Alternative Refrigerants And Cycles For Compression .
14Alternatives in Refrigeration and Air ConditioningCHAPTER 2Alternative Refrigerants and Cycles forCompression Refrigeration Systems2.1INTRODUCTIONRefrigerant is the substance which is used as working fluid in a thermodynamic cycle, undergoes aphase change from liquid to vapour and produces cooling. These are used in refrigeration, airconditioning, and heat pumping systems. They absorb heat from one area, such as an air conditionedspace, and reject it into another, such as outdoors, usually through evaporation and condensation,respectively. These phase changes occur both in absorption and mechanical vapour compressionrefrigeration systems, but they do not occur in systems operating on a gas cycle using a fluid suchas air (ASHRAE Handbook, 1997, Fundamentals, Chapter 18).The chronological evolution of refrigerants has been shown in Table 2.1 (Radermacher andHwang, 2005). The first refrigerant used in a continuous refrigeration system by William Cullen in1755 was water. But the credit for building the first vapour compression refrigeration system goesto Jakob Perkins who used sulphuric (ethyl) ether obtained from India rubber as refrigerant. In thebeginning, the goal was to produce refrigeration only; whatever substance gave the desired resultswas used as refrigerant. All refrigerants were either flammable or toxic at that point in time. In1930’s, Thomas Midgley introduced R-12 (CF2Cl2, i.e., Dichlorodifluoromethane) and R-11 (CFCl3,i.e., Trichloromonofluoromethane) as nontoxic and nonflammable refrigerants. This led todevelopments of a series of CFCs and HCFCs which deemed to be stable, nontoxic, nonflammable,and having a desired boiling point substances. During that period the main objective was safety anddurability. The CFCs were not only being used as refrigerant but also as solvent, foam blowingagent, aerosol and in fire extinguishers. Later in 1980s, it was discovered that halogens and CFCsand other related substances react with ozone layer in atmosphere and thin down the ozone layerbecause of their higher atmospheric lifetime. Halogen, which results from the breakdown of CFCsin atmosphere combines with greenhouse gases and enhances the global warming threat. Internationalconsensus was made to stop production and use of halogenated refrigerants for which MontrealProtocol came into existence in 1987. In 1997, Kyoto Protocol was ratified to limit the green housegases causing global warming. Recent attention towards depletion of stratospheric ozone layer andglobal warming put a question mark to the present use of refrigerant in refrigeration and air conditioning(RAC) industry.
16Alternatives in Refrigeration and Air ConditioningYearRefrigerantChemical Makeup, 3/25/52 wt%)1990sR410AR32/R125(50/50 wt%)1990sR404AR125/R143a/R134a(44/52/4 wt%)2000sR417AR134a/R125/R600(50/46.6/3.4 wt%)R422AR134a/R125/R600a(11.5/85.8/3.4 wt%)R423AR134a/R27ea(52.5/47.5 wt.%)R432AR1270/ RE170(80/ 20 wt%)R433AR1270/R290(30/70 wt%)First Developer/UserThese protocols initiated the search of alternative refrigerants and cycles, which are not onlyenvironment-friendly but also, consist of all desired properties of an ideal refrigerant and cycle. TheHCFCs can be utilized as interim solution because of its low Ozone Depletion Potential (ODP) andGlobal Warming Potential (GWP) compared to CFCs. HCFC-123, HFC-134a can be used in lowpressure and medium pressure systems. As no single substance can pass under ODP, GWP, toxicity,flammability, cost and efficiency criteria simultaneously, the search has already been started to findsuitable azeotropic and zeotropic blends. These synthesized substances are expected as potentialrefrigerants in future which can fulfil desired requirements.2.2 ALTERNATIVE REFRIGERANTSBefore the discovery of ozone hole in early 1970s, the refrigeration and air-conditioning industrywas relying heavily on CFCs, HCFCs, Halons (BFCs) and their azeotropics. CFCs contain onlychlorine, fluorine and carbon atoms but they cause ozone depletion (ODP of CFCs varies between0.3 and 1) and have very long atmospheric life time (a few centuries). CFCs which have been inextensive use are R-11, R-12, R113, R114, R115, etc. Halons or BFCs contain bromine, fluorine andcarbon atoms. For example, R-13B1 and R12B1 are BFCs. Their ozone depletion potential is veryhigh, for example, ODP of R-13B1 is 10 and it was in use since 1995 for very low temperaturevapour compression refrigeration systems. However, after the discovery of ozone hole the era foralternative refrigerants has started.
