Ejector expansion refrigeration system: Ejector design and performance evaluation

Use of a two-phase flow ejector as an expansion device in vapor compression refrigeration systems is one of the efficient ways to enhance its performance. The present work aims to design a constant-area two phase flow ejector and to evaluate performance characteristics of the ejector expansion refrigeration system working with R134a. In order to achieve these objectives, a simulation program is developed and effects of operating conditions and ejector internal efficiencies on the system performance are investigated using EES software. Comparison between present results and published experimental data revealed that the developed model can predict the system COP with a maximum error of 2.3%. The system COP increased by 87.5% as evaporation temperature changed from −10 °C to 10 °C. Finally, correlations to size ejector main diameters as a function of operating conditions, system cooling capacity and ejector internal efficiencies are reported.     

Thermodynamic performance assessment of carbon dioxide blends with low-global warming potential (GWP) working fluids for a heat pump water heater

Blends of CO₂ with ten low-global warming potential (GWP) working fluids are evaluated for use in a heat pump water heater. The effects that the discharge pressure, component ratio, hot-water outlet temperature and chilled water inlet temperature have on the coefficient of performance (COP) of heat pump are analyzed when the pinch point of the heat exchange is considered. It is found that temperature glide of zeotropic mixture has a good thermal match with the temperature change of water as two pinch points appear in the gas cooler/condenser or evaporator. The good thermal match in the heat exchangers promotes the system COP. Addition of low-GWP working fluids to pure CO₂ can reduce the high-side pressure. The results show that CO₂/R41 and CO₂/R32 are suitable candidates for heat pump water heaters because of their high COP and low high-side pressure in comparison with those of a pure CO₂ cycle.     

A study of working fluids for heat driven ejector refrigeration using lumped parameter models

This paper studies the influence of working fluids over the performance of heat driven ejector refrigeration systems performance by using a lumped parameter model. The model used has been selected after a comparison of different models with a set of experimental data available in the literature. The effect of generator, evaporator and condenser temperature over the entrainment ratio and the COP has been investigated for different working fluids in the typical operating conditions of low grade energy sources. The results show a growth in performance (the entrainment ratio and the COP) with a rise in the generator and evaporator temperature and a decrease in the condenser temperature. The working fluids have a great impact on the ejector performance and each refrigerant has its own range of operating conditions. R134a is found to be suitable for low generator temperature (70–100 °C), whereas the hydrocarbons R600 is suitable for medium generator temperatures (100–130 °C) and R601 for high generator temperatures (130–180 °C).     

Energy and exergy analysis of zeotropic mixture R290/R600a vapor-compression refrigeration cycle with separation condensation

This paper proposes a modified vapor-compression refrigeration cycle (MVRC) system operating with the zeotropic mixture R290/R600a for domestic refrigerator-freezers. In the MVRC system, a phase separator is introduced to enhance the overall system performance. A theoretical energy and exergy analysis on the performance of the MVRC is carried out by using the developed mathematical model, and then compared with that of the traditional vapor-compression refrigeration cycle (TVRC) operating with the refrigerant R600a and the zeotropic mixture R290/R600a, respectively. According to the simulation results of these two cycles, the MVRC can give the most excellent performances in the COP (coefficient of performance), the volumetric refrigeration capacity, the total exergy destruction and the exergetic efficiency under the same given operating conditions. Therefore, the performance characteristics of the MVRC may show its promise in domestic refrigerator-freezer applications.     

Thermodynamic analyses on an ejector enhanced CO2 transcritical heat pump cycle with vapor-injection

In this paper, an ejector enhanced vapor injection CO₂ transcritical heat pump cycle with sub-cooler (ESCVI) for heating application in cold regions is proposed. The thermodynamic analysis using energetic and exegetic methods is carried out to predict the performance characteristics of the ejector enhanced cycle, and then compared with those of the conventional vapor injection heat pump cycle with sub-cooler (SCVI). The simulation results demonstrate that the ejector enhanced cycle exhibits better performance than the conventional vapor injection cycle under the specified operating conditions. The improvements of the maximum system COP and volumetric heating capacity could reach up to 7.7% and 9.5%, respectively. Exergetic analysis indicates that the largest exergy destruction ratio is generated at the compressor followed by the evaporator and gas cooler. Additionally, the exergy efficiency of the ejector is introduced to quantify the effectiveness of the exergy recovery process, which may be a new criterion to evaluate the performance of the ejector enhanced vapor compression cycle.     

