_r), mixing chamber length (L_m), diffuser length (L_d), and nozzle outlet position (NXP), are analyzed in detail. The D_r has a decisive influence on the momentum exchange in the mixing phenomenon between the primary flow and secondary flow in the mixing chamber where the normal shock position changes accordingly. The L_m mainly affects the intensive mixing flow which leads the normal shock to appear prematurely. The L_d should be long enough for boosting back pressure and reducing the effect on the mixing process. The NXP has no effect on the normal shock position. The results show that the critical back pressure increases with the rise of normal shock position and the impact weight of L_m, L_d and NXP can be treated as 21∶10∶1 approximately and the D_r is thought to be a decisive factor. This weight analysis method will be helpful for designing ejectors used in the high back pressure condition of the SOFC anode recirculation system.     

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.     

Transient characteristics investigation of the integrated ejector-driven hydrogen recirculation by multi-component CFD simulation

The hydrogen supply of the fuel cell system is realized by the cooperation of multiple components. Transient characteristics of a single component can affect the performance of other components. In this study, a three-dimensional multi-component computational fluid dynamics (CFD) model was developed to investigate the synergistic transient characteristics of the hydrogen recirculation components such as hydrogen injector, ejector, and purge valve in an 80 kW PEMFC. The results show that the entrainment performance of the ejector is reduced under unsteady purge conditions compared with steady conditions. The pressure fluctuation of the secondary flow is significant even under purge closed durations. There are drastic changes in velocity and pressure in the ejector, especially in the mixing chamber. Moreover, an abundant hydrogen supply capacity of the injector is necessary to deal with the excessive anode pressure fluctuation. The feedforward-feedback integrated control of the injector is a more efficient strategy to reduce pressure fluctuations compared with the feedback control.     

Simulation and experimental measurements of 10-kW PEMFC passive hydrogen recovery system

Simulations are performed to examine the performance of a vacuum ejector in the hydrogen recovery loop of a 10-kW PEMFC system. The simulations commence by examining the effects of the primary flow fluid pressure and secondary flow temperature on the recirculation ratio and hydrogen stoichiometric ratio. Further simulations are then performed to investigate the temperature, pressure, velocity and Mach number distributions within the ejector for various values of the primary flow inlet pressure and temperature. A prototype ejector is fabricated using a 3D printing technique. Experiments are performed to evaluate the gas tightness and gas recovery performance of the ejector under realistic operating conditions. The simulation results show that the recirculation ratio and hydrogen stoichiometric ratio increase with a decreasing primary flow inlet pressure and secondary flow inlet temperature. As the primary flow inlet pressure increases, the pressure, velocity, and Mach number in the mixing chamber increase, and the hydrogen recovery performance decreases. Furthermore, as the temperature of the primary fluid flow increases, the stability of the isentropic flow condition within the ejector is enhanced. The experimental results show that the prototype vacuum ejector has a maximum gas leakage of just 0.7 psi and a minimum hydrogen recirculation rate of 59.3%. Consequently, it has significant potential for passive hydrogen recovery in large-scale fuel cell systems.     

Modelling and optimization of two-phase ejectors for cooling systems

A one-dimensional compressible flow model, which is based on the control volume approach, has been formulated to model and optimize one and two-phase ejectors in steady-state operation with particular reference to their deployment in a jet cooling system. The working fluid can be both single-component (NH₃) and two-component (NH₃–H₂O). The developed model takes into account the duct effectiveness, wall friction, momentum loss, ejector geometry, shock waves as well as the acceleration of the induced flow in the conical part of the mixing section. Neither the usual assumption of mixing at constant pressure over the mixing chamber cross section nor that of a constant mixing chamber cross section were made. A comparison with other computation methods as well as with available experimental data from the literature is presented. The performance is significantly influenced by the ejector geometry.     

R141b气液两相喷射器性能研究

考虑实际流体性质、混合室阻力和喉部激波现象,采用等压混合模型,根据质量守恒、动量守恒和能量守恒建立中心进气两相喷射器一维模型。以R141b为工质,研究在不同入口参数和混合室截面积变化比(混合室喉部截面积与混合室入口截面积之比)下喷射器的升压特性以及入口参数和混合室截面积变化比对喷射器出口压力和喷射系数的影响。结果表明:在一定工况下,入口主蒸汽压力每增加0.5 MPa,喷射器出口压力提高约0.002 MPa;入口引射液体压力每增加0.1 MPa,出口压力约升高0.6 MPa。相对于入口主蒸汽参数的变化,入口引射液体参数变化对喷射器的升压特性影响更大。另外,随着混合室截面变化比的增大,升压效果下降。在入口引射液体参数为0.1 MPa/299 K和0.2 MPa/321 K的条件下,混合室截面积比分别增至0.6和0.4时,出口处蒸汽不能完全凝结。研究结果适用于大部分工质,为喷射器的设计和运行提供理论指导。     

Supersonic Flow Structure in the Entrance Part of a Mixing Chamber of 2D Model Ejector

The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow parameter development in the entrance part of the mixing chamber of the ejector. Numerical results are obtained by means of both the straight solution of shock waves in supersonic flow field using classical relations of parameters of shock waves and the Fluent 6 program. Results of numerical solutions are compared with experimental pictures of flow fields. Flow structure development in the mixing chamber is analysed in detail.     

Performance of anodic recirculation by a variable flow ejector for a solid oxide fuel cell system under partial loads

An anode gas recycle (AGR) system driven by a variable flow rate ejector was developed for use in small-scale solid oxide fuel cell (SOFC) systems. The partial load conditions were simulated through recycling power generation experiments to clarify the fundamental characteristics of the variable flow ejector by using actual 1 kW-class SOFC equipment at the steady state. We achieved power generation in a range of recirculation ratios under partial load conditions of 62.5%–80% by controlling the recirculation characteristics with the developed ejector by using a needle. Results showed that the recirculation ratio can be controlled in the range of 0.595–0.694 by adjusting the driving energy with the ejector even at a partial load where the fuel gas flow rate of the ejector changes. Furthermore, the effect of the recirculation ratio on SOFC output was discussed based on the results of gas analyses and temperature measurements. As the recirculation ratio increased, the fuel concentration at the SOFC inlet decreased and the water vapor concentration increased. However, the effect of the recirculation ratio on the stack temperature and output power was proposed to be small. In addition, it was confirmed that the operation was performed under safe conditions where no carbon deposition occurred by circulating the steam generated inside the SOFC without an external water supply. Ejector characteristics during power generation experiments were lower than those at room temperature, which indicates that an ejector upstream pressure of approximately 20–170 kPa gauge pressure was required. Variations in the fluid properties of the driver gas in the ejector motive nozzle heated by the hot suction gas were found to degrade the performance of the ejector installed in the SOFC system, as compared with the results of simulation experiments at room temperature. Nevertheless, the recirculation ratio range required for operation could be satisfied by adjusting the flow velocity of the driving gas through needle control.