换热器性能的-经济评价-吴双应

:1998-07-28;＊,:(1968-),,,,,、.:400044:1001-2060(1999)06-0437-04换热器性能的经济评价()　　＊　　:通过对换热器传热与流动过程的火用经济分析,提出了一项换热器性能的火用经济评价指标———单位传热量的总费用η,并对顺流、交叉流和逆流三种流型的换热器进行了火用经济分析和优化。本文的有关方法和结论可为工程上换热器的性能评价提供参考。:;;:TK1241　,,,,。,KΔP,,,;Q()N,,,,。,、,Webb[1],(PEC),,QN,,。,Bejan[2],,,;,,。,,,。,[3,4],,Q,,。,,,,,,,,。,,。,,、、,η,。2　,14(84)　　　　　　　　　　　　199911。1,,,。图1　典型换热过程　　,“i”,“o”;“c”,“h”;“t”,“s”;“∞”。[5]:de=CP(1-T∞/T)dT+V-(T-T∞)(VT)PdP(1):V。:Δe=∫Po,ToPi,TiCP(1-T∞/T)dT+∫Po,ToPi,TiV-(T-T∞)(VT)PdP(2),,ΔeT=∫Po,ToPi,TiCP(1-T∞/T)dT(3),ΔeP=∫Po,ToPi,TiV-(T-T∞)(VT)PdP(4)ΔEΔEhΔEc,,ΔeTh0,ΔePh0,,ΔE=-ΔEh-ΔEc=-Gh(ΔeTh+ΔePh)-Gc(ΔeTc+Δepc)=(-GhΔeTh-GcΔeTc)+(-GhΔePh-GcΔePc)=ΔET+ΔEPΔET;ΔEP;G。ΔETΔEP。2.1　ΔET(3),,:ΔeT=CP(To-Ti-T∞lnToTi)(6),ΔET=GhCPhT∞lnThoThi+GcCPcT∞lnTcoTci(7),R=GcCPc/GhCPhNTU=KF/GcCPcε=(Tco-Tci)/(Thi-Tci):Tho=Thi-εR(Thi-Tci)(8)Tco=Tci+ε(Thi-Tci)(9)ε=f(R,NTU,)(8)(9)(7)ΔET=GhCPhT∞ln1-εR(1-C)+Rln1+ε(1/C-1)(10),C=Tci/Thi。2.2　ΔEp(4),,。,,PV=R′T(4):Δep=R′T∞lnPoPi(11),ΔEp=-GhR′hT∞lnPhoPhi-GcR′cT∞lnPcoPci(12)■Pc■PhΔPc=Pci-Pco,ΔPh=Phi-Pho(13)ΔEp=-T∞[GhR′hln(1-ΔPh/Phi)+GcR′cln(1-ΔPc/Pci)](14),R′。,V=const,(4):Δep=V(Po-Pi)=-VΔP(15)·438·　　　　　　　　　　　　　　　　　　1999ΔEp=GhVhΔPh+GcVcΔPc(16)[6]NTU,ΔP/Pi=FNTU(17),Ft=18β·1EutStt(ft+diLξt)Fs=18β·1EusStt(fs+dide+diLξs),Eu(=Pi/ρu2);St(=K/ρuCp);f;ξ;β;L;di;de。(17)(14)、(16)ΔEp::ΔEp=-T∞[GhR′hln(1-FhNTU)+GcR′cln(1-FcNTU)](18):ΔEp=GhVhPhiFhNTU+GcVcPciFcNTU(19)(5)(10)(18)(19),—、—、—、—。3　,Q,,、()。,,,,,;,,,(),,,“”“”n,,n=3～5[7]。,Q:C=Ce(ΔET+nΔEp)+I/τ(20),τ;Ce;I,[8]:I=(Io+IF·F)[12(i+j)·(N+1)+1+0.07N]/N(21),F;Io;IF;N;i;j。,:η=CQ=Ce(ΔET+nΔEp)+I/τQ(22),Q=GcCPcε(Thi-Tci)(23)(10)(18)(19)(21)(22)(23)—、—、—、—η。,,NTUopt(Fopt)η。4　图2　R一定时,η与NTU的关系—,,67℃,0.20MPa,,15℃,0.15MPa,5000kg/h;1000W/m2.℃;1000+700F;10,15%,2%;Ce=6.94×10-8$/J;7200。(、、)。2R=0.6ηNTU。·439·6　　　　　　　　　.　　　　　　　　　　　　　　图3　不同R下,η与NTU的关系,ηNTU,ηNTUopt,NTUopt()NTUopt()NTUopt(),ηmin()ηmin()ηmin(),,。图4　最佳传热单元数与R的关系3ηRNTU。,,ηR,R,;NTUR。R:ηNTU=0(24)(10)(19)(22)(23)(24),。4,,NTUopt,,R,NTUopt,NTUopt,,,2。5　———η。,,,,η。〔1〕　WebbRL.Performanceevaluationcriteriaforuseofenhancedheattransfersurfacesinheatexchangerdesign.Int.J.HeatMassTransfer,1981,24(4)∶715～726.〔2〕　BejanA.Generalcriterionforratingheatexchangerperfor-mance.Int.J.HeatMassTransfer,1978,21∶655～658.〔3〕　,..,1996,15(6)∶44～47.〔4〕　,..,1998,38(4)∶50～53.〔5〕　..:,1998.〔6〕　,,.().,1993,3(4)∶7～13.〔7〕　..,1985,6(4)∶311～314.〔8〕　..:,1986.