Cột chêm

1

I. TRCH YU: a) Mc ch th nghim: - Kho st c tnh ng lc hc lu cht v kh nng hot ng ca ct chm bng cch xc

nh: o nh hng ca vn tc dng kh v lng ln tn tht p sut ( gim p) khi i qua

ct. o S bin i ca h s ma st ct kh fck theo chun s Reynolds (Re) ca dng kh

v suy ra cc h thc thc nghim.

o S bin i ca tha s lin h gia gim p ca dng kh qua ct kh v qua ct t theo vn tc dng lng.

o Gin gii hn kh nng hot ng ca ct (gin ngp lt v gia trng). b) Phng php th nghim: - Cho dng kh vi cc lu lng khc nhau qua ct c cha cc vt chm bng s. Ln lt

kho st gim p khi ch c dng kh chuyn ng qua ct (ct kh) v khi c dng kh chuyn ng qua ct kt hp vi dng lng chy t trn xung vi lu lng khc nhau (ct t).

II. C S L THUYT: a) gim p ca dng kh:

- gim p Pck ca dng kh qua ct ph thuc vo vn tc khi lng G ca dng kh qua ct kh (khng c dng chy ngc chiu). Khi dng kh chuyn ng trong cc khong trng gia cc vt chm tng dn vn tc th gim p cng tng theo. S gia tng ny theo ly tha t 1,8 n 2,0 ca vn tc dng kh.

Pck = Gn Vi n = 1,8 2,0. (1) - Khi c dng lng chy ngc chiu, cc khong trng gia nhng vt chm b thu hp li.

Dng kh do di chuyn kh khn hn v mt phn th tch t do gia cc vt chm b lng cht lng chim c. Khi tng vn tc dng kh ln, nh hng cn tr ca dng lng tng ln u n cho n mt tr s ti hn ca vn tc kh, lc gim p ca dng kh tng vt ln. im ng vi tr s ti hn ca vn tc kh ny c gi l im gia trng. Nu tip tc tng vn tc dng kh qu tr s ti hn ny, nh hng cn tr h tng gia

dng lng v dng kh rt ln, Pc tng mau chng khng theo phng trnh (1) na. Dng lng lc ny chy xung cng kh khn, ct chm im lt.

b) H s ma st fck theo Rec khi ct kh: - Chilton v Colburn ngh mt h thc lin h gia gim p ca dng kh qua ct chm

kh vi vn tc khi lng ca dng kh qua ct.

wh

hg

ckck

D

ZGfP

2

2 , N/m2

Z: chiu cao phn chm, m. G: vn tc khi lng dng kh da trn mt n v tit din ct, kg/s.m2. Dh: kch thc c trng ca vt chm, m.

g: khi lng ring ca pha kh, kg/m3.

h: h s iu chnh dng cho vt chm rng.

w: h s hiu chnh nh hng ca thnh ct ln xp ca ct chm. - Sherwood tng hp kt qu ca mt s nghin cu v a ra tr s sau cho vng s Raschig:

h = 0,35

w = 1 - Tuy nhin, Zhavoronkov ngh mt h thc khc chnh xc hn v a c tr s

xp ca ct chm vo h thc:

2

eG

ck

ck

D

ZGfP

2

22 , N/m2

Vi:

: xp ca vt chm.

:a

De

4 ng knh tng ng ca vt chm, m.

a: din tch b mt ring ca vt chm, m2/m3. - H s ma st fck l hm s theo chun s v th nguyn Rec, vi Rec c tnh theo cng

thc sau:

a

GGDe

c

4Re

: nht ca dng kh, kg/ms. - Zhavoronkov xc nh c khi dng kh chuyn t ch chy tng sang ch chy

ri ng vi tr s Rec = 50. Trong vng chy ri, 50 < Rec < 7000 vi ct chm ngu nhin. Ta c:

20

83,

Re

,

c

ckf

- Tuy nhin, cc h thc tng qut trn khng c chnh xc lm v khng xem xt c ton b nh hng ca hnh dng vt chm.

c) gim p Pc khi ct t: - S lin h gia gim p ct kh Pck v ct t Pc c th biu din nh sau:

Pc = Pck

- Do c th d kin fc = fck

Vi : h s ph thuc vo mc xi ti ca dng lng L, kg/m2s/

- Leva ngh nh hng ca L ln nh sau:

= 10L hay log = L

- Gi tr ty thuc vo loi, kch thc, cch thc sp xp vt chm (xp ngu nhin hay theo th t) v ln ca lu lng dng lng L. Th d vi vt chm l vng s Raschig

12,7mm, chm ngu nhin, xp = 0,586; gi tr ca L t 0,39 n 11,7 kg/m2s v ct hot ng trong vng di im gia trng.

