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Hoc lieu Mo Vietnam - Vietnam Open Educational Resources module: m13176 1
THIT K H THNG VNCHUYN V PHAN PHI KHNG
KH
V Ch Chnh
This work is produced by Hoc lieu Mo Vietnam - Vietnam Open Educational Resources and licensed under the
Creative Commons Attribution License
Tm tt ni dung
THIT K H THNG VN CHUYN V PHAN PHI KHNG KH
1 THIT K H THNG VN CHUYN V PHAN PHI KHNG KHH thng phn phi v vn chuyn khng kh bao gm cc phn nh sau:
- H thng ng ng gi- H thng cc ming thi v ht
- Qut gi.
1.1 THIT K H THNG KNH GI
Trong h thng iu ho khng kh h thng knh gi c chc nng dn v phn gi ti cc ni khc nhautu theo yu cu.
Nhim v ca ngi thit k h thng knh gi l phi m bo cc yu cu c bn sau :- t gy n .- Tn tht nhit nh.- Tr lc ng ng b.- ng ng gn, p v khng lm nh hng m quan cng trnh.- Chi ph u t v vn hnh thp.- Tin li cho ngi s dng.- Phn phi gi cho cc h tiu th u.
1.1.1 H thng knh gi
1.1.1.1 phn lai
ng ng gi c chia lm nhiu loi da trn cc c s khc nhau :* Theo chc nng :
Version 1.1: Jul 24, 2010 10:12 am GMT+7http://creativecommons.org/licenses/by/3.0/
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Theo chc nng ngi ta chia h thng knh gi ra lm cc loi ch yu sau :- Knh cp gi (Supply Air Duct - SAD)- Knh hi gi (Return Air Duct - RAD)
- Knh cp gi ti (Fresh Air Duct)- Knh thng gi (Ventilation Air Duct)- ng thi gi (Exhaust Air Duct)* Theo tc gi :Theo tc ngi ta chia ra loi tc cao v thp, c th nh sau :Bng 6-1
Figure 1
* Theo p sutTheo p sut ngi ta chia ra lm 3 loi : p sut thp, trung bnh v cao nh sau :- p sut thp : 95 mmH2O- p sut trung bnh : 95 -> 172 mmH2O
- p sut cao : 172 -> 310 mmH2O* Theo kt cu v v tr lp t :- Knh gi treo- Knh gi ngm
1.1.1.2 H thng knh gi ngm
- Knh thng c xy dng bng gch hoc b tng v i ngm di t. Knh gi ngm thng kt hpdn gi v lp t cc h thng ng nc, in, in thoi i km nn gn gng v tit kim chi ph nichung.
- Knh gi ngm c s dng khi khng gian lp t khng c hoc vic lp t cc h thng knh gitreo khng thun li, chi ph cao v tun hon gi trong phng khng tt.
- Knh gi ngm thng s dng lm knh gi hi, rt t khi s dng lm knh gi cp do s nh hng
cht lng gi sau khi x l do m mc trong knh, c bit l knh gi c hot ng lu ngy. Khixy dng cn phi x l chng thm knh gi tht tt.- Knh thng c tit din ch nht v c xy dng sn khi xy dng cng trnh.- H thng knh gi ngm thng c s dng trong cc nh my dt, rp chiu bng. Cc knh gi
ngm ny c kh nng thu gom cc si bng to iu kin kh bi trong xng tt. V vy trong cc nhmy dt, nh my ch bin g thu gom bi ngi ta thng hay s dng h thng knh gi kiu ngm.
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1.1.1.3 H thng ng kiu treo.
H thng knh treo l h thng knh c treo trn cc gi t trn cao. Do yu cu i vi knhgi treo l :
- Kt cu gn, nh- Bn v chc chn- Dn gi hiu qu, thi cng nhanh chng.V vy knh gi treo c s dng rt ph bin trn thc t (hnh 6.1).
