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Refrigeration
Published in Irving Granet, Jorge Luis Alvarado, Maurice Bluestein, Thermodynamics and Heat Power, 2020
Irving Granet, Jorge Luis Alvarado, Maurice Bluestein
In September 1987, an international meeting was held in Montreal, Canada, to discuss the effects of chlorofluorocarbon (CFC) refrigerants on the atmosphere. In June 1990, representatives of 93 nations met in London and amended the 1987 Montreal Agreements. Basically, the London Amendments called for the complete phasing out of CFC refrigerants by the year 2000. Hydrochlorofluorocarbon (HCFC) refrigerants are to be phased out by the year 2020, with the absolute deadline being the year 2040. The refrigerant hydrofluorocarbon (HFC) contains no chlorine and poses no threat to the ozone layer. However, HFC-134a, a replacement for R-11 and R-12 refrigerants and used primarily in autos and refrigerators, has a global warming potential that is 420 times higher than that of carbon dioxide. Further study could lead to regulation on the use of HFC-134a as well as other HFCs. Household units have been using R-22, which is in the process of being replaced by a new refrigerant, R-410A.
Experimental Performance Measurements
Published in Reinhard Radermacher, Yunho Hwang, Vapor Compression Heat Pumps, 2005
Reinhard Radermacher, Yunho Hwang
The two binary refrigerants require careful design considerations, especially heat exchangers, pipes and compressors, due to the much higher operating pressures. Although these binary refrigerants need significant system modification, they have the benefit of higher steady state and seasonal performances. These benefits could be even greater if the system is designed specifically for these fluids. Overall, the binary fluids perform better than R22. R410A has a cooling seasonal performance that is 2.6% better than R22 and a heating seasonal performance that is essentially the same as R22. R410B has cooling and heating seasonal performances that are 1.7 and 1.8% better than R22, respectively.
Organic Air Pollutants
Published in Stanley Manahan, Environmental Chemistry, 2017
Structural formulas of several organohalides that are potentially important in the atmosphere are shown in Figure 11.4. Dichloromethane is a volatile liquid with excellent solvent properties and a number of industrial uses. It is commonly employed as an extracting solvent for organic-soluble substances determined in chemical analysis. Dichlorodifluoromethane is one of the chlorofluorocarbon (CFC) compounds once widely manufactured as a refrigerant and subsequently found to cause stratospheric ozone depletion. HCFC-124, 1-chloro-1,2,2,2-tetrafluoroethane, was developed as a substitute for CFC compounds in refrigerants and propellants. It has a C–H bond that is acted upon by hydroxyl radical and thus is largely eliminated in the troposphere, but still has some capacity to destroy stratospheric ozone. HFC-134a has also been developed as a CFC substitute. It is destroyed by reaction with hydroxyl radical in the troposphere and does not deplete stratospheric ozone, but is a powerful greenhouse gas. As of 2016, a very popular refrigerant for home air conditioning systems is R-410A, consisting of a mixture of difluoromethane (CH2F2) and pentafluoroethane (CHF2CF3), compounds that do not contain ozone depleting Cl and have H atoms susceptible to attack by HO• radicals leading to relatively rapid degradation. Vinyl chloride is the monomer used to manufacture huge quantities of polyvinylchloride plastics. Trichloroethylene is a widely used solvent employed in applications such as dry cleaning. The PCB compounds consist of a family of compounds containing two aromatic rings joined as shown in the example in Figure 11.4 and containing from 1 to 10 chlorine atoms. Some of the brominated alkanes, commonly called halons, effectively quench fires and have been the predominant materials used in aircraft fire extinguishers. The simplest chlorinated aromatic compound is chlorobenzene, which is used in chemical synthesis. Other common halogenated aromatics include a variety of derivatives of aromatic hydrocarbons with varying numbers of Cl and sometimes Br atoms attached to benzene and toluene hydrocarbon rings. PCBs are a group of many compounds formed by the chlorination of biphenyl that have extremely high physical and chemical stabilities and other qualities that led to their being used in many applications, including heat transfer fluids, hydraulic fluids, and dielectrics until their manufacture and use were banned in the 1970s because of their pollution potential, mostly in the hydrosphere, geosphere, and biosphere. Their air pollution potential is limited by their low volatilities.
Convective boiling of R-410A in 5.0 and 7.0 mm outer diameter microfin tubes
Published in Experimental Heat Transfer, 2020
Microfin tubes are widely used in residential air conditioners or heat pumps. Microfins are known to enhance the heat transfer with marginal pressure drop increase. For evaporation, the enhancement is induced by the increase of heat transfer area, the turbulence induced by fins and early transition from stratified flow to annular flow [1]. In Table 1, available studies on R-410A evaporation in microfin tubes, which is the subject of present investigation, are summarized. R-410A has been replacing R-22, which has long been a refrigerant of residential air conditioners or heat pumps. Bogart and Thors [2] tested 9.5 mm outer diameter (O.D.) microfin tube, and compared the results with those of R-22. R-410A yielded 50% higher heat transfer coefficient and a 40% lower pressure drop. Inoue et al. [3] tested 8.0 mm O.D. microfin tube, and obtained 1.2 and 1.5 times higher heat transfer coefficients for R-410A than for R-22. Kim et al. [4] tested two microfin tubes (9.5 mm O.D. and 7.0 mm O.D). The heat transfer enhancement factor ranged from 1.8 to 2.5 for the 9.5 mm O.D. microfin tube and from 1.1 to 1.6 for the 7.0 mm O.D. microfin tube. The pressure drop penalty factor ranged from 1.2 to 2.6.