= 0,084

- Mt s ti liu cn biu din s ph thuc gia t s ck

c

p

p

vi h s xi ti nh sau:

322

7513

g

q

F

GA

L

L

L

Re

,

- Khi A< 0,3 cho vt chm bng s c d < 30mm, ta c:

L

L

L

ck

c

Fa

G

Ap

p

4

1

13

Re

)(

3

d) im lt ca ct chm: - Khi ct chm b ngp lt, cht lng chim ton b khong trng trong phn chm, cc dng

chy b xo trn mnh lit, hin tng ny rt bt li cho s hot ng ca ct chm. Gi gi tr ca GL tng ng vi trng thi ny l GL*.

- Zhavoronkov kt lun rng trng thi ngp lt xy ra khi hai nhm s sau c s lin h nht nh vi nhau cho mi ct.

202

31 2

,

t

L

Gck

g

vaf

v L

G

G

L

2

Vi fck: h s ma st ct kh. v: vn tc di ca dng kh ngay trc khi vo ct, m/s.

t: nht tng i ca cht lng so vi nc, ,nc

l

t

nu cht lng l nc th

t = 1.

- Do s lin h 1, 2 trn gin log1 - log2 s xc nh mt gin lt ca ct chm, phn gii hn hot ng ca ct chm di ng ny.

III. THIT B V PHNG PHP TH NGHIM: a) S thit b th nghim: - Thit b th nghim gm c:

o Ct thy tinh, bn trong l cc vng s Raschig xp chm ngu nhin. o H thng cp kh gm c:

Bm (qut) thi kh BK. ng dn kh. p k sai bit ch U. Lu lng k kh F c chia t 8 n 100%.

o H thng cp nc gm: Thng cha nc bng nha N. Bm cht lng BL. Lu lng k lng Fl c chia t 0 dn 1,6.

b) Cc s liu lin quan n ct chm: - Ct thy tinh:

o ng knh d = 0,09 m. o Chiu cao H = 0,805 m. o Chiu cao phn chm Z = 0,42 m.

- Vt chm xp ngu nhin, vng Raschig ng knh 12,7mm, b mt ring a = 370 380

m2/m3, xp = 0,586. - ng knh ng thp y ct D = 0,09m. c) Phng php th nghim: - Kha li tt c van lng (t 1 n 4). - M van 5 v kha van 6. - Cho qut chy trong 5 pht thi ht m trong ct. Tt qut. - M van 1 v 2, sau cho bm chy.

4

- M van 3 v t t kha van 1 iu chnh mc lng y ct ngang bng vi ng nh mc g. Tt bm v kha van 3.

- o gim p ca ct kh: o Kha tt c cc van lng li. M van 6 cn van 5 vn ng. Cho qut chy ri t t

m van 5 chnh lu lng kh vo ct.

o ng vi mi gi tr lu lng kh chn ta c Pck trn p k U theo mmH2O. o xong tt qut, ngh 5 pht.

- o gim p khi ct t: o M qut v iu chnh lu lng kh qua ct khong 15 20%. o M van 1 v cho bm chy. Dng van VL ti lu lng k chnh lu lng lng

(lu lng k lng c vch chia 0,1; 0,2; ;1,6). Nu VL m ti a m phao vn khng ln th dng van 1 tng lng lng.

o ng vi lu lng lng chn (v d: 0,1; 0,2) c nh, ta chnh lu lng kh

v c gim p Pc ging nh Pck trc . Ch l tng lng kh n im lt th thi.

Ch : - Trong qu trnh o gim p ca ct t cn canh gi mc long y ct lun n nh

chiu cao y bng cch chnh van 4. Nu cn, tng cng van 2 nc trong ct thot v bnh cha (van 2 dng x nhanh khi gim lu lng kh).

