船用真空海水淡化装置液_汽引射器的数值模拟及试验研究

根据一维引射特性方程估算理想的用于船舶真空海水淡化装置的引射器参数,然后用数值计算和试验的方法对液-汽引射器的工作特性进行了研究。结果表明:随着工作流体压力的增大引射系数增大,一定程度后对引射系数的贡献不再显著;引射流体压力越大引射系数越大,但考虑到海水在低温下蒸发的要求引射流体压力不宜过高,工程中需综合考虑;喷嘴直径与接收室直径之比为0.4324时,引射器性能最佳。     

一种流量可调的燃料电池用引射器的数值分析

针对质子交换膜燃料电池(proton exchange membrane fuel cell,PEMFC)高低负荷工况对氢气量的不同需求,提出一种新型引射器,采用计算流体动力学(computational fluid dynamics,CFD)方法对该引射器进行仿真分析,研究不同混合室收敛角对引射器性能的影响。仿真结果表明,在高低两种工况下,引射器的引射系数均随混合室收敛角的增大先增大后减小,最佳的混合室收敛角为9°～15°。选取混合室收敛角12°内的引射器进行内部流场分析,通过速度场及压力场的分布,研究高低负荷工况下引射器对回流氢气的作用规律。     

采用双节流装置的CO2引射制冷系统的变工况性能实验研究

对采用双节流装置的跨临界CO_2引射制冷循环系统在不同工况下的性能进行了实验研究,比较了影响引射器性能和系统COP的因素。实验结果表明,在固定引射器几何尺寸的条件下,气体冷却器出口压力为8.5MPa、蒸发温度为-5和-1℃时,引射比随气冷器出口温度的增大而逐渐增大,系统COP则呈下降趋势;当气冷器出口温度为41℃、蒸发温度为-5℃时,工作流体、引射流体质量流量及引射比均随着气冷器出口压力的增大而出现不同程度的增加,系统COP则呈下降趋势。在相同工况条件下,采用两段式喷嘴引射器的双节流跨临界CO_2制冷系统的COP整体上大于传统带有膨胀阀的跨临界CO_2制冷系统的COP。     

同轴度对引射器性能影响的数值分析

船用燃气轮机需要安装引射器来降低红外特征,受限于机舱尺寸,引射器的主喷管和混合管往往不能同轴线布置。为了研究主喷管和混合管在非同轴线布置下对引射器的影响,本文以某燃气轮机上带有冷却孔的引射器为研究对象,采用数值模拟的方法研究了主喷管相对混合管轴线偏离±30%,±50%,±70%时引射器的性能,并且对比了冷却孔在开闭状态下的性能。结果表明：当冷却孔关闭时,主喷管向负方向偏移时压力损失系数最大提高4.3%,向正方向偏移时压力损失系数最大提高2.5%;当冷却孔开启时,偏移方向对压力损失系数没有明显影响,且引射器内部的燃气总温降低100~150 K。     

间隙对气波引射性能影响的实验研究

气波引射器是一种新型的高效动态引射装置,转子与端板处间隙宽度对引射性能产生重要影响。通过实验研究进出口间隙宽度以及转速对气波引射器高低压气体流量和引射性能的影响。结果表明:随着入口间隙宽度增大,高压气体质量流量小幅增大,而低压气体质量流量大幅降低,设备的引射性能急剧降低,宽度由0.15 mm增至0.55 mm,等熵效率减小约15%,而出口间隙宽度对设备的流量和性能影响较小。当设备的运转速度偏离设计转速时,气波引射器的引射性能将急剧降低,在一定的转速偏离范围内,高压气体质量流量增大,而低压气体质量流量逐渐降低。     

两相流引射循环系统实验研究及引射器性能数值模拟

用ANSYS CFX软件对两相流引射制冷循环中的引射器内部流动进行了数值模拟,分析了混合室直径和喷嘴喉部直径对引射器性能的影响;根据数值模拟结果加工了引射器试件,对R134a两相流引射器及引射循环制冷系统性能进行了实验研究,探讨了固定工况条件下引射器喷嘴喉部直径和混合室直径的优化匹配。实验与模拟结果均表明,在固定工况条件下,存在使引射比及COP分别达到最大的最佳混合室直径和喷嘴喉部直径组合。在冷凝温度为55℃、蒸发温度为3℃的工况下,当混合室直径为16mm、喷嘴喉部直径为2.0mm时引射器的引射比达到最大值,而两相流引射循环制冷系统的COP在混合室直径为16mm、喉部直径为1.7mm时最高,模拟与实验结果的变化趋势是一致的,但二者的引射比值误差较大。     