18Alternatives in Refrigeration and Air ConditioningFurther, the alternative refrigerants are classified as:1. Pure refrigerants (i.e., single component refrigerants)(a) Natural refrigerants, i.e., inorganic and organic compounds(b) Hydrofluorocarbons (HFCs)2. Refrigerant mixtures/blends(a) Based on the number of pure components, i.e., binary / ternary /quaternary(b) Azeotropic /near azeotropic / zeotropic (non-azeotropic)2.2.1 Pure Refrigerants (Single Component Refrigerants)Natural refrigerants are those substances which exist in our biosphere, for example, air, water,ammonia (which are inorganic compounds) and hydrocarbons. Natural refrigerants are non-ozonedepleting and also have negligible global warming potential. On the other hand, HFCs contain onlyhydrogen, fluorine, and carbon atoms and cause no ozone depletion but have high global warmingpotential. HFCs group include R-134a, R-32, R-125, and R-245ca.2.2.2 Refrigerant Mixtures/Blends (Multi-Component Refrigerants)(a) Binary/Ternary/Quaternary Refrigerant Mixtures/BlendsBinary mixtures, as the name suggests, consist of two pure refrigerant components mixed in requiredproportions. For example, R-410A is a binary mixture of R125 and R32 in equal proportions byweight. Similarly, ternary and quaternary mixtures contain three and four pure refrigerants respectively.R-407C is a ternary mixture comprising R-32/ R-134a/ R-125 (23%/52%/25% by weight).(b) Azeotropic Mixtures/BlendsAn azeotropic is a mixture of multiple components (refrigerants) of volatilities that evaporate andcondense as a single substance and do not change in volumetric composition or saturation temperaturewhen they evaporate or condense at constant pressure. HFCs azeotropics are blends of refrigerantwith HFCs. ASHRAE assigned numbers between 500 and 599 for azeotropes. HFCs azeotropeR-507, a blend of R-125/R-143, is a commonly used refrigerant for low-temperature vapourcompression refrigeration systems.An azeotropic mixture has a temperature-pressure-concentration diagram where the saturatedvapour and saturated liquid lines coincide at a range of concentrations, as shown in Fig. 2.2. At thepoint or region where the saturated vapour and liquid lines merge, the mixture of the two substancesbehaves with the properties of a single substance, having properties different from either of itsconstituents.Even combinations that are azeotropic at certain concentrations at one pressure may not beperfectly azeotropic at another pressure, as shown in Fig. 2.3.The azeotropic concentration changes as the pressure increases. Usually, the azeotropic regionshifts toward the high concentration of the low- temperature boiling refrigerant (material A in thiscase). Even the azeotrope R-502, which has been used successfully for many years, was subject tofractional distillation at certain operating pressures.(c) Near Azeotropic and Zeotropic (Non-Azeotropic) Refrigerant Mixture/BlendsA near azeotropic is a mixture of refrigerants whose characteristics are near those of an azeotropic.It is thus named near azeotropic because the change in volumetric composition or saturation
Alternative Refrigerants and Cycles for Compression Refrigeration Systems 19TemperatureDew-point lineBubblepoint line0Fig. 2.2AzeotropiczoneFraction of material A1.0An Azeotropic Mixture of Materials A and B in the Range of 50-to-60% of re0Fraction of material A1.0Fig. 2.3 A Shift in the Azeotropic Region as the Pressure Changestemperature is rather small, such as, 0.5 C to 1.1 C. ASHRAE assigned numbers between 400 and499 for near azeotropic/zeotropic refrigerant mixtures. R-404A (R-125/R-134a/R-143a) andR-407B (R-32/R-125/R 134a) are HFCs near azeotropic refrigerant mixture (NARM). R-32 isflammable; therefore, its composition is usually less than 30% in the mixture. HFCs near azeotropicrefrigerant blends are widely used for vapour compression refrigeration systems.The diagram of the temperature-pressure-concentration relationship of an ideal zeotropic mixturemight appear as shown in Fig. 2.4. In a zeotropic mixture, the concentration of the two substancesin the vapour is different from that in the liquid at a given pressure and temperature. There arecertain applications where the properties of a zeotrope are advantageous, such as in the autocascadesystem for ultra low temperatures. For conventional industrial refrigeration systems, however, the