Figure 2
1- Trn b tng 5- Thanh st 2- Thanh treo 6- Bng thu tinh cch nhit3- on ren 7- ng gi4- Bu lng + ai c 8- Vt nHnh 6.1 : H thng knh gi treo
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Figure 3
* Vt liu s dng : Tole trng km, inox, nha tng hp, foam nh hnh.Trn thc t s dng ph bin nht l tn trng km c b dy trong khong t 0,5 - > 1,2mm theo tiu
chun qui nh ph thuc vo kch thc ng ng. Trong mt s trng hp do mi trng c n mncao c th s dng cht do hay inox. Hin nay ngi ta c s dng foam lm ng ng : u im nh, nhng gia cng v ch to kh, do c im kch thc khng tiu chun ca ng ng trn thc t.
Khi ch to v lp t ng gi treo cn tun th cc qui nh v ch to v lp t. Hin nay Vitnam vn cha c cc qui nh c th v thit k ch to ng ng. Tuy nhin chng ta c th tham khocc qui nh cc ti liu nc ngoi nh DW142, SMACNA. Bng 6.2 trnh by mt s qui cch v chto v lp t ng ng gi.
Bng 6.2 : Cc qui nh v gia cng v lp t ng gi* Hnh dng tit din :Hnh dng knh gi rt a dng : Ch nht, trn, vung, . .vv. Tuy nhin, knh gi c tit din hnh ch
nht c s dng ph bin hn c v n ph hp vi kt cu nh, d treo , ch to, bc cch nhit vc bit cc chi tit ct, xuyt, chc 3, chc 4 . .vv d ch to hn cc kiu tit din khc.
* Cch nhit: trnh tn tht nhit, ng ng thng bc mt lp cch nhit bng bng thy tinh,hay stirofor, bn ngoi bc lp giy bc chng chy v phn x nhit. trnh chut lm hng ngi ta cth bc thm lp li st mng.
- Khi ng ng i ngoi tri ngi ta bc thm lp tn ngoi cng bo v ma nng
- ng ng i trong khng gian iu ha c th khng cn bc cch nhit. Tuy nhin cn lu khi hthng mi hot ng, nhit trong phng cn cao th c kh nng ng sng trn b mt ng.* Ghp ni ng:- tin cho vic lp rp, ch to, vn chuyn ng ng c gia cng tng on ngn theo kch c
ca cc tm tn. Vic lp rp thc hin bng bch hoc bng cc np tn. Bch c th l nhm c, st Vhoc bch tn.
* Treo :- Vic treo ng ng ty thuc vo kt cu cng trnh c th : Treo tng, trn nh, x nh .- Khi ni knh gi vi thit b chuyn ng nh qut, ng c th cn phi ni qua ng ni mm kh
chn ng theo knh gi.
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- Khi kch thc ng ln cn lm gn gia cng trn b mt ng gi.- ng ng sau khi gia cng v lp rp xong cn lm kn bng silicon.
1.1.2 Thit k h thng knh gi1.1.2.1 Cc c s l thuyt
Quan h gia lu lng v tc gi ra ming thi.Nhim v ca ngi thit k h thng knh gi l phi m bo phn b lu lng gi cho cc ming
thi u nhau. Gi s tt c cc ming thi c kch c ging nhau, lu lng gi ra cc ming thi bngnhau ta ch cn khng ch tc gi trung bnh cc ming thi bng nhau l c.
