给水排水工程专业外文翻译密封的建筑排水系统和通气系统.docx
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给水排水工程专业外文翻译密封的建筑排水系统和通气系统.docx
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给水排水工程专业外文翻译密封的建筑排水系统和通气系统
外文原文:
Sealedbuildingdrainageandventsystems
—anapplicationofactiveairpressuretransientcontrolandsuppression
Abstract
Theintroductionofsealedbuildingdrainageandventsystemsisconsideredaviablepropositionforcomplexbuildingsduetotheuseofactivepressuretransientcontrolandsuppressionintheformofairadmittancevalvesandpositiveairpressureattenuatorscoupledwiththeinterconnectionofthenetwork'sverticalstacks.
Thispaperpresentsasimulationbasedonafour-stacknetworkthatillustratesflowmechanismswithinthepipeworkfollowingbothappliancedischargegenerated,andsewerimposed,transients.Thissimulationidentifiestheroleoftheactiveairpressurecontroldevicesinmaintainingsystempressuresatlevelsthatdonotdepletetrapseals.
Furthersimulationexerciseswouldbenecessarytoprovideproofofconcept,anditwouldbeadvantageoustoparallelthesewithlaboratory,andpossiblysite,trialsforvalidationpurposes.Despitethiscautiontheinitialresultsarehighlyencouragingandaresufficienttoconfirmthepotentialtoprovidedefinitebenefitsintermsofenhancedsystemsecurityaswellasincreasedreliabilityandreducedinstallationandmaterialcosts.
Keywords:
Activecontrol;Trapretention;Transientpropagation
Nomenclature
C+-——characteristicequations
c——wavespeed,m/s
D——branchorstackdiameter,m
f——frictionfactor,UKdefinitionviaDarcyΔh=4fLu2/2Dg
g——accelerationduetogravity,m/s2
K——losscoefficient
L——pipelength,m
p——airpressure,N/m2
t——time,s
u——meanairvelocity,m/s
x——distance,m
γ——ratiospecificheats
Δh——headloss,m
Δp——pressuredifference,N/m2
Δt——timestep,s
Δx——internodallength,m
ρ——density,kg/m3
ArticleOutline
Nomenclature
1.Introduction—airpressuretransientcontrolandsuppression
2.Mathematicalbasisforthesimulationoftransientpropagationinmulti-stackbuildingdrainagenetworks
3.Roleofdiversityinsystemoperation
4.Simulationoftheoperationofamulti-stacksealedbuildingdrainageandventsystem
5.Simulationsignconventions
6.Waterdischargetothenetwork
7.Surchargeatbaseofstack1
8.Sewerimposedtransients
9.Trapsealoscillationandretention
10.Conclusion—viabilityofasealedbuildingdrainageandventsystem
1.Airpressuretransientsgeneratedwithinbuildingdrainageandventsystemsasanaturalconsequenceofsystemoperationmayberesponsiblefortrapsealdepletionandcrosscontaminationofhabitablespace[1].Traditionalmodesoftrapsealprotection,basedontheVictorianengineer'sobsessionwithodourexclusion[2],[3]and[4],dependpredominantlyonpassivesolutionswhererelianceisplacedoncrossconnectionsandverticalstacksventedto
atmosphere[5]and[6].Thisapproach,whilebothprovenandtraditional,hasinherentweaknesses,includingtheremotenessoftheventterminations[7],leadingtodelaysinthearrivalofrelievingreflections,andthemultiplicityofopenrooflevelstackterminationsinherentwithincomplexbuildings.Thecomplexityoftheventsystemrequiredalsohassignificantcostandspaceimplications[8].
Thedevelopmentofairadmittancevalves(AAVs)overthepasttwodecadesprovidesthedesignerwithameansofalleviatingnegativetransientsgeneratedasrandomappliancedischargescontributetothetimedependentwater-flowconditionswithinthesystem.AAVsrepresentanactivecontrolsolutionastheyresponddirectlytothelocalpressureconditions,openingaspressurefallstoallowareliefairinflowandhencelimitthepressureexcursionsexperiencedbytheappliancetrapseal[9].
However,AAVsdonotaddresstheproblemsofpositiveairpressuretransientpropagationwithinbuildingdrainageandventsystemsasaresultofintermittentclosureofthefreeairpaththroughthenetworkorthearrivalofpositivetransientsgeneratedremotelywithinthesewersystem,possiblybysomesurchargeeventdownstream—includingheavyrainfallincombinedsewerapplications.
Thedevelopmentofvariablevolumecontainmentattenuators[10]thataredesignedtoabsorbairflowdrivenbypositiveairpressuretransientscompletesthenecessarydeviceprovisiontoallowactiveairpressuretransientcontrolandsuppressiontobeintroducedintothedesignofbuildingdrainageandventsystems,forboth‘standard’buildingsandthoserequiringparticularattentiontobepaidtothesecurityimplicationsofmultiplerooflevelopenstackterminations.Thepositiveairpressureattenuator(PAPA)consistsofavariablevolumebagthatexpandsundertheinfluenceofapositivetransientandthereforeallowssystemairflowstoattenuategradually,thereforereducingthelevelofpositivetransientsgenerated.
