Unit-9--Sedimentation

Unit9SedimentationImportantWordsandExpressions•sedimentation[sedimenteiʃn]n.沉淀，沉降；沉积；淤积；沉降法•tendency[tendənsi]n.倾向，趋势；（话或作品等的）旨趣,意向；性情;癖好•quiescent[kwi’esnt]adj.不活动的，静态的，休眠的•discretesettling自由沉淀•hinderedsettling拥挤沉淀•reagentn.反应物，试剂•coefficient[kəuifiʃnt]n.系数；测定某种质量或变化过程的率；程度；协同因素adj.共同作用的；合作的。•boundary[baundri]n.分界线；范围；（球场）边线•buoyant[bɔiənt]adj.轻快的；活泼的；有浮力的，易浮的；•unevenly[ʌn'i:vnli]adv.不规则地；不稳定地；不平行地；•laminar['læminə]adj.薄片装的，薄层的；层状的，板状的；流线的；层流的•turbulent[tɜ:bjələnt]adj.湍流的，激流的；混乱的，骚乱的；吵闹的；强横的Text•Theimpuritiesinwatermaybeeitherdissolvedorsuspended.Theeasiestwaytoremovethesuspendedmaterialistolettheforceofgravitydothework.•Underquiescentconditions,whenflowvelocitiesandturbulenceareminimal,particlesthataredenserthanwaterwillbeabletosettletothebottomofatank.•Thisprocessiscalledsedimentation,andthelayerofaccumulatedsolidsatthebottomofthetankiscalledsludge.•水中的杂质可以是溶解的或悬浮的。去除悬浮物最简单的方法是让重力做这项工作。•在静态条件下，当流速和湍流最小的时候，粒子比水稠，粒子就能沉降到罐的底部。•这个过程称为沉淀，同时，罐底积累固体的层称为污泥。•Thesettlingbasins,thesettlingtanksorsedimentationtanksarepondsconstructedforthepurposeofremovingentrainedsolidsbysedimentation.•Clarifiersaresettlingbasinsbuiltwithmechanicalmeansforcontinuousremovalofsolidsbeingdepositedbysedimentation.•沉降盆，沉降池或沉淀池是为了通过沉淀除去夹带固体而构建的池塘。•澄清器是由机械方式连续去除由沉淀放置（安置）的固体而建立的沉降盆。•Thespeedatwhichsuspendedparticlessettletowardthebottomofatankdependsontheirsizeaswellasontheirdensity.[1]•Thelargerandheavierparticleswillnaturallysettlefasterthansmallerorlighterparticles.•Theforcesopposingthedownwardforceofgravityincludebuoyancyandfriction(drag).•Thetemperatureandviscosityofthewaterareadditionalfactorsthataffecttheparticle-settlingrate.•池中悬浮颗粒沉淀到池底的速度取决于它们的大小和密度。•大而重的粒子沉降（速度）要快于小而轻的粒子。•与向下的重力相反的力包括浮力和摩擦力（阻力）。•水的温度和粘度是影响粒子沉降率的附加因素。•Thenatureofthesedimentationprocessalsovarieswiththeconcentrationofsuspendedparticlesandtheirtendencytointeractwithoneanother.•Inadilutesuspension,wheretheparticlesarefreetosettlewithoutinterference,theprocessiscalledfreesettlingordiscretesettling.•Astheconcentrationincreases,theparticlestendtointeractandinterferewiththefreemovementofoneanother;thisissometimescalledhinderedsettling.[2]•沉淀过程中的本质也随着悬浮颗粒的浓度和他们之间相互作用的趋势而变化（改变）。•在稀悬浮液中颗粒是自由地无干扰沉降，这个过程被称为自由沉降或离散沉淀。•当浓度增加时，颗粒倾向于相互作用，干扰其他颗粒的自由运动，这有时被称为拥挤沉淀。•Inasedimentationtanktheremaybeuptofourdifferentzonesortypesofsettlingthatoccuratdifferentdepths,andexactmathematicalanalysisoftheprocesscanbequitecomplicated.Thissectiondiscussessomecommonfactorsrelatedtodiscreteparticlesettling.