Performance analysis of a combined vapor compression cycle and ejector cycle for refrigeration cogeneration

A hybrid vapor compression refrigeration (HVCR) system, which combines a vapor compression refrigeration (VCR) system and an ejector refrigeration (ER) system, was developed. The waste heat energy from the gas cooler in the VCR system is applied as driven source towards ER system.Thermodynamic investigations on the performance of the HVCR system, using CO₂ as a refrigerant, are performed with energetic and exergetic methods, and the comparative analyses with the VCR system are conducted. Comprehensive effects of key operating parameters on the system performance are also studied. The results indicate that for the same cooling capacity, the coefficient of performance (COP) of the HVCR system shows 25% higher COP and the total mechanical power consumption is reduced by 20% than that of conventional VCR system, respectively. The performance characteristics of the proposed cycle show its application potential in cooling and air-conditioning.     

蒸汽压缩/喷射制冷系统喷射器设计及节能分析

蒸汽压缩/喷射制冷系统是一种有效的节能系统,可以减少节流膨胀损失,降低压缩机压力比,提高制冷系统效率。选择5种计算工况对蒸汽压缩/喷射制冷系统进行计算,研究喷射器结构与蒸发温度和冷凝温度的变化规律,并与普通蒸汽压缩系统对比,从制冷量、压缩机耗功、性能系数三个角度分析新系统的节能效果。计算结果表明蒸汽压缩/喷射制冷系统在低温工况条件下节能效果最优,制冷量最大可提高29%,压缩机耗功最大可降低65%,COP值最大可提高63%。     

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。     

两级蒸发对跨临界CO_2引射制冷系统影响的实验研究

两级蒸发引射制冷循环中通过二级蒸发器不仅能调节引射器出口干度还能提高系统效率。通过改变第二蒸发器冷冻水流量对两级蒸发引射制冷系统进行实验研究,并与改变引射器面积比的调控效果进行比较。结果表明:在实验工况范围内,气冷器压力、第一蒸发器压力和压缩机流量都随第二蒸发器冷冻水流量的增加而增大;而且引射器面积比越大,气冷器压力越高而蒸发器压力和压缩机流量越低。同时,系统引射系数随第二蒸发器冷冻水流量的增加而降低,而制冷量和COP则升高,尤其是在小引射系数下,系统制冷量和COP提高的更为明显。本研究为引射循环提供了另外一种良好的调控思路。     

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.     

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.     

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.     

一个柴油机驱动的复合制冷循环

介绍了一个用柴油机驱动的复合制冷循环，即用柴油机主机带动压缩式循环，同时利用柴油机排气和缸套水的热量作源驱动吸收式循环。热力学分析和数值计算表明，此复合循环由于实现了不同品位热源的合理利用，减少了不可逆损失，其能效比普通式循环或直燃式吸收循环可分别提高19％和58％。     

毛细泵循环蒸汽喷射式制冷系统的研究

提出一种将毛细抽吸两相回路(CPL)与喷射式制冷技术相结合的新型制冷系统的设计方式,系统主要使用太阳能或低品位能作为驱动热能,利用喷射器和毛细芯的毛细抽吸作用来实现工质循环;分析系统的工作原理和运行过程,并利用实际气体等动量变化率的设计方法对系统的核心部件喷射器进行设计计算,并利用设计计算结果,计算分析在给定工况条件下,系统运行性能及能量利用效率。     

Theoretical study and design of a low-grade heat-driven pilot ejector refrigeration machine operating with butane and isobutane and intended for cooling of gas transported in a gas-main pipeline

This paper describes the construction and performance of a novel combined system intended for natural gas transportation and power production, and for cooling of gas transported in a gas-main pipeline. The proposed system includes a gas turbine compressor, a combined electrogenerating plant and an ejector refrigeration unit operating with a hydrocarbon refrigerant. The combined electrogenerating plant consists of a high-temperature steam–power cycle and a low-temperature hydrocarbon vapor power cycle, which together comprise a binary vapor system. The combined system is designed for the highest possible effectiveness of power generation and could find wide application in gas-transmission systems of gas-main pipelines. Application of the proposed system would enable year-round power generation and provide cooling of natural gas during periods of high ambient temperature operation. This paper presents the main results of a theoretical study and design performance specifications of a low-grade heat-driven pilot ejector refrigeration machine operating with butane and isobutane.     

Performance analysis of a two-stage mechanical compression–ejector cooling cycle intended for micro-trigeneration system

This paper provides the results of a performance analysis of a two-stage mechanical compression–ejector cooling cycle. In the proposed cooling system the compression process is realized in two stages: by a mechanical compressor as the first stage and by an ejector as the second stage. Ammonia (R717) is investigated as the working fluid for the cooling system in the present study. The influence of the middle pressure, and evaporating and condensing temperatures on the characteristics of the cooling system is analyzed. Based on the obtained results a pilot small-scale two-stage refrigeration unit with cooling capacity of 10 kW intended for application in micro-trigeneration systems is designed.     

