离心式冷水机组制冷剂选择的探讨

阐述了离心式冷水机组的两种替代制冷剂HFC134a和HCFC123的性能,综合比较了这两种制冷剂的安全性、效率和其它一些因素。从安全性能来讲,HFC134a占有优势;在效率方面,HCFC123略高于HFC134a;由于HCFC123的ODP不为零,根据蒙特利尔议定书这一强制性条约,它将限制禁用;同时京都议定书也要求限制HFCs的排放量。最后文中结合了中国国情对HCFC123的使用进行了风险分析,认为就目前而言,HFC134a应当成为替代剂的主流。     

美国CFC_s替代物市场动态

进入九十年代美国CFC_s替代物市场的发展引人注目。Du Pont公司的SUVACold-MP制冷剂即HFC134a已开始投入大规模工业化生产,这种新型制冷剂主要用于取代目前广泛使用于冷水机组以及其他固定式中温制冷设备中的CFC12。对用于替代CFC11以SUVA Centri-MP命名的HCFC123制冷剂的初步研究表明,其毒性和安全性指标均允许该种制冷剂投入使用。多家制冷设备生产企业已按使用HCFC123的要求对原     

离心式冷水机组的制冷剂选择

描述冷水机组特别是大型机组最常用的替代制冷剂。总结了蒙特利尔议定书所制定的制冷剂淘汰时间表。对冷水机组(压缩式与吸收式)目前所使用的制冷剂进行探讨,包括大气寿命、ODP与GWP。概述了离心式冷水机组的最低能效标准。对主要的制冷剂进行科学评估。介绍了除R-123以外的其他替代制冷剂。研究表明,R-123作为目前离心式冷水机组应用最广泛的制冷剂,其ODP与GWP较低,且大气寿命短,放射率低,效率高。对中国而言R-123至少在未来的几十年内仍具有非常显著的环境和经济优势。     

美国环境保护署将出版CFC_s替代品安全性手册

美国环境保护署将出版部分CFC_s替代品安全性手册。该手册将收录已经获得批准可用于冷出机组、房间空调器等制冷设备的替代CFC_s制冷剂。这些替代制冷剂包括HFC—134a、HCFC—123、HCFC—141b、HCFC—124、HFC—125、HFC—32、HFC—152a等等。有关人士指出,由于HCFC—141b对臭氧层损害能     

基于HFO的混合制冷剂R514A在离心式冷水机组中直接替代R123制冷剂的试验研究

R514A是一种低GWP,不可燃、基于HFO-1336mzz(Z)的新一代制冷剂,其物性参数与R123接近。因此,本文选择R514A作为原R123离心式冷水机组的替代制冷剂开展试验研究。依据GB/T18430.1—2007规定的试验工况,针对直接充注R514A和原制冷剂R123的机组性能进行测试,对比研究R123和R514A在离心式冷水机组中的机组输入功率、制冷量、性能系数(COP)、压缩机吸/排气压力、压缩机排气温度,并计算综合部分负荷性能系数(IPLV)值。结果表明:在对原机组结构不做任何改动,仅更换机组润滑油的情况下,R514A机组与原R123机组相比压缩机吸/排气压力和排气温度较为接近,COP和IPLV性能略有提升。     

HFC134a在离心式冷水机组中的应用

在空调用离心式冷水机组中,制冷剂一般采用 R11和 R12为最多。这两种氟里昂对大气臭氧层的危害最大,是《蒙特利尔协议》限制和禁用的主要品种,该协议规定从2000年起全面禁止生产和使用。目前各国的有关专家都在致力于寻找其替代物,一些工业发达国家经过研究试验已经找到了两种在热力学指标方面较为理想的替代品,并已有少量产品供应,这两种制冷剂即 HFC134a 和 HCFC123。     