- Khi tt my phi tt bm lng BL trc, m ti a van 4 sau tt qut BK. - Nu s xut nc trn vo ng dn kh th m van x nc pha bng.

IV. KT QU TH NGHIM:

Kt qu:

Bng 1:Kt qu s liu th

L= 0 L= 0,2 L= 0,4 L= 0,6 L= 0,8 L=1 L=1,2 L=1,4 L=1,6

10 2 2 2 3 3 3 4 4 6

20 6 5 6 8 11 12 15 18 26

30 12 13 14 18 30 27 37 45 57

40 16 16 24 20 48 51 93 92

45 122

50 26 32 36 43 85 103

60 37 45 53 73 135

70 47 61 95 175 250

80 60 83 187 273

90 76 119 325

100 93 155

Lu lng kh G

o giam ap theo cac che o L khac nhauP

5

Bng 2: Cc tr s kt qu khi ct kh L = 0

Bng 3: Cc tr s khi ct t L=0,2


G. % fck Reck

10 7,658 49,702

20 5,743 99,404

30 5,105 149,107

40 3,829 198,809

50 3,982 248,511

60 3,935 298,213

70 3,673 347,915

80 3,590 397,618

90 3,592 447,320

100 3,561 497,022

1401,429

1775,143

2172,214912,330

60,000

76,000

93,000

0,699

0,786

0,873

588,600

745,560

0,611

140,143

280,286

373,714

607,286

864,214

1097,786

58,860

117,720

156,960

255,060

362,970

461,07047,000

6,000

12,000

16,000

26,000

37,000

46,71419,620

0,175

0,262

0,349

0,437

0,524

G, kg/s.m2 Pck, (mmH2O) Pck, N/m2 Pck/Z, (N/m

2)/m

0,087 2,000

G. % fck fc Rec

10 1,000 7,658 7,658 31,595

20 0,833 5,743 4,786 31,595

30 1,083 5,105 5,531 31,595

40 1,000 3,829 3,829 31,595

50 1,231 3,982 4,901 31,595

60 1,216 3,935 4,786 31,595

70 1,298 3,673 4,766 31,595

80 1,383 3,590 4,966 31,595

90 1,566 3,592 5,625 31,595

100 1,667 3,561 5,935 31,595

362,970

461,070

588,600

745,560

912,330

19,620

58,860

117,720

156,960

255,060

1520,550

46,714

116,786

303,643

373,714

747,429

1051,071

1424,786

1938,643

2779,500

3620,357

19,620

49,050

127,530

156,960

313,920

441,450

598,410

814,230

1167,390

0,611

0,699

0,786

0,873

2,000

5,000

13,000

16,000

32,000

45,000

0,087

0,175

0,262

0,349

0,437

0,524

61,000

83,000

119,000

155,000

G, kg/s.m2 Pc, mmH2O Pc, N/m2 Pc/Z, (N/m

2)/m Pck, N/m2

G. % fck fc Rec

10 1,000 7,658 7,658 63,189

20 1,000 5,743 5,743 63,189

30 1,167 5,105 5,956 63,189

40 1,500 3,829 5,743 63,189

50 1,385 3,982 5,514 63,189

60 1,432 3,935 5,637 63,189

70 2,021 3,673 7,423 63,189

80 3,117 3,590 11,187 63,189

90 4,276 3,592 15,363 63,1890,786 325,000 3188,250 7591,071 745,560

0,699 187,000 1834,470 4367,786 588,600

0,611 95,000 931,950 2218,929 461,070

0,524 53,000 519,930 1237,929 362,970

0,437 36,000 353,160 840,857 255,060

0,349 24,000 235,440 560,571 156,960

0,262 14,000 137,340 327,000 117,720

0,175 6,000 58,860 140,143 58,860

0,087 2,000 19,620 46,714 19,620


2)/m Pck, N/m2

6






G. % fck fc Rec

10 1,500 7,658 11,486 94,784

20 1,333 5,743 7,658 94,784

30 1,500 5,105 7,658 94,784

40 1,250 3,829 4,786 94,784

50 1,654 3,982 6,586 94,784

60 1,973 3,935 7,764 94,784

