1

Th nghiem QTTB

Mach lu chat

1. TRCH YEU

1.1 Muc ch th nghiem:

Khao sat s chay cua nc phong th nghiem trong mot he thong ong dan co ng knh khac nhau va co cha lu lng ke mang chan, venturi cung cac bo phan noi ong nh cut, van ch T. Th nghiem 1 : He so lu lng ke ca mng chn (Cm) va venturi (Cv) vi cc chy khc nhau. Th nghiem 2 : He so ma sat f theo che o chay (Re) cho ong 1 va

Th nghiem 3 :Thit lp gin c tuyen van , xac nh loi van va pham vi ng dung cua van , chieu dai tng ng ( lt )1.2 Phng phap th nghiem Th ngiem 1 : Cho dong chay lu chat qua thiet b co gan lu lng ke mang chan va venturi. oc ton that cot ap ng vi tng lu lng dong chay va tng lu lng ke.

Th nghiem 2 : Cho dong lu chat chay qua mang chan va lan lt qua ong 1 va ong . Chnh van e thay oi lu lng dong chay, oc ton that cot ap cua mang chan va ong. Lap lai th nghiem vi chieu dai ong l=0.9m va l=1.5m

Th nghiem 3 : Cho dong lu chat chay qua mang chan va van. ng vi tng o m cua van, oc ton that cot ap qua mang va van.1.3 Kt qu th nghim Th nghiem 1:Ln 1

W(l)t(s)Pm(cmH2O)Pv(cmH2O)

184,72

196,33

21284

313157

414198,5

5153013,5

61549,521

7167030

Ln 2

W(l)t(s)Pm(cmH2O)Pv(cmH2O)

1642

187,53,5

29135,7

31118,58,2

41135,515,5

5133716,5

61362,522,5

7156628,5

Ln 3

W(l)t(s)Pm(cmH2O)Pv(cmH2O)

14125,5

1513,56

28178

383114

4123415

5124419

6135825,5

7146728,5

Th nghiem 2:ng 1"

l = 0,9 ml = 1,5 m

P mngP ngP mngP ng

2,50,79,52

142163

386296,5

41,56,8336

50,58,5448

559,552,59,5

56955,510,5

579,559,311,5

609,860,511,5

6210,161,511,6

ng 1/2"

l = 0,9 ml = 1,5 m

P mngP ngP mngP ng

0,511,56

13927

13,3251441

1933,527,579

3153,535,598,5

34,56538,5109

3872,540112

40,57041114,5

41,37241,5116

42,17342116,5

Th nghiem 3:13/41/21/4

P mngP vanP mngP vanP mngP vanP mngP van

30,230,15,20,823,5

6,70,218,50,412,85,72231

26,50,338,20,722,5328,840,5

45,30,3521,153,327,54360

570,4611,260,58,350,370

63,30,565,51,1658,353,874,5

66,50,568,51,3679,755,578

58,50,469,81,168,895779

70,30,570,31,269,5957,880,3

71,30,571,5170,57,35981,5

1.4 Nhn xt kt qu th nghim2. C S LY THUYET 2.1 Lu lng ke mang chan va venturi :

Nguyen tac: o s giam ap suat cua lu chat khi chay qua dung cu e xac nh lu lng .

Vn tc trung bnh v tr (2) c tnh t cng thc tng k nng lng:

Trong o: C : he so cua mang chan va venturi, phu thuoc vao che o chay (Re)

: o giam ap suat qua mang chan hay venture, N/m2

: Trong lng rieng cua lu chat , N/m3

, t so ng knh co venturi hay lo mang chan tren ng knh ong.

Do lu lng qua mng chn hay venturi:

Q= V2A2= V11

2.2 Ton that nang lng do s chay trong ong dan:

Khi lu chat chay trong ong, xay ra hien tng mat nang lng do ma sat thanh ong va do tr lc cuc bo tai nhng v tr co tiet dien ong thay oi, thay oi hng dong chay

Ton that do ma sat :

T phng trnh Bernoulli ta c:

V =0 v (Z=0 =>

Hf: thy u tn tht ma st trong ng, mTn tht ny lin h vi tha s ma st bng phng trnh Darceyweisbach:

f: he so ma sat, phu thuoc vao che o chay (Re)

L: chiu di ng, m

D: ng knh ng, m

Chy tng Re < 2300 =64

Chy qu v chy ri

ng thnh nhn

ng thnh nhmNgoai ra co the xac nh he so ma sat bang cach s dung gian o Moody(f theo Re va ) Ton that cuc b:

La ton that nang lng do tr lc cuc bo nh s thay oi tiet dien chay, hng chay b can tr bi van, ong noi, cho ot m hay ot thu...

oi vi van hay khuc noi, ton that c bieu dien bi phng trnh :

Le: chieu dai tng ng cua van hay khp noi c nh ngha la chieu dai cua mot ong thang co cung s tn tht nang lng vi van hay khuc noi trong nhng ieu kien giong nhau.