Mathematical modeling and thermodynamic investigation of the use of two-phase ejectors for work recovery and liquid recirculation in refrigeration cycles

This paper presents the results of a numerical investigation on the performance of ejector cycles in which the work recovered is used to recirculate liquid through the evaporator. The ejector recirculation cycle, in which the ejector is only used to recirculate liquid and improve evaporator performance, and the standard ejector cycle, in which the ejector can be used to both recirculate liquid and directly unload the compressor, are investigated. The analysis uses a microchannel evaporator and refrigerants R134a, R410A, and CO₂. It is seen that fluids that have large throttling loss but gain little benefit from liquid recirculation (CO₂) should use the ejector to directly unload the compressor, while fluids that have lower throttling loss but gain significant benefit from liquid recirculation (R134a) should use the ejector to improve evaporator performance through liquid recirculation. It is also seen that the ejector recirculation cycle is better suited for ejector off-design operation.     

Theoretical assessment of an ejector enhanced oil flooded compression cycle

Compressor loss and throttling loss are major thermodynamic losses in basic vapor compression cycle. For this reason, an ejector enhanced oil flooded compression cycle is proposed. To evaluate the performance, a mathematical model is established and the performance of this cycle with R32 as the working fluid is investigated. Furthermore, basic cycle, ejector enhanced basic cycle and oil flooded compression cycle have also been investigated. The comparison results show that the developed cycle has a maximum of 4.3% and 4% COP improvement at the evaporation temperature of −25 °C and the condensation temperature of 45 °C over the oil flooded compression cycle and the ejector enhanced basic cycle respectively. In addition, the effects of internal heat exchanger on the developed cycle are also studied. In comparison to the ejector enhanced basic cycle with 50% efficient internal heat exchanger, the COP improvement of the developed cycle rises up to a maximum of 8.5%. The results show that the proposed cycle has large potential applications for the ejector cycle enhancement.     

DME或R600a与角鲨烷为工质对的吸收式制冷循环性能分析

本文分析了R600a/角鲨烷和DME/角鲨烷工质对在单效和压缩辅助吸收式制冷循环中的热力学性能.利用NRTL模型关联了两种工质对的汽液相平衡数据,分析了发生温度、蒸发温度和压缩机压比对循环性能系数(COP)、 效率和循环倍率的影响.结果表明:R600a工质对的性能更优.相比于单效循环,压缩辅助循环性能明显更高.在蒸发温...     

Thermodynamic investigation and optimization of novel ejector-expansion CO2/NH3 cascade refrigeration cycles (novel CO2/NH3 cycle)

The present study thermodynamically evaluated the ejector utilization's impact on the performance of the cascade cycle that uses CO₂ and NH₃ as refrigerants. The theoretical analysis on the functional features based on the first and second laws of the thermodynamics illustrates the facts that the maximum cop and the maximum second law efficiency are on average7 and 5 percent higher than the conventional cycle. However, the exergy destruction rates roughly 8 percent lower as compared to the conventional cycle. Therefore, the novel ejector-expansion cascade cycle is a promising refrigeration cycle from the thermodynamically and practical points of view. A linear regression through the terms of T_eva, T_cond, ΔT yields to three useful correlations for maximum COP, maximum second law efficiency, and in accordance with their optimal temperature.     

Theoretical energy performance evaluation of different single stage vapour compression refrigeration configurations using R1234yf and R1234ze(E) as working fluids

R1234yf and R1234ze(E) have been proposed as alternatives for R134a in order to work with low GWP refrigerants, but this replacement results generally in a decrease of the performance. For this reason, it is interesting to explore ways to improve the system performance using these refrigerants. In this paper, a comparative study in terms of energy performance of different single stage vapour compression configurations using R1234yf and R1234ze(E) as working fluids has been carried out. The most efficient configuration is the one which uses an expander or an ejector as expansion device. On the other hand, using an internal heat exchanger in a cycle which replaces the expansion valve by an expander or an ejector could produce a detrimental effect on the COP. However, for all the configurations the introduction of an internal heat exchanger produces a significant increment on the cooling capacity.     