Alternative Refrigerants and Cycles for Compression Refrigeration Systems 21time dependency spreads from 20 to 100 years and written as GWP20 (for 20 years), GWP100 (100years lifetime), etc. Emission of one kg of R-134a is roughly equivalent to emission of 1300 kg ofCO2 in 100 years, so GWP100 of R-134a is 1300. Thus, the GWP of a greenhouse gas is an indexrelative to that of CO2 to trap heat radiated from earth to space.(c) Total Equivalent Warming Impact (TEWI): It is the factor to evaluate the environmentaleffect of GHGs in an appliance. TEWI provides the measure of the environmental impact of GHGsfrom manufacture, operation, service and end of life disposal of the equipment. It takes account ofboth the emissions of refrigerants and indirect emissions due to energy consumption and fossilfuels used. TEWI combines the effects of direct emissions of refrigerants (and also the foaminsulation blowing agents) from appliance during its lifetime with the indirect emission of CO2 fromthe combustion of fossil fuels and generation of electricity use by the appliance or the system.TEWI is defined by the following equation:TEWI mref . GWPref . Z mba . GWPba t.E.fwhereTEWI : Total Equivalent Warming Impact in kg CO2mref Mass of refrigerant in kgGWPref Global Warming Potential of refrigerant in kg CO2Z Number of charges of refrigerant during service lifemba Mass of blowing agent in kgGWPba Global Warming Potential of blowing agent in kg CO2t Service life of appliance in yearE Annual energy consumption of appliance in kWh/yrf CO2 factor of energy conversion in kg CO2/kWhelThe first two terms on the right hand side of the TEWI equation are for direct contribution ofrefrigerants during servicing and blowing agents to global warming and the last term is for thecontribution to global warming due to the energy consumed during the lifetime of the appliance.There can be many additional factors to consider, for example, emission during the initial chargeand recovery of refrigerants at the end of life of the appliance.The TEWI can also be expressed as follows (Bitzer Refrigerant Report 16):TEWI (GWP L n) (GWP m [1 – α recovery ]) (n Eannual β)TEWILeakageRecovery lossesDirect GWPGWPLnm Global warming potential Leakage rate per year System operating time Refrigerant chargeαrecovery Recycling factorEannual Energy consumption per yearβ CO2-Emission per kWhEnergyconsumptionIndirect GWP[CO2-related][kg][Years][kg][kWh][Energy Mix]
HFCR125/290/22(38.0/2.0/60.0)0.033, 2310Ice machinesR403BR-290/22/218(5.0/56.0/39.0)0.031, 4310Very low temperature singlestage refrigeration, it is also areplacement for R13B1R408AR-125/143a/22(7.0/46.0/47.0)0.026, 3020R134aPure0, 1300R152aPure0, 120R125Pure0, 3400R143aPure0, 4300R32Pure0, 550R227ea(CF3CHF-CF3)Pure0, 3500Compatible withmineral oil,Alkylbenzeneand polyolesterlubricantMedium* and low**temperature commercial andindustrial direct expansionrefrigeration systemsR12, R22ΘCompatible withpolyolesterlubricant forstationaryequipment andpolyalkalineglycol forautomotive airconditioningsystemsHousehold appliances,refrigeration (commercialand self-contained equipment),centrifugal chillers andautomotive air conditioningUsed as partcomponentsof blendsN.A.N.A.R12B1,R114 ΘPolyolester oilSuitable for air conditioningdevices functioning in hightemperature environments, hightemperature heat pumps, andthermal collectors.Contd.Alternative Refrigerants and Cycles for Compression Refrigeration Systems 25Substitutes(Long-termAlternatives)R402B