Tr lc nay bng th nng rieng tieu tn thng tr lc do b phn ta ang xet gay ra:

so sanh 2 cong thc tren ta co:

t o ta co:

3. THIET B TH NGHIEM

3.1 Dung cu & thiet b :

Mot he thong ong dan va van co kch thc khac nhau, lap at nh trong tai lieu hng dan.

Bm

ong ho o thi gian.So lieu kch thc 4 ong dan bang ong:

ng knh going knh ngoaing knh trong

1

3/8(2.54cm)(1.90cm)

(1.27cm)

(0.951cm)1.1250.875

0.625

0.5(2.68cm)(2.22cm)

(1.59cm)

(1.27cm)1.0250.785

0.545

0.43(2.6cm)(2,0cm)

(1.39cm)

(1.09cm)

o nham e= 0.000005

Mang chan: loi vao: 2.6cm

ng knh lo: 1.59cm

Venture: loi vao: 2.6cm

ng kch co: 1.59cm

3.2 Phng php th nghim Nhng ieu can tuan thu trc khi tien hanh th nghiem :

- ong van so 13 va so 15 trc khi m hay tat may bm e tranh bot kh lot vao he thong.

- Trong suot thi gian lam th nghiem, van 14 luon m, van 4 va 5 luon ong. - Ch tien hanh th nghiem khi mc chat long trong cot ap bang nhau.1.Th nghiem 1: Trac nh lu lng ke mang chan va venturi - M van 16 va 17 cho nc vao bnh en vach toi a (48l).

- M van 1, 2, 3, 9 va ong van 12.

- Cho bm chay va t t, m van 13 sau o khoa lai va kiem tra mc nc trong cot ap ke mang va venturi co bang nhau cha. Neu cac cot chat long bang nhau trong tng nhanh (cua mang va venturi) chung ta tien hanh lam th nghiem. Con neu cha bang nhau th tiep tuc m, ong van 13.

- Khi mc chat long trong cot ap cua mang chan hay venturi a bang nhau, ta tien hanh lam th nghiem.

- Ta chon lu lng trc tuy y. T t m van 15. ng vi moi o m van 15 vi lu lng a chon ta oc cot ap cua venturi, mang chan va thi gian. Khi het nc trong bnh cha phai ong van 15 lai, m van 13 va m van 16 cho nc vao bnh cha. Lap lai th nghiem nay t 2 en 3 lan.Chu y: Cac van V1, V2, , V10; V1, V2, , V10 va Vk1, Vk2, , Vk5 dung e ieu chnh khi mc nc trong cac cot ap ke b mat hoan toan. 2.Th nghiem 2: Thiet lap gian o f theo Re cho ong 1 va

a. Cho ong 1

Ta gi nguyen o m cua cac van trong th nghiem 1. m van VA2, ong van VB1. Kiem tra mc nc trong cot ap ke ong 1. Neu mc nc bang nhau th ta tien hanh th nghiem. Dung van 13 e chnh lu lng (giong chnh van 15 trong th nghiem 1). ng vi moi o m cua van 13 ta oc o giam ap cua mang chan va ong 1 o dai l = 0.9m. Van 13 chnh en o m toi a. o xong cho oan 0.9m ta khoa van VA2 va m VB1, tiep tuc o o giam ap cho oan ong 1 vi l = 1.5 m.

b. Cho ong

Ta m van 12, ong van so 2. M van VA2, ong van VA3. Tng t nh o tren ong 1, ta kiem tra mc nc trong cot ap ke cua ong . Neu bang nhau ta tien hanh o. Neu khong bang nhau ta dung van 13 e chnh mc chat long (ong roi m van 13). Khi nao mc chat long trong cot ap bang nhau roi tien hanh o. o xong oan 0.9m, ta khoa VA2 va VA3 roi tien hanh o oan l = 1.5m.3. Th nghiem 3:

Sau khi tien hanh th nghiem xong tren ong , m van so 2 va ong van so 12 e tien hanh th nghiem 3.Ta ong van VB1. Van so 9 van e m hoan toan. Dung van 13 e chnh lu lng giong th nghiem 2. ng vi moi o m cua van 13 ta oc o giam ap cua mang va van.

