A Review on Technologies for the Use of CO2 as a Working Fluid in Refrigeration and Power Cycles

The use of carbon dioxide as a working fluid has been the subject of extensive studies in recent years, particularly in the field of refrigeration where it is at the heart of research to replace CFC and HCFC. Its thermodynamic properties make it a fluid of choice in the efficient use of energy at low and medium temperatures in engine cycles. However, the performance of transcritical CO2 cycles weakens under high temperature and pressure conditions, especially in refrigeration systems;On the other hand, this disadvantage becomes rather interesting in engine cycles where CO2 can be used as an alternative to the organic working fluid in small and medium-sized electrical systems for low quality or waste heat sources. In order to improve the performance of systems operating with CO2 in the field of refrigeration and electricity production, research has made it possible to develop several concepts, of which this article deals with a review of the state of the art, followed by analyzes in-depth and critical of the various developments to the most recent modifications in these fields. Detailed discussions on the performance and technical characteristics of the different evolutions are also highlighted as well as the factors affecting the overall performance of the systems studied. Finally, perspectives on the future development of the use of CO2 in these different cycles are presented.

Entropy Analysis of Vapor-Compression Refrigeration System by Using the Second Law of Thermodynamics

By means of the Second Law of Thermodynamics,thispaper gives out the entropy analysis method for vapor-comperession refrigeration system.The thermal irrevers-ibility of the system charged with R12 and its hopeful al-ternative refrlgerant R134a have been studied respective-ly.On the basis of all the research results of this paper,the measure used to save energy for vapor-compressionrefrigeration system has been put out.

Energy,exergy,and economic analysis of compression-absorption cascade refrigeration cycle using different working fluids

Compression-absorption cascade refrigeration cycle(CACRC)combined with vapor-compression refrigeration and absorption refrigeration cycle attracts great interest due to the less electricity consumption and utilization waste heat.In this work,the performance of the CACRC system was investigated using 16 refrigerants in the vapor compression section and H_(2)O-LiBr in the absorption refrigeration section.Energy,exergy and economic analysis of the CACRC system were carried out and the results were compared.Results show that RE170/H_(2)O-LiBr presents the better coefficient of performance and exergy efficiency amongst all the studied fluids.In addition,the economic optimization,multi-objective optimization,and thermodynamic optimization of the CACRC system based on the RE170/H_(2)O-LiBr working fluid were also carried out.

Experimental Performance of TJR02 as an Alternative Refrigerant to R22 in a Small-Scale Cold Storage

A refrigerant mixture TJR02 was developed and the comparison experiment was performed on a singlestage vapor compression refrigeration system originally designed for R22.Experimental results show that TJR02 can be directly used in the system without modifying the original system or changing lubricant.By replacing R22 with TJR02,cooling rate gets faster and at least 20% of energy is saved.The actual detection in the standard test-bed verifies the experimental results and indicates that the adoption of TJR02 leads to greater efficiency and wider application.And the lower the refrigeratory temperature is,the more obvious the energy saving effects will be.

An Update Review on Performance Enhancement of Refrigeration Systems Using Nano-Fluids

Considering the issues of energy saving and environment protection,the performance of refrigeration systems requires to be improved.In recent years,nano-fluids have attracted greatly attention from the researchers due to their outstanding thermal characteristics.In this work,the published investigations on the preparation and characterization of nano-fluids have been discussed at first.Furthermore,the key thermo-physical properties of nano-fluids,such as thermal conductivity,viscosity,specific heat and density have been summarized.Finally,the performance enhancements in different types of refrigeration systems by using nano-fluids have been reviewed.It is concluded that nano-fluids as refrigerant,lubricant or secondary fluid have wide potential application in refrigeration systems.

