visualization of air flow around obstacles in laminar flow type clean room with laser light sheet

7/28/2019 Visualization of Air Flow around Obstacles in Laminar Flow Type Clean Room with Laser Light Sheet

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8 th INTERNATIONAL SYMPOSIUHON C O N T l ~ ' 1 : 1 N A T I O N CONTROL~ I L A : - I , S E P T , 9 , L O , 1 l an d 12,1986

Visualization of Air Flow around Obstacles in Laminar Flow TypeClean Room with Laser Light Sheet

S. AKABAYASHI*, S. tlURAKAtlI*, S. KAIO*, S. CHIRlFU***Institute of Industrial Science, University of Tokyo,7-22-1 Roppongi Minato-ku Tokyo l06,Japan**Takasago Thermal Engineering Co. ,Ltd.Kanda Chiyoda-ku Tokyo 101, Japan(Formerly Contract Researcher of Institut8of Industrial Science, University of Tokyo)

1.1 NTRODUCTI ONRecently, in such advanced technological areas as LSI factories orchemical industries, a clean room system has become indispensable equipmentfor precise control of airborne contaminants. The a ir flow in a laminar flowtype clean room is very simple when no apparatuses are set up or no operatorsare present. However there is much equipment and Inany operators in an actualclean room, and these generate dust into the a ir flow. Horeover, the a ir flowaround such apparatus or operators is usually highly turbulent and swirly andthus likely to contaminate manufacturing processes.I t is thus important to desi@l an a ir flow system which can exhaustthe dust generated in the room eff icient ly and which does not diffuse thedust into the larger area of the room. In a laminar flow type clean room, dust

is expected to be exhausted without diffusion by means of the plug flowsystem. But since the a ir flow is disturbed by the turbulence generated by theapparatus or operators, i t is essential that the characteristics of the a irflow around flow obstacles such as operators and apparatus be clarified.In this study a scale model of the laminar flow type clean room isused to visualize the a ir flow patterns in i t . Rectangular prism models withvarious shapes are used as simplified apparatus. For the flow visualization,a laser light sheet [1) ,2) 1 and fine magnesium carbonate powder are adoptedas the l ight source and the tracer respectively. The laser beam is scatteredby t racer part ic les and they are photographed and recorded on video tapes[3)J. Both standing vortexes and turbulent flow around apparatus are analyzedin detai l . Basic design data are obtained by observing the flow patternsaround apparatus of many shapes and arrangements.

2.DESCRIPTION OF EXPERIMENTAL METHOD2.1 Clean Room Model and Apparatus Mode!

Fig.l shows the 1/6 scale model of th e laminar flow type clean rOomwhose dimension is 6m(width)x6m(depth)x3m(height) in actual size. This modelis composed of a plenum chamber, an exhaust chamber, and a clean room. Partof the ceiling is made of a wire mesh and a perforated metal sheet so as tomodel a RITA f i l ter . The floor is made of honeycomb shapes and a perforated

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metal o:heet which is the model for a. f loor grating. In a l l experiments, thesupply a ir velocity a t the ceiling is se t a t about 0.35m/s, which is the sameas that of an actual size clean room. Consequently the Reynolds number of themodel clean room is 1/6 compared with that of the actual size clean room. I t',las confirmed in advance that reducing the Reynolds number has l i t t le affecton the a ir flow pattern.