First and second law investigation of waste heat based combined power and ejector-absorption refrigeration cycle

In the proposed cogeneration cycle, a LiBr-H₂O absorption refrigeration system is employed to the combined power and ejector refrigeration system which uses R141b as a working fluid. Estimates for irreversibilities of individual components of the cycle lead to possible measures for performance improvement. Results of exergy distribution of waste heat in the cycle show that around 53.6% of the total input exergy is destroyed due to irreversibilities in the components, 22.7% is available as a useful exergy output, and 23.7% is exhaust exergy lost to the environment, whereas energy distribution shows 44% is exhaust energy and 19.7% is useful energy output. Results also show that proposed cogeneration cycle yields much better thermal and exergy efficiencies than the previously investigated combined power and ejector cooling cycle. Current investigation clearly show that the second law analysis is quantitatively visualizes losses within a cycle and gives clear trends for optimization.     

一种新型喷射-压缩复合循环制冷系统节能运行优化工况点的探讨

CCRS是使用机械压缩机的制冷循环（RAC／MC）和使用喷射器的冷却循环（EJC）复合的一种新型节能循环系统，其中EJC是由RAC／MC的余热驱动的，并作为RAC／MC的底部循环，通过分析表明，CCRS的COP值比单独压缩制冷循环系统的COP有明显提高，而且合理的喷射冷却循环工况对COP值的提高有很大影响，在喷射工况一定时，发生器中温度的变化，使得系统的制冷量和COP存在极限值，此时对应的工况即系统的最佳工况，具有实际指导意义，同时还比较了系统使用R22和R134a作为压缩式制冷循环制冷剂的性能差异。     

Experiment and simulation on the performance of an autocascade refrigeration system using carbon dioxide as a refrigerant

The main purpose of this study is to investigate the performance of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the advantages of this system is the possibility of keeping the highest pressure of the system within a limit by selecting the composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide. Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power, refrigeration capacity, and coefficient of performance (COP) with respect to the mass fraction of R744 in R744/134a and R744/290 mixtures are presented at different operating conditions. Experimental results show similar trends with those from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but COP tends to decrease while the system pressure rises.

Résumé

The main purpose of this study is to investigate the performance of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the advantages of this system is the possibility in keeping the highest pressure of the system within a limit by selecting the composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide. Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power, refrigeration capacity, and coefficient of performance (COP) with respect to the mass fraction of R744 in R744/134a and R744/290 mixtures are presented at different operating conditions. Experimental results show similar trends with those from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but COP tends to decrease while the system pressure rises.     

基于非共沸工质的喷射式功冷并供循环㶲经济性分析

从热力学第一、二定律和经济性的角度，对一种新型的基于非共沸工质的喷射式功冷并供循环进行热经济性分析。并在此基础上对循环进行参数分析，研究工质组分比、蒸发温度、冷凝温度、膨胀机膨胀比、蒸汽发生器出口温度5个关键参数对循环热效率、㶲效率和资金成本率的影响。最后，以㶲效率最大化和成本率最小化为目标优化函数，采用NSGA-II算法得出帕累托最优解系，并使用TOPSIS方法进行决策，得出最优决策点，即㶲效率为0.131 9，资金成本率为1.94×10^-5美元/s。     

Drop-in replacement in a R134 ejector refrigeration cycle by HFO refrigerants

The present work reports a numerical analysis of a single-phase supersonic ejector working with R134a as well as hydrofluoroolefin (HFO) refrigerants R1234yf and R1234ze(E). Comparisons were made regarding the ejector performances under varying operating conditions and refrigerant mixture proportions. The calculations have been then extended to an existing ejector heat driven refrigeration cycle (EHDRC). R1234yf appears to be a good candidate for drop-in replacement of R134a in a real EHDRC, while using R1234ze(E) would induce some modifications due to its thermodynamic properties. Maintaining the same pressure ratio for the ejector would lead on one hand to better entrainment ratio using R1234ze(E) and on the other hand to reduced coefficient of performance (COP) and cooling power by 4.2% and 26.6% in average, respectively. Using R1234yf under the same conditions induces a decrease of 5.2% for the entrainment ratio, 9.6% for the COP and 19.8% for the cooling power in average.     

