CHNG 7 TNH TON THIT K H THNG

NG NG DN NC Trong cc k thut iu ho khng kh c s dng cc loi ng ng nc nh sau : - ng ng nc gii nhit cho cc thit b ngng t. - ng ng nc lnh lm lnh khng kh. - ng ng nc nng v hi bo ho si m khng kh - ng ng nc ngng.

Mc ch ca vic tnh ton ng dn nc l xc nh kch thc hp l ca ng ng, xc nh tng tn tht tr lc v chn bm. lm c iu cn phi bit trc lu lng nc tun hon. Lu lng c xc nh t cc phng trnh trao i nhit.

7.1 H thng ng ng dn nc * Vt liu ng ng : Ngi ta s dng nhiu loi vt liu khc nhau lm ng ng c th nh sau : Bng 7-1 : Vt liu ng dn nc

Chc nng Vt liu

1. ng nc lnh chiller - Thp en hoc thp trng km - ng ng cng

2. ng nc gii nhit v nc cp

- ng thp trng km - ng ng cng

3. ng nc ngng hoc x cn

- ng thp trng km - ng ng cng - ng PVC

4. Bo ho hoc nc ngng bo ho

- ng thp en - ng ng cng

5. Nc nng - ng thp en - ng ng cng

* c tnh ca ng ng thp Cc loi ng thp en thng c s dng dn nc c nhiu loi vi dy mng khc nhau. Theo mc dy ngi ta chia ra lm nhiu mc khc nhau t Schedul 10 n Schedul 160. Trn bng 7-2 cc loi ng k hiu ST l ng c dy tiu chun, cc ng XS l loi ng c chiu dy rt ln Bng 7-2 : c tnh ca ng ng thp

ng knh danh

ngha in mm

ng knh trong mm

ng knh ngoi mm

p sut lm vic at

Loi

1 / 4 1 / 4 3/8 3/8 1 / 2

6,35 6,35 9,525 9,525 12,7

9,245 7,67 12,52 10,74 15,798

13,716 13,716 17,145 17,145 21,336

13 61 14 58 15

40ST 80XS 40ST 80XS 40ST

159

1 / 2 3 / 4 3 / 4

1 1

1.1/4 1.1/4 1.1/2 1.1/2

2 2

2.1/2 2.1/2

3 3 4 4 6 6 8 8 8 10 10 10 12 12 12 12 14 14 14 14

12,7 19,05 19,05 25,4 25,4 31,75 31,75 38,1 38,1 50,8 50,8 63,5 63,5 76,2 76,2 101,6 101,6 152,4 152,4 203,2 203,2 203,2 254 254 254

304,8 304,8 304,8 304,8 355,6 355,6 355,6 355,6

13,868 20,93 18,46 26,64 24,3 35,05 32,46 40,98 38,1 52,5 49,25 62,71

59 77,927 73,66 102,26 97,18 154,05 146,33

205 202,171 193,675 257,45 254,5 247,65 307,08 303,225 298,45 288,95 336,55 333,4 330,2 317,5

21,336 26,67 26,67 28,83 28,83 42,164 42,164 48,26 48,26 60,325 60,325 73,025 73,025 88,9 88,9 114,3 114,3

168,275 168,275 219,07 219,07 219,07 273,05 273,05 273,05 323,85 323,85 323,85 323,85 355,6 355,6 355,6 355,6

53 15 48 16 45 16 42 16 40 16 39 37 59 34 54 30 49 49 85 37 45 78 34 43 62 32 41 53 76 34 41 48 76

80XS 40ST 80XS 40ST 80XS 40ST 80XS 40ST 80XS 40ST 80XS 40 ST 80XS 40ST 80XS 40ST 80XS 40ST 80XS

30 40ST 80XS

30 40ST 80XS 30ST

40 XS 80

30 ST 40 XS 80

ng ng ng c chia ra cc loi K, L, M v DWV. Loi K c b dy ln nht, loi

DWV l mng nht. Thc t hay s dng loi L. Bng 7-3 trnh by cc c tnh k thut ca mt s loi ng ng khc nhau. Bng 7-3 : c tnh ca ng ng ng

ng knh danh ngha

in mm Loi ng knh

trong, mm ng knh ngoi, mm

1.1/4 1.1/2

2 3 4 5

31,75 38,1 50,8 76,2 101,6 127

DWV DWV DWV DWV DWV DWV

32,89 39,14 51,84 77,089 101,828 126,517

34,925 41,275 53,975 79,375 104,775 130,185

160

6 8 8 8 8 10 10 10 12 12 12

152,4 203,2 203,2 203,2 203,2 254 254 254

304,8 304,8 304,8

DWV K L M

DWV K L M K L M

151,358 192,6

196,215 197,74 200,83

240 244,475 246,4 287,4 293,75 295,07

155,57 206,375 206,375 206,375 206,375 257,175 257,175 257,175 307,975 307,975 307,975