Prospect Evaluation of Low-GWP Refrigerants R1233zd(E)and R1336mzz(Z)Used in Solar-Driven Ejector-Vapor Compression Hybrid Refrigeration System

In this paper,the entrainment ratio,pump work,heat loads of heat exchangers and COPthermal were theoretically evaluated for a solar-driven ejector-vapor compression hybrid refrigeration system with R1233zd(E)and R1336mzz(Z)as the working fluids.The evaluation of the utilization potentials of R1233zd(E)and R1336mzz(Z)was presented by comparing the system performance with that of R245fa,a commonly used refrigerant in the ejector system.The results indicated that the systems with R1233zd(E)and R1336mzz(Z)had a higher entrainment ratio and lower pump work.The pump works when using R1233zd(E)and R1336mzz(Z)can be up to 14.59%and 38.05%lower than those of R245fa,respectively.Meanwhile,the system showed the highest COPthermal utilizing R1233zd(E)followed by that of R245fa,with the R1336mzz(Z)system having the lowest value.The differences between R1233zd(E)and R1336mzz(Z)systems,R1233zd(E)and R245fa systems were 4.33%and 2.0%,respectively.This paper was expected to provide a good reference for the utilizing prospect of R1233zd(E)and R1336mzz(Z)in ejector refrigeration systems.

Performance analysis of cogeneration systems based on micro gas turbine(MGT),organic Rankine cycle and ejector refrigeration cycle

In this paper,the operation perfonnance of three novel kinds of cogeneration systems under design and off-design condition was investigated.The systems are MGT(micro gas turbine)+ORC(organic Rankine cycle)for electricity demand,MGT+ERC(ejector refrigeration cycle)for electricity and cooling demand,and MGT+ORC+ERC for electricity and cooling demand.The effect of 5 different working fluids on cogeneration systems was studied.The results show that under the design condition,when using R600 in the bottoming cycle,the MGT+ORC system has the lowest total output of 117.1 kW with a thermal efficiency of 0.334,and the MGT+ERC system has the largest total output of 142.6 kW with a thermal efficiency of 0.408.For the MGT+ORC+ERC system,the total output is between the other two systems,which is 129.3 kW with a thermal efficiency of 0.370.For the effect of different working fluids,R123 is the most suitable working fluid for MGT+ORC with the maximum electricity output power and R600 is the most suitable working fluid for MGT+ERC with the maximum cooling capacity,while both R600 and R123 can make MGT+ORC+ERC achieve a good comprehensive performance of refrigeration and electricity.The thermal efficiency of three cogeneration systems can be effectively improved under oredesign condition because the bottoming cycle can compensate for the power decrease of MGT.The results obtained in this paper can provide a reference for the design and operation of the cogeneration system for distributed energy systems(DES).

Critical assessment of R410A alternatives for mini-split air conditioners in the Egyptian market

In this study,the potential implementation of three different low-GWP refrigerants(R32,R452B,and R454B)as replacements for R410A was investigated.The study was performed using a simulation tool developed by the authors called RACHP-Lab,which is a vapor compression system simulation tool developed based on physics-based simulation for typical mini-split air conditioners.The simulation study was carried out and validated using experimental performance data of 10 different air conditioning units available in the Egyptian market.The units included fixed-speed or variable-speed compressors and operated in cooling or heating modes.Drop-in replace-ment with the new refrigerants was carried out.For R32,the capacity increased between 4.9%and 13%for cooling cases,and 6.3%and 12.4%for heating cases.However,COP did not improve in all cases.For R452B and R454B with direct replacement,the capacity nearly remained the same,with an increase of COP between 1.6%and 8.0%.Soft optimization was also conducted on cooling cases where compressor suction superheat,condenser subcooling,and compressor volumetric speed were optimized to maximize COP while maintaining the original capacity of R410A.R32 showed an improvement of COP over R410A between 4.6%and 15.5%,while for R452B and R454B between 2.2%and 13.2%.

