局部通風設(shè)計

局部通風系統(tǒng)

Source

Path WorkerLocalExhaustVentilation局部排風

(Ref.ACGIH-IndustrialVentilationManual)GeneralVentilation全面通風

(Ref.ASHRAE-62)ENGINEERINGCONTROLSVENTILATION通風GeneralandLocalVentilationGeneralVentilation

全面通風LocalExhaustVentilation

局部通風全面通風LOCALEXHAUSTVENTILATION(LEV)局部排風January12,20237SOMECOMMONMYTH常見問題LEVSYSTEMS

局部排風系統(tǒng)

1.Fans風機 2.Hoods排風罩 3.Ducts風管 4.Stacks排氣筒 5.AirCleaners空氣凈化器

LOCALEXHAUSTSYSTEM

局部排風系統(tǒng)TypesofHood

排風罩的類型Totalenclosures全密閉罩Partialenclosures局部密閉罩Captorhoods收集式吸氣罩Receptorhoods接受式排風罩TYPESOFHOODS

排風罩類型密閉罩半密閉罩January12,202316捕集罩TypesofLocalExhaustHoodandtheEffectiveness收集罩半密閉罩全密閉罩DESIGNINGHOODS

排風罩設(shè)計1.Enclosedtheprocessasmuchaspossiblewhilenotinterferingwithworker.

在不影響工人操作的情況下，排風罩盡可能包括整個操作范圍。2.Placethehoodsothatcontaminantsaredrawnawayfromthebreathingzoneoftheworker.

排風罩的位置適當，應(yīng)能將有害物從工人呼吸帶處排出。3.Locatethehoodascloseaspossibletothepointofgenerationofcontamination(tominimizeairvolumeandforeffectivecapture).

排風罩應(yīng)盡可能靠近有害物的產(chǎn)生點，可以減少所需風量、提高捕集效率。WORKERPOSITIONEFFECT

工人位置的影響VelocityTerms風速CaptureVelocity控制風速FaceVelocity面風速DuctVelocity風管風速CAPTUREVELOCITY

控制風速Thevelocityofairinducedbyahoodtocaptureemittedcontaminantsfromthesourceexternaltothehood.在排風罩外部的污染源處，捕集逸散污染物的氣流速度。CAPTUREVELOCITY控制風速Thevelocityofairinducedbyahoodtocaptureemittedcontaminantsfromthesourceexternaltothehood.在排風罩外部的污染源處，捕集逸散污染物的氣流速度。Notfacevelocity!罩口風速這種情況下有意義嗎?HowtoAssessitsEffectiveness?有害物發(fā)散的狀態(tài)舉例控制風速要求(m/s)無速度的揮發(fā)到靜止的空氣中溶劑從容器內(nèi)揮發(fā)；涂料干燥0.3–0.5低速度的發(fā)散到基本靜止的空氣中電焊；錫焊；液體轉(zhuǎn)移0.5-

1.0中等速度的發(fā)散到運動的空氣中粉碎；噴漆1.0-

2.5高速度的發(fā)散到的運動的空氣中切割；打磨；噴砂2.5-

10January12,202324控制風速要求CaptureVelocity不同形狀排風罩的風量計算January12,202328不同形狀排風罩的風量計算MaximumCaptureDistanceShouldNotBeMoreThan1.5TimestheDuctDiameter

最大捕集距離不超過風罩直徑的1.5倍。RuleofThumbforSimpleCaptureHoods排風罩的基本規(guī)則

RelationshipBetweenCapture,Working&BreathingZones

排風罩的有效區(qū)域

DUCTVELOCITY

風管風速

Airvelocitythroughtheductcross-section.

風管橫截面的風速Whensolidmaterialispresentintheairstream,ductvelocitymustbeequaltoorgreaterthantheminimumairvelocityrequiredtomovetheparticlesintheairstream.

當風管氣流中存在固體顆粒時，風管風速應(yīng)不小于能將顆粒物移動的最小風速。RANGEOFMINIMUMDUCTDESIGNVELOCITIES

風管最小設(shè)計風速的范圍

SHORTCIRCUITING短路MinimumStackHeightinRelationtoImmediateRoofLineorCenterofAnyAirIntakeontheSameRoof

屋頂進風口與屋頂排氣口的高度要求ENERGYLOSSESINTHELEVSYSTEM

局部排風系統(tǒng)能力損失HOODENTRYLOSS排風罩進口阻力ELBOWLOSS彎頭阻力BRANCHENTRYLOSS支管入口阻力WEATHERCAPLOSS風帽阻力FRICTIONLOSS摩擦阻力DUCTCONTRACTLOSS

管徑改變導致的阻力排風罩進口阻力(hoodentryloss)January12,202336彎頭阻力January12,202337支管入口阻力January12,202338摩擦阻力January12,202339選擇合適的風管風速通風系統(tǒng)的阻力與風管風速的平方成正比高風速：風道截面積較小，系統(tǒng)造價低；

但系統(tǒng)阻力大，設(shè)備能耗大；

設(shè)備內(nèi)部易受磨損低風速：系統(tǒng)阻力小，設(shè)備能耗?。?/p>

風道截面積較大，系統(tǒng)造價高；

風速過低易導致粉塵沉積，堵塞風道

January12,202340FANLAWS

風機定律WHAT

DO

THE

FAN

LAWS

TELL

US?