* S gin n v nhit ca cc loi ng ng

Trong qu trnh lm vic nhit ca nc lun thay i trong mt khon tng i rng, nn cn lu ti s gin n v nhit ca ng ng c cc bin php ngn nga thch hp.

Trn bng 7-4 l mc gin n ca ng ng ng v ng thp, so vi trng thi 0oC. Mc gin n hu nh t l thun vi khong thay i nhit . b gin n trong k thut iu ho ngi ta s dng cc on ng ch U, ch Z v ch L.

Bng 7-4 : Mc gin n ng ng

Mc gin n, mm/m Khong nhit

ng ng ng thp 0 10 20 30 40 50 60 70

0 0,168 0,336 0,504 0,672 0,840 1,080 1,187

0 0,111 0,223 0,336 0,459 0,572 0,684 0,805

Ngoi phng php s dng cc on ng nu trn , trong thc t b gin n ngi

ta cn s dng cc ron gin n, dng ng mm cao su nu nhit cho php. * Gi ng ng

treo ng ng ngi ta thng s dng cc loi st ch L hoc st U lm gi . Cc gi phi m bo chc chn, d lp t ng ng v c khu hp l. Khi khu nh th s lng gi tng, chi ph tng. Nu khu ln ng ng s vng, khng m bo chc chn. V th ngi ta qui nh khong cch gia cc gi . Khong cch ny ph thuc vo kch thc ng ng, ng ng cng ln khong cch cho php cng ln.

Bng 7-5 : Khu hp l ca gi ng thp

ng knh danh ngha ca ng , mm

Khu m

T 19,05 31,75 38,1 63,5 76,2 88,9

2,438 3,048 3,657

161

101,6 152,4 203,2 n 304,8 355,6 n 609,6

4,267 4,877 6,096

Bng 7-6 : Khu hp l ca gi ng ng

ng knh danh ngha ca ng , mm

Khu m

15,875 22,225 28,575 34,925 53,975 66,675 130,175 155,575 206,375

1,829 2,438 3,048 3,657 4,267

7.2 Tnh ton ng ng dn nc v chn bm 7.2.1 Lu lng nc yu cu

Lu lng nc yu cu c xc nh tu thuc trng hp c th - Nu nc s dng gii nhit bnh ngng my iu ho

Kp

kn tC

QG = . (7-1)

- Lu lng nc lnh

Op

OkNL tC

QG = . (7-2)

- Lu lng nc nng

NNp

SINN tC

QG = . (7-3)

trong : Qk, Qo v QSI - Cng sut nhit bnh ngng, cng sut lnh bnh bay hi v cng sut

b gia nhit khng kh, kW. tn, tNL, tNN - chnh nhit nc vo ra bnh ngng, bnh bay hi v b sy.

Thng t 3 5 oC. Cp - Nhit dung ring ca nc, Cp 4186 J/kg.oC.Dc theo tuyn ng lu lng thay i v vy cn phi thay i tit din ng ng mt

cch tng ng.

7.2.2 Chn tc nc trn ng ng Tc ca nc chuyn ng trn ng ng ph thuc 2 yu t

- n do nc gy ra. Khi tc cao n ln , khi tc nh kch thc ng ng ln nn chi ph tng - Hin tng n mn : Trong nc c ln cn bn nh ct v cc vt khc , khi tc cao kh nng m mn rt ln

162

Bng 7-7 : Tc nc trn ng ng

c ca nc Trng hp T- u y ca bm - u ht ca

ng ln g hp thng thng

2,4 3,6 bm

- ng x - ng gp - ng h- Cc trn- Nc thnh ph

1,2 2,1 1,2 2,1 1,2 4,5 0,9 3,0 1,5 3

0,9 2,1

7.2.3. Xc nh ng knh ng dn n hnh xc nh ng knh

trong ca ng nh sau :

trong : V- Lu lng th tch nc chuyn ng ang tnh, m3/s

ng ring ca nc, kg/m3

ng 7-7, m/s

.2.4. Xc nh tn tht p sut ng

- Phng php xc nh theo cng thc

t p sut theo cng thc

-5)

trong

* H s tr lc ma st - Khi chy tng Re = d/ 104 :

..dlpms = 2

163

2..