R143a/125/134a0,1680R12, R500Compatiblewith traditionaland newlubricants; inmost cases nochange oflubricant typeduring retrofitis required.Automotive air conditioningsystems designed for R12stationary air conditioningsystems. Medium temperaturestationary refrigeration systemsdesigned for R12, such assupermarket display cases, foodstorage/processing. It is a servicerefrigerant and replacement forHCFC blends such as, R401A andR409A.R407CR134a/125/32(52/25/23)0, 1650R22Polyolester oilMedium temperature commercialand industrial direct expansionrefrigeration and A/CR417AR600/134a/125(3.4/50.0/46.6)0, 2240Mineral, alkylbenzene or fullysyntheticlubricantsCommercial refrigeration displaycabinetsR417BR600/134a/125(2.75 /18.25/79)0, 2920Mineral oilR422DR125/134a/600a(65.1/13.5/3.4)0, 2620Compatible with Medium and low temperaturemineral and alkyl- commercial and industrial directbenzene Oilexpansion refrigerationR427AR32/125/143a/134a 0, 2010(15/25/10/50)Polyolester oilTo replace R-22 in existingequipment for a wide range oftemperatures. To retrofit lowtemperature refrigeration units aswell as air conditioninginstallations. Many industrialinstallations in commercialrefrigeration (supermarkets,etc.,in industrial refrigerationContd.Alternative Refrigerants and Cycles for Compression Refrigeration Systems 27R437A
30Alternatives in Refrigeration and Air Conditioning2.3.1 Lorenz CycleThe main assumption of Carnot cycle (single, two or mixed phase) is that the cycle accepts andrejects heat at a constant temperature level throughout the heat absorption and heat rejection process.However, in most applications, heat is supplied by or rejected to a fluid (air, water, brine etc.) whosetemperature changes during the heat exchange processes (Fig. 2.5). This leads to the presence ofso called pinch point, and thus, at points 1 and 4 and at points 6 and 8 the temperature differencesbetween both fluid streams become very small, consequently, the heat transfer rate becomes less.The entropy generation or exergy destruction is also small due to the fact that heat is transferredover a small temperature difference. In contrast, at points 2 and 3 and also for points 5 and 7, thetemperature differences are large, the heat transfer rate is more as well and so is the entropyproduction or exergy destruction.TCondensing refrigerant8Temperature57Cooling water341Chilled water2Evaporating refrigerantEntropyFig. 2.56sHeat Exchange in Refrigerant Mixture/ Blend and Heat Absorbing and Rejecting MediumThe Lorenz Cycle (Radermacher and Hwang, 2005) addresses this issue. This cycle is for aworking fluid that changes its temperature (i.e., it has a temperature glide) during the course of itsphase change (evaporation and condensing) (Fig. 2.5). In the ideal case, the change in temperaturethroughout during both phase change processes matches that of the fluid (heat absorbing or rejectingmedium), thus the overall entropy production or exergy destruction reduces significantly and theexergetic efficiency of the cycle improves to the largest possible extent, too. The refrigerant mixtures/blends have the potential to approach the requirements of the Lorenz cycle depending on the degreeto which they match the application glide in both the evaporator and the condenser. It should benoted that even for the same heat exchange area, a Lorenz cycle for the blends that better matchesthe source and sink glides gives higher cycle efficiency because it operates at an improved meantemperature than the corresponding pure refrigerant.2.3.2Transcritical Carbon Dioxide Compression Refrigeration Cycle(Singh, 2009)In a transcritical carbon dioxide compression refrigeration cycle, the supercritical CO2 is expandedto a subcritical state. The throttling loss is very large as compared to conventional refrigeration
