Safe use of refrigerants for process applications

This paper examines safety issues, with emphasis on central refrigeration plant for process applications. Plantroom hazards including refrigerant leakage, excess pressure, fire and noise are covered. It is concluded that routine surveys which are being conducted in connection with the chlorofluorocarbon and hydrochlorofluorocarbon phase-outs present an opportunity for examining safety issues.     

Ignition hazard evaluation on A2L refrigerants in situations of service and maintenance

To restrict the progress of the global warming, A2L refrigerants such as 2,3,3,3-tetrafluoroprop-1-ene (R1234yf), (Z/E)-1,3,3,3-tetrafluoroprop-1-ene (R1234ze), and difluoromethane (R32) have been expected of alternatives to the standard refrigerants currently in use. The ignition hazard of A2L refrigerants under plausible accident situations in service and maintenance was examined experimentally for two cases: leakage of an A2L refrigerant from a pinhole in a pipe or hose (Scenario 1), and leakage of an A2L refrigerant into an item of equipment used for service and maintenance, such as a collection device (Scenario 2). In Scenario 1, the location of the flammable zone and the possibility of a jet flame being formed instantaneously on contact with an ignition source were examined. Even when R1234yf leaked from a 4 mmϕ pinhole (corresponding to breakage of a pipe), the flammable zone extended only about 10 cm from the pinhole in the downstream region. In an ignition test with a continuous spark as the ignition source, a pale emission appeared only near the spark, and the flame did not propagate to the rest of the refrigerant jet. In Scenario 2, the accumulation and ignition behaviors of A2L refrigerants in a model collection device were examined experimentally. Ignition and flame propagation occurred in a test on a model collection device lacking slits, whereas when slits wider than 20 mm were present, ignition and flame propagation did not occur. Even if R1234yf leaked into the model collection device, provided that slits of an effective width were present, the R1234yf could diffuse through slits and barely accumulated, and no ignition or flame propagation occurred.     

气相色谱-质谱法快速筛查气态制冷剂产品中的热点管控类卤代烃

建立了利用气相色谱-质谱法快速筛查气态制冷剂产品中的10种热点管控类卤代烃的分析方法。采用气密性微量注射器对气态制冷剂样品进行取样,刺透瓶盖隔垫加入到顶空瓶中,自动进样;以GS-GasPro(多孔层开管,60 m×0.32 mm)为色谱柱,采用电子轰击离子源,全扫描模式采集。测试结果显示:目标物的体积分数在0.50%~100.00%范围内,相对响应因子的相对标准偏差(RSD)均小于20%;线性相关系数r均在0.999以上;检出限(3.143倍标准偏差)为0.01%~0.05%。对实际样品进行加标回收,回收率为79.5%~102%,测定值RSD为0.5%~3.1%。该方法可为快速、准确、批量筛查气态制冷剂产品中的多种热点管控类卤代烃提供技术支撑。     

Turbulent deflagrations of mildly flammable refrigerant-air mixtures

With current concerns around global climate change, new hydrofluorocarbons with low Global Warming Potential (GWP) are being evaluated as alternative refrigerants. These alternative refrigerants, however, may be mildly flammable (as defined by the A2L safety group classification) and pose safety concerns for the heating, ventilation, air conditioning, and refrigeration (HVAC/R) industry. Consequently, careful assessments of different flammability characteristics and risks for these refrigerants are essential for their safe use in actual applications. In this study, deflagration propagation measurements for different mildly flammable refrigerants, including difluoromethane (R-32) and 2,3,3,3-tetrafluoropropene (R-1234yf), were undertaken in different geometries including a 9.1-m long conduit test rig and a closed cubical 12.5 m³ volume. Different tests were conducted for full volume deflagrations as well as with and without obstructions. Turbulent deflagration speeds for well-mixed, refrigerant-air mixtures have been shown to be orders of magnitude larger than their corresponding laminar flame speed values that are used in classifying flammable refrigerants in safety standards. Testing has also quantified the resulting severity as measured by the event overpressure which was shown to worsen with increased congestion or confinement as a consequence of increased induced turbulence. This work illustrates the importance for severity evaluations for actual large-scale or congested geometries of concern in practical applications. Even for mildly flammable refrigerants characterized by laminar flame speeds <2 cm/s, which is lower than the 10 cm/s limit for A2L refrigerants, relatively fast deflagrations can be generated for very congested geometries where downstream turbulence is generated as the flame front passes over obstacles in these situations.     