70 3,723 3,673 13,674 94,784

80 4,550 3,590 16,332 94,7840,699 273,000 2678,130 6376,500 588,600

0,611 175,000 1716,750 4087,500 461,070

0,524 73,000 716,130 1705,071 362,970

0,437 43,000 421,830 1004,357 255,060

0,349 20,000 196,200 467,143 156,960

0,262 18,000 176,580 420,429 117,720

0,175 8,000 78,480 186,857 58,860

0,087 3,000 29,430 70,071 19,620


2)/m Pck, N/m2

G. % fck fc Rec

10 1,500 7,658 11,486 126,378

20 1,833 5,743 10,529 126,378

30 2,500 5,105 12,763 126,378

40 3,000 3,829 11,486 126,378

50 3,269 3,982 13,018 126,378

60 3,649 3,935 14,358 126,378

70 5,319 3,673 19,535 126,3780,611 250,000 2452,500 5839,286 461,070

0,524 135,000 1324,350 3153,214 362,970

0,437 85,000 833,850 1985,357 255,060

0,349 48,000 470,880 1121,143 156,960

0,262 30,000 294,300 700,714 117,720

0,175 11,000 107,910 256,929 58,860

0,087 3,000 29,430 70,071 19,620


2)/m Pck, N/m2

G. % fck fc Rec

10 1,500 7,658 11,486 157,973

20 2,000 5,743 11,486 157,973

30 2,250 5,105 11,486 157,973

40 3,188 3,829 12,204 157,973

50 3,962 3,982 15,775 157,9730,437 103,000 1010,430 2405,786 255,060

0,349 51,000 500,310 1191,214 156,960

0,262 27,000 264,870 630,643 117,720

0,175 12,000 117,720 280,286 58,860

0,087 3,000 29,430 70,071 19,620


2)/m Pck, N/m2

G. % fck fc Rec

10 2,000 7,658 15,315 189,567

20 2,500 5,743 14,358 189,567

30 3,083 5,105 15,741 189,567

40 5,813 3,829 22,255 189,567

45 7,176 3,214 23,065 189,5670,393 122,000 1196,820 2849,571 166,770

0,349 93,000 912,330 2172,214 156,960

0,262 37,000 362,970 864,214 117,720

0,175 15,000 147,150 350,357 58,860

0,087 4,000 39,240 93,429 19,620


2)/m Pck, N/m2

G. % fck fc Rec

10 2,000 7,658 15,315 221,162

20 3,000 5,743 17,230 221,162

30 3,750 5,105 19,144 221,162

40 5,750 3,829 22,016 221,162

0,262 441,450 1051,071 117,720

0,087

156,960

45,000

0,349 92,000 902,520 2148,857

4,000 39,240 93,429 19,620

0,175 18,000 176,580 420,429 58,860


2)/m Pck, N/m2

7


Bng 11:Cc tr s ca ct lt

Bng 12: Cc kt qu v h thc thc nghim

Mi lin h L Kt qu thc nghim

S ph thuc ca Log(Pck/Z) vo Log(G) 0,0, y = 2,2694x + 3,6773

S ph thuc ca Pc/Z vo G

0,2 y = 4332,6x - 840,86

0,4 y = 9030,7x - 2017,8

0,6 y = 9274,6x - 1855,2

0,8 y = 9971,9x - 1608,3

1,0 y = 6391,9x - 759,11

1,2 y = 9135,5x - 1047,8

1,4 y = 11,258x - 0,7212

1,6 y = 9,5041x - 0,568

S ph thuc ca Log(fck) vo Reck 0,0 y = 3E-06x2 - 0,0021x +

0,9567

S ph thuc ca fcu vo Recu

0,2 y = 4E-14x + 31,595

0,4 y = -9E-15x + 63,189

0,6 y = -8E-15x + 94,784

0,8 y = -4E-14x + 126,38

1,0 y = 1E-13x + 157,97

1,2 y = 189,57

1,4 y = 7E-14x + 221,16

1,6 y = -4E-12x + 252,76

S ph thuc ca log() theo L

G=10% y = 0,3107x - 0,0787

G=20% y = 0,4909x - 0,1768

G=30% y = 0,4717x - 0,0786

