Experimental evaluation of the effect of an internal heat exchanger on a transcritical CO_2 ejector system

This study presents experimental results focused on a performance comparison of a transcritical CO2 ejector system without an internal heat exchanger(IHX) (EJE-S) to a transcritical CO2 ejector system with an IHX(EJE-IHX-S) . The comparison includes the effects of changes in operating conditions such as cooling water flow rate and inlet temperature. Experiments are conducted to assess the influence of the IHX on the heating coefficient of performance(COPr) ,heating capacity,entrainment ratio,pressure lift,and other parameters. The primary flow rate of the EJE-IHX-S is higher than that of the EJE-S. The pressure lift and actual ejector work recovery are reduced when the IHX is added to the transcritical CO2 ejector system. Using a more practical performance calculation,the compression ratio in the EJE-S is reduced by 10.0%-12.1%,while that of EJE-IHX-S is reduced only by 5.6%-6.7% compared to that of a conventional transcritical CO2 system. Experimental results are used to validate the findings that the IHX weakens the contribution of the ejector to the system performance.

Computational Analysis of Mixing Guide Vane Effects on Performance of the Supersonic Ejector-Diffuser System

The flow field in the ejector-diffuser system and its optimal operation condition are hardly complicated due to the complicated turbulent mixing, compressibility effects and even flow unsteadiness which are generated inside the ejector- diffuser system. This paper aims at the improvement in ejector-diffuser system by focusing attention on entrainment ratio and pressure recovery. Several mixing guide vanes were installed at the inlet of the secondary stream for the purpose of the performance improvement of the ejector system. A Computational Fluid Dynamics (CFD) method based on Fluent has been applied to simulate the supersonic flows and shock waves inside the ejector. A finite volume scheme and density-based solver with coupled scheme were applied in the computational process. Standard k-ω turbulent model, implicit formulations were used considering the accuracy and stability. Previous experimental results showed that more flow vortexes were generated and more vertical flow was introduced into the stream under a mixing guide vane influence. Besides these effects on the secondary stream, the mixing guide vane effects on the shock system of the primary stream were also investigated in this paper. Optimal analysis results of the mixing guide vane effects were also carried out in detail in terms of the positions, lengths and numbers to achieve the best operation condition. The comparison of ejector performance with and without the mixing guide vane was obtained. The ejector-diffuser system performance is discussed in terms of the entrainment ratio, pressure recovery as well as total pressure loss.

Effect of an Internal Heat Exchanger on the Performances of a Double Evaporator Ejector Refrigeration Cycle

A theoretical investigation is presented about a double evaporator ejector refrigeration cycle(DEERC).Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger(IHX).The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure.Moreover,the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor.To assess accurately the influence of the IHX on the DEERC performance,a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors.The model also accounts for the friction effect in the ejector mixing section.The equations of this model are solved using an Engineering Equation Solver(EES)for different fluids.These are:R134a as baseline fluid and other environment friendly refrigerants used for comparison,namely,R1234yf,R1234ze,R600,R600a,R290,R717 and R1270.The simulation results show that the DEERC with an IHX can achieve COP(the coefficient of performance)improvements from 5.2 until 10%.

车用燃料电池引射器设计及测试评价方法研究

在研究开发车用燃料电池引射器时,湿氢流量监测困难、台架技术难度大、试验成本高,并且存在安全隐患和能源浪费问题。为此,在推导空气与氢气、空气与100%RH的氢在相同工作条件下的流量变化关系式的基础上,针对110 kW燃料电池,试制引射器进行空气和氢气测试,并结合数值仿真分析。结果发现:车用燃料电池引射器引射流体中水蒸气质量分数达到40%~50%;在相同工作条件下,空气与氢气的体积和质量流量分别等于其气体常数比值的平方根和比值倒数的平方根,其中空气与氢气的体积和质量流量之比分别为3.786和0.2641。工作、引射和混合流体质量流量的空气实测与仿真数据之间的平均相对误差分别为4.48%、4.54%和2.78%;空气实测数据经折算后与氢气测试数据相吻合,与湿氢的仿真数据平均偏差率分别为5.4%和6.11%;氢气测试数据经折算也与湿氢仿真数据相吻合。因此,空气测试数据经处理可以用于车用燃料电池引射器特性研究。