Measurement and Prediction of Vapor Pressure for H20 ＋ CHaOH] C2HsOH ＋ [BMIM][DBP] Ternary Working Fluids

The ionic liquid, 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]) was prepared and the vapor pressures of three set of binary solutions H2O(1)/CH3OH(1)/C2H5OH(1) + [BMIM][DBP](2) were measured at different temperature and in the ILs mole fraction range from 0.1 to 0.6 with a static equilibrium apparatus. The measured vapor pressures were correlated with Non-Random Two Liquid (NRTL) activity coefficient model and the average relative deviations (ARD) between experimental and correlated vapor pressures for these binary solutions were 3.19%, 2.42% and 2.95%, respectively. Then, the vapor pressures of two set of ternary solutions H2O(1) + CH3OH(2)/C2H5OH(2) + [BMIM][DBP](3) were measured with an inclined boiling apparatus and further predicted with NRTL activity coefficient model based on the binary interaction parameters coming from fitting the vapor pressures of the binary solutions. The results indicated that the ternary solutions containing [BMIM][DBP] were shown a strong negative deviation from Raoult's Law when the mole fraction of [BMIM][DBP] was larger than 0.2, which meant that ternary solutions could absorb the refrigerant vapors at the same or below solution temperature. Meanwhile, the average relative deviations between experimental and predicted vapor pressures for ternary solutions were 2.92% and 3.06%, respectively. Consequently, the NRTL active coefficient model used for non-electrolyte solutions was still valid for predicting vapor-liquid equilibrium of binary or ternary solutions containing ILs.

Cycle performance studies on a new HFC-161/125/143a mixture as an alternative refrigerant to R404

In this paper, a new ternary non-azeotropic mixture of HFC-161/125/143a （0.15/0.45/0.40 in mass fraction）, as a promising mixed refrigerant to R404A, is presented. The ozone depletion potential （ODP） of the new refrigerant is zero and its basic thermodynamic properties are similar to those of R404A, but its global warming potential （GWP） is much smaller than those of R507A and R404A. Meanwhile, theoretical calculations show that, under the working condition 1 （the average evaporation temperature： -23℃, the average condensing temperature： 43℃, the superheat temperature： 28℃, the subcooling temperature： 5 ℃）, the volumetric refrigerating effect and specific refrigerating effect of the new mixture are 2.33% and 15.48% higher, re- spectively, than those of R404A. The coefficient of performance （COP） of the new mixture is 5.19% higher than that of R404A and the pressure ratio of the new mixture is 0.82% lower than that of R404A. Equally, under the working condition II （the average evaporation temperature： -40℃, the average condensing temperature： 35℃, the superheating temperature： 30 ~C, the subcooling temperature： 5℃）, the volumetric refrigerating effect and specific refrigerating effect of the new mixture are 2.24% and 20.58% higher, respectively, than those of R404A. The COP of the new mixture is 4.60% higher than that of R404A and the pressure ratio of the new mixture is similar to that of R404A. The performances of the new mixture and R404A are compared in a vapor compressor refrigeration apparatus originally designed for R404A under several working conditions （condensing temperatures： 35-45℃, evaporation temperatures： -40--20℃）. Experimental results show that the new mixture can obtain a higher COP, by 6.3% to 12.1%, and a lower pressure ratio, by 1.8% to 6.6%, compared to R404A; although the discharge temperature of the new mixture is slightly higher than that of R404A. The advantages of the new mixture will be further verified in the actual system.

Simulation study on performance of a dual-source hybrid heat pump unit with alternative refrigerants

To solve the problems of single heat source heat pump systems in severe cold regions,a dual-source hybrid heat pump unit(DSHHPU)is proposed.The mathematical models of the DSHHPU when charging R134a or its alternative refrigerants R32,R290 and R600a were established respectively,and the performance was simulated and analysed.The results showed that the four refrigerants have different performance characteristics in different aspects.In heat pipe mode,the heating capacity and evaporating pressure of R32 are 36.94%and 59.94%higher than those of R134a.The heating capacity and evaporating pressure of R290 are 5.73%and 22.99%lower than those of R134a.The heating capacity and evaporating pressure of R600a are 43.29%and 68.08%lower than those of R134a.In vapour compression heating mode,the discharge temperature of R32,R290 and R600a are 184.88,72.98 and 66.44%of that of R134a.The coefficient of performance(COP)of R32,R290 and R600a are 72.65,111.59 and 117.94%of that of R134a.Finally,the effects of radiation intensity and ambient temperature on key performance parameters of the different refrigerants were analysed.The research results provide a reference for research on refrigerant replacements for multi-heat source composite heat pump systems.