Xong th nghiem vi o m hoan toan ta ong van so 9 lai 1 vong se c o m , roi tiep tuc o nh tren. Khi nao m het c van 13, luc o o giam ap cua mang va van khong thay oi, ngha la o o m a xong. Tiep tuc khoa van so 9 them 1 vong na ta se c o m roi tiep tuc o.

Nh vay ta a th nghiem xong vi 4 o m khac nhau cua van so 9 : m hoan toan, m , m va o m .

Tr lc theo o m cua van cho trong bang sau :o mHoan toan

(0,080.262.0617

V ta khong kiem nghiem c he so ma sat f theo tng o m van cua th nghiem 3 nen khi tnh lt ta s dung ket qua cua th nghiem 2 cho ong 1 vi chieu dai 1.5m.5. TNH TOAN KET QUA THNGHIEM: 5.1 Kt qu tnh tonBang 4: He so lu lng ke mang chan va venturi: STTWttbQ (m3/s)v (m/s)Pv/g(mH2O)Pm/g(mH2O)ReCvCm

116,00,0001670,8400,03170,069016616,180,990,67

217,30,0001360,6870,04170,091013595,050,710,48

329,70,0002071,0420,05900,126720626,980,900,61

4310,70,0002811,4160,09730,215028039,800,950,64

5412,30,0003241,6330,13000,295032334,180,950,63

6513,30,0003751,8890,16330,370037386,400,980,65

7613,70,0004392,2110,23000,566743769,440,970,62

87150,0004672,3500,29000,676746525,290,910,60

Bang 5: Tha so ma sat trong ong dan ng knh 1_ dai 0,9mng 1" (l = 0,9 m)

P mngP ngQvRef

0,0250,0070,0000860,1615226,020,15222

0,1400,0200,0002130,40112967,010,07064

0,3800,0600,0003600,67821958,020,07391

0,4150,0680,0003770,71123002,640,07633

0,5050,0850,0004180,78825511,950,07756

0,5500,0950,0004380,82426686,930,07922

0,5600,0900,0004420,83226941,800,07364

0,5700,0950,0004460,84027194,520,07629

0,6000,0980,0004580,86327940,370,07456

0,6200,1010,0004660,87828427,850,07422

Tha so ma sat trong ong dan ng knh 1_ dai 1,5mng 1" (l = 1,5 m)

P mngP ngQvRef

0,0950,0200,0001730,32610568,340,06381

0,1600,0300,0002280,43013913,320,05522

0,2900,0650,0003120,58819040,240,06389

0,3300,0600,0003340,63020383,250,05146

0,4400,0800,0003890,73323723,490,05065

0,5250,0950,0004270,80426040,030,04992

0,5550,1050,0004400,82826814,640,05204

0,5930,1150,0004550,85827767,940,05315

0,6050,1150,0004600,86728062,950,05204

0,6150,1160,0004640,87428306,680,05159

Tha so ma sat trong ong dan ng knh 1/2_ dai 0,9mng 1/2" (l = 0,9 m)

P mngP ngQvRef

0,0050,0100,0000370,2424182,3710,05188

0,0100,0300,0000530,3486028,5920,07491

0,1330,2500,0002071,36423607,370,04071

0,1900,3350,0002501,64728494,330,03744

0,3100,5350,0003232,13236890,050,03568

0,3450,6500,0003422,25539031,520,03872

0,3800,7250,0003602,37341072,560,03901

0,4050,7010,0003722,45542476,470,03521

0,4130,7200,0003762,48042917,020,03547

0,4210,7300,0003802,50543353,560,03525

Tha so ma sat trong ong dan ng knh 1/2_ dai 1,5mng 1/2" (l = 1,5 m)