22.

2dl

p tdcb ==

mVd ,..4=

Re64=

2)64,1Relog82,1( =

(7-4)

(7-6)

(7-8)

(7-9)

(7-7)

1

* H o bng 7-8.

Bng 7-8 : H s ma st

H s

s ma st cc b ly the

V tr - T- Qua van - Ct 45o tiu

o ong ln h

75% 50%

0% 0%

0,5 2 3

bnh vo ng

chunn- Ct 90 tiu chu

- Ct 90o bn knh c- Ch T n, hnh chn- Ch T, Nhnh ph - Qua ng tht - Qua ng m - Khp ni - Van cng m 100% m m m 25% - Van cu c m 10 m 5

0,35 0,75 0,45 0,4 1,5 0,1 0,25 0,04 0,20 0,90 4,5 24,0 6,4 9,5

i vi on ng m t cc b c th theo cng thc sau :

trong : A1, A2 - ln lt l tit din a ng

ng hp ng ng thu hp t ngt th h s tr lc ma st c th tra theo bng 7-9. Cn n ng c ng knh nh.

rng t ngt, h s tn th tnh

21 A2

1[ =

A (7-10)

u vo v u ra c

Trlu l tc dng tnh tn tht trong trng hp ny l o Bng 7-9 : H s ma st on ng t m

T s A2/A1 H s 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

0,37 0,35 0,32 0,27 0,22 0,17 0,10 0,06 0,02

0 * Xc nh tr lc cc b bng di ng

xc nh tr lc cc b ngoi c c nh nh h r lc cc b , ngi ta cn c i ra tn tht ma st tng v ng vi n l chiu di tng ng.

ng ng nc.

tng ch xng

t scch qui

Di y l chiu di tng ng ca mt s thit b

164

Bng 7- 10 : Chiu di tng ng ca cc loi van (mt ng ng)

knh in

60 Y Y gc ca chiu mt c Y ren

Van 1 chiu nng

ng Van cu Van o

Van 45o Van Van Van 1 Lc Y L

lt bch 3/8

2

5,180

6,705 8,839

2,438

4,572

1,829

2,743 3,657

1,829

2,743 3,657

0,183 0,213 0,274 0,305

1,524

3,048

-

8,229 8,534 12,800 14,630

-

1,219 1,524 2,743

Van 1

Van 1 cd g gc

1/2 3/4 1

11/411/22 1/2

3 31/24 5 6 8 10 12 14 16 18 20 24

5,486

11,582 13,106 16,764 21,031 25,603 30,480 36,576 42,672 51,816 67,056 85,344 97,536 109,728 124,968 140,208 158,496 185,928

2,743 3,353

6,096 7,315 9,144 10,668 13,106 15,240 17,678 21,641 26,882 35,052 44,196 50,292 56,388 61,010 73,152 83,820 97,536

2,134

4,572 5,486 7,315 8,839 10,668 12,496 14,325 17,678 21,336 25,910 32,000 39,624 47,240 54,864 60,960 71,628 80,772

2,134

4,572 5,486 7,315 8,839 10,66812,49614,32517,67821,33625,91032,00039,62447,24054,86460,96071,62880,772

0,457 0,548 0,701 0,853 0,975 1,219 1,372 1,829 2,134 2,743 3,657 3,692 4,572 5,182 5,791 6,705 7,620

1,829 2,438

4,267 4,877 6,096 7,620 9,144 10,66812,19215,24018,28824,38430,48036,57641,14845,72050,29260,96073,152