冷却通道对引射器红外辐射特性影响的研究

为降低燃气轮机排气系统中的引射器排气温度,从而减少排出燃气的红外辐射强度,本文提出了一种具有冷却通道的亚音速引射器结构,并提出了评价冷却通道引射器的综合系数。在原有的引射器喷嘴内增加冷却通道,使冷气直接与主流中心位置的高温气体掺混,破坏排气包覆性分布,达到提高主流温度均匀性、降低中心温度的目的。本文运用数值模拟的方法,研究引射器内冷却通道数量、冷却通道进深和排气通道的排布对引射器内阻力特性、换热特性、出口温度分布特性的综合影响。研究结果表明:单排冷却通道排布时,通道数量与换热特性成正比,与阻力损失成反比;双排冷却通道排布时,阻力损失降低。双排12通道引射器可有效降低出流总温,均匀主流温度,综合系数最高。

-30至50℃车辆工况下CO_(2)喷射器的适应性研究

为推动喷射器回收膨胀功技术的实车应用,本文开展了-30~50℃宽温区运行工况下车用压缩-引射式CO_(2)热泵系统制冷制热性能及喷射器膨胀功回收特性研究,重点分析了工作喷嘴对固定尺寸喷射器变工况适应性的影响。结果表明:制冷工况下随着环境温度升高,喷射系数递减,而升压比递增;制热工况下随着环境温度降低,喷射系数和升压比均先增大后减小;制冷工况下喷射器回收膨胀功占最大可回收膨胀功的16.7%~37.2%,制热工况下为9.9%~41.3%;以高温制冷工况设计的固定尺寸喷射器难以适应低温制热工况,偏离设计工况时,喷嘴出口过膨胀会造成激波能量损失,而低温制热工况下喷嘴出口因欠膨胀会导致喷射器无引射效果。

塑料外壳注射模设计

按照塑件结构设计了1副两板注射模,为了降低模具制造成本,将定模板适当增厚,省去定模座板,为了减少塑件表面的流痕和方便修剪浇口凝料,将塑件上浇口对应的位置设计成凹形。针对塑件侧面的扣位结构,采用由斜导柱驱动的侧滑块机构脱模,对模具两侧的滑块设置减速弹簧,降低滑块在合模时的速度,以减少滑块对模具零件的撞击。斜推杆与安装座之间通过圆弧形扣位相连,简化了模具结构,根据塑件结构,采用推管与推杆相结合的推出方式脱模,并根据模具结构设置“直通+隔片式水井”相结合的多个冷却回路的随形冷却系统。

跨临界CO_(2)两相引射器喷嘴扩张段传热的影响分析

跨临界CO_(2)引射器主动流入口状态对引射器性能具有显著影响,主动喷嘴壁面传热会改变主动流状态,其对引射器性能的影响有待研究。基于均质平衡模型假设,构建了跨临界CO_(2)两相引射器的CFD模型,模拟研究了喷嘴扩张段传热对引射器性能和流场结构的影响,并分析了对冷凝器出口分流引射膨胀制冷系统性能的影响。研究结果表明:引射器引射系数随喷嘴扩张段热流密度和喷嘴扩张段长度的增大而增大,但在适用热流密度(小于120 kW/m^(2))下并不明显,引射系数变化范围在1%以内,其影响可以忽略不计;喷嘴扩张段传热对引射器内部流场的影响较小,喷嘴扩张段内流体温度略有升高,引射器出口干度略有增加,喷嘴出口和混合室内混合流的马赫数也略有增加;对于冷凝器出口分流引射膨胀制冷系统,利用引射器壁面传热可以过冷流体,系统COP显著提高,COP最大提升比例为8.89%。总体而言,对引射器主动喷嘴扩张段加热,对引射器性能影响甚微,但对冷凝器出口分流引射膨胀制冷系统的性能有较明显的提高。

