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.

Coupling effect of evaporation and condensation processes of organic Rankine cycle for geothermal power generation improvement

Organic Rankine cycle(ORC)is widely used for the low grade geothermal power generation.However,a large amount of irreversible loss results in poor technical and economic performance due to its poor matching between the heat source/sink and the working medium in the condenser and the evaporator.The condensing temperature,cooling water temperature difference and pinch point temperature difference are often fixed according to engineering experience.In order to optimize the ORC system comprehensively,the coupling effect of evaporation and condensation process was proposed in this paper.Based on the laws of thermodynamics,the energy analysis,exergy analysis and entropy analysis were adopted to investigate the ORC performance including net output power,thermal efficiency,exergy efficiency,thermal conductivity,irreversible loss,etc.,using geothermal water at a temperature of 120℃as the heat source and isobutane as the working fluid.The results show that there exists a pair of optimal evaporating temperature and condensing temperatures to maximize the system performance.The net power output and the system comprehensive performance achieve their highest values at the same evaporating temperature,but the system comprehensive performance corresponds to a lower condensing temperature than the net power output.

Effect of dry-wet cycles on dynamic properties and microstructures of sandstone:Experiments and modelling

Underground pumped storage power plant(UPSP)is an innovative concept for space recycling of abandoned mines.Its realization requires better understanding of the dynamic performance and durability of reservoir rock.This paper conducted ultrasonic detection,split Hopkinson pressure bar(SHPB)impact,mercury intrusion porosimetry(MIP),and backscatter electron observation(BSE)tests to investigate the dynamical behaviour and microstructure of sandstone with cyclical dry-wet damage.A coupling FEM-DEM model was constructed for reappearing mesoscopic structure damage.The results show that dry-wet cycles decrease the dynamic compressive strength(DCS)with a maximum reduction of 39.40%,the elastic limit strength is reduced from 41.75 to 25.62 MPa.The sieved fragments obtain the highest crack growth rate during the 23rd dry-wet cycle with a predictable life of 25 cycles for each rock particle.The pore fractal features of the macropores and micro-meso pores show great differences between the early and late cycles,which verifies the computational statistics analysis of particle deterioration.The numerical results show that the failure patterns are governed by the strain in pre-peak stage and the shear cracks are dominant.The dry-wet cycles reduce the energy transfer efficiency and lead to the discretization of force chain and crack fields.

Refrigeration Performance Analysis and Its Applicability of a New Metal Hydride Couple in Auto Air-conditioning

With COP and dynamic characteristics in refrigeration cycle as criteria,a new metal hydride couple——LaNi 4.61 Mn 0.26 Al 0.13 /La 0.6 Y 0.4 Ni 4.8 Mn 0.2 was selected by establishing calculation procedure and metal hydride selection model.The experimental results show that the refigeration cycle of the selected couple is good in the performance.The recovered waste heat and refrigeration power from exhaust gas of several kinds of automobile are calculated by waste-heat formula,coefficient R Q and COP.Refrigeration cycle of the new couple can satisfy the air-conditioning requirement of truck and car and is not enough in passenger car,according to the respective cooling load.

Performance comparison of the solar-driven supercritical organic Rankine cycle coupled with the vapour-compression refrigeration cycle

In this study,a parametric analysis was performed of a supercritical organic Rankine cycle driven by solar parabolic trough collectors(PTCs)coupled with a vapour-compression refrigeration cycle simultaneously for cooling and power production.Thermal efficiency,exergy efficiency,exergy destruction and the coefficient of performance of the cogeneration system were considered to be performance parameters.A computer program was developed in engineering equation-solver software for analysis.Influences of the PTC design parameters(solar irradiation,solar-beam incidence angle and velocity of the heat-transfer fluid in the absorber tube),turbine inlet pressure,condenser and evaporator temperature on system performance were discussed.Furthermore,the performance of the cogeneration system was also compared with and without PTCs.It was concluded that it was necessary to design the PTCs carefully in order to achieve better cogeneration performance.The highest values of exergy efficiency,thermal efficiency and exergy destruction of the cogeneration system were 92.9%,51.13%and 1437 kW,respectively,at 0.95 kW/m2 of solar irradiation based on working fluid R227ea,but the highest coefficient of performance was found to be 2.278 on the basis of working fluid R134a.It was also obtained from the results that PTCs accounted for 76.32%of the total exergy destruction of the overall system and the cogeneration system performed well without considering solar performance.