Comparative thermodynamic performance analysis of a cascade system for cooling and heating applications

In this study, a comparative thermodynamic performance analysis of cascade system (CCS) for cooling and heating applications is presented and compared for different refrigerant couples. The CCS consists of the low-temperature cycle (LTC) and high-temperature cycle (HTC). The CO₂ was used as working fluid in LTC, whereas the HFE 7000, R134a, R152a, R32, R1234yf, and R365mfc refrigerants were used in HTC. The heating and cooling coefficients of performance (COP_ht, COP_cl) and exergy efficiency of CCS are investigated parametrically according to various factors such as the evaporator, condenser, and reference temperatures. After thermodynamic analyses are completed, the COP_cl of CCS is obtained as 1.802, 1.806, 1.826, 1.769, 1.777, and 1.835 for CO₂-HFE7000, CO₂-R134a, CO₂-R152a, CO₂-R32, CO₂-R1234yf, and CO₂-365mfc refrigerant couples, respectively. Furthermore, the heat exchanger has the highest exergy destruction rate, whereas the expansion valves have the lowest of exergy destruction rate.     

Harmful and Needless Emission of Refrigerant and Countermeasures

Abstract

Refrigerants used in refrigerators are an important source of ozone depleting substances released into the atmosphere, and can have a significantly negative effect on the hole in the ozone layer. But most emission of refrigerants is man-made, unreasonable and needless. Since in most emission cases the refrigerants are contained in the refrigerators, we can retrieve them by some technique that changes the ‘manual emission’ into manual retrieving. To promote the retrieval action and diminish the pollution, society can use economic, administrative and technical countermeasures, which can create a ‘good-cycle’ both ‘harnessing pollution and earning income simultaneously’, reinforce the motive of retrieving, and retrieve most proportion of refrigerants used by all refrigerators. This ‘good-cycle’ method can be easily promoted, and also a valuable way to promote other forms of environmental protection. The three countermeasures have almost no social cost, even no cost at all.     

综合气候环境试验室载冷剂方案选择研究

目的为综合气候环境试验室集中冷源选择适用、合理的载冷剂方案。方法通过对试验室制冷需求进行分析,制定试验室制冷系统方案。对载冷剂运行原理进行分析,得到综合气候环境试验室载冷剂使用工况和需要考虑的因素。最后综合分析和对比常用载冷剂的物性参数,总结出适用于综合气候环境试验室集中冷源的载冷剂方案。结果中温机组的载冷剂选择Dynalene HC-50。结论选择的载冷剂适用于综合气候环境试验室集中冷源载冷剂系统的使用工况,方案合理。     

Harmful and Needless Emission of Refrigerant and Countermeasures

Refrigerants used in refrigerators are an important source of ozone depleting substances released into the atmosphere, and can have a significantly negative effect on the hole in the ozone layer. But most-emission of refrigerants is man-made, unreasonable and needless. Since in most emission cases the refrigerants are contained in the refrigerators, we can retrieve them by some technique that changes the ＇manual emission＇ into manual retrieving. To promote the retrieval action and diminish the pollution, society can use economic, administrative and technical countermeasures, which can create a ＇good-cycle＇ both ＇harnessing pollution and earning income simultaneously＇, reinforce the motive of retrieving, and retrieve most proportion of refrigerants used by＇all refrigerators. This ＇good-cycle＇ method can be easily promoted, and also a valuable way to promote other forms of environmental protection. The three countermeasures have almost no social cost, even no cost at all.     

大型气候环境实验室冷媒的分析选择

目的选择适用于大型气候环境实验室制冷系统的制冷剂和载冷系统的载冷剂。方法通过对气候环境实验室制冷系统和载冷系统的特性分析,提出制冷剂和载冷剂的选用原则。对常用制冷剂和载冷剂的物性分别进行对比分析,综合考虑环保性、制冷内循环特性、循环风系统和空气补偿系统对冷媒的要求等因素优选制冷剂和载冷剂。结果复叠制冷机组的高、低温段制冷剂分别选用R507和R23,中高温载冷剂选用AS-6,低温载冷剂选用AST-30。结论提出的冷媒介质选择方案适用于大型气候环境实验室。