Lu lng gi chuyn ng qua cc ming thi c xc nh theo cng thc:
Figure 4
(6-1)gx - Lu lng gi ra mt ming thi, m3/sfx - Tit din thot gi ca ming thi, m2.vx - Tc trung bnh ca gi ra ming thi, m/sQuan h gia ct p tnh trn ng v vn tc khng kh ra cc ming thi .Tc trung bnh vx u ra ming thi c tnh theo cng thc :
Figure 5
(6-2)Thc ra do b nn p khi ra khi ming thi nn tit din b gim v nh hn tit din thot gi thc.Theo nh lut Becnuli p sut tha ca dng khng kh (cn gi l p sut tnh H t) chuyn thnh
ct p ng ca dng khng kh chuyn ng ra ming thi :
Figure 6
px, l p sut tuyt i ca dng khng kh trong ng dn trc ming thi, N/m2po l p sut khng kh mi trng ni gi thi vo, N/m2beta H s thu hp dng ph thuc iu kin thi ra ca dng khng khHt - Ct p tnh ti tit din ni t ming thi , N/m 2(6-3) T rt ra :
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Figure 7
Theo (6-1) v (6-3) c th nhn thy m bo phn b gi cho cc ming thi u nhau ngi thitk phi m bo p sut tnh dc theo ng ng khng i l c.
V vy thay v kho st tc ra ming thi v x (hay gx vtit din ca cc ming thi u nhau) ta khost phn b ct p tnh Ht dc theo ng ng xem xt vi iu kin no phn b ct p tnh s ngu trn ton tuyn ng.
S phn b ct p tnh dc ng ng dn gi.Xt mt ng ng gi, tc gi trung bnh v ct p tnh ca dng khng kh ti tit din c mingthi u tin l mega1 v H1 , ca ming thi th 2 l mega2 v H2 ... v ca ming thi th n l meganv Hn (hnh 6-2).
Tr khng thy lc tng ca ng ng l tngdeltapTheo nh lut Becnuli ta c :
Figure 8
(6-4)
Figure 9
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Hnh 6.2 : Phn b ct p tnh dc theo knh giHay:
Figure 10
T suy ra :
Figure 11
(6-5)Thnh phn p(mega21 - mega2n)/2 gi l gim ct p ng.Nh vy duy tr ct p tnh trn tuyn ng khng i deltaH =0 ta phi thit k h thng knh gi
sao cho p(mega21 - mega2n)/2 - tngdeltap = 0Ta c cc trng hp c th xy ra nh sau:Trng hp p(mega21 - mega2n)/2 = tngdeltap : Gim ct p ng bng tng tn tht trn tuyn
ng.Nh vy ct p ng bin mt phn b vo tn tht trn tuyn ng.
Khi : H1 = Hn ngha l ct p tnh khng thay i dc theo ng ng. y l trng hp l tng,tc v lu lng cc ming thi s u nhau.Trng hp p(mega 2 1 - mega 2 n )/2> tngdeltap hay H 1 < H nGim ct p ng ln hn tng tn tht p lc trn tuyn ng.Trong trng hp ny ta c Hn > H1 , phn ct p ng d tha gp phn lm tng ct p tnh cui
ng ng, lng lng gi cc ming thi cui ln hn, hay gi dn vo cui tuyn ng.Trng hp ny c th xy ra khi :- Tc on u qu ln, nn p sut tnh trn trong ng rt nh trong khi tc on cui nh.
Trong mt s trng hp nu tc i ngang qua tit din ni lp cc ming thi on u qu ln thcc ming thi u c th tr thnh ming ht lc to nn hin tng ht kiu EJect. khc phc,cn gim tc on u, tng tc on cui. V th khi lu lng dc theo knh gi gim th phi gimtit din tng ng duy tr tc gi, trnh khng nn tc gim t ngt .
- ng ng ngn, t tr lc cc b nhng c nhiu ming thi hoc on r nhnh. Trng hp ny tr
lc tngdeltap rt nh, nhng tc gim nhanh theo lu lng. khc phc cn gim nhanh tit dinon cui nhm khng ch tc ph hp.Trng hp p(mega 2 1 - mega 2 n )/2< tngdeltap hay H 1 > H nGim ct p ng nh hn tng tn tht p lc trn tuyn ng.Trong trng hp ny gi tp trung vo u tuyn ng.Nguyn nhn gy ra c th l:- Tc on u nh, p sut tnh ln nn lu lng gi ca cc ming thi u ln v cui tuyn ng
lu lng khng ng k.- Tn tht ng ng qu ln : ng ng qu di, c nhiu ch khc khuu.