面向月球基地的自循环热管理及发电系统研究

针对月球基地热管理需求,根据月面热环境特点,设计了一种面向月球基地的新型自循环热管理及发电系统。系统将有机朗肯循环(ORC)和喷射制冷循环(ERC)相结合,以仪器设备散热和太阳能或核能废热为热源,以外部冷背景为冷源,系统内一部分的工质吸收热源,通过有机朗肯循环发电,另一部分工质通过蒸发器吸收航天员日常工作环境中的热量,为航天服和科学研究提供冷量。系统不需要外部电力,可以独立运行,实现发电与制冷。经分析模型计算,在满足月球基地热量收集、传输和排散的基础上,可以实现最大废热制冷率40%以上,总废热利用效率50%以上.

耦合溴化锂制冷机组的燃气-蒸汽联合循环性能分析

燃气-蒸汽联合循环机组的运行性能容易受到环境温度的影响,使得机组在电力负荷需求高峰期面临出力不足的问题.为了解决这一问题,基于EBSILON软件,对耦合溴化锂制冷机组的SGT5-4000F型燃气-蒸汽联合循环进行仿真建模,并将冷却装置加装到压气机入口处,模拟分析进气温度对联合循环输出功率和循环效率的影响规律.研究表明:通过改变压气机进气温度可知降低进气温度可使得联合循环发电功率提高4.73%-6.10%.在温度较高的夏季工况,在燃气轮机的压气机进气口处加装进气冷却装置可以提高机组的性能,并且温度越高,联合循环输出功率提高的效果更好.

渔船柴油机余热利用系统设计与热力学分析

为充分利用渔船柴油机余热,提出一种以CO_(2)为工质的新型余热利用技术,通过能源梯级利用,实现发电、制冷、制淡水的三联供系统。建立船舶余热驱动的CO_(2)超临界发电、跨临界制冷及蒸馏制淡水循环系统的热力学稳态模型,并以排气温度293℃、排气热量1668 kW的Wärtsilä6L45B型船舶柴油机为例,模拟分析关键热力参数对系统性能、余热利用的影响。研究结果表明,该余热利用系统可为渔船提供6.7~284.0 kW的净发电量,同时可为船上-40℃的速冻库和4℃的食品保鲜库分别提供22~150 kW和194~1311 kW的冷量用于速冻、保鲜或舱内空调,并提供5.25~12.75 t/d的淡水;通过控制膨胀机入口压力和海水淡化温度,灵活控制系统输出的净发电量、中低温冷量和淡水量以满足渔船在航行、捕捞等工作阶段对不同能量的需求。通过柴油机余热利用技术提供的电能、制冷量以及淡水,可减少渔船对柴油的消耗,具有明显的节能效果,为远洋作业渔船的余热利用提供参考。

两级节流双循环耦合冰箱节能研究

双循环耦合冰箱在系统耦合运行时,冷冻循环冷凝压力下降,冷凝器出口制冷剂未完全冷凝,冷藏循环提供的冷量被用来处理未完全冷凝的制冷剂,系统难以发挥设计的节能能力。为解决该问题,本文提出一种两级节流双循环耦合系统,在冷冻冷凝器和耦合过冷器之间添加节流装置,使系统能够发挥相应的节能作用。本文制冷剂选取R600a,在环境温度为25℃,冷冻室温度为-18℃的条件下,通过Matlab模拟系统实际运行状态并搭建实验装置进行验证。研究结果表明:在设计工况下,系统单独运行和耦合运行均能够保证冰箱稳定运行,同时耦合运行状态的COP比独立运行状态提升约9%。

混合工质对喷射式冷电联供循环性能的影响

通过耦合动力循环和喷射式制冷循环,喷射式冷电联供循环可以在中低温热能的驱动下同时进行制冷和发电,在可再生能源利用、余热回收等领域有重要的应用价值。不同于单一功能的动力循环,冷电联供循环需要同时保证热源和循环之间、载冷流体和循环之间形成良好的温度匹配。在动力循环中,有机闪蒸循环被认为能够很好地实现变温热源和循环之间的温度匹配。在制冷循环中,非共沸工质能够尽可能地实现循环和载冷流体之间的温度匹配。因此,在基于有机闪蒸循环的喷射式冷电联供循环中使用非共沸工质,可以同时实现热源和循环之间、载冷流体和循环之间较好的温度匹配。通过建立数学模型,研究了R600a/R601a混合工质对该冷电联供循环性能的影响。结果表明,当R600a的质量组分为0.3时,循环的㶲效率达到最大值37.38%,比采用R600a纯工质提高了4.20%,比采用R601a纯工质提高了6.30%。