- - - - -

18,288 23,380 33,528 45,720 57,192 76,200

- - - - -

0,914

3,048 4,267 6,096 12,192

- - - - - - - - - - - -

chiu dng cu

ging van cu

hiu n

ging van gc

B 7- 1 g t

T

ng 1 : Chiu di tn ng c a T, c

ng chnh ng

knh Ct 90o

Ct 90di

Ct 90o

ngoi

Ct 45o

Ct 45ren

g

Ct 180o chun

ng nhnh

d khng i

d gim 25%

d gim 50%

o o

in chun ren trong

chun tronren

ren ngoi

3/8 1/2 3/4 1

0,609 0,792

0 0,305 0,427 0,518

0

0,274 0,396

0,975 1,250 1,524

0,

0 0,701 0,792 11/411/22

21/23 1/234 5 6 8

10 12 14 16 18

0,427 0,487

1,006 1,219 1,524 1,829 2,286 2,743 3,048 3,692 4,877 6,096 7,620

9,1144 10,363 11,582 12,800

,274

0,701 0,792 1,006 1,249 1,524 1,798 2,042 2,500 3,050 3,692 4,877 5,791 7,010 7,925 8,839

,7010,762 0 ,9751,250 1,707 1,920 2,500 3,048 3,657 4,572 5,182 6,400 7,620

- - - - - -

0,213 0,244

0,518 0,640 0,792 0,975 1,220 1,432 1,585 1,981 2,408 3,048 3,962 4,877 5,486 6,096 7,010

0,335 0 ,3960,487 0,640 0,914 1,036 1,371 1,585 1,951 2,225 2,591 3,353 3,962

0,701 0,762

1,707 1,920 2,500 3,048 3,657 4,572 5,182 6,400 7,620

10,060 12,800 15,240 16,760 18,897 21,336

0,823 0,914 1,220

2,133 2,438 3,048 3,657 4,572 5,486 6,400 7,620 9,144

12,190 15,240 18,288 20,726 23,774 25,910

274 0,305 0,427

,5180,701 0,792 1,006 1,249 1,524 1,798 2,042 2,500 3,050 3,692 4,877 5,791 7,010 7,925 8,839

0,366 0,427 0,579

0,945 1,128 1,432 1,707 2,133 2,438 2,743 3,657 4,267 5,486 7,010 7,925 9,144

10,670 12,192

0,427 0,487 0,609

1,006 1,219 1,524 1,829 2,286 2,743 3,048 3,692 4,877 6,096 7,620

9,1144 10,363 11,582 12,800

165

20 24

15,240 18,288

10,058 12,192

- -

7,925 9,144

24,690 28,650

30,480 35,050

10,058 12,192

13,411 15,240

15,240 18,288

7 hi ng ca i

k , d/D t thu, d

Bng - 12 : C u di t ng mt s trng h p c b t

ng nh t m /D ng ng ni vo thng in mm 1 /2 3/4 1/2 /4 1 1/4 3/4 (1) (2) (3) (4) 3/8 1 /2

1.1/4

9,512

0,760

1

52

0,360

52

01

111

1

1

3 /4 19,051

1.1/2 2

2.1/2 3

3.1/2 4 5 6 8 10 12 14 16 18 20 24

25 ,7

0,427 0,548

0,244 0,335

0,092 0,122

0,2130,274

0,1520,213

0,09140,122

0,457 0,548

0,244 0,305

0,40,5

57 48

111

0,3350,457

1

25,4 31,75 38,1 50,8 63,5 76,2 88,9 101,6 127

152,4 203,2 254

304,8 355,6 406,4 457,2 508

609,6

2

0,457 0,609

0,10,975

1,432 1,768 2,438 3,05 3,962 4,572 5,181 7,315 8,839

- - - - - - - -

0,914 1,097 1,463 1,859 2,438 2,804 3,353 4,572 6,705 7,62 9,753 2,496

- - - - -

,2130,305 0,366 0,488 0,609 0,792 0,914 1,158 1,524 1,829 2,591 3,353 3,962 4,877 5,486 6,096

- -

6 0,3050

0,10,487

0,7010,8841,22 1,5241,9812,3472,7433,6574,572

- - - - - - - -

,3660,5480,67 0,9141,1581,4931,8292,0722,7433,3534,5726,0967,62

- - - - -

,2130,305 0,366 0,488 0,609 0,792 0,914 1,158 1,524 1,829 2,591 3,353 3,962 4,877 5,486 6,096