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- Tit din ng ng c gim qu nhanh khng tng ng vi mc gim lu lng nn tc dctheo tuyn ng gim t, khng gim thm ch cn tng. V th ct p tnh u tuyn ng ln hn cui tuynng.
V vy khi thit k ng ng cn phi ch :- Thit k gim dn tit din ng ng dc theo chiu thi mt cch hp l , tu thuc vo tr lc cang ng.
S phn b ct p tnh trn ng ng ht.Xt mt knh ht, tc trung bnh v ct p tnh ca dng khng kh ti tit din c ming ht u
l mega1 v H1 , ca ming ht th 2 l mega2 v H2 ... v ca ming ht th n l megan v Hn .Tr khng thy lc tng ca ng ng l tngdeltapHnh 6.3 : Phn b ct p tnh dc theo knh htTheo nh lut Becnuli ta c :
Figure 12
Hay:
Figure 13
Hay :
Figure 14
(6-6)
deltaH = 0 ta phi m bo : p(mega21 - mega2n)/2 - tngdeltap = 0Hay ni cch khc tc gi dc theo chiu chuyn ng ca dng khng kh phi gim dn v mc gim phi tng ng vi mc tng tn tht tngdeltap.
Do lu lng dc theo chiu chuyn ng ca gi trong knh ht tng dn v tc gi cng phi gimdn , v th tit din knh ht phi ln dn.
1.1.2.2 Mt s vn lien quan ti thit k ng ng
La chn tc khng kh trn ng ngLa chn tc gi c lin quan ti nhiu yu t.
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Figure 16
a, b l cnh ch nht, mmTuy tn tht ging nhau nhng tit din trn 2 ng khng ging nhau
Figure 17
- ng knh tng ng ca ng van:A - Tit din ng van :
Figure 18
Figure 19
a, b l cnh di v cnh ngn ca van, mmp L chu vi mt ct : p = .b + 2(a-b), mmBng 6-4 : ng knh tng ng ca ng ch nht
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Figure 21
Tn tht p sut trn ng ng giC 2 dng tn tht p lc:- Tn tht ma st dc theo ng ng deltapms- Tn tht cc b cc chi tit c bit : Cn, ct, t, van ...Tn tht ma stTn tht ma st c xc nh theo cng thc :
Figure 22
- H s tr lc ma stl - chiu di ng, md - ng knh hoc ng knh tng ng ca ng, mp - Khi lng ring ca khng kh, kg/m3
mega - Tc khng kh chuyn ng trong ng , m/sH s tr lc ma st c th tnh nh sau :
i vi ng nhm hoc tn mng b mt bn trong lng v tit din trn
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Figure 23
Figure 24
trong :Re l tiu chun Reynolds : Re = megad/ - nht ng hc ca khng kh , m2/s* i vi b mt nhm
Figure 25
k1 l h s mc g gh trung bnh, mBng 6-5
Figure 26
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i vi ng bng nha tng hp
-i vi polyetilen
Figure 27
-i vi vinylpast
Figure 28
Vic tnh ton theo cc cng thc tng i phc tp, nn ngi ta xy dng th xc tn thtma st, c th nh sau:
T cng thc (6-9) ta c th vit li nh sau :
Figure 29
l - Chiu di ng ng, mdeltap1 - Tn tht p lc trn 1m chiu di ng ng, Pa/mNgi ta xy dng th nhm xc nh deltap1 trn hnh 6.4. Theo th ny khi bit 2 trong cc
thng s sau : lu lng gi V (lt/s), tc khng kh mega (m/s) trong ng ng, ng knh tngng dt (mm) l xc nh c tn tht trn 1m chiu di ng ng. Phng php xc nh theo thrt thun li v nhanh chng.