自复叠制冷技术研究进展

自复叠制冷技术在低温领域的应用十分广泛。本文首先介绍了自复叠制冷技术的原理,并与单级压缩、多级压缩及复叠制冷技术进行比较,指出了自复叠制冷技术具有结构简单、制冷温区宽的优势。从自复叠制冷系统的循环特性、混合工质的选择和配比优化、系统流程优化三方面,对当前自复叠制冷技术的研究进行分析总结。最后,展望该技术的发展前景,为拓宽该技术的应用提供参考。

食用油罐内冷媒管降温模拟试验与优化

为缓解食用油在储藏过程中出现的热分层现象,设计内置冷媒管的食用油储罐,并通过调整冷媒流动方式、冷媒流量和冷媒温度等对储油进行降温对比试验。结果表明:采用上供式和下供式降温均可在储油温度整体下降的同时有效缩小上下层温差(1.93、3.67℃),且与自然降温(6.79℃)相比,热分层现象得到明显改善。采用下供式降温的效率最高,较上供式提高了约20%,且下层油温较上供式低约1.9℃。基于Ansys(Fluent)商用计算流体动力学软件平台,通过数值模拟进一步研究了采用下供式的冷媒流量对下层油温的影响。结果显示下供式降温可有效阻隔外部传热,而下层温度变化集中在低温区域,对远离入口侧区域的影响并不明显。

新PFASs限制法案提案下汽车空调替代制冷剂的对比与展望

随着基加利修正案在中国的通过实施,在我国汽车空调领域逐渐减少或淘汰R134a制冷剂已变成不可回避的事实,而目前国际上最主要的汽车空调替代制冷剂为R1234yf、CO_(2)和R290,目前我国在3种替代制冷剂的选用方面还没有明确方向。德国等5国也在近日提出了对PFASs的限制法案建议,R1234yf也被纳入了受限名单,使用前景不容乐观。在此背景下,从环保性、安全性、经济性以及系统性能等方面对R1234yf、CO_(2)和R290进行对比,总结了相关的研究成果和结论,并对最新的PFAS物质限制法案提案中涉及汽车空调的内容进行整理和分析,为我国汽车空调领域替代制冷剂的研究提供方向,并以此为基础对未来汽车空调替代制冷剂的选择进行展望。

制冷装置柔性接触式密封机构性能提升的关键技术研究进展

柔性接触式密封机构在制冷装置中起到重要的隔热隔湿作用。针对装配状态下刚-柔多体接触对其性能提升带来的技术挑战,从柔性接触式密封机构技术特点和总体发展出发,综述了影响其性能提升的测量、建模等关键性问题的研究现状,并对未来的发展趋势进行了展望。结果表明:基于反向热平衡的热传递测量技术精度不足,引入滤波算法可降低热流信号噪声波动;现有示踪气体技术未考虑湿空气在刚柔接触界面中的流动扩散,应运用界面微观检测及接触动力学理论来明确流动型式,构建匹配的示踪源和检测回路;对柔性接触式密封机构热流固耦合建模研究尚处于空白,仅建立了传热数值模型与流动平均解析方程,可采用数值计算温度、变形场与解析计算渗流参数的迭代算法来建立耦合模型。未来,除开展测量与建模的基础研究外,还需突破“尺寸效应”技术瓶颈,实现密封组件间的良好配合,应用超低导热材料和电磁感应技术,以提升密封机构的隔热隔湿作用。