.?;" ~ ~ ~ ~ L h , " ~ ~ I O " Lm'; ; 6 1 ~ : > - : ~ ~ h . (41


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(J ) Simple Rectangular Prism liadel and Side Flow Separations(Photo 1)... Photo 1 shows the a i r flow in a clean room model in which therectangular prism model i s ius ta l led a t the center of the f loor. The a ir flo'.4

co l l ides with the top surface of themodel. Then i t separates into two flowsand reaches to the. side walls. I t isclearly observed tha t the flow isseparated from the apparatus a t i t s topcorner. The separated flow reattachesto the side walls.. Stancing vortexes

lnducecl luto these vortexes \appear inside the ~ ~~ e p a r a t i o n . Contaminants ( ~ ) I . ~ \do not seem to be exhausted . ~easi ly . .Al>." Flow Pat-c,,,,,

(2) Effects of Corner Cl1tting(Photo 2).In order to decrease theseparated reg ion , the r i gh t corner ofthe top surface was cut off.. Photo 2shows that the separating point on th eright side wall moves down to the loweredge of the cut off plane .. But the sizeof separation does notchange. Consequently, bycutting off the top corner,i t is possible to lowe.r thepoint 'of separation apartfrom the top surface "hieh Air Flow Pat tcmis to be. clean.

0) Effect of Suction at Separating Area(Photo 3).In order t.o remove the separating area, a ir inlet.s are. se.t into th eupper side wall of the apparatus model. The size is 9S0mm(l.'idth)>


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3.2 Air Flow around Apparatus Adjacent to Wall

en Arranging Apparatus in Contact withi.1all(Photo 4).Ihe basic model is se t incontact with a wall. Photo 4 shows thatthe separation which occurs a t the r ightside wall is ju s t the same as that inphoto 'I. On the l e f t side of the topsurface, a standing vortex appears nearthe wall. If contaminants ~are dispersed in th i s J \ ~ ) \egion, they are not ))exhausted eas i ly .

Ai, f l o ~ Patt.ern

(2) Arranging Apparatus Apart from Wall(Photo 5).The basic model i s se t apar tfrom the wall. The distance between thewall and the apparatus is 100mm inactual size. The standing vortex abovethe upper surface near the walldisappears, so that contaminants can beexpected to be exhaustedsmoothly.

Ai,- flow Pat.tern

with Wall

Photo.S ArrQnging AppclrQtus Aped from Well!

3.3 Air Flow around Two Apparatuses

(D Arranging Two Apparatuses in Contactwith Each Other(Photo 6).Two basic models are arrangedin contact with each other . P h ~ t o 6shows t ha t the a ir flow is stagnantabove the center of the top surface andis highly turbulent. There are;.-____ ,standing vortexes a t theside walls of the apparatus.

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(2) Arranging Two Apparatuses with Some Distance(Photo 7) .Two basic models are arrangedwith a small gap between them whichreaches to the f loor exhaust. Thedistance between two apparatuses i slOOmm, Photo 7 shows that the a ir flowabove the center of the top surface isnot stagnant and is not turbulentcompared with the case ofPhoto 6. Contaminantsgenerated a t the top surfacewill thus be exhaustedimmediately. Air flow Patten> Pho to ]O)Arranging Two Apparatuses of DifferentHeights in Contact with Each Other(PhotD 8).Two apparatuses of dilfer-eutheights are arranged in contac t witheach other. One i s 1, 400mm in height( l e f t ) , the other i s 600mm in height(rigbt) . Photo 8 shows thea ir flow around the twomodels. A standing vortexappears on the right side ofthe ta l ler one. The a ir flowis stagnant above the topsurface of lower one.

(4) Arranging Two Apparatuses of DifferentHeights Separately{Photo 9}.Photo 9 shows the a ir flowaround two models. As compared withPhoto 8, the standing vortex on ther ight 5 ide of the ta l l e r one becomesmuch smaller and nostagnation occurs above thetop surface of the lower

one.

Arranging Two Apparatuses. Separately

Arrcmging Two Appordus8s SepQnde/y3.4 Air F[ow Influenced by Operator Standlng near th e Apparatus

CD Case where Operator Stands UprightBeside Apparatus(Photo lO}.Photo 10 shows the a ir flowaround the operator and the apparatus.The a ir flow on the l e f t side of theapparatus is different from that on ther ight side. The a ir flow around the.operator is smooth and isnot very turbulent.