HCFC—123的毒性试验

HCFC—123(即CF_3CHCL_2)是替代CFC11作为制冷剂和发泡剂的最有希望的产品。在短期试验中,表明HCFC—123无重大毒性。最近杜邦和同盟—信号公司向美国环境保护局通报说,暴露于HCFC—123的雄鼠会在胰腺和睾丸发生良性肿瘤,暴露的剂量越大,则老鼠所得肿瘤数目越多。为此杜邦公司把操作人员的暴露限度每班(8h)从100ppm降低到     

基于双级离心式冷水机组的低GWP制冷剂制冷循环特性分析

对比多种低GWP制冷剂在双级压缩与单级压缩制冷循环中的性能差异,并分析各制冷剂用于双级离心式冷水机组时,机组性能系数COP对有效过热度、过冷度、吸排气压损和压缩比分配系数(中间压力)等主要参数变化的敏感度.研究结果表明,低压替代制冷剂的安全性更优,且理想制冷循环的COP更高,但是其在变过冷度和变吸排气压损特性方面逊于中...     

在未得到最终制冷剂前的替代工质

概述了制冷剂的排放或泄漏对大气的影响,评价了常用的两种过渡制冷剂HCFC123及HFC134a。     

美国如何从氯氟化物和氢氯氟碳化物向代用制冷剂过渡

美国是世界最大的空调和制冷设备市场之一。作为空调和制冷设备的主要消费市场,美国消耗了大部分氯氟碳化物(CFC)和氢氯氟碳化物(HCFC)产品。 美国是在蒙特利尔条约上签字的首批国家之一,并且承担起自已的责任,制定了一项全国法律,叫做1990年美国清洁空气法。美国已经开始逐步减少CFC的生产和使用,制造厂商也将遵循这项法律,达到或者超过蒙特利尔条约规定的要求。 HCFC-22是美国使用最广泛的制冷剂。这是因为家用和小型商用单元空调设备得到普及,而它们几乎全部依靠HCFC - 22。显然,逐步减少HCFC - 22的生产,将对美国产生重大影响。目前规定HCFC - 22的完全停产期限是2020年。美国空调与制冷协会(ARI)制定了HCFC - 22的代用制冷剂鉴定计划(AREP),帮助制造厂商获得多种HCFC - 22和R502的代用制冷剂性能数据。有些代用制冷剂具有同基本制冷剂几乎相同的效果,有时甚至还超过基本制冷剂的性能。目前,尚未发现一种代用制冷剂可以作为通用制冷剂,在所有制冷应用场合使用。     

Nucleate boiling heat transfer coefficients of pure halogenated refrigerants

Nuclate pool boiling heat transfer coefficients (HTCs) of HCFC123, CFC11, HCFC142b, HFC134a, CFC12, HCFC22, HFC125 and HFC32 on a horizontal smooth tube of 19.0 mm outside diameter have been measured. The experimental apparatus was specially designed to accomodate high vapor pressure refrigerants such as HFC32 and HFC125 with a sight glass. A cartridge heater was used to generate uniform heat flux on the tube. Data were taken in the order of decreasing heat flux from 80 to 10 kW m⁻² with an interval of 10 kW m⁻² in the pool of 7 °C. Test results showed that HTCs of HFC125 and HFC32 were 50–70% higher than those of HCFC22 while HTCs of HCFC123 and HFC134a were similar to those of CFC11 and CFC12 respectively. It was also found that nucleate boiling heat transfer correlations available in the literature were not good for certain alternative refrigerants such as HFC32 and HCFC142b. Hence, a new correlation was developed by a regression analysis taking into account the variation of the exponent to the heat flux term as a function of reduced pressure and some other properties. The new correlation showed a good agreement with all measured data including those of new refrigerants of significantly varying vapor pressures with a mean deviation of less than 7%.     

Performance evaluation of environmentally benign refrigerants in heat pumps 1: A simulation study

An overview of the performance characteristics of possible working fluids in vapour-compression industrial heat-pump systems for medium to high temperature applications is presented. The refrigerants studied include HFC12, HCFC22 HFC134a, HCFC142b, HFC152a, a tenary blend of HCFC22 (40%), HCFC124 (43%) and HFC152a (17%), and NH₃. The calculations are made for all the refrigerants for the same operating conditions and are compared with each other. For high-temperature applications, a compression- absorption heat-pump cycle (with NH₃-H₂O as the working fluid) is described. Its performance characteristics are discussed and compared with vapour-compression cycles with HCFC142b as the working fluid by using the concept of ‘thermodynamic temperature’.     