Alternative Refrigerants and Cycles for Compression Refrigeration Systems 31systems due to the higher pressure change during the expansion. Thus, basic transcritical carbondioxide refrigeration cycle offers lower efficiencies when compared to HCFCs and HFCs.In the basic transcritical CO2 compression refrigeration cycle (Fig. 2.6), the refrigerant vapourscoming out of the evaporator (EVA) is compressed using compressor (COM) above the criticalconditions (Pcr 73.77 bar and Tcr 31.10oC) and then cooled in a gas cooler (GCO). Then, thiscooled gas is throttled in an expansion valve (EXP) and low temperature and low pressure liquidCO2 enters the evaporator.T Constt.GCO3P2EXP4COMEVA1hFig. 2.6 Transcritical Carbon Dioxide Refrigeration Cycle2.42.4.1THERMODYNAMIC ANALYSIS OF VAPOUR COMPRESSION REFRIGERATIONCYCLE WITH ALTERNATIVE REFRIGERANTSVapour Compression Refrigeration (VCR) SystemAprea et al. (1996) reported that VCR systems are normally used for cold storage and supermarketrefrigeration. These systems operate between condensing temperature of 35 C and evaporatingones in the range of (–)40 C to 0 C. The suitable working fluid for these applications is the refrigerantR502 which is an azeotropic mixture of refrigerants HCFC22 and R115. Both of these refrigerantsare harmful to ozone layer. The ozone depletion potential for HCFC22 and R115 is 0.055 and 0.4respectively (Calm and Hourahan, 2001). Aprea et al. (1996) experimentally evaluated generalcharacteristics and system performances of substitutes for R502 in a refrigeration plant. Theyexamined R402A, R402B, R403B, R408A, R404A, R407A and FX40. All substitutes showedperformances very close to those of R502 except R403B whose COP was found to be about 8%lower than that of R502.
34Alternatives in Refrigeration and Air ConditioningPark et al. (2008a, b) experimentally tested the thermodynamic performance of R433A, R432Aand HCFC22 in a heat pump bench tester under air conditioning and heat pumping conditions. BothR432A and R433A offer similar vapour pressure to HCFC22 for possible ‘drop-in’ replacement.The test results showed that the COP of R433A was 4.9-7.6% higher than that of HCFC22 whilethe capacity of R433A was found to be 1.0-5.5% lower than that of HCFC22 under both testconditions. The COP of R432A was found to be 8.5-8.7% higher than HCFC22 and its refrigeratingcapacity was 1.9-6.4% higher than that of HCFC22 under both test conditions. The compressordischarge temperatures of R432A and R433A were lower than that of HCFC22. The amount ofcharge required for both these refrigerants was 50-57% lower than that of HCFC22 due to their lowdensity. Overall, both these refrigerants are good long-term environment-friendly alternatives toreplace HCFC22 in residential air conditioners and heat pumps due to their excellent thermodynamicand environmental properties with minor adjustments.Chen (2008) carried out the performance analysis, using simulation software, of R410A as along-term alternative refrigerant with zero ODP (ozone-depleting-potential) for replacing HCFC22in a split-type residential air conditioner. It was deduced that the adoption of R410A could be helpfulfor air conditioners to decrease their heat exchanger size or improve their operation efficiency forpower saving. Moreover, compared to HCFC22, R410A could, in fact, help alleviate its overallimpact on global warming through significantly reducing the indirect global warming impact.Arora et al. (2007) carried out the exergy analysis of a vapour compression refrigeration systemwith HCFC22, R407C and R410A.The results were computed for actual vapour compression cyclewithout liquid vapour solution heat exchanger. It was concluded that R410A is a better alternative ascompared to R407C, with high coefficient of performance and low exergy destruction ratio whenconsidering for refrigeration applications. For air-conditioning applications, R407C is a betteralternative than R410A.Lorentzen (1995), Calm (2008), Wang and Li (2007) and Riffat et al. (1997) had advocated theuse of natural refrigerants such as ammonia, propane, CO2, water and air. The fourteenth refrigerantreport released by Bitzer International specifies R717 (ammonia), R723 (60% ammonia 40%dimethyl ether), HC290 (propane) and HC1270 (propylene) as long-term halogen free alternativerefrigerants to HCFC22 and R502 (Bitzer International: Refrigerant Report no. 14-Edition A-50114, 2007). Palm (2008) reported that vapour pressure curves of the propane and propene are quitesimilar to those of HCFC22 and ammonia, indicating that the application areas would be same.Recently, air conditioning provided by ammonia refrigeration systems has found applications oncollege campuses and office parks, small-scale buildings such as convenience stores, and largeroffice buildings. These applications have been achieved by using water chillers, ice thermal storageunits, and district cooling systems (http://www.iiar.org//aaranswers history.cfm?). Pearson (2008)reported that the benefits of using ammonia for water chilling applications have been reported bymany authors. Moreover, ammonia is widely used in industrial systems for food refrigeration, coldstorage, distribution warehousing and process cooling. It has more recently been proposed for usein applications such as water chilling for air conditioning systems.Siller et al. (2006) have reported that ammonia is not a contributor to ozone depletion, greenhouseeffect or global warming. Thus, it is an “environment-friendly” refrigerant. Ammonia has no
36Alternatives in Refrigeration and Air poratorExpansionvalveFig. 2.7QeSchematic Diagram of a Vapour Compression Refrigeration System with Liquid Vapour Heat Exchanger(lvhe) (Dincer, 2003)DTsb, lvhe2s2Pc333p4111PeDTsh, lvhehFig. 2.8 P-h Diagram of VCR System Shown in 2.8(a)pressure losses in evaporator and condenser. The main components of a vapour compressionrefrigeration (VCR) system are evaporator, compressor, condenser and a throttling device (expansionvalve). A liquid vapour heat exchanger may be incorporated between the liquid line and suction lineto transfer the heat from hot liquid refrigerant leaving the condenser to the cold suction vapourentering the compressor. It improves the overall system performance in some cases.
Alternative Refrigerants and Cycles for Compression Refrigeration Systems 417. The effects of sub-cooling in condenser and superheating in evaporator are neglected.8. Difference between evaporator and cold room temperature, (Tr – Te ) is taken as 2 C.Two groups of variations in COP, EDR and exergetic efficiency are plotted. In the first groupcondensing temperature is varied between 30 and 60 C for a constant evaporating temperatureequal to – 40 C. In the second case condenser temperature is taken as –55 C whereas evaporatortemperature is varied. The data assumed for plotting Figs. 3.5 to 3.10 is identical as mentionedabove except the evaporator and condenser temperatures are (–) 25 C and 55 C respectively.2.4.1.3 Results and DiscussionEffect of Condenser TemperatureIt is observed from Fig. 2.9 (a) and (b) that with increase in condenser temperature, COP of theVCR system reduces. This happens because with the increase in condenser temperature, the drynessfraction of the liquid refrigerant at the exit from expansion device increases and consequently thecooling capacity goes down. Simultaneously, the power consumed by the compressor also increasesbecause of increase in pressure ratio across the compressor and both these factors cause COP toreduce. The COP of R507A is slightly better than R404A. R502 exhibits better COP than bothR507A and R404A. The COP for R502 is 3.7% to 25% and 5.7% to 23 % higher in comparison toR507A and R404A respectively. Ammonia and HCFC22 outperform the other three refrigerants.The HCFC22 performs better in comparison to ammonia up to 40 C condensation