城市轨道交通杂散电流对沿线变电站偏磁特性的影响研究

为研究城市轨道交通动态运行时杂散电流对沿线变电站偏磁特性的影响,文章基于上海某220 kV变电站及其附近城市轨道交通系统,利用CDEGS软件建立“轨道交通系统-变电站交流电网”耦合仿真模型,对地铁“启动-惰行-制动-停止”一个完整运行周期下轨道交通系统各结构层次电位和电流变化规律、杂散电流空间分布及变压器中性点偏磁直流进行仿真分析,并与现场检测数据进行对比。结果表明:在此仿真模型中,仅牵引变电站向列车供电时钢轨电位低,对变压器中性点偏磁直流影响较小;制动列车跨区间供电时钢轨电位大幅提高,最大可达25.424 V,变压器中性点偏磁直流可达1.2 A;列车运行105 s钢轨泄漏电流总量最大,可达21.647 A,列车启动12 s,钢轨泄漏电流总量17.908 A,流入变压器中性点电流比例最大,可达3.473%。列车一个完整运行周期下,某些钢轨区间钢轨电位存在正负交替变化,可能导致变压器中性点偏磁直流反向。

Solar cycle dependence of the seasonal variation of auroral hemispheric power

Although much has been done on the hemispheric asymmetry (or seasonal variations) of auroral hemispheric power (HP), the dependence of HP hemispheric asymmetry on solar cycle has not yet been studied. We have analyzed data during 1979-2010 and investigated the dependence of HP hemispheric asymmetry/seasonal variation for the whole solar cycle. Here we show that (1) the hemispheric asymmetry of HP is positively correlated to the value of solar F10.7 with some time delay; (2) it is closely related to the coupling function between the solar wind and magnetosphere; and (3) the winter hemisphere receives more auroral power than the summer hemisphere for Kp ~0 to 6. The statistic results can be partly understood in the framework of the ionospheric conductivity feedback model. The similarity and differences between our results and previous results are discussed in the paper.

蒸汽动力循环耦合正、逆制冷循环的电站空冷系统

文中提出一种电站汽轮机凝汽器新型间接空冷系统,它通过特制的双相变换热器将蒸气压缩制冷循环及与其并联的逆制冷循环和蒸汽动力循环串接耦合,以使系统能根据环境温度的高低,分别利用正、逆制冷循环的相互切换和制冷设备运行参数的调整将蒸汽动力循环的平均放热温度降低到和水冷系统的相近或更低,从而使该系统既节水又低耗：而且还可增强空冷系统的环境适应能力：高环境温度时段能满发,低环境温度时段无冻害。文中介绍了该系统的组成和工作原理,预测了系统的主要效果,进行了粗略的经济、社会效益估计,指出了有待进一步深入研究的问题。分析得出结论：新空冷系统的原理可信,技术可行,效果显著。

低温热源喷射式发电制冷复合系统特性分析

提出一种低温热源喷射式发电制冷复合系统。该系统将有机物朗肯循环与喷射式制冷循环相结合,利用透平排气驱动喷射器工作,同时实现发电和制冷的功能。在定义系统评价指标的基础上,选取性能优良的有机物R245fa作为工质,建立系统仿真模型,进行计算分析。计算结果表明,在热源蒸发温度Tg=120℃,制冷蒸发温度Te=7℃,冷凝温度Tc=25℃的标准工况下,系统的热力学第一定律效率可达37%,热力学第一定律折合效率可达15.6%,火用效率可达37.5%。分析同时表明,提高热源蒸发温度Tg,提高制冷蒸发温度Te,降低冷凝温度Tc,有利于提高系统的工作性能;提高透平膨胀比β可以提高系统电冷比R。