G. % fck fc Rec

10 3,000 7,658 22,973 252,756

20 4,333 5,743 24,887 252,756

30 4,750 5,105 24,249 252,7560,262 57,000 559,170 1331,357 117,720

0,087 6,000 58,860 140,143 19,620

0,175 26,000 255,060 607,286 58,860


2)/m Pck, N/m2

L, gppm/ pht L, kg/s.m2 G*, % L/G* 1 2 v fck

0,400 3,951 90,000 5,027 0,1817 0,172 0,675 3,592

0,600 5,927 80,000 8,479 0,1436 0,290 0,600 3,59

0,800 7,903 70,000 12,934 0,1123 0,442 0,524 3,673

1,000 9,878 50,000 22,605 0,0623 0,773 0,375 3,982

1,200 11,854 45,000 30,163 0,0406 1,032 0,337 3,214

1,400 13,830 40,000 39,626 0,0382 1,355 0,300 3,829

1,600 15,805 30,000 60,325 0,0287 2,063 0,225 5,1050,262

0,786

0,699

0,611

G*, Kg/s.m2

0,393

0,437

0,349

8

th:

th 1: Biu din log(Pck/Z) theo log G

th 2: Biu din Log fck theo Reck

y = 1,6606x + 3,4019R = 0,9969

0,000

0,500

1,000

1,500

2,000

2,500

3,000

3,500

-1,200 -1,000 -0,800 -0,600 -0,400 -0,200 0,000

log(P

ck/Z

)

log G

log Pck/Z theo log G

log Pck/Z theo log G

Linear (log Pck/Z theo log G)

9

th 3: Biu din Pc /Z theo L v Log G

th 4: Biu din log theo L (ti vi v tr ca G di im gia trng)

Chn b tr G ti 3 v tr u tin (10%, 20%, 30%)

y = -0,3601x2 + 1,8838x + 3,6133

y = -1E-14x2 + x - 3E-15

y = 0,2184x2 + 2,8594x + 4,0291

y = 4E-15x2 + x - 1E-17

y = 1,7812x2 + 4,2179x + 4,3592

y = x - 3E-15

0,100

0,600

1,100

1,600

2,100

2,600

3,100

3,600

4,100

4,600

-1,200 -1,000 -0,800 -0,600 -0,400 -0,200 0,000

0,2 log(DPc/Z) 0,4 logG0,4 log(Pc /Z /Z) 0,6 logG0,6 log(Pc /Z) 0,8 logG0,8 log(Pc /Z ) 1 logG1 log(Pc /Z) 1,2 logG1,2 log(Pc /Z ) 1,4 logG1,4 log(Pc /Z ) 1,6 logG1,6 log(Pc /Z ) Poly. (0,4 logG)Poly. (0,4 log(Pc /Z /Z)) Poly. (0,6 logG)

y = 0,3107x - 0,0787

y = 0,4909x - 0,1768

y = 0,4717x - 0,0786

-0,2

-0,1

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8

Log

L

Series1 Series2 Series3

Linear (Series1) Linear (Series2) Linear (Series3)

10

th 5: Gin lt ca ct log1 theo log2

th 6: Biu din logfc theo logRec

-1,8

-1,6

-1,4

-1,2

-1

-0,8

-0,6

-0,4

-0,2

0

-1 -0,8 -0,6 -0,4 -0,2 0 0,2 0,4log

1

log 2

Gin lt ca ct log (1) theo log (2)

y = 0,5x

y = 0

y = -0,25x + 1

y = 0,5x + 0,5

y = 0,6667

y = -0,25x + 1

y = 0,1667x + 0,6667

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

0 0,5 1 1,5 2 2,5 3

logf

c

logRec

11

V. BN LUN:

Cu 1: nh hng ca G ln gim p khi ct kh v ct t.

-Da vo th ta thy:

oi vi cot kho: khi G tang th o giam ap tang theo, log(Pc/Z) tang tuyen tnh vi

logG.

i vi ct t:khi G tng th gim p cng tng nhng khng tng mt hm tuyn tnh

na m theo mt ng cong. gim p tng theo nhng vng r rt nh trong gin

l thuyt cp.

T th ta thy lc u khi G cn nh th (Pc/Z) tng chm sau khi G ln

th (Pc/Z) bt du tng nhanh v khi vt qua gii hn im lt th (Pc/Z) tng

rt nhanh.

