有机朗肯循环复合系统中喷射器能量分析

有机朗肯循环利用太阳能、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。有机朗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朗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。     

有机朗肯循环与再热式循环低温热源发电系统热力性能研究

针对120℃以下的低温余热热源,探讨了基本有机郎肯循环发电系统和再热式有机朗肯循环发电系统模型的基本原理.从热力学第一定律角度出发,研究了纯工质R245fa和非共沸混合工质R21/R245fa在基本有机郎肯循环系统中,以及纯工质R245fa在再热式有机郎肯循环系统中,三种形式的有机郎肯循环系统热力性能随蒸发温度的变化情况.与纯工质基本有机郎肯循环系统相比,再热式有机郎肯循环最大可提高系统净输出功7.08％,而混合工质对提高整个系统热力性能具有较大的优势,净输出功和热效率最大可提高4.67％和2.91％.     

新型可调式喷射器性能的计算与分析

提出在喷射器喷嘴内插入喷针来调节喷射器工作参数的方案,建立了可调武喷射器性能计算模型,分析了喷嘴截面积变化对喷射系数、气体压力、气体流量等参数的影响。结果表明,通过对喷射器喉口面积的调节,可以实现把出口流量控制在一个稳定的区域内,从而减小喷射器入口参数对出口参数以至整个系统的影响。可调式喷嘴可拓宽喷射器的有效工作范围。     

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%。     

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...     

车用柴油机有机朗肯循环余热回收系统性能计算研究

以某车用柴油机排气余热为研究对象,建立有机朗肯循环(ORC)余热回收系统热力学模型,分析主要设计参数包括对ORC余热回收系统性能有影响的蒸发压力、冷凝压力、蒸发器出口工质过热度、冷凝器出口工质过冷度等,通过自编程序计算研究了工质流量、系统热效率等系统性能参数的变化规律。研究结果表明:提高系统的蒸发压力,降低冷凝压力有利于提高系统的性能;对于R123工质,过热度增加对系统的性能影响不大,而对于乙醇工质,过热度增加有利于系统效率提高;冷凝器出口工质过冷度的增加给循环性能带来不利影响。     

车用柴油机-有机朗肯循环联合系统的设计及分析

针对一台车用柴油机全工况范围内排气能量的变化规律,设计了一套有机朗肯循环(organic Rankine cycle,ORC)余热回收系统,进而与车用柴油机耦合形成了车用柴油机-有机朗肯循环联合系统。ORC余热回收系统采用非共沸混合工质R416A,以高效回收柴油机的排气能量。采用螺杆膨胀机作为有机朗肯循环系统的动力输出部件,通过试验测试确定螺杆膨胀机的最优工况点(进气压力1.7MPa、膨胀比8、等熵效率0.65),进而设定有机朗肯循环系统的最优运行参数。研究结果表明:加装有机朗肯循环系统后,与原柴油机相比,车用柴油机-有机朗肯循环联合系统的输出功率最大提升了30.6kW,热效率最大提升了10.99%,余热回收效率最高可达10.61%,有效燃油消耗率最大降低了35g/(kW·h)。     

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。     

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。     

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。     

CFD modelling and experimental investigation of an ejector refrigeration system using methanol as the working fluid

This paper presents results of computational fluid dynamic (CFD) analysis and experimental investigation of an ejector refrigeration system using methanol as the working fluid. The CFD modelling was used to investigate the effect of the relative position of the primary nozzle exit within the mixing chamber on the performance of the ejector. The results of the CFD were used to obtain the optimum geometry of the ejector, which was then used to design, construct and test a small‐scale experimental ejector refrigeration system. Methanol was used as the working fluid, as it has the advantage of being an ‘environmentally friendly’ refrigerant that does not contribute to global warming and ozone layer depletion. In addition, use of methanol allows the ejector refrigeration system to produce cooling at temperatures below the freezing point of the water, which of course would not be possible with a water ejector refrigeration system. CFD results showed that positioning the nozzle exit at least 0.21 length of the mixing chamber throat's diameter upstream of the entrance of the mixing chamber gave better performance than pushing it into the mixing chamber. Experimental values of coefficient of performance (COP) between 0.2 and 0.4 were obtained at operating conditions achievable using low‐grade heat such as solar energy and waste heat. Copyright © 2001 John Wiley & Sons, Ltd.     