含亚乙烯基氢氟烯烃的研究进展

对含亚乙烯基的氢氟烯烃(v-HFOs)的合成路线和应用进行了综述。目前,在氟-氯交换、异构化、脱卤化氢、选择性加氢、加氢脱氯、调聚等合成v-HFOs的主要路线中,氟-氯交换的路线具有起始原料易得、容易实现大规模生产的特点,是合成v-HFOs的最佳路线。v-HFOs特殊的分子结构使其具有优异的传热性能、清洁性能、发泡性能和刻蚀性能,主要用作制冷剂、热泵工质、清洗剂、发泡剂和刻蚀剂,特别是E型v-HFOs[(E)-v-HFOs]具有优异的电绝缘性能,分别与其优良的传热性能和清洗性能进行多领域交叉,实现了(E)-v-HFOs应用于浸没式液冷和带电清洗的新场景。展望了v-HFOs的未来发展趋势,提出了今后的研究重点,应开发高活性的氟化催化剂,环保绿色的新型合成路线以及v-HFOs的新型应用。

非共沸工质CO_(2)/R1234yf商超增压制冷系统性能分析

为满足商超制冷领域系统能效提升和制冷剂替代的需求,提出了非共沸工质CO_(2)/R1234yf商超增压制冷系统,通过建立热力学模型,与纯CO_(2)商超增压制冷系统进行对比。结果表明:CO_(2)/R1234yf商超增压制冷系统可在最优的CO_(2)质量分数(0.94)及最优排气压力(8.81 MPa)下获得最大COP(1.40);CO_(2)/R1234yf商超增压制冷系统COP与纯CO_(2)系统相比具有显著提升,环境温度为35℃时,提升7.25%;CO_(2)/R1234yf商超增压制冷系统APF提升率为2.68%~4.72%,系统APF随典型城市所处纬度的增加而增大。CO_(2)/R1234yf商超增压系统(火用)效率随CO_(2)质量分数的增加呈先增后减趋势,CO_(2)质量分数为0.95时获得最高(火用)效率,为0.18,相比纯CO_(2)系统提升4.62%。

钻井液冷却装置技术发展现状及展望

随着国内油气钻井向着万米深井开发,钻井过程中井底温度越来越高,因此需要对钻井液降温冷却以保护井下工具仪器。而国内钻井液冷却装置普遍存在设备超大、超高以及设备冷却降温幅度不大的现状。本文从介绍国外钻井液冷却装置技术现状出发,阐述了国外钻井液冷却装置技术现状;同时结合国内钻井工况,重点分析了国内自然冷却、开式冷却、闭式冷却和强制冷却4种钻井液冷却装置的工作原理、优缺点和适应范围。结合国内钻井技术发展现状,为保障冷却装置降温效果,结合道路运输和环保要求,分析了冷却装置降温机理研究、工程适应性、应用局限性和装置可靠性等关键技术难题,提出了冷却装置技术研发思路,为开发研制适应性强、可靠性高和冷却效果显著的装置提供参考。

替代制冷剂R290与R404A的对比特性研究

本文研究了R290与R404A在低温转子式压缩机中的性能差异,在冷凝温度54.4℃,蒸发温度-23.3℃,根据理论及实测数据得出结论,R290制冷能力比R404A低16%左右,功率、电流比R404A低20%左右;在冷凝温度54.4℃,蒸发温度-6.7℃,根据理论及实测数据得出结论,R290制冷能力比R404A低14%左右,功率、电流比R404A低20%左右。

新型制冷剂R1234ze(E)及其混合工质研究进展

低GWP值制冷剂R1234ze(E)(trans-1,3,3,3-tetrafluoropropene)作为R134a较为理想的替代品而被关注,但其单一成分的热力学性能和传输特性并不理想,在R1234ze(E)中混入R32成分可以有效改善其热力学性能。本文概述了低GWP值工质R1234ze(E)及其与R32混合物的热物性特征、传输特性及系统运行性能方面的研究现状,并与目前常用的制冷工质进行比较分析,指出R1234ze(E)与R32混合工质有望成为新型低GWP值替代工质。