- -

,853

0,427 0,548 ,127

1,615 2,012 2,743 3,657 4,267 5,181 6,096 8,23 0,058 4,325 8,288 22,25 26,21 29,26 35,05 43,28 49,68

0,792 1,006 1,341 1,707 2,194 2,59 3,048 4,267 5,791 7,315 8,839 11,28 3,716 15,24 7,678

21,336 25,298

0,853 1,127

0,670

1,615 2,012 2,743 3,657 4,267 5,181 6,096 8,23 0,0584,3258,28822,25 26,21 29,26 35,05 43,28 49,68

,8231,28 1,5242,0732,6513,3533,9624,8776,0967,62 0,68814,0217,37

20,11723,4727,43

32,91839,624

Cc tr ng ni ng (1) - N yn ng t ng vo thng v ng ng n (2) - N yn ng t n ng ng v n (3)- N n ng t n ng n h h

ng v ng g n c

. Cc th thng xy dng tn tht p sut cho 1m chiu di ng ng. Khi bit 2

trong ba thng s : Lu lng nc tun hon (L/s), ng knh ng (mm) v tc chuyn v chn tc s xc nh c kc

ng hp ng vo th : c chu u

ni bg g n

g mt vi cnh thng. c ch th g r a n i bng mt vi cnh thng.

c chuy ng vo thng v g

i nn

ln khi nh l

i cnh tn khi

ng. nh th(4) - Nc chuyn ng t thng ra ng

ng.

7.2.4.2 Xc nh tn tht p sut theo th Ngoi cch xc nh theo cng thc, trn thc t ngi ta hay s dng phng php

th

ng (m/s). Thng thng chng ta bit trc lu lng h thc ng v tn tht p sut cho 1m ng.

166

Hnh 7-1 : Tn tht p sut (Pa/m) trn ng dn thp en Schedul 40

Hnh 7-2 : Tn tht p sut (Pa/m) trong ng dn nc bng ng rn hnh 7-2 biu din th xc nh tn tht p sut (Pa/m) trong cc ng dn ng

loai K, L, M

Hnh 7-3 : Tn tht p sut (Pa/m) trong cc ng dn nc bng plastic

nh 7-3 trnh by th xc nh tn tht p sut trong cc ng dn plastic . Khi xy d th ngi ta ly nhit nc l 20oC.

V d 1

T

Hng

: Xc nh tn tht p sut trn mt tuyn ng thp 100mm trc u y bm, bi

lt1 = 6 x 3,048m = 18,28 m

Lt = 50 + 18,28 + 1,372 = 69,652 a bm , theo bng tc nm trong khong 2,4 3,6 m/s. Chn = 3 m/s.

c nh c L= 25 Li/s v p = 800 Pa/m

t chiu di tng l 50m, 01 van ca v c 6 ct 90o- Chiu di tng ng ca 6 ct 90o

- Chiu di tng ng ca van chn lt2 = 1,362 m

- Tng chiu di tng ng m

- i vi on ng trc u y c

- Cn c vo th hnh 7-1 , x - Tng tn tht trn ton tuynp = 69,652 x 800 = 55.722 Pa = 0,557 bar

167

168

nh gin n

i nhit bng nc bt buc phi s dng thp gii nhit. Thp gii nhit c s dng gii nhit nc lm mt bnh ngng trong h

hp gii nhit RINKI (Hng Kng) Cu to gm : Thn v y thp bng nha composit . Bn trong c cc khi si nha c

ng c 02 khi. Ngoi ra bn trong cn c h th

p FRK-80 c cng sut gii nhit 80 Ton

c v khi lng c

g ring ca nc : C = 1 kCal/kg. o ra thp t = 4oC

7.3 Thp gii nhit v b7.3.1 Thp gii nhit Trong h thng iu ho khng kh gi

thng lnh my iu ho khng kh. Trn hnh 7-4 trnh by cu to ca mt thp gii nhit Hnh 7-4 : T

tc dng lm ti nc, tng b mt tip xc, thng ng phun nc, qut hng trc. H thng ng phun nuc quay xung quanh trc khi

c nc phun. M t qut t trn nh thp. Xung quanh phn thn cn c cc tm li , c th d dng tho ra v sinh y thp, cho php quan st tnh hnh nc trong thp nhng vn ngn cn rc c th ri vo bn trong thp. Thn thp c lp t mt vi tm ring bit, cc v tr lp to thnh gn tng sc bn cho thn thp.