Hnh 6-4 : th xc nh tn tht ma stTn tht cc bTn tht p lc cc b c xc nh theo cng thc:
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Figure 30
Tr s C tr lc cc b ph thuc hnh dng, kch thc v tc gi qua chi tit.Nu tc trn ton b ng u th c th xc inh
Figure 31
.C 2 cch xc nh tn tht cc b :- Xc nh tn tht cc b theo cng thc (6-16), trong h s C c xc nh cho tng kiu chi tit
ring bit: Ct, cn, T, Chc ...vv
Figure 32
- Qui i ra di ng thng tng ng v xc nh theo cng thc tn tht ma st:
Figure 33
Di y chng ti ln lt gii thiu cch tnh tn tht cc b theo 2 cch ni trn.Xc nh h tn tht cc b theo h s C
Figure 34
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deltapcb - Tn tht tr lc cc b , N/m2C - H s tr lc cc b.p - Khi lng ring ca khng kh. Ly p = 1,2 kg/m 3
mega - Tc gi i qua chi tit nghin cu , m/sCt tit din trn
Figure 35
Hnh 6-5: Ct tit din trnCt tit din trn c cc dng ch yu sau:- Ct 90o tit din trn, cong u- Ct 90o tit din trn, ghp t 3->5 on- Ct 90o ni thng gc- Ct tit din trn alfao cong u hoc ghp.- Ct 90 o , tit din trn, cong u .H s tr lc cc b C c tra theo t s R/d bng 6.6 di y:R - Bn knh cong tm ct ng, md - ng knh trong ca ng, mBng 6.6 : H s
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Figure 36
i vi ct khc 90o cn nhn h s hiu chnh K cho bng 6.7 di y:Bng 6.7 : H s xt ti nh hng ca gc ct
fi 0o 20o 30o 45o 60o 75o 90o 110o 130o 150o 180o
K 0 0,31 0,45 0,60 0,78 0,90 1,00 1,13 1,2 1,28 1,4Table 1
. Ct 90 o , tit din trn, ghp t 3-5 onBng 6.8 : H s
Figure 37
R - Bn knh cong tm ct ng, md - ng knh trong ca ng, mCt tit din trn, ghp thng gcBng 6.9 : H s C
Figure 38
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alfa- Gc ca ctCt tit din ch nht
Figure 39
Hnh 6-6: Ct tit din ch nhtTrn hnh 6-6 l cc dng ct tit din ch nht c th c.- Trng hp 1 : Ct 90o, tit din ch nht, cong u. Yu cu k thut l bn knh trong R1 tu chn,
nhng khng nn qu b. Ti u l R1= 0,75W , R2=1,75W v R = 1,25W- Trng hp 2 : Ct 90o, thng gc v khng c cnh hng. Loi ny t dng trn thc t.- Trng hp 3 : Ct 90o, thng gc v c cc tm hng dngcnh n vi bc cnh l S, on thng
ca cnh l L- Trng hp 4 : Ct 90 o , thng gc v c cc cnh hng dng kh ng, bc cnh S, bn knh
cong ca cnh l R.Ct 90 o , tit din hnh ch nht , cong uR - Bn knh cong tm ct ng, mmH - Chiu cao ca ct (khi t nm), mm
W - Chiu rng ca ct : W = R 2 - R1R1, R2 - Bn knh trong v ngoi ca ct, mmBng 6.10 : H s C
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Figure 42
trong :
R - Bn knh cong ca cnh hng, mmS- Bc cnh hng, mmL- di phn thng ca cnh hng, mm* S liu tham khoCt 90 o , tit din ch nht, thng gc, c cnh hng i (dng kh ng)Bng 6.13 : H s C
Figure 43
trong :R- Bn knh cong ca cnh hng, mmS - Bc cnh, mm
htt // d / t t/ 13176/1 1/