temperaturewhereas above 40 C, ammonia gives better COP.The exergetic efficiency is expressed using equation (2.14). For constant evaporation temperature,only numerator (i.e., COPvcr ) changes and denominator (COPrr ) remains constant therefore exergeticefficiency is directly proportional to COP of the VCR cycle. Thus, it also reduces, likewise COP,with increase in condenser temperature. The trends of variation in exergetic efficiency are similar totrends of COP curve for these refrigerants. Even the percentage difference in exergetic efficiencyof R502 and R507A and R404A are also analogous. Exergy destruction ratio is inversely proportionalto exergetic efficiency as expressed in equation (2.19) and hence EDR curves are approximatemirror images of exergetic efficiency curves as depicted in Fig. 2.9 (b).Effect of Variation in Evaporation TemperatureIn the second group (Refer Fig. 2.10 (a), (b) and (c)), the variation of COP, EDR and exergeticefficiency, with evaporating temperature (– 40 C to 0 C) for a constant condensing temperatureequal to 55 C, have been plotted. The COP increases with increase in evaporator temperaturebecause of reduction in compressor work and increase in cooling capacity. The COPs of R507Aand R404A are lowest among the refrigerants considered. In the ascending order of COPs, thesequence of refrigerants is R404A followed by R507A, R502, R22 and R717. The COP curves ofR507A and R404A overlap each other at 55 C condenser temperature. This overlapping of COPcurves may not exist at condenser temperatures above or below 55 C because the values of COPobtained at 55 C were identical for – 40 C evaporation temperature also (refer Fig 2.8 (a)). TheCOP of R502 is approximately 17% higher at –40 C and 10% higher at 0 C in comparison toR507A and R404A.
42Alternatives in Refrigeration and Air .80.60.4253035404550556065Condenser temperature ( C)Variation of COP versus Condenser TemperatureR502 (EDR)R404A (EDR)R22 (EDR)R507A (hex)R717 (hex)7650.6R507A (EDR)R717 (EDR)R502 (hex )R404A (hex )R22 (hex )0.550.50.45EDR0.440.3530.30.252Exergetic efficiencyFig. 2.9(a)0.210.1502530Fig. 2.9(b)35404550Condenser temperature ( C)5560650.1Exergetic Efficiency and EDR versus Condenser TemperatureFigure 2.10 (b) and (c) illustrates the variation of EDR and exergetic efficiency with evaporationtemperature. The trend of EDR curves is approximate mirror image of exergetic efficiency curves.The reason for such a behaviour has already been explained. Figure 2.10 (c) illustrates the variationof exergetic efficiency with evaporator temperature. The significant feature of Fig. 2.10 (c) is therise and fall of the exergetic efficiency with increase in evaporation temperature. Such behaviour of
Alternative Refrigerants and Cycles for Compression Refrigeration Systems 22R404A0.15R507A0.2R220.25R502dcomp & dc0.30Fig. 2.11(a)Efficiency Defects in Compressor and Condenser for Various .1R404Ade0.15R507AR5020.2R404 Ade & dt0.25dt0Fig. 2.11(b) Efficiency Defects in Evaporator and Throttle Valve for Various Refrigerantsalso increases with increase in degree of sub-cooling. The increase in COP and exergetic efficiencyis maximum for R507A among all the refrigerants and lowest for ammonia.Effect of Superheating in EvaporatorFigure 2.13(a) and (b) illustrates the effect of superheating in evaporator on COP and exergeticefficiency. It is observed that superheating does not have much effect on COP and exergetic efficiencyas shown in these figures. In case of R717 there is slight drop in COP and exergetic efficiency. Forother refrigerants there is slight increase in COP and exergetic efficiency.Effect of Effectiveness of Liquid Vapour Heat ExchangerThe effect of variation in effectiveness of liquid vapour heat exchanger on COP and exergeticefficiency is shown in Fig. 2.14 (a) and (b). It is understood that COP and exergetic efficiencyincrease with increase in effectiveness of ‘lvhe’.