保温杯盖热流道塑料模具设计

对保温杯盖的结构进行了分析,并根据产品的结构设计两板模结构,采用热流道浇注系统。针对产品上的外螺纹,采用Half滑块成型。为了提高生产效率,采用一模八腔。为了防止产品出现注塑不饱满的现象,在定模镶件内部再设置小镶件。为了防止产品产生缩水,设计了一套冷却效果良好的冷却系统:在动模型芯的内部设置两头螺纹的螺杆;在定模内、外镶件上沿外圆柱面各设置了一道环状冷却水路;在滑块上设置随形直通式水路。为了使排气系统避开定模小镶件外圆柱面上的冷却水路,在小镶件内部开设排气孔,通过排气孔将型腔中的空气排出。根据产品结构与模具结构,采用推件板将产品顶出。为了不影响外螺纹滑块的结构,将推件板设置在动模镶件表面的方框内,并利用动模型芯作为导向机构,可防止推件板在运动过程中出现卡死的现象。

大功率PEMFC氢气系统建模与仿真

针对大功率车用燃料电池发动机的氢气系统进行建模,基于MATLAB/Simulink平台搭建氢气系统核心部件模型及其控制模型,并集成氢气系统整体模型,基于该模型进行2种常见汽车行驶工况—CLTCP和NEDC工况的动态仿真,结果表明,所建控制模型能较好保证阳极入口压力满足工作压力需求,并将阴极和阳极的压差维持在0.02 MPa,2种工况的氢气利用率分别为99.67%和99.76%,表明该模型可以用于大功率车用PEMFC系统开发。

Numerical Study on Flow-Induced Vibration of Ejector Structure

High-speed airflow in wind tunnel tests usually causes dramatic vibration of ejector structure,which may lead to fatigue and even destruction of the wind tunnel.Therefore,analyzing and solving the flow-induced vibration problem is a tough and indispensable part of the wind tunnel security design.In this paper,taking a kind of two-stage ejector as the study object,multiple numerical simulation methods are adopted in order to carry out research on the analysis technique of the flow-induced vibration characteristics of ejector structure.Firstly,the structural dynamics characteristic is analyzed by using the ejector structural dynamics numerical model,which is built on the basis of finite element method.Secondly,the complex flow phenomenon is explored applying numerical fluid-dynamics model of the inner flow field of the ejector,which is constructed on the basis of finite volume method.Finally,based on the two numerical models above,the vibration response of the ejector structure induced by the high-speed airflow is computed via the fluid-solid coupling technique.The comparison of the simulation results with the actual vibration test indicates that these numerical simulation methods can accurately figure out the rule of flow-induced vibration of ejectors.

Sewerage Force Adjustment Technology for Energy Conservation in Vacuum Sanitation Systems

The vacuum sanitation is the safe and sound disposal approach of human excreta under the specific environments like flights, high speed trains and submarines. However, the propulsive force of current systems is not adjustable and the energy consumption does not adapt to the real time sewerage requirement. Therefore, it is important to study the sewerage force adjustment to improve the energy efficiency. This paper proposes an energy conservation design in vacuum sanitation systems with pneumatic ejector circuits. The sewerage force is controlled by changing the systematic vacuum degree according to the amount of the excreta. In particular, the amount of the excreta is tested by liquid level sensor and mass sensor. According to the amount of the excreta, the relationship between the excreta amount and the sewerage force is studied to provide proper propulsive force. In the other aspect, to provide variable vacuum degrees for different sanitation requirements, the suction and discharge system is designed with pneumatic vacuum ejector. On the basis of the static flow-rate characteristics and the vacuum generation model, the pressure response in the ejector circuit is studied by using the static flow rate characteristics of the ejector and air status equation. The relationship is obtained between supplied compressed air and systematic vacuum degree. When the compressed air is supplied to the ejector continuously, the systematic vacuum degree increases until the vacuum degree reaches the extreme value. Therefore, the variable systematic vacuum degree is obtained by controlling the compressed air supply of the ejector. To verify the effect of energy conservation, experiments are carried out in the artificial excreta collection, and the variable vacuum-degree design saves more than 30% of the energy supply. The energy conservation is realized effectively in the new vacuum sanitation systems with good application prospect. The proposed technology provides technological support for the energy conservation of vacuum sanitation systems.