TogetherwiththeuseofAAVstheintroductionofthePAPAdeviceallowsconsiderationofafullysealedbuildingdrainageandventsystem.
Fig.1illustratesbothAAVandPAPAdevices,notethatthewaterlesssheathtrapactsasanAAVundernegativelinepressure.
Fig.1.Activeairpressuretransientsuppressiondevicestocontrolbothpositiveandnegativesurges.
Activeairpressuretransientsuppressionandcontrolthereforeallowsforlocalizedinterventiontoprotecttrapsealsfrombothpositiveandnegativepressureexcursions.Thishasdistinctadvantagesoverthetraditionalpassiveapproach.Thetimedelayinherentinawaitingthereturnofarelievingreflectionfromaventopentoatmosphereisremovedandtheeffectofthetransientonalltheothersystemtrapspassedduringitspropagationisavoided.
2.Mathematicalbasisforthesimulationoftransientpropagationinmulti-stackbuildingdrainagenetworks.
ThepropagationofairpressuretransientswithinbuildingdrainageandventsystemsbelongstoawellunderstoodfamilyofunsteadyflowconditionsdefinedbytheStVenantequationsofcontinuityandmomentum,andsolvableviaafinitedifferenceschemeutilizingthemethodofcharacteristicstechnique.Airpressuretransientgenerationandpropagationwithinthesystemasaresultofairentrainmentbythefallingannularwaterinthesystemverticalstacksandthereflectionandtransmissionofthesetransientsatthesystemboundaries,includingopenterminations,connectionstothesewer,appliancetrapsealsandbothAAVandPAPAactivecontroldevices,maybesimulatedwithprovenaccuracy.Thesimulation[11]provideslocalairpressure,velocityandwavespeedinformationthroughoutanetworkattimeanddistanceintervalsasshortas0.001 sand300 mm.Inaddition,thesimulationreplicateslocalappliancetrapsealoscillationsandtheoperationofactivecontroldevices,therebyyieldingdataonnetworkairflowsandidentifyingsystemfailuresandconsequences.Whilethesimulationhasbeenextensivelyvalidated[10],itsusetoindependentlyconfirmthemechanismofSARSvirusspreadwithintheAmoyGardensoutbreakin2003hasprovidedfurtherconfidenceinitspredictions[12].
Airpressuretransientpropagationdependsupontherateofchangeofthesystemconditions.Increasingannulardownflowgeneratesanenhancedentrainedairflowandlowersthesystempressure.Retardingtheentrainedairflowgeneratespositivetransients.Externaleventsmayalsopropagatebothpositiveandnegativetransientsintothenetwork.
Theannularwaterflowinthe‘wet’stackentrainsanairflowduetotheconditionof‘noslip’establishedbetweentheannularwaterandaircoresurfacesandgeneratestheexpectedpressurevariationdownaverticalstack.Pressurefallsfromatmosphericabovethestackentryduetofrictionandtheeffectsofdrawingairthroughthewatercurtainsformedatdischargingbranchjunctions.Inthelowerwetstackthepressurerecoverstoaboveatmosphericduetothetractionforcesexertedontheairflowpriortofallingacrossthewatercurtainatthestackbase.
Theapplicationofthemethodofcharacteristicstothemodellingofunsteadyflowswasfirstrecognizedinthe1960s[13].TherelationshipsdefinedbyJack[14]allowsthesimulationtomodelthetractionforceexertedontheentrainedair.Extensiveexperimentaldataallowedthedefinitionofa‘pseudo-frictionfactor’applicableinthewetstackandoperableacrossthewaterannularflow/entrainedaircoreinterfacetoallowcombineddischargeflowsandtheireffectonairentrainmenttobemodelled.
ThepropagationofairpressuretransientsinbuildingdrainageandventsystemsisdefinedbytheStVenantequationsofcontinuityandmomentum[9],
(1)
(2)
Thesequasi-linearhyperbolicpartialdifferentialequationsareamenabletofinitedifferencesolutiononcetransformedviatheMethodofCharacteristicsintofinitedifferencerelationships,Eqs.(3)–(6),thatlinkconditionsatanodeonetimestepinthefuturetocurrentconditionsatadjacentupstreamanddownstreamnodes,Fig.2.
Fig.2.StVenantequationsofcontinuityandmomentumallowairflowvelocityandwavespeedtobepredictedonanx-tgridasshown.Note
.
FortheC+characteristic:
(3)
when
(4)
andtheC-characteristic:
(5)
when
(6)
wherethewavespeedcisgivenby
c=(γp/ρ)0.5.
(7)
Theseequationsinvolvetheairmeanflowvelocity,u,andthelocalwavespeed,c,duetotheinterdependenceofairpressureanddensity.Localpressureiscalculatedas
(8)
Suitableequationslinklocalpressuretoairflowortotheinterfaceoscillationoftrapseals.
Thecaseoftheappliancetrapsealisofparticularimportance.Thetrapsealwatercolumnoscillatesundertheactionoftheappliedpressuredifferentialbetweenthetransientsinthenetworkandtheroomairpressure.TheequationofmotionfortheU-bendtrapsealwater
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