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。     

Design-theoretical study of cascade CO2 sub-critical mechanical compression/butane ejector cooling cycle

In this paper an innovative micro-trigeneration system composed of a cogeneration system and a cascade refrigeration cycle is proposed. The cogeneration system is a combined heat and power system for electricity generation and heat production. The cascade refrigeration cycle is the combination of a CO₂ mechanical compression refrigerating machine (MCRM), powered by generated electricity, and an ejector cooling machine (ECM), driven by waste heat and using refrigerant R600. Effect of the cycle operating conditions on ejector and ejector cycle performances is studied. Optimal geometry of the ejector and performance characteristics of ECM are determined at wide range of the operating conditions. The paper also describes a theoretical analysis of the CO₂ sub-critical cycle and shows the effect of the MCRM evaporating temperature on the cascade system performance. The obtained data provide necessary information to design a small-scale cascade system with cooling capacity of 10 kW for application in micro-trigeneration systems.     

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.     

一种新型跨临界CO2冷电联供系统热力分析

提出一种新型跨临界二氧化碳（trans-critical carbon dioxide,TCO₂）再压缩循环和喷射器制冷循环耦合的冷电联供系统。该系统在输出电能的同时,利用低品位热能驱动喷射器工作输出冷量。以输出电量1 MW为设计目标,对比冷电联供系统和再压缩发电系统的性能,研究联供系统各部件（火用）损和主要热力参数对其性能的影响。结果表明：联供系统利用CO₂余热驱动喷射器输出冷量,循环热效率高于单一再压缩系统;加热器（火用）损所占比例最大,回热器次之;透平进口温度、压力和背压对联供系统工质流量、循环效率、输出功率、加热器功率、压缩机耗功及喷射器制冷量等参数影响较大;而冷凝温度和蒸发温度仅对制冷循环制冷量影响较大。在设定条件下,联供系统的循环热效率和（火用）效率可分别达到46.99%和47.21%。     

跨临界CO2两相流引射制冷系统性能实验研究

对跨临界CO2两相流引射制冷系统性能进行了实验,分析了工况及引射器几何参数对系统性能的影响,结果表明:在实验工况范围内,跨临界CO2两相流引射制冷系统制冷量和COP随气体冷却器压力的升高而升高,随气体冷却器出口温度的升高而降低。对于使用不同喉部直径喷嘴的系统,在相同工况下,引射器喷嘴喉部直径较大的系统的性能较好。对于使用不同直径混合室的系统,随着气体冷却器压力的升高,使用小直径混合室的系统COP变化较大;当气体冷却器压力较低时,使用大直径混合室的系统COP较高,而当气体冷却器压力较高时,使用小混合室直径的系统性能较好。在相同工况下,与传统跨临界CO2循环进行比较,两相流引射制冷循环系统COP最大可提高14%。     

Development and performance analysis of a multi-temperature combined compression/ejection refrigeration cycle using environment friendly refrigerants

A combined compression/ejection refrigeration cycle intended for the simultaneous production of cold for refrigeration and freezing, and operating based on environment friendly refrigerants is proposed and analyzed in this study. This makes it possible to valorize the low-temperature heat sources in the ejector cycle, thereby reducing the share of mechanical energy otherwise required to operate the conventional two-stage vapor compression system.A selection of eight candidates' fluids was performed. The developed simulation model helped to establish the strong dependence between system performances and the ratio of the cooling capacities of refrigeration and freezing. In addition to the effect of the temperature level of cold production, the influence of the ambient temperature on system performance was also analyzed when using refrigerants R290, R152a and R134a.     

Performance of vapor compression systems with compressor oil flooding and regeneration

Vapor compression refrigeration technology has seen great improvement over the last several decades in terms of cycle efficiency through a concerted effort of manufacturers, regulators, and research engineers. As the standard vapor compression systems approach practical limits, cycle modifications should be investigated to increase system efficiency and capacity. One possible means of increasing cycle efficiency is to flood the compressor with a large quantity of oil to achieve a quasi-isothermal compression process, in addition to using a regenerator to increase refrigerant subcooling.In theory, compressor flooding and regeneration can provide a significant increase in system efficiency over the standard vapor compression system. The effectiveness of compressor flooding and regeneration increases as the temperature lift of the system increases. Therefore, this technology is particularly well suited towards lower evaporating temperatures and high ambient temperatures as seen in supermarket refrigeration applications. While predicted increases in cycle efficiency are over 40% for supermarket refrigeration applications, this technology is still very beneficial for typical air-conditioning applications, for which improvements in cycle efficiency greater than 5% are predicted. It has to be noted though that the beneficial effects of compressor flooding can only be realized if a regenerator is used to exchange heat between the refrigerant vapor exiting the evaporator and the liquid exiting the condenser.     

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.     

双分层水箱太阳能喷射制冷循环特性

本文提出一种采用双分层水箱的太阳能喷射制冷循环,分层水箱热分层显著,颇具可用能储存优势,结合大小水箱各自的优势弥补因太阳日辐射量波动而导致太阳能利用率不高、太阳能驱动的喷射制冷效率较低等问题。采用逐时冷负荷分析法分析了双分层水箱太阳能喷射制冷系统特性,结果表明:该制冷循环高品位能耗约为普通机械压缩制冷循环的1/5,较传统水箱太阳能喷射制冷循环全天工作时间约多4 h,日产冷量提高36.8%,且分层水箱喷射制冷系统的逐时制冷量与办公室逐时冷负荷更吻合。