46Alternatives in Refrigeration and Air 0.80246Degree of sub-cooling, DTsb ( C)810Fig. 2.12(a) Effect of Sub-cooling in Condenser on 46Degree of sub-cooling, DTsb ( C)810Fig. 2.12(b) Effect of Sub-cooling in Condenser on Exergetic EfficiencyAn increase in effectiveness of ‘lvhe’ from 0 to 1 causes sub-cooling of saturated liquid in‘lvhe’ which accounts for increase in the cooling effect. Simultaneously superheating of the suctionvapour causes isentropic compression to take place along the isentropic lines having reduced slopethereby increasing the compressor power input. The combined effect of both these factors accountsfor increase in the COP of all refrigerants under consideration except ammonia for which COPreduces. The exergetic efficiency of R502, R507A, R404A and HCFC 22 increases whereas itreduces for R717.
Alternative Refrigerants and Cycles for Compression Refrigeration Systems ree of superheating, DTsh ( C)Fig. 2.13(a)810Effect of Superheating in Evaporator on COP0.35R507AhexR502R404AR717R220.250.150Fig. 2.13(b)246Degree of superheating, DTsh ( C)810Effect of Superheating in Evaporator on Exergetic EfficiencyEffect of Variation in Isentropic Efficiency of CompressorFigure 2.15(a) and (b) show the effect of variation in compressor efficiency on COP and exergeticefficiency. With increase in isentropic effi
2. Refrigerant mixtures/blends (a) Based on the number of pure components, i.e., binary / ternary /quaternary (b) Azeotropic /near azeotropic / zeotropic (non-azeotropic) 2.2.1 Pure Refrigerants (Single Component Refrigerants) Natural refrigerants are those substanc
Bruksanvisning för bilstereo . Bruksanvisning for bilstereo . Instrukcja obsługi samochodowego odtwarzacza stereo . Operating Instructions for Car Stereo . 610-104 . SV . Bruksanvisning i original
10 tips och tricks för att lyckas med ert sap-projekt 20 SAPSANYTT 2/2015 De flesta projektledare känner säkert till Cobb’s paradox. Martin Cobb verkade som CIO för sekretariatet för Treasury Board of Canada 1995 då han ställde frågan
service i Norge och Finland drivs inom ramen för ett enskilt företag (NRK. 1 och Yleisradio), fin ns det i Sverige tre: Ett för tv (Sveriges Television , SVT ), ett för radio (Sveriges Radio , SR ) och ett för utbildnings program (Sveriges Utbildningsradio, UR, vilket till följd av sin begränsade storlek inte återfinns bland de 25 största
Hotell För hotell anges de tre klasserna A/B, C och D. Det betyder att den "normala" standarden C är acceptabel men att motiven för en högre standard är starka. Ljudklass C motsvarar de tidigare normkraven för hotell, ljudklass A/B motsvarar kraven för moderna hotell med hög standard och ljudklass D kan användas vid
LÄS NOGGRANT FÖLJANDE VILLKOR FÖR APPLE DEVELOPER PROGRAM LICENCE . Apple Developer Program License Agreement Syfte Du vill använda Apple-mjukvara (enligt definitionen nedan) för att utveckla en eller flera Applikationer (enligt definitionen nedan) för Apple-märkta produkter. . Applikationer som utvecklas för iOS-produkter, Apple .
The International Symposium on New Refrigerants and Environmental Technology 2018 . Hitoshi Hashimoto (Refrigerants related to International Standards WG, JRAIA) Overview: Risk Assessment of Mini-split Air Conditioners using A3 Refrigerant . Development of low-GWP refrigerants for low temperature applications Robert E Low (Mexichem UK Ltd.) .
This presentation and SAP's strategy and possible future developments are subject to change and may be changed by SAP at any time for any reason without notice. This document is 7 provided without a warranty of any kind, either express or implied, including but not limited to, the implied warranties of merchantability, fitness for a .
6 Introduction to Linguistic Field Methods :, We have also attempted to address the lack of a comprehensive textbook that p.resents the rudiments of field methodology in all of the major areas of linguistic inquiry. Though a number of books and articles dealing with various aspects offield work already exist esee for example Payne 1951, Longacre 1964, Samarin 1967, Brewster 1982, and other .