•ParticleSettlingTheory•Thesettlingofdiscrete,non-flocculatingparticlescanbeanalyzedbymeansoftheclassiclawsofsedimentationformedbyNewtonandStokes.•沉淀池中可能有多达四个不同的发生在不同的深度的沉降区域或类型，并且，精确的数学分析过程可能是相当复杂的。本节讨论相关的离散颗粒沉降一些共同的因素。•粒子沉降理论•离散的，非絮凝粒子的沉降可以借助于由牛顿和斯托克斯形成的经典沉淀定律进行分析。•Size,shapeandspecificgravityoftheparticlesdonotchangewithtime.•Settlingvelocityremainsconstant.•Ifaparticleissuspendedinwater,itinitiallyhastwoforcesactinguponit:(1)forceofgravity:•大小，形状和颗粒的比重不随时间而改变。•沉降速度保持不变。•如果将颗粒悬浮在水中，它最初具有两个力在其上作用：（1）重力的作用：•Becausethedragforceactsintheoppositedirectiontothedrivingforceandincreasesasthesquareofthevelocity,accelerationoccursatadecreasingrateuntilasteadyvelocityisreachedatapointwherethedragforceequalsthedrivingforce:[3]•由于摩擦阻力与驱动力方向相反，且随速度的平方增大，加速度下降，直到达到一个稳定的速度使得摩擦阻力与驱动力相等。•CalculatevelocityusingStokeslaworturbulentexpression.CalculateandcheckReynoldsnumber.CalculateCD.Usegeneralformula.Repeatfromstep2untilconvergence.•FactorsAffectingSedimentation•Severalfactorsaffecttheseparationofsettleablesolidsfromwater.Someofthemorecommontypesoffactorstoconsiderare:•计算速度使用斯托克斯定律或湍流方程计算并检查雷诺数。计算CD。使用通用公式。重复步骤2，直到收敛。•影响沉降的因素几个因素会影响可沉淀的固体从水中分离。要考虑的一些比较常见因素的类型是:•ParticleSizeThesizeandtypeofparticlestoberemovedhaveasignificanteffectontheoperationofthesedimentationtank.Becauseoftheirdensity,sandorsiltcanberemovedveryeasily.Thevelocityofthewater-flowchannelcanbeslowedtolessthanonefootpersecond,andmostofthegravelandgritwillberemovedbysimplegravitationalforces.•Incontrast,colloidalmaterial,smallparticlesthatstayinsuspensionandmakethewaterseemcloudy,willnotsettleuntilthematerialiscoagulatedandflocculatedbytheadditionofachemical,suchasanironsaltoraluminumsulfate.[4]•粒子尺寸被去除粒子的尺寸大小和类型对沉淀池的操作有显著的影响。比重的原因，沙子或淤泥能够很容易地被去除。渠道中水流动的速度可以减缓至每秒小于一英尺，而大部分的碎石和砂砾会通过简单的重力被除去。•与之相反，胶体物质、细小颗粒悬浮在水中，使水看上去呈云状浑浊，这时只有投加如铁盐或硫酸铝之类的化学药剂对之进行混凝和絮凝才能使之沉淀。•Theshapeoftheparticlealsoaffectsitssettlingcharacteristics.•Aroundparticle,forexample,willsettlemuchmorereadilythanaparticlethathasraggedorirregularedges.•Allparticlestendtohaveaslightelectricalcharge.Particleswiththesamechargetendtorepeleachother.•Thisrepellingactionkeepstheparticlesfromcongregatingintoflocsandsettling.•粒子的形状也影响其沉降特性。例如，一个圆形颗粒会比有粗糙的或不规则边缘的颗粒更容易沉淀。•所有粒子往往有一个轻微的电荷。粒子具有相同电荷相互排斥。•这种排斥作用使颗粒聚集成絮体和沉淀。•WaterTemperatureAnotherfactortobeconsideredintheoperationofasedimentationbasinisthetemperatureofthewaterbeingtreated.Whenthetemperaturedecreases,therateofsettlingbecomesslower.Theresultisthatasthewatercools,thedetentiontimeinthesedimentationtanksmustincrease.•Asthetemperaturedecreases,the