Phn di y thp c cc ng nc sau : ng nc vo, ng nc ra, ng x cn, ng cp nc b sung v ng x trn.

Khi chn thp gii nhit ngi ta cn c vo cng sut gii nhit . Cng sut c cn c vo m hiu ca thp. V d th

Bng 7-3 di y trnh by cc c tnh k thut ca thp gii nhit RINKI. Theo bng ta c th xc nh c lu lng nc yu cu, cc thng s v cu tr

a thp. T lu lng ca thp c th xc nh c cng sut gii nhit ca thp Q = G.Cn.tnG- Lu lng nc ca thp, kg/s Cn- Nhit dun ntn - chnh lch nhit nc v n

169

Kch thc ng ng Qut Khi lng n MODEL

LL(L/s) m h H D Vo Ra X trn X y B sung m3/ph mm kW Tinh C nc dB

FRK-8 1,63 170 950 1600 930 40 40 25 15 70 530 0,20 54 185 46,010 2,17 170 1085 1735 930 40 40 25 15 85 630 0,20 58 195 50,015 3,25 170 990 665 1170 50 50 25 15 140 630 0,37 70 295 50,520 4,4 170 1170 1845 1170 50 50 25 15 170 760 0,37 80 305 54,025 5,4 180 1130 1932 1400 80 80 25 15 200 760 0,75 108 400 55,030 6,5 180 1230 2032 1400 80 80 25 15 230 760 0,75 114 420 56,040 8,67 200 1230 2052 1580 80 80 25 15 290 940 1,50 155 500 57,050 10,1 200 1200 2067 1910 80 80 25 15 330 940 1,50 230 800 57,560 13,0 270 1410 2417 1910 100 100 25 20 420 1200 1,50 285 1100 57,080 17,4 270 1480 2487 2230 100 100 25 20 450 1200 1,50 340 1250 58,090 19,5 270 1480 2487 2230 100 100 25 20 620 1200 2,25 355 1265 59,5

100 21,7 270 1695 2875 2470 125 125 50 20 680 1500 2,25 510 1850 61,0125 27,1 270 1740 3030 2900 125 125 50 20 830 1500 2,25 610 2050 60,5150 32,4 270 1740 3030 2900 150 150 50 20 950 1500 2,25 680 2120 61,0175 38,0 350 1740 3100 3400 150 150 50 25 25 1150 1960 3,75 760 2600 61,5200 43,4 350 1840 3200 3400 150 150 50 25 25 1250 1960 3,75 780 2750 62,5225 48,5 350 1840 3200 3400 150 150 50 25 25 1350 1960 3,75 795 2765 62,5250 54,2 590 1960 3760 4030 200 200 80 32 32 1750 2400 5,50 1420 2950 56,5300 65 680 1960 3860 4030 200 200 80 32 32 2200 2400 7,50 1510 3200 57,5350 76 680 2000 4160 4760 200 200 80 32 32 2200 2400 7,50 1810 3790 61,0400 86,7 720 2100 4300 4760 200 200 80 32 32 2600 3000 11,0 2100 4080 61,0500 109 720 2125 4650 5600 250 250 100 50 50 2600 3000 11,0 2880 7380 62,5600 130 840 2450 5360 6600 250 250 100 50 50 3750 3400 15,0 3750 9500 66,0700 152 840 2450 5360 6600 250 250 100 50 50 3750 3400 15,0 3850 9600 66,0800 174 940 3270 6280 7600 250 250 100 80 80 5000 3700 22,0 5980 14650 74,0

1000 217 940 3270 6280 7600 250 250 100 80 80 5400 3700 22,0 6120 14790 74,0

Bng 7-13: Bng c tnh k thut ca thp gii nhit RINKI

7.3.2 Bnh (thng) gin n Trong cc h thng ng dn nc kn thng c trang b bnh gin n. Mc ch ca bnh gin n l to nn mt th tch d tr nhm iu ho nhng nh hng do gin n nhit ca nc gy ra, ngoi ra bnh cn c chc nng b sung nc cho h thng trong trng hp b r r . C 2 loi bnh gin n : Loi h v loi kn. Bnh gin n kiu h l bnh m mt thong tip xc vi kh tri trn pha u ht ca bm v v tr cao nht ca h thng.

cao ca bnh gin n phi m bo to ra ct p thu tnh ln hn tn tht thu lc t v tr ni thng bnh gin n ti u ht ca bm.