風機定律告訴了我們什么？TherelationshipbetweenvolumetricairflowandHPiscubic風量和風機功率的關(guān)系是三次方的關(guān)系Therefore,todoubletheairflowyoumustincreasethehorsepowerby

因此，為了讓風量增加一倍，風機功率要變?yōu)樵瓉淼?倍CostforelectricityisproportionaltofanHP.

所需電費與風機功率成比例Illustratesimportanceofproperdesignandlowlosses說明優(yōu)化設(shè)計和低能量損失的重要性Pressure

壓力Forairtoflowtheremustbeapressuredifferenceandairwillflowfromthehigherpressuretothelowerpressure空氣的流動需要有壓力差,空氣從壓力高的位點移向壓力低的位點

Pressureisconsideredtohavetwoforms:壓力通常分為兩種:staticpressure(Ps)靜壓

velocitypressure(Pv)動壓Withthesumofthesebeingtotalpressure(Pt).

靜壓和動壓之和為全壓StaticPressure

靜壓Staticpressureisdefinedasthepressureexertedinalldirectionsbyafluidthatisstationary靜壓定義為靜止氣流向各個方向施加的壓力

Ifthefluidisinmotion(asisthecaseinaventilationsystem),staticpressureismeasuredat90°tothedirectionoftheflowsoastoeliminatetheinfluenceofmovement(ie:

velocity)如果氣流是運動的(如在通風系統(tǒng)中），靜壓為垂直于氣流運動方向測得的壓力，以消除氣流運動的影響（如風速）StaticPressure(Cont)

靜壓FAN(-)SUCTIONSIDE(+)PRESSURESIDECanbebothpositiveandnegativedependingifitismeasuredonthedischargeorsuctionsideofafan在風機的進風側(cè)為負壓，出風側(cè)為正壓。January12,202346VelocityPressure

動壓Definedasthatpressurerequiredtoaccelerateairfromzerovelocitytosomevelocityandisproportionaltothekineticenergyoftheairstream定義為將氣流速度從零加速到一定流速所需要的壓力，與氣流的動能成正比。

Insimpleterms,velocitypressureisthekineticenergygeneratedinaventilationsystemasaresultofairmovement簡單的說，動壓就是通風系統(tǒng)中氣流運動的能量的動能。VelocityPressure(cont)

動壓 =Densityofair(kgm-3)

v

=Airvelocityms-1 Pv=Velocitypressure(PaieNm-2)VelocityPressure(cont) Ifstandardtemperatureandpressureconditionsareinexistence,ie:

= 1.2kgm-3 Then Pv = 0.6v2Relationshipis:Pt=Ps+Pv

總壓=靜壓+動壓

全壓測定局部通風系統(tǒng)效果評估January12,202352

SmokeTubesIndicatingAirMovement

發(fā)煙管顯示氣流的運動

SmokeTubes

發(fā)煙管測量控制風速（非罩口風速）January12,202355MeasuringFaceVelocity

測量罩口風速（僅適用于密閉罩、半密閉罩）Hot-wireAnemometer

熱線風速儀

PitotTubes

皮托管（風管風速，動壓、靜壓測量）PitotTubeandManometerwithDigitalReadout

皮托管和壓力計

1.

Blockingoffhoodorinlet

排風罩或進氣口阻塞

2.Leakage(discolorationatseamand

turns)接合處或轉(zhuǎn)彎處漏風

3.Fanswiredincorrectly風機連接不當

4.Slippingdrivebelts傳動帶松弛

5.Burnedoutmotors電機燒毀IDENTIFYINGLEVPROBLEMS

識別局部排風系統(tǒng)存在的問題ReducedFlowRate風量降低的可能原因Pluggedordentedducts風管阻塞或管壁有凹陷Slippingfanbelts風機傳動帶松弛Openaccessdoors檢查門未關(guān)閉Holesinducts,elbows管道、彎道有漏洞Closedblastgatetobranch,oropenblastgatestootherbranches,orcorrodedandstuckblastgates調(diào)風閥關(guān)閉,或調(diào)風閥指向其它支道,或調(diào)風閥被腐蝕或受阻Fa