Energy and exergy analysis of novel solar bi‐ejector refrigeration system with injector

Energy and exergy balances were done on a novel solar bi‐ejector refrigeration system with R123, whose circulation pump is replaced by an injector. The analysis result of the novel system was compared with that of the original one. The effect of operation condition on system energy efficiency, exergy efficiency and exergy loss was analyzed, and the dynamic performance of a designed solar bi‐ejector refrigeration system was also studied. The comparative results indicate that under the same operating condition, the novel system and the original system have equal energy efficiency, exergy efficiency and exergy loss, and the only difference between them is the exergy losses of the generators and the added injector. The other conclusions mainly include: the solar collector has the largest exergy loss rate of over 90% and for the bi‐ejector refrigeration subcycle, the ejector has the largest exergy loss rate of about 5%; the total exergy loss changes inversely proportional to the evaporation temperature and positively proportional to the condensation temperature; when the other parameters are fixed, there exists an optimum generation temperature, at which the overall energy and exergy efficiencies are both the maximum and the total exergy loss is the minimum. The study points out the direction for optimizing the novel solar bi‐ejector refrigeration system. Copyright © 2009 John Wiley & Sons, Ltd.     

太阳能喷射/压缩复合制冷循环性能研究

研究了一种太阳能喷射/压缩复合制冷循环,由太阳能集热子系统、喷射制冷子系统及压缩制冷子系统组成,系统充分利用热电两种能源以及两种制冷方法各自的优点,优化喷射制冷子系统工作性能的同时,改善压缩式子系统的工作条件,从而提高复合制冷循环性能的同时节约高品位电能。采用性能较好的高蒸发温度式喷射制冷带走压缩机排气余热具有实际意义。通过数值模拟的手段分析系统性能及其主要影响因素,并优化工作条件。研究表明,与相同工作条件下的单压缩制冷循环相比,复合制冷循环工作日全天候运行时电力性能系数提升约为31.5%,节电优势显著。存在一个最佳的喷射子系统蒸发温度使得复合制冷循环性能系数达到运行工况的最大值。     

Performance testing of a novel ejector refrigerator for various controlled conditions

The paper presents the experimental results of a novel ejector refrigerator that was designed to be suitable for an air‐conditioning application using vacuum tube solar collectors for vapour generation. The primary flow of the ejector is controlled using a spindle in order to provide fine tuning for ejector operation as heat input changes with solar radiation. Water, the most environmentally friendly substance is used as the working fluid. The performance of the ejector was tested for a range of controlled primary flows, boiler temperatures, condensation capacities using different primary nozzles with different lengths. The effect of the operating conditions and nozzle length on the performance of the ejector was analyzed. It was found that in the tested boiler temperature range of 84–96°C the maximum cooling capacity (4.01 kW) of the ejector with short nozzle is much higher than that of the ejector with long nozzle (2.9 kW) on the spindle position of 21 mm. However, the ejector with long nozzle has increased COP when the boiler temperature is below 88°C and has higher critical back pressure. Copyright © 2010 John Wiley & Sons, Ltd.     

The first and second law analysis on an organic Rankine cycle with ejector

In consideration of the low efficiency of the organic Rankine cycle (ORC) with low-grade heat source (LGHS), an organic Rankine cycle with ejector (EORC) and a double organic Rankine cycle (DORC) based on the ORC is introduced in this paper. The thermodynamic first law and second law analysis and comparison on the ORC, EORC and DORC cycles are conducted on the cycle’s power output, thermal efficiency, exergy loss and exergy efficiency. Water is chosen as the LGHS fluid, and the same temperature and mass flow rate of the water is the standard condition for the comparative analysis on the cycles. The emphasis is on the thermodynamic performance at the maximum net power output of the cycles. The results show the power output is higher in the EORC and DORC compared to the ORC. And the cycle’s exergy efficiency could be ranked from high to low: DORC > EORC > ORC.     

An experimental study on the organic Rankine cycle to determine as to how efficiently utilize fluctuating thermal energy

Thermal properties of the available energy such as maximum temperature and thermal energy capacity are greatly influenced to the design of energy conversion system like the organic Rankine cycle (ORC). Useful thermal energy can be obtained from: waste heat energy, geothermal energy, solar heat energy, biomass energy, and so on. However, these cannot usually be supplied at constant levels. Hence, the temperature and flowrate of the thermal energy can vary while the ORC is working. In order to efficiently utilize such fluctuating thermal energy, an experimental study was conducted while adjusting the mass flowrate and the temperature of the working fluid. Three supersonic nozzles and an impulse type turbine were applied. The supersonic nozzle was adopted to increase the spouting velocity for efficient operation of the impulse turbine. The nozzle was designed to reach a velocity of Mach 1.6 at the nozzle exit, and three nozzles were used to control the mass flowrate in this experiment. The experimental results were compared with the predicted results obtained by the cycle analysis.     