(何静芳　编辑)·440·　　　　　　　　　　　　　　　　　　1999Onthebasisofthewaterwallthermodynamictestofa600MWboilerunitandthroughtheuseofafinite-ele-mentanalyticalmethodananalysiswasconductedofthedynamicvariationwithheattransferconditionsofmem-branewaterwalltubewalltemperaturedistributionofalow-circulationratioboiler.Theanalysisaimsatidenti-fyingtheunderlyingbasiccauseofwaterwalltubewalltemperaturefluctuations.Theresultsoftheanalysisshowthatthebasiccauseleadingtothefluctuationsofthewaterwalltubewalltemperatureliesinthedeteriora-tionofin-tubeheattransfer.Inthecourseofaheattransferdeteriorationtakingplaceinsidethetubesofasin-gle-sideheatedwaterwallthetemperaturedifferencebetweenthefire-facingtubeinnerandoutertubewallsur-facehasarelativelysmalltime-dependentfluctuation.However,thewaterwallperipheraltemperaturediffer-encesuffersadrasticfluctuationtriggeredbythewalltemperaturefluctuationsofthefire-facingouterwall.Keywords:waterwall,temperaturefield,finiteelement=Exergy-economicEvaluationofaHeatExchangerPerformance[,]/WuShuangying(ChongqingUniversity)//JournalofEngineeringforThermalEnergy&Power.-1999,14(6).-437～440Basedontheexergy-economicanalysisofheatexchangerheattransferandflowprocesstheauthorhascomeupwithaheatexchangerperformanceevaluationindex,theso-calledηcriterion,definedasthetotalcostperunitquantityofheattransferred.Furthermore,conductedwastheexergy-economicanalysisandoptimizationofthreetypesofheatexchangers,i.e.,down-flow,cross-flowandcounter-flow.Themethodsemployedandre-sultspresentedinthispapercanserveasaguideduringtheperformanceevaluationofheatexchangers.Keywords:heatexchanger,exergy-economicanalysis,performanceevaluation=DevelopmentandFabricationofaComputer-basedVisualSys-temforThree-dimensionalTemperatureFields[,]/ZhangShishuai,LuoJun,ZhuMaoshu,etal(CentralUniversityofScience&Technology)//JournalofEngineeringforThermalEnergy&Power.-1999,14(6).-441～442Describedinthispaperisacomputer-basedvisualsystemforthevisualizationtreatmentofathree-dimensionaltemperaturefieldencounteredinengineeringthermophysicsbytheuseofcomputergraphicandimagetech-niques.Theabove-citedsystemincludesavarietyofmodules,whichareusedforperformingsuchfunctionsasthemodelbuildingofthethree-dimensionaltemperaturefield,colormapping,setting-upofavisualmodel,ex-tractionofasectionalplane,thesettingofvisualangle,etc.ThesystemisdevelopedandrealizedonaWindows95platformwiththehelpofVisualC.Keywords:three-dimensionaltemperaturefield,visualsystem,modelbuilding=TheDesignandDevelopmentofaLarge-sizedAnthracite-firedSub-critical-pressureUtilityBoilerwithaTangentialfiringSystem[,]/ChenJirong,GaoFeng(HarbinBoilerCo.Ltd.)//JournalofEngineeringforThermalEnergy&Power.-1999,14(6).-443～446T