Application of an ejector in autocascade refrigeration cycle for the performance improvement

This paper presented a novel autocascade refrigeration cycle (NARC) with an ejector. In the NARC, the ejector is used to recover some available work to increase the compressor suction pressure. The NARC enables the compressor to operate at lower pressure ratio, which in turn improves the cycle performance. Theoretical computation model based on the constant pressure-mixing model for the ejector is used to perform a thermodynamic cycle analysis for the NARC with the refrigerant mixture of R23/R134a. The effects of some main parameters on cycle performance were investigated. The results show the NARC has an outstanding merit in decreasing the pressure ratio of compressor as well as increasing the COP. For NARC operated at the condenser outlet temperature of 40 °C, the evaporator inlet temperature of −40.3 °C, and the mass fraction of R23 is 0.15, the pressure ratio of the ejector reaches to 1.35, the pressure ratio of compressor is reduced by 25.8% and the COP is improved by 19.1% over the conventional autocascade refrigeration cycle.     

Thermodynamic assessment of high-temperature heat pumps using Low-GWP HFO refrigerants for heat recovery

Reducing energy consumption by utilizing heat recovery systems has become increasingly important in industry. This paper presents an exploratory assessment of heat pump type heat recovery systems using environmentally friendly refrigerants. The coefficient of performance (COP) of 4 cycle configurations used to raise the temperature of heat media to 160 °C with a waste heat at 80 °C is calculated and compared for refrigerants R717, R365mfc, R1234ze(E), and R1234ze(Z). A multiple-stage “extraction” cycle drastically reduces the throttling loss and exergy loss in the condensers, resulting in the highest COP for R1234ze(Z). A cascade cycle using R1234ze(Z) and R365mfc has a relatively high COP and provides practical benefits. Even under adverse conditions, the primary energy efficiency is greater than 1.3 when the transmission end efficiency of the electric power generation is 0.37. The assessment demonstrated that high-temperature heat pumps are a promising approach for reducing primary energy consumption for industrial applications.     

Experimental evaluation of an ejector as liquid re-circulator in a falling-film water chiller

To experimentally evaluate the performance of an ejector working as a liquid re-circulator in a horizontal-tube falling-film evaporator with R134a, experimental tests are performed using a horizontal-tube falling-film water chiller prototype. Experimental observations on intertube liquid flow pattern of tube bundle validate the feasibility of the liquid re-circulation system using a liquid–liquid ejector. The analysis results show that the influence of the motive flow rate on the entrainment ratio of the ejector is small, and the average entrainment ratio of the ejector is about 2.03. With the increase of the valve opening of the regulating valve, the evaporating capacity of the falling-film water chiller rises 4.8%, from 940.2 kW with the re-circulation ratio of one, to 985.5 kW with the re-circulation ratio of 1.135. The COP of the falling-film water chiller reaches a maximum and then drops down with the increase of the re-circulation ratio, and the optimal re-circulation ratio is 1.135.     

Investigation of ejector-equipped Joule–Thomson refrigerator operating below 77 K

The lowest attainable refrigeration temperature of a nitrogen based Joule–Thomson refrigerator is generally limited to 77 K since the compressor suction pressure is usually higher than atmospheric pressure. The Joule–Thomson process with an ejector is proposed to achieve a refrigeration temperature as low as 68 K by adjusting the evaporation pressure down to 28 kPa and boosting the return stream pressure up to 147 kPa. A one-dimensional numerical model is developed to predict the performance of the ejector at cryogenic temperature, and its accuracy is compared with experimental data. The analysis results show that the addition of the ejector in the Joule–Thomson refrigeration cycle increases up to 5 times the overall efficiency, where the maximum achievable COP and exergy efficiency are 0.0195 and 6.65%, respectively. Other featured advantages of the proposed Joule–Thomson refrigeration cycle with ejector are the simplicity of cycle, minimization of mechanical moving components, cost effectiveness, and high reliability compared to other cryogenic refrigeration methods using pumps or cold compressors in Joule–Thomson cycles.     

采用不同膨胀机构的跨临界CO2循环性能分析

运用热力学第一定律和第二定律对跨临界CO2基本循环、膨胀机循环、喷射器循环和涡流管循环进行了分析,计算了各循环各个部件的损失,比较了各循环性能系数和总损失。计算结果表明,采用膨胀机、喷射器和涡流管等膨胀设备代替基本循环中的节流阀后,由于这些改进膨胀设备的损失小于基本循环节流阀的损失,同时改进循环中压缩机的损失小于基本循环的压缩机损失,从而减小了循环总损失,提高了循环的COP。膨胀机循环的COP远大于其它跨临界CO2循环,其次为喷射器循环和涡流管循环。