Condensation heat transfer coefficients of binary HFC mixtures on low fin and Turbo-C tubes

In this study, external condensation heat transfer coefficients (HTCs) are measured for nonazeotropic refrigerant mixtures (NARMs) of HFC32/HFC134a and HFC134a/HCFC123 on a low fin and Turbo-C tubes. All measurements are taken at the vapor temperature of 39 °C with the wall subcooling of 3–8 °C. Test results showed that condensation HTCs of NARMs on enhanced tubes were severely degraded from the ideal values showing up to 96% decrease. HTCs of the mixtures on Turbo-C tube were degraded more than those on low fin tube such that HTCs of the mixtures at the same composition were similar regardless of the tube. The mixture with larger gliding temperature differences (GTDs), HFC134a/HCFC123, showed a larger heat transfer reduction from the ideal values than the mixture with smaller GTDs, HFC32/HFC134a. Heat transfer enhancement ratios of the enhanced tubes with NARMs were almost 2 times lower than those with pure refrigerants and they decreased more as the GTDs of the mixtures increased.     

冰淇淋机制冷系统性能及新型环保制冷剂热力学分析

针对软冰淇淋机首先确定了其计算工况，在分析冰淇淋机制冷循环的基础上，应用NIST的REFPROPV6.0软件编写了通用的计算程序，对不同工质的冰淇淋机循环过程进行了计算。经过计算可以发现，纯质HFC134a,HFC125,HFC143a,HFC32和HFC152a等中没有一种工质的热工性能，安全性能和环境性能可以完全满足替代要求，根据蒸气压相似原则，考虑各纯质的优缺点及混合制冷剂配对原则，确定了混合工质HFC134a/HFC32(70/30mass%)作为冰淇淋机的替代制冷剂。     

Condensation heat transfer coefficients of enhanced tubes with alternative refrigerants for CFC11 and CFC12Coefficients de transfert de chaleur de condensation de tubes à surface augmentée fonctionnant avec des frigorigènes de remplacement de CFC11 et de CFC12

In this study, condensation heat transfer coefficients (HTCs) of a plain tube, low fin tube, and Turbo-C tube were measured for the low pressure refrigerants CFC11 and HCFC123 and for the medium pressure refrigerants CFC12 and HFC134a. All data were taken at the vapor temperature of 39°C with a wall subcooling of 3–8°C. Test results showed that the HTCs of HFC123, an alternative for CFC11, were 8.2–19.2% lower than those of CFC11 for all the tubes tested. On the other hand, the HTCs of HFC134a, an alternative for CFC12, were 0.0–31.8% higher than those of CFC12 for all the tubes tested. For all refrigerants tested, the Turbo-C tube showed the highest HTCs among the tubes tested showing almost an 8 times increase in HTCs as compared to the plain tube. Nusselt's prediction equation yielded a 12% deviation for the plain tube data while Beatty and Katz's prediction equation yielded a 20.0% deviation for the low fin tube data.     

A study on the performance of multi-stage heat pumps using mixturesEtude sur la performance de pompes à chaleur multi-étagées utilisant des mélanges

Multi-stage heat pumps composed of a condenser, evaporator, compressor, suction line heat exchanger, and low and/or high stage economizers are studied by computer simulation. Their thermodynamic performance and design options are examined for various working fluids. In the simulation, HCFC22/HCFC142b and HFC134a are studied as an interim and long term alternatives for CFC12 while HFC32/HFC134a and HFC125/HFC134a are studied as long term alternatives for HCFC22. The results indicate that the three-stage super heat pump with appropriate mixtures is up to 27.3% more energy efficient than the conventional single-stage system with pure fluids. While many factors contribute to the performance increase of a super heat pump, the most important factor is found to be the temperature matching between the secondary heat transfer fluid and refrigerant mixture, which is followed by the use of a low stage economizer and suction line heat exchanger. The contribution resulting from the use of a high stage economizer, however, is not significant. With the suction line heat exchanger, the system efficiency increases more with the fluids of larger molar liquid specific heats. From the view point of volumetric capacity and energy efficiency, a 40%HCFC22/60%HCFC142b mixture is proposed as an interim alternative for CFC12 while a 25%HFC32/75%HFC134a mixture is proposed as a long term alternative for HCFC22.     