基于CFD正交实验的引射雾化喷嘴仿真研究

气水比对喷雾冷却换热有重要影响,为研究不同结构和工况对引射雾化喷嘴喷雾气水比的影响,对实验中用到的环流引射雾化喷嘴,采用流体力学仿真软件FLUENT建立了环流气体辅助雾化喷嘴模型,对该喷嘴的流场进行了数值模拟。分析模拟气体压力、喷嘴的出水口伸出长度、气体环缝大小等参数对引射喷雾量的影响。结果表明:气体环缝大小对气水比影响最显著;进水管出口端的负压值随伸出长度先增加再减小,水孔伸出长度存在一最佳位置L=0.10mm;工作气体消耗量主要受气体环缝大小影响,其次是工作压力大小,水口伸出长度影响最小。     

上海东海天然气引射调峰试验

本文介绍了天然气输配特性以及引射调峰装置在上海北蔡储配站的应用，进行了引射调峰试验并绘制了引射器的特性曲线。结果表明，通过引射调峰可提高球罐利用率，达到用气高峰时增加调峰量，低谷时增加储气量。在去冬今春的实际运行中的取得了较好的效果。     

多喷嘴液液引射器的试验与数值模拟研究

采用控制变量法,模拟研究了不同进出口压力等因素对多喷嘴液液引射器性能及增压效果的影响规律。结果表明,在引射泵组中,随着工作压力和引射压力增大,引射器的引射系数和引射流量都增大;而随着出口压力增大,引射器的引射系数和引射流量减小;引射器出口压力的增加对引射泵组中的泵前增压效果优于工作压力和引射压力;泵前压力随引射器进出口压力的增大而增大。试验在综合考虑泵的效率和增压效果后,采用30%回流率,引射泵组可提高1.59 m压头,与模拟结果 1.54 m吻合较好。     

引射比对生物柴油斯特林发动机喷雾特性影响的仿真研究

基于斯特林发动机的喷雾特性,建立了某斯特林发动机旋流引射、喷雾的数学物理模型,模拟了高背压下生物柴油斯特林发动机在不同引射比下的喷雾过程。研究发现:生物柴油喷雾锥角随引射比的增大而增大,大引射比下的喷雾油束前端出现了明显的凹型回缩锋面;引射比越大,喷雾贯穿距越小;增大引射比,液滴速度增大,索特平均直径减小,粒径方差减小。高背压下,增大引射比能增大燃油混合气的空间分布,提高喷雾雾化效果。     

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.     

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.     

自然工质两级喷射器组合中间压力分配

建立了两级喷射制冷系统和两级喷射器组合的性能分析模型。以水、氨、R290、R600a为工质,研究了两级喷射器组合中间压力分配比与喷射系数的关系,当第一级和第二级喷射器的喷射系数相近时出现使总喷射系数最大的中间压力最佳分配比。探讨了不同工况下最佳分配比与总压缩比和膨胀比之间的关系。膨胀比一定时,最佳分配比随总压缩比的增大先增大,然后减小,最后又逐渐增大;膨胀比对最佳分配比也有一定影响,但与总压缩比的取值区间相关联。绝热指数是影响最佳分配比的重要因素,对处于相同最佳分配比工况的不同工质,绝热指数越大则所需的总压缩比也越大。提出了两级喷射器组合中各级喷射器结构选择方法。     

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.     

Experimental and Numerical Analysis on the Internal Flow of Supersonic Ejector Under Different Working Modes

Supersonic ejectors involve very complex phenomena such as interaction between supersonic and subsonic flows, shock trains, instabilities, which strongly influences the performance of supersonic ejector. In this study, the static pressure distribution along the ejector wall and Mach number distribution along the axis are used to investigate the internal flow field of supersonic ejector. Results indicate that when the back pressure is much less than the critical back pressure, there are two series of shock trains, and the change of the back pressure will not affect the flow field before the effective area section, so the entrainment ratio would remain constant. The second shock train moves further upstream and is combined with the first shock train to form a single shock train as the back pressure rises. When the back pressure is greater than the critical back pressure, the position of the shock train, the static pressure at its upstream and the entrainment ratio, will be affected. The “effective area section” in the mixing tube is obtained. The effective area section position moves downstream with the increase of the primary flow pressure, while it moves upstream with the increase of the secondary flow pressure. The entrainment ratio shows inversely proportional relationship with the effective section position. Besides, the first shock train length increases with the increase of primary flow pressure or secondary flow pressure. The critical back pressure represents direct proportional relationship to the first shock train length.     