喷射式氨-水吸收制冷系统的研究

在传统吸收制冷系统中引入喷射器,根据喷射器理论和吸收制冷循环理论,对新制冷系统的工作性能进行了模拟。分别探讨了冷凝温度、喷射器压缩比等参数对系统性能系数和发生温度的影响。结果表明,在原有吸收制冷系统结构变化不大的情况下,尽管系统性能系数有所下降,但系统发生温度却显著降低,因此,低品位的热源将有可能成为氨吸收制冷的加热热源,对于节能减排具有重要的意义。     

Particular characteristics of transcritical CO2 refrigeration cycle with an ejector

The present study describes a theoretical analysis of a transcritical CO₂ ejector expansion refrigeration cycle (EERC) which uses an ejector as the main expansion device instead of an expansion valve. The system performance is strongly coupled to the ejector entrainment ratio which must produce the proper CO₂ quality at the ejector exit. If the exit quality is not correct, either the liquid will enter the compressor or the evaporator will be filled with vapor. Thus, the ejector entrainment ratio significantly influences the refrigeration effect with an optimum ratio giving the ideal system performance. For the working conditions studied in this paper, the ejector expansion system maximum cooling COP is up to 18.6% better than the internal heat exchanger cycle (IHEC) cooling COP and 22.0% better than the conventional vapor compression refrigeration cycle (VCRC) cooling COP. At the conditions for the maximum cooling COP, the ejector expansion cycle refrigeration output is 8.2% better than the internal heat exchanger cycle refrigeration output and 11.5% better than the conventional cycle refrigeration output. An exergy analysis showed that the ejector expansion cycle greatly reduces the throttling losses. The analysis was also used to study the variations of the ejector expansion cycle cooling COP for various heat rejection pressures, refrigerant temperatures at the gas cooler exit, nozzle efficiencies and diffuser efficiencies.     

Performance analysis of a waste‐heat‐powered thermodynamic cycle for multieffect refrigeration

A multieffect refrigeration system that is based on a waste‐heat‐driven organic Rankine cycle that could produce refrigeration output of different magnitudes at different levels of temperature is presented. The proposed system is integration of combined ejector–absorption refrigeration cycle and ejector expansion Joule–Thomson (EJT) cooling cycle that can meet the requirements of air‐conditioning, refrigeration, and cryogenic cooling simultaneously at the expense of industrial waste heat. The variation of the parameters that affect the system performance such as industrial waste heat temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector refrigeration cycle (ERC) and EJT cycles was examined, respectively. It was found that refrigeration output and thermal efficiency of the multieffect cycle decrease considerably with the increase in industrial waste heat temperature, while its exergy efficiency varies marginally. A thermal efficiency value of 22.5% and exergy efficiency value of 8.6% were obtained at an industrial waste heat temperature of 210°C, a turbine inlet pressure of 1.3 MPa, and ejector evaporator temperature of 268 K. Both refrigeration output and thermal efficiency increase with the increase in turbine inlet pressure and ERC evaporator temperature. Change in EJT cycle evaporator temperature shows a little impact on both thermal and exergy efficiency values of the multieffect cycle. Analysis of the results clearly shows that the proposed cycle has an effective potential for cooling production through exploitation of lost energy from the industry. Copyright © 2014 John Wiley & Sons, Ltd.     

Exergy analysis of ejector‐refrigeration cycle using water as working fluid

Exergy is based on the second law of thermodynamics and is the only rational basis for evaluating the system performance. The aim of this paper is to study in detail the irreversibilities in the steam‐ejector refrigeration system. The influence of the cycle parameters is analysed on the basis of the first and second law and the results indicated the components with the greater irreversibility. A better quality of the ejector has more effect on the system performance than the better quality of other components, because the ejector at first and the condenser at second have the greater exergy loss of the system. For the refrigeration system the maximum coefficient of performance varying between 0.4 to 0.6 and the second law efficiency remains close to 0.17 for generator pressure 6 bar, condenser temperature 44–50°C and evaporator temperature 4–8°C. Also the study showed that the second law analysis quantitatively visualizes losses within a system and gives clear trends for optimization. Copyright © 2005 John Wiley & Sons, Ltd.