Thermodynamic analysis and optimization of a new ammonia based combined power/cooling cycle

186 Pages·2002·6.5 MB·English

by  Lu, Shaoguang, 1970-

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.