Fuel ejector design and simulation model for anodic recirculation SOFC system

In this paper, a new modeling technique for fuel ejectors with high entrainment ratio, low pressure increment and over heated working gases in an anodic recirculation solid oxide fuel cell (SOFC) system is presented. By utilizing the thermodynamic, fluid dynamic principles and chemical constraints inside ejectors and employing a two-dimensional function to compute fluid velocity, the developed model involves no more than nine algebraic equations and this is very simple compared to all existing models. The detailed procedures for fuel ejector design and simulation are provided and its effectiveness is verified through simulation and compared with testing results. It shows that the proposed model is more accurate than presently available models, and therefore can be better used for ejector design and performance simulations. The ejector performances for both situations of stand-alone and integrated into the SOFC system are also studied.     

叶片前缘气膜冷却离散孔下游流动特性的试验研究

以燃气轮机叶片为研究对象,设置主流风速为10 m/s,采用热膜风速仪作为测量工具,对气膜冷却叶片压力面和吸力面下游指定位置的二维速度进行了测量.结果表明:当射流比增大时,压力面和吸力面主射流掺混中心上移,在叶片型面曲率梯度较大处会出现回流现象,混合流体贴壁性变差.吸力面速度u梯度明显增加,吸力面流体贴壁性好于压力面.随着χ/d的增加,压力面一侧速度u逐渐变得不规则,在叶片曲率较大处的近壁区出现了明显的二次流,吹风比对吸力面一侧速度v的影响比对压力面一侧的影响小.     

Optimization Study of a Coanda Ejector

The Coanda effect has long been employed in the aerospace applications to improve the performances of variousdevices.This effect is the ability of a flow to follow a curved contour without separation and has well been util-ized in ejectors where a high speed jet of fluid emerges from a nozzle in the ejector body, follows a curved sur-face and drags the secondary flow into the ejector.In Coanda ejectors,the secondary flow is dragged in the ejec-tor due to the primary flow momentum. The transfer of momentum from the primary flow to the secondary flowtakes place through turbulent mixing and viscous effects.The secondary flow is then dragged by turbulent shearforce of the ejector while being mixed with the primary flow by the persistence of a large turbulent intensitythroughout the ejector.The performance of a Coanda ejector is studied mainly based on how well it drags thesecondary flow and the amount of mixing between the two flows at the ejector exit.The aim of the present studyis to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector per-formance.The effect of various factors,such as,the pressure ratio, primary nozzle and ejector configurations onthe system performance has been evaluated based on a performance parameter defined elsewhere.The perform-ance of the Coanda ejector strongly depends on the primary nozzle configuration and the pressure ratio.The mix-ing layer growth plays a major role in optimizing the performance of the Coanda ejector as it decides the ratio ofsecondary mass flow rate to primary mass flow rate and the mixing length.     

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.     

匹配新能源电能并网的压缩空气储能站性能研究

  [目的]  压缩空气储能系统在电能释放环节依托节流降压阀进行调压的方法,存在较大的空气压力能损失,降低了压缩空气储能系统的能量转换效率。  [方法]  引入喷射调压理论,通过高压流体对低压流体的自动卷吸作用获得中压流体的方法来完成调压过程,减少由节流降压阀引起的压力能损失。在研究过程中,分别构建了融合“节流阀调压”、“固定式匹配器调压”以及“可调式匹配器调压”三种不同调压方式的压缩空气储能系统并进行了性能比较分析。  [结果]  研究结果表明:“固定式匹配器调压”方法与“可调式匹配器调压”方法通过压力能回收,使得首台膨胀机可做功气流总量分别增加了2%与4.1%,储能系统的能量转换效率也由节流阀调压储能系统的59.26%分别提升至59.60%与59.97%。  [结论]  性能优化后的压缩空气储能系统能够服务于新能源电能并网需求,通过储能站与新能源电能发电站形成联合体的方式,促进新能源电能的消纳。