Khi lu lng lng cng tng th ct cng d gn n im lt hn. T th thu

c ta thy vng sau im gia trng th gi tr P tng ln rt nhanh v t ngt.

Ta thy vng sau im gia trng th thp chm hot ng tt nht nhng thc t, rt kh vn hnh ch ny nguyn do l on thng biu din ch ny rt dc,

chnh lch vn tc kh rt nh ch cn s sy mt cht l ct chm chuyn

sang lm vic ch cun theo cht lng bi cun ngc tr ra theo dng kh.

Cu 2: Mc ch v cch s dng gin theo Re.

Gin f theo Re nhm biu hin s ph thuc ca tr lc ( h s ma st) i vi lu lng ca dng lu cht.Khi lu lng dng lu cht tng th tr lc nh v ngc li.

Mc ch: nhm xc nh c lu lng hp l vn hnh ct tr lc nh v thu c hiu sut truyn khi tt nht gia hai pha vi nhau m ct vn khng b lt.

Cch s dng gin f theo Re:gi s khi ta bit 1 trong 2 gi tr f hoc Re th ta c th ging 1 ng thng song song vi trc honh hoc trc tung,ng thng ny s ct gin ti mt im.V ti giao im ta li k tip mt ng thng song song vi trc tung hoc trc honh.Gi tr ca trc tung hoc trc honh chnh l gi tr ng vi gi tr m chng ta c ban u.

Cu 3: S lin h gia cc i tng kho st c theo d on khng?Nu khng gii thch l do. S lin h gia cc i tng tng kho st gn vi vi d on. C th l cc mi lin h sau:

Log(Pck/Z) - logG :ph thuc gn nh tuyn tnh vi nhau theo 1 ng thng m c s l thuyt nhn nh.

Log(Pc/Z) logG:ti cc gi tr L=0,2; 0,4,P tng gn nh tuyn tnh. Nhng khi ta chnh lu lng lng cng tng L=0,6; 0.8,.th P tng mt cch t ngt v hu nh khng cn tuyn tnh na.

Log - L: c th xem nh tuyn tnh vi nhau.

12

Tuy nhin trong qu trnh tin hnh th nghim vn cn nhiu nguyn nhn gay sai s. Nhng

nguyn nhn dn n sai s c th l do:

S dng bm v qut a lu lng lng v lu lng kh cha u. Do qu trnh lm th nghim chm nn nc trn vo ng dn kh..

Cac ieu kin th nghim khong n nh va khong giong nhau cac lan o.

Sai s khi oc va trong thao tac th nghim (do ngi oc oc khong chnh

xac, do ieu chnh lu lng kh va long cha chnh xac).

Ct nc duy tr y ct l khng u. C lc nhch ln, c lc nhch

xung.

VI. PH LC

a) Chuyn i lu lng

xF

GmskgG K

60

286,0.(%).)./( 2

K, dL: khi lng ring ca dng kh, dng lng

F = * d2/4 d = 0.09m

b) Tnh fck bng cng thc:

ZG

DPf

eKck

ck

..

...

2

2

2

Trong :

=0,568 : xp ca vt chm.

:4

aDe

ng knh tng ng ca vt chm, m.

a = 375 m2/m3: din tch b mt ring ca vt chm, m2/m3.

Z = 0,42 m : chiu cao phn chm

c) Tnh fc bng cng thc:

fc = .fck

Tnh bng cng thc:

Pc = .Pck

d) i n v o p sut

N/m2 =1 mmH2O/10000* 9,81*10^4

Tnh Reck bng cng thc:

13

a

GGDec

4Re

Tnh im lt ca ct chm

202

31 2

,

t

L

Gck

g

vaf

L

G

G

L

2

VII. TAI LIEU THAM KHAO :

[1] Tp th CBGD b mn My - Thit b, Th nghim Qu trnh-Thit b, i hc Bch Khoa Tp.HCM.

[2] Gio trnh truyn khi ,GS.TSKH.Nguyn Bin, i hc Bch khoa H Ni [3] V B Minh, Truyn khi, i hc Bch Khoa Tp.HCM.

Documents

Cột chêm