Thermodynamic analysis and optimization of a new ammonia based combined power/cooling cycle PDF
Preview Thermodynamic analysis and optimization of a new ammonia based combined power/cooling cycle
THERMODYNAMICANALYSISANDOPTIMIZATION OFANEWAMMONIABASEDCOMBINEDPOWER/COOLINGCYCLE By SHAOGUANGLU ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 2002 ACKNOWLEDGMENTS Iwouldliketosincerelythankmyadvisor,Dr.D.YogiGoswami,forhispatient guidanceandsupport.IalsooweagreatdealofthankstoDr.S.A.Sherif,Dr.Z.M. Zhang,Dr.J.PetersonandDr.U.H.Kurzwegfortheirtimeandeffortservingasmy supervisorycommittee.SpecialthanksgotoDr.C.K.Hsiehforhisinvaluableassistance. MygratitudegoesouttoMr.CharlesGarrestonwhosemarvelousexperienceandskills playedavitalroleinthedesignandconstructionoftheexperimentfacility.Inaddition,I would also like to thank Feng Xu, SanjayVijayaraghavan, GunnarTamm, Viktoria ObergMartinfortheirhelpandvaluableadvice. IthankMs.BarbaraWalkerforher valuableassistance.Also,Ifeelhonoredtohaveworkedwithsomanybrilliantgraduate studentswhosefriendshipandsupportmakemefeelathomewhenIamfarawayfrom myhomeland. 11 TABLEOFCONTENTS Page ACKNOWLEDGEMENTS ii NOMENCLATURE v ABSTRACT ix CHAPTERS ENERGYRESOURCES 1 1 GeothermalEnergy 2 4 UtilizationofGeothermalResources 3 Electricitygeneration 3 Directheatuses 4 Environmentimpact 4 SolarEnergy 5 Flat-PlateCollector 6 ConcentratingCollector 7 SolarPond 7 2AMMONIA-BASEDCOMBINEDPOWER/COOLINGCYCLE 9 OrganicRankineCycle 9 Multi-ComponentCycle 12 Ammonia-BasedCombinedPower/CoolingCycle 15 Ammonia/WaterMixtureasWorkingFluid 20 WhyAmmonia/Water? 20 ThermodynamicPropertiesofAmmonia/WaterMixture 22 3SIMULATIONANDPARAMETRICANALYSIS 23 ParametricAnalysis 23 IrreversibilityAnalysis 44 OPTIMIZATIONOFAMMONIA-BASEDCOMBINEDPOWER/COOLINGCYCLE 55 IntroductiontoOptimization 55 MathematicalFormulation 55 OptimalityConditions 56 Unconstrainedoptimization 57 iii Constrainedoptimization 58 GeneralizedReducedGradientAlgorithm 63 DescriptionoftheProblem 72 VariableTemperatureHeatSource 72 OptimizationModelfortheCycle 75 OptimizationProgram 79 OptimizationResults 79 OptimizationWithDifferentObjectiveFunctions 84 EffectofAmbientTemperature 87 5APPLICATIONSOFTHENOVELCYCLE 91 SolarThermalEnergy 91 OptimizationResults 95 EffectofWaterStorageTemperature 97 WasteHeat EffectofHeatSourceTemperature 100 EffectofSinkTemperature 103 LowTemperatureRefrigeration 121 6CONCLUSIONS 132 APPENDIX CYCLESIMULATIONPROGRAMWITHOPTIMIZATION 137 LISTOFREFERENCES 170 BIOGRAPHICALSKETCH 174 IV NOMENCLATURE COPideai:coefficientofperformanceforanidealrefrigerationcycle fi”:massfractionatpoint2”,definedasm2"/mi fa:massfractionsatpoint4,definedasm4/mi f(x):objectivefunction g\:generalizedreducedgradient g(x):inequalityconstraints h(x):equalityconstraints h0:enthalpyoftheheatsourcefluidatambienttemperature h‘hns:inletenthalpyoftheheatsourcefluid h™':outletenthalpyoftheheatsourcefluid hx:enthalpyoftheworkingfluidatpointx(refertoFig.2.7) H:Hessianmatrix L:lowerboundofvectoroffreevariables L:Lagrangefunction mhs:massflowrateofheatsourcefluid mx:massflowrateoftheworkingfluidatpointx(refertoFig.2.7) -Phigh:cyclehighpressure Piow:cyclelowpressure Qabsorber :absorberheatrejection Qboiier boilerheatinput Qcoo, :refrigerationoutput Qahs0rber 'rectifierheattransfer Qsuperheater superheatinput s0:entropyoftheheatsourcefluidatambienttemperature s£:inletentropyoftheheatsourcefluid s°hsu' :outletentropyoftheheatsourcefluid :entrancetemperatureofheatsourcefluid