Performance Analysis of an Organic Rankine Cycle with a Preheated Ejector

The so-called organic Rankine cycle(ORC)is an effective technology allowing heat recovery from lower temperature sources.In the present study,to improve its thermal efficiency,a preheated ejector using exhaust steam coming from the expander is integrated in the cycle(EPORC).Considering net power output,pump power,and thermal efficiency,the proposed system is compared with the basic ORC.The influence of the ejector ratio(ER)of the preheated ejector on the system performances is also investigated.Results show that the net power output of the EPORC is higher than that of the basic ORC due to the decreasing pump power.Under given working conditions,the average thermal efficiency of EPORC is 29%higher than that of ORC.The ER has a great impact on the performance of EPORC by adjusting the working fluid fed to the pump,leading to significant variations of the pump work Moreover,the ER has a remarkable effect on the working fluid temperature lift(TL)at the evaporator inlet,thus reducing the evaporator heat load.According to the results,the thermal efficiency of EPORC increases by 30%,when the ER increases from 0.05 to 0.4.

THERMAL CALCULATION FOR ANTI-ICERWITH MICRO-EJECTOR

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内部混合式油雾应急润滑系统引射结构几何影响因素研究

为探究结构参数对应急润滑系统引射结构性能的影响,以某型航空发动机内部混合式油雾应急润滑系统引射结构为对象,通过油气两相流数值模拟并结合试验验证,分析了空气喷嘴直径、滑油引油管直径等结构参数对滑油引射流量、引射系数的影响规律,并基于敏感性分析方法,获得了引射滑油流量关于不同结构参数的敏感性系数。结果表明,滑油引射流量的计算结果与试验结果最大误差不超过11%;存在最佳的空气进口段直径、空气喷嘴直径和混合室直径使得引射滑油流量达到最大,而滑油流量随空气喷嘴出口直径、引油管直径的增大呈现出逐渐增加的趋势;对比分析各结构参数敏感性系数,发现混合室直径、空气进口段直径、引油管直径是影响引射结构性能的三个重要参数。

悬浮物清除系统的射流器两相紊流数值模拟研究

通过水系统悬浮物清除系统所需射流器建立的三维紊动射流数学模型,对特殊结构形式的射流器进行流场结构和射流紊流动力学性能的研究,通过数学模型计算射流器的紊流流场分布,掌握流场的流体动力学机理,从而获得最接近射流器紊流流场实际状态的描述方法。

新型小汽机耦合多级蒸汽引射器供热系统及性能分析

提出一种新型热电联产机组小汽机耦合多级蒸汽引射器供热系统,实现了对供热抽汽的能量梯级利用,以降低热电联产机组直接抽汽供热带来的蒸汽品质浪费以及机组冷端损失。机组一部分供热抽汽通过并联蒸汽引射器系统引射机组排汽,两者混合后对热网水进行两级加热;另一部分蒸汽进入背压小汽机做功后,进入耦合热网换热器加热热网回水,使其达到规定的热网供水温度。以某330 MW热电联产机组为研究对象,通过EBSILON 15.0软件对系统进行精准建模计算,并进行了详细的系统热力性能分析和经济性分析。结果表明:相比案例系统,新系统的整体标煤耗量降低了4.18 t/h,热电联产总效率提升了3.22个百分点,发电煤耗下降15.84 g/(kW·h);新系统的年化新增收益可达570.02万元,具有较好的经济性收益。

压缩空气储能系统供冷性能提升

绝热压缩空气储能系统能够实现冷热电三联输出。若应用压缩空气储能系统代替制冷设备供冷,则可利用抵扣的制冷设备投资抵消一部分储能系统投资,从而缩短储能系统回收周期。另外,错峰用电可减少夏季大规模供冷设备对峰电资源的消耗。本工作构建了气罐容积5000 m^(3),气罐贮存压力范围4.6~10.0 MPa的绝热压缩空气储能系统,系统产出的冷量通过引射器产出冷气的方式供给用户,模拟了系统充释能过程以获得系统的能量产出特性。以供冷季节产冷最大化,非供冷季节产电最大化为主目标,分析确定了系统关键配置以及运行参数。研究结果表明,该系统在供冷季节的最大产冷量为36.96 GJ,可为190户供冷。与以经济效益最大化为目标的压缩空气储能三联产系统相比,本系统的供冷能力提升287.76%。调控预热热水流量可以改变系统能量产出比例,以使系统匹配用户多变的能量需求。若运行在最大供冷工况下,本系统回收周期为12.39年。本工作构建的系统旨在为绝热压缩空气储能系统在制冷方面的应用提供一条新的思路,为夏季大规模供冷提供新的方法。