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1、FLOWEQUALIZATIONFlowequalizationistheprocessofmitigatingchangesinflowratethroughaportionofasystembyprovidingstoragetoholdwaterwhenitisarrivingtoorapidly,andtosupplyadditionalwaterwhenitisarrivinglessrapidlythandesired.Inmanywatertreatmentsystems,itisusefultoimple
2、mentflowequalizationdownstreamoftheplant,becausethedownstreamdemandisnotsteady,butingeneral,thetreatmentprocessesworkmoreefficientlyiftheflowratethroughthemissteady.Intreatingwastewater,therateatwhichthewastearrivesatthetreatmentprocessmightvarydramaticallyduring
3、theday,soitisconvenienttoequalizetheflowbeforefeedingittothevarioustreatmentsteps.Ineithercase,theengineeringissueisdecidinghowlargeanequalizationbasinisrequiredtoallowthetreatmentprocessestooperatewithasteady,averageflow.Consider,forexample,anequalizationbasin(i
4、.e.,areservoir)downstreamofadrinkingwatertreatmentplant.Theflowrateoutofthebasinvariesinapredictableway,butwewishtotreattherawwateratasteady,averagerate.Howbigabasinisrequiredsothatwecanstorethe“excess”treatedwateruntilitisneededlater?Wecananswerthisquestionbywri
5、tingamassbalanceonwater,withthebasinasthecontrolvolume.Waterisneithergeneratednordestroyedbyanychemicalreactionstakingplaceinthebasin,sor=0inthemassbalance.Also,the"concentration"ofwaterinthetankisconstantandequaltothedensityofwater.TherequiredvaluesofQoutareknow
6、nasafunctionoftime,andweintendtooperatewithQinequaltoQavgatalltimes.Themassbalancecanthereforebewrittenasfollows:TheprecedingequationsimplysaysthattherateofchangeinthevolumeofwaterstoredinthebasinoveranyshorttimeperiodΔtequalsthedifferencebetweentheinfluent(avera
7、ge)andeffluentflowratesduringthatperiod.Rearrangingslightly:Tousetheequationtodeterminetherequiredstoragevolume,wecomputethechangeintheamountofwaterinthereservoirovertime,startatsometimethatwedesignateast=0.Wedon'tknowhowmuchwaterisinthebasinatt=0,sowejustcalltha
8、tvolumeV(0)anddealwithitlater.WecanthenusetheknownvaluesofQavgandQ(t)tocomputethechangeinthevolumeofwaterinthebasinbetweent=0andanyfuturetime;i.e.,wecancompute