THUNG GIAN N

B

AC

1

2

BM

Hnh 7-5 : Lp t thng gin n Trn hnh 7-5 , ct p thu tnh on AB phi m bo ln hn tr lc ca on AC, nu khng nc v trn ng (1) khng tr v u ht ca bm m b y vo thng gin n lm trn nc. Khi lp thm trn ng ht ca bm cc thit b ph, v d nh lc nc th cn phi tng cao on AB. tnh ton th tch bnh gin n chng ta cn c vo mc tng th tch ca nc cho bng 7-14 . Bng 7-14 : Gin n th tch nc theo nhit

t, oC 5 10 15 20 25 30 35 40 45 50

% Th tch 0,02 0,11 0,19 0,28 0,37 0,46 0,55 0,69 0,90 1,11 t, oC 55 60 65 70 75 80 85 90 95 100

% Th tch 1,33 1,54 1,76 2,11 2,49 2,85 3,10 3,35 3,64 4,00 Bnh gin n kiu kn c s dng trong h thng nc nng v nhit cao . Bnh gin n kiu kn khng m ra kh quyn v vn hnh p sut kh quyn. Bnh cn trang b van x kh. Bnh gin n kiu kn c lp t trn ng ht ca bm, cho php khi vn hnh p sut ht ca bm gn nh khng i. Trong h thng iu ho chng ta t gp bnh gin n kiu kn.

170

7.4 Lp t h thng ng ng nc Khi lp t h thng ng ng nc cn lu b tr sao cho tr lc trn cc nhnh ng u nhau, mun vy cn b tr sao cho tng chiu di cc nhnh u nhau. Trn hnh 7-6 trnh by s ng dn nc lnh cung cp cho cc FCU v AHU . hnh 7-6a , ta thy chiu di ca cc nhnh ABGHA, ABCFGHA v ABCDEFGHA l khng u nhau , do tr lc ca cc nhnh khng u nhau. S ny gi l s ng quay v trc tip. y l s n gin, d lp t v tng chiu di ng ng nh. Tuy nhin do tr lc khng u nn cn lp t cc van iu chnh iu chnh lng nc cp cho cc nhnh u nhau. hnh 7-6b l s ng quay v khng trc tip , trong trng hp ny chiu di ng i ca cc nhnh n cc FCU v AHU u nhau. Cc FCU (AHU) c ng cp nc di th ng hi nc ngn v ngc li. Cn lu khi tr lc ca cc FCU u nhau th nn s dng s khng trc tip. Nu cc FCU c tr lc khc nhau th v mt kinh t nn chn s loi trc tip , lc cn s dng cc bin php khc hiu chnh cn thit. Mt trong nhng bin php m ngi ta hay p dng l s dng van cu trn ng ht. Hnh 7-6 : Cc loi s b tr ng ng Trn hnh 7-7 trnh by hai trng hp lp t ng ng theo s khng trc tip , phng n thng c p dng cho h thng kn. Hnh 7-7a trnh by minh ha ng vi trng hp cc FCU b tr vi cao khc nhau v trn hnh 7-7b l trng hp cc FCU b tr trn cng mt cao. Trong trng hp ny ngoi vic cn ch b tr ng ng i v v cho cc nhnh u nhau, ngi thit k cn lu ti ct p tnh do ct nc to nn. Theo cch b tr nh trn qung ng i cho tt c cc FCU gn nh nhau v ct p tnh u nhau, do m bo phn b nc n cc nhnh u nhau.

171

Hnh 7-7 : Cch b tr ng ng cp nc FCU

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172

7.1 H thng ng ng dn nc7.2 Tnh ton ng ng dn nc v chn bm7.2.1 Lu lng nc yu cu7.2.2 Chn tc nc trn ng ng7.2.3. Xc nh ng knh ng dn7.2.4. Xc nh tn tht p sut7.2.4.1 Xc nh tn tht p sut theo cng thc7.2.4.2 Xc nh tn tht p sut theo th

7.3 Thp gii nhit v bnh gin n7.3.1 Thp gii nhit7.3.2 Bnh (thng) gin n

7.4 Lp t h thng ng ng nc