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(2) Case where Operator Bends Over Apparatus(Photo 11).Photo 11 shows the a i r flowaround the operator and the apparatus.The a i r flow around the operator isturbulent and a standing vortex appearsbetween the top surface of the apparatusand the operator. On the r ight s ide

wall t.here i s no effec t from r - - ~ ~ c - ,the operator and the a ir flowpattern i s also the same asthat of the basic model(Photo 1).

3.5 Ai r Flow Disturbed by Obstacle ot Ceiling(1) Flow Obstacle a t Ceiling(Photo 12).

The flow obstacle, whichrepresents some kinds of l ightingfixtures or ceil ing beams, i s installeda t the cei l ing. Photo 12 shows tha tturbulence is generated by the obstaclea t the ceil ing and i t s scale ~ ~ I O O . ..and intensi ty is maintained ~ ~ a \ 'Iat the floor level. ~

Ai r flow Pntte""

(2) Install ing Apparatus inside TurbulentWake of Obstacle a t Ceiling(Photo 13).The basic model i s set insidethe wake of the obstacle a t the ceiling.The standing vortex above the topsurface of the apparatus becomes muchlarger in this case and i t is extremelyturbulent . ~ o o ~ u

ot Ceiling

Ai r F l o ~ Pattern Photo.13 Turbulence Generoted ot Ceiling.Colliding with Apparatus SurftlcG

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3.6 Turbu!ence Generated by TableTo analyze the air flow aroundmore complicated apparatus, the flowaround a table is visualized as anexample. The a ir flow pattern above the

top surface of the table is nearly equalto that of the basic model. but underthe table the flow is highly turbulent.

4. CONCLUS IONSThe a ir flow in a laminar flow type clean room is analyzed by meansof the laser l ight sheet visualization system. The results are as follows.

(1) The a ir flow is separated at the corners of the top surface of therectangular prism model. Contaminants which are induced into the inside of theseparation do not seem to be exhausted smoothly.(2) Suction at the separating area is very effective in removing theseparation.0) When the apparatus i s se t in contact with the wall, a standing vortexappears above the top surface. To exhaust contaminants smoothly i t isdesirable to set the apparatus apart from the wall.(4) When two apparatuses are arranged in contact, a stagnant region appearsabove the top surface. Just as in 0), i t is desirable to arrange the twoapparatuses separately.When an operator is standing upright beside an apparatus, the a ir flowaround the apparatus is not influenced by the operator. When an operator isbending over an apparatus, standing vortex appears between the top surfaceof the apparatus and the operator.(6) Turbulence generated by obstacles at the ceil ing is maintained at thefloor.m The a ir flow in the space beneath an apparatus such as a table is highlyturbulent and the contaminants here do not seem to be exhausted smoothly.

REFERENCES1 )Maile, H. , ,"METHODE DE VISUALISATION QUANTITATIVE PAR CHRONOPHOTOGRAPHIELASER", Proc. Colloque., Designing with the Wind, Nantes, IX3-1-3-7,P981)2)Balint, J . t . , and ti .Ayrault,et aI, : "l:1easurement. of "t;he ~ n c e n t r ~ t l . O n .o fAerosol Particles in Turbulent Flows through Laser Vlsuallzatl0n Comblned wlthImage Processing", 6th International Symposium on Contaminantion Control, 105-108,(1982) .3)l1urakamLS . S.Kato, S.Akabayashi, : "Visualization with Laser bgh t SheetApplied to Internal and External Air Flow in Building EnvironmentalEngineering", Fluid Control & l1esurement 691-696, (1985) . .4)l1urakami, S., S.Kato, S.Chirifu,: "Visualization of Air Flow 1n Lamnar FlowType Clean Room with Laser Light Sheet",Journal of the Flow VisualizationSociety of Japan, Vo1.5,No.18 229-234,(1985)

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visualization of air flow around obstacles in laminar flow type clean room with laser light sheet

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