基于多电磁环网的功率转移研究与分析

随着电网用电负荷和输送功率的不断增大,电网也不断建设加强升级,出现环网和更高一级电压等级的网架结构。由于高电压等级网架建设还在初期,因此在很多地方出现了多电磁环网网架结构,多电磁环网网架对提高电网的供电可靠性有利。但是环网运行同时也将带来许多问题,如保护的配置,正常环网解环及故障解环引起的功率转移,运行线路过载等问题。多端有源的环网在环网打开时,将出现功率的转移变化,对多端供电网络产生一定的影响,影响安全自动装置动作定值设定,调度员运行控制及事故处理,保护相关定值整定等等。预先分析出环网结构打开后的功率分配对运行方式安排、事故处理,安全自动装置定值设定,防止事故扩大、保证电网安全稳定运行至关重要。通过对多电网环网打开后的功率转移进行分析,提出了功率转移比概念以及影响功率转移的因素,提出了环网线路打开后功率转移产生问题的注意事项。运用PSASP程序对某电网进行模拟仿真分析,验证了相关结论的正确性。

复合制冷循环间接空冷系统变工况特性分析

基于复间冷系统的组成及其功能,建立复间冷系统变工况数学模型,提出了工作于环境高温时段的制冷循环过程中,汽轮机排汽压力的变工况计算模型。该模型揭示出压缩机功耗、环境气温、迎面风速、排汽热负荷等主要因素对汽轮机排汽压力的影响;工作于环境低温时段的逆制冷循环(动力循环)过程中,膨胀机输出功率的变工况计算模型,分析得出汽轮机排汽压力、工质过热度、环境气温、迎面风速、排汽热负荷等运行因素对膨胀机输出功率的影响。以600MW虚拟复间冷机组为例,定量阐明了诸影响因素对汽轮机排汽压力和膨胀机输出功率的影响规律。

压缩和吸收式制冷复合循环电站空冷系统性能评价

针对电站传统空冷技术的种种缺陷,曾提出蒸汽动力循环耦合以氨为制冷剂的正、逆制冷循环的电站空冷系统(以下简称复合循环空冷系统)。复合循环的正制冷循环可根据机组负荷特性和安装地的气象条件选用氨蒸气压缩制冷循环或氨水吸收式制冷循环。为便于设计选型,简要介绍复合循环空冷系统的两制冷循环的构成及工作原理,建立复合循环空冷系统性能评价指标;并根据模拟计算机组安装地的典型年-气温分布进行2种方案的性能评价指标的计算分析及2种方案能级和能耗的对比分析。算例表明:氨水吸收式制冷复合循环空冷系统的性能评价指标和能级和能耗均明显优于氨蒸气压缩式制冷复合循环空冷系统,前者还有望用于高温时段长的南方地区。

一种新型的电站间接空气冷却系统

在蒸汽动力循环耦合正、逆制冷循环的电站空冷系统(简称原系统)的基础上,首次将氨吸收制冷工艺应用到汽轮机排汽冷却,提出了一种基于氨吸收式制冷复合循环的间接空冷系统(简称新型系统)。通过改进,新型系统在环境高温时段,利用氨吸收制冷循环的设备代替了复合空冷系统的压缩机,降低了能耗;在环境低温时段,增设了氨气过热器及氨气轮机产能发电,充分利用了环境低温资源。介绍了新型系统的组成和工作原理,并与原系统进行了对比分析,指出了有待进一步深入研究的问题。

太阳能喷射式电冷联供系统的性能分析

提出了一种新型太阳能热有机物喷射式电冷联供系统,并建立了相应的热力学模型.在此基础上,选取R245fa作为工质,采用Matlab软件对系统进行了仿真计算,分析了发生温度、冷凝温度、蒸发温度、涡轮膨胀比及太阳辐照度对系统性能的影响.结果表明:在太阳辐照度为800W/m2的条件下,在57.3m2的集热面积上可以获得2.03kW的净发电功率和2.85kW的制冷功率,完全能满足普通家庭的日常用电和制冷;提高发生温度、提高蒸发温度、降低冷凝温度或增加太阳辐照度均有利于提高系统的工作性能;提高涡轮膨胀比可以提高系统的电冷比.

我国工业余热回收利用技术综述

节能减排主要依靠工业领域,工业余热利用是重要内容。本文从余热利用过程能量转换情况角度,概述了国内用于余热利用的热交换技术、热功转换余热发电技术及余热制冷制热技术及其设备的技术特点及应用概况,分析了工业余热利用中的存在的问题,认为需进一步推广余热锅炉及低温汽轮机余热发电技术,提高中高温余热的利用率,需要强化研究并掌握有机朗肯循环等300℃以下低温余热发电技术,积极向工程应用推广,提高低品位余热利用率。