T™‘:exittemperatureofheatsourcefluid T0 :ambienttemperature ^absorber:absorbertemperature Toiler:boilertemperature ^rectifier:rectifiertemperature Superheater:superheatertemperature Tboiiermin:minimumboilertemperature frectifiermin:minimumrectifiertemperature Tx:temperatureatstatepointx(refertoFig.2.7) ATmin:minimumtemperaturedifferencerequiredintheheatexchangers Afpjn:temperaturedifferenceatpinchpointintheboiler Ar™n :minimumtemperaturedifferencerequiredatpinchpoint VI : U:upperboundofvectoroffreevariables wmax:availabilityorexergyperunitmassofheatsourcefluid W net:cyclenetpoweroutput W p :pumpworkinput Wt :turbineworkoutput x:vectoroffreevariables x*:localminimum -*•turbine-vaporqualityatturbineexit Greek: s:relativeerror r|i:Firstlawefficiency r\2:Secondlawefficiency A.:Lagrangemultiplier jo.:Lagrangemultiplier Superscripts: in:inletcondition out outletcondition Subscripts: 0:ambientcondition D:dependentvariables vii high:highpressure hs:heatsource I:independentvariables ideal:idealcondition low:lowpressure max maximum : min:minimum p:pump pin:pinpoint R:reducedgradient t:turbine x:statepointxinFig.2.7 AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy THERMODYNAMICANALYSISANDOPTIMIZATION OFANEWAMMONIABASEDCOMBINEDPOWER/COOLINGCYCLE By ShaoguangLu May2002 Chairman:D.YogiGoswami MajorDepartment:MechanicalEngineering A detailedthermodynamic analysis ofacombinedthermalpowerandcooling cycle is conducted. This cycle innovatively combines Rankine and absorption refrigerationcyclesandusesammonia-watermixtureasaworkingfluid.Itcanprovide poweroutput aswell asrefrigerationwithpowergenerationasaprimarygoal. The conceptofthiscycleisbasedontheuniquefeatureofamulti-componentworkingfluid, varyingtemperatureboilingprocess.Therefore,abetterthermalmatchisobtainedinthe boilerbetweensensibleheatsourceandworkingfluid. Italsotakesadvantageofthelow boiling temperature ofammonia vapor so that a temperature lower than ambient is achievedattheexitoftheturbine.Thiscyclecanbeusedasabottomingcycleusing wasteheatfromatoppingcycleorasanindependentcycleusinglowtemperaturesources suchasgeothermalandsolarenergy. IX Aparametricanalysishasbeenconductedfortheproposedcycleunderidealized conditions. Ithelpstounderstandthebehaviorofthecycleandalso showsthatcycle working conditions could be optimized for best performance. The effect of irreversibilitiesonthecycleperformancehasalsobeenstudied. Anoptimizationalgorithm,GeneralizedReducedGradient(GRG)algorithm,is introduced to optimize theperformance oftheproposed cycle. It searches a feasible regionoffreevariablesdefinedbytheirconstraintstooptimizetheperformancecriteria. Second lawefficiencyischosenastheprimaryoptimizationobjectivewhilethecycle couldbeoptimizedforanyotherperformanceparameter. Cycle performance over a range of source and ambient temperatures was investigated.Itwasfoundthatforasourcetemperatureof360K,whichisintherangeof flat plate solar collectors, both power and refrigeration outputs are achieved under optimum conditions. All performance parameters, including first and second law efficiencies, andpowerandrefrigerationoutputsdecreaseastheambienttemperature goesup.Ontheotherhand,forasourceof440K,optimumconditionsdonotprovideany refrigeration.However,refrigerationcanbeobtainedevenforthistemperatureundernon- optimumperformanceconditions.Inaddition,somespecificapplicationsoftheproposed cyclearestudied.
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