Comparative efficiencies and implications for greenhouse gas emissions of chiller refrigerants

This paper summarizes analyses of refrigerant options for chillers. It presents tabulated global warming potentials and other environmental data for candidate refrigerants. The paper discusses briefly the historic progression in refrigerant release reductions and presents analyses to compare the efficiencies of historic and current refrigerant options. The 28 refrigerants addressed include chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), hydrofluorocarbon (HFC), hydrocarbon (HC), and inorganic (such as ammonia) fluids. The paper discusses the relative importance of the refrigerant-related and energy-related components of chiller emissions.     

Molecular properties of alternative refrigerants derived from dielectric-constant measurements

A review of the current work in Lisbon on the measurement of the dielectric constant of the liquid phase of some environmentally acceptable refrigerants proposed as alternative replacements of the chlorofluorocarbons (CFCs), responsible for the destruction of the ozone layer, is presented. Measurements on HCFC 141b, HCFC 142b, HCFC 123, HFC 134a, HFC 152a, and HFC 32 samples of stated purities of 99.8 mass% or better were performed as a function of pressure and temperature, in the temperature range from 200 to 300 K and at pressures up to 20 MPa. The ratio of the capacitances of a cell filled with the sample and under vacuum was measured with a direct capacitance method. The dielectric-constant measurements have a repeatability of 0.003% and an accuracy of 0.1%. The theory developed by Vedam et al. based on the Eulerian Strain and the Kirkwood equation for the variation of the modified molar polarization with temperature and density were applied to obtain the dipole moments of the refrigegrants in the liquid state, to obtain a physical insight of the molecular behavior, and to understand the equilibrium configuration of these liquids. Invited paper presented at the Fourth Asian Thermophysical Properties Conference. September 5–8, 1995, Tokyo, Japan.     

Transferts de chaleur lors de la condensation du mélange HFC23/HFC134a à l'intérieur d'un tube lisse horizontal

The environmental effects of the depletion of stratospheric ozone due to refrigerants containing chlorine, have resulted in international treaties, laws and amendments (Copenhagen, 1992, to the Montreal protocol, 1987) to phase out and eliminate many common refrigerants. HCFC22 is one of these refrigerants and no such single component alternative has been discovered for this fluid. Zeotropic refrigerant mixtures (binary or ternary) are being considered as potential replacements for HCFC22. Evaporation and condensation heat-transfer characteristics, and inside tubes of heat exchangers, due to the use of zeotropic refrigerant mixtures, have been a subject of fundamental importance in evaluating the heat exchanger performances in the refrigeration and air-conditioning industry.In this study, it is proposed to determine the heat transfer and pressure drop coefficients during in-tube condensation of zeotropic mixture HFC23/HFC134a in a smooth copper tube with an inside diameter of 8.92 mm. The test section of three passes of 2 m each; it is a counter flow double-pipe heat exchanger with water flowing in the annulus and refrigerant in the inner tube. This test section is instrumented with temperature and pressure sensors. We have tested HCFC22, HFC134a, and three refrigerant mixtures of HFC23/HFC134a at different compositions to appreciate the effect of glide on heat transfer. The quality was from 1 to 80%, the heat flux ranged from 2 to 50 kW m⁻² and mass flux varied from 80 to 480 kg m⁻²s⁻¹. In these conditions, no effect of a glide on the heat-transfer coefficient was observed; this result was confirmed by using an equilibrium condensation curve analysis. The pressure drop can be calculated with classical correlations but with physical properties of the mixture.