P mngP ngQvRef

0,0150,0610,0000660,4317466,280,05860

0,0900,2700,0001681,11019212,280,03983

0,1400,4100,0002131,40224254,840,03795

0,2750,7900,0003042,00134630,910,03587

0,3550,9850,0003472,29039624,280,03416

0,3851,0900,0003632,39141356,750,03470

0,4011,1210,0003702,43842199,040,03425

0,4101,1450,0003752,47142752,290,03411

0,4151,1600,0003772,48643026,530,03412

0,4201,1650,0003802,50243299,200,03383

Bang 6: chieu dai tng ng cua van: mP mngP vanQvv2/2gfRelt

0,030,0029,44E-050,1780,001610,070625753,5890,0003

0,0670,0020,0001440,2720,003760,064948790,4650,0003

0,2650,0030,0002980,5610,016030,0562518155,970,0004

0,4530,0030,0003950,7440,028230,0531924090,690,0004

M hon ton0,570,0040,0004460,840,035970,0519227194,520,0004

0,6330,0050,0004710,8880,040180,0513628740,730,0004

0,6650,0050,0004840,9110,042330,0510929498,220,0004

0,5850,0040,0004520,8520,036970,0517827569,70,0004

0,7030,0050,0004980,9380,044880,050830375,70,0004

0,7130,0050,0005020,9450,045560,0507230602,870,0004

0,030,0019,44E-050,1780,001610,070625753,5890,001

0,1850,0040,0002460,4640,010970,058415020,710,0012

0,3820,0070,0003610,680,023580,0541422018,910,0012

0,520,0110,0004250,80,032650,0524225908,910,0013

M 3/40,610,0120,0004620,8710,038640,0515628185,050,0013

0,6550,0110,000480,9040,041650,0511829263,390,0013

0,6850,0130,0004910,9260,043670,0509429962,920,0013

0,6980,0110,0004960,9350,044540,0508430261,550,0013

0,7030,0120,0004980,9380,044880,050830375,70,0013

0,7150,010,0005030,9470,045690,0507130648,120,0013

0,0520,0080,0001260,2380,002880,066687690,4040,008

0,1280,0570,0002030,3820,007440,0606912368,320,0088

0,2250,030,0002730,5150,013490,0572216654,580,0094

0,5330,2750,0004310,8110,033510,0522926248,590,0102

M 1/20,6050,0830,000460,8670,038310,051628062,950,0104

0,650,0830,0004780,90,041320,0512229145,340,0105

0,670,0970,0004860,9150,042660,0510529615,010,0105

0,6880,090,0004930,9280,043870,0509130032,070,0105

0,6950,090,0004950,9330,044340,0508630192,870,0105

0,7050,0730,0004990,940,045020,0507830421,260,0105

0,020,0357,62E-050,1440,001050,073684645,6950,06

0,220,310,000270,5080,013180,0573516458,310,0771

0,2880,4050,0003110,5860,017510,0557618970,860,0793

0,430,60,0003840,7240,026720,0534823437,540,0827

M 1/40,5030,70,0004180,7860,031530,0526125458,60,084

0,5380,7450,0004330,8150,033850,0522426378,190,0846

0,5550,780,000440,8280,034980,0520726814,640,0849

0,570,790,0004460,840,035970,0519227194,520,0851

0,5780,8030,0004490,8460,036510,0518527395,190,0852

0,590,8150,0004540,8560,037310,0517427693,750,0854

5.2 o th

Gian o the hien moi quan he cua lu lng Q oi vi hieu so thuy au ap suat va qua mang chan va ong venturi. Gin th hin mi quan h h s lu lng k Cm v Cv theo Re. Tha so ma sat f theo Re ong 1 Tha so ma sat f theo Re ong 0.5

Lu lng Q theo ap suat 1 vai o m cua van c tuyn ring v c tuyn van gn vo mng ng ny T o th lu lng Q theo o m cua van ta tm c cac lu lng.

Tnh Q/Q max ta co bang so lieu sau ( vi P = 5cmH2O) mQQmaxQ/Qmax

0,250,000090,016430,0056

0,50,000330,02035

0,750,001270,07718

10,016431

6. BAN LUAN1. Gian o bieu dien lu lng Q oi vi hieu so thuy dau ap suat qua mang chan va Venturi :

o chenh cot ap tang theo luy tha 2 oi vi lu lng p=K1Q

ng vi mot gia tr Q, Pm > Pv th ton that nang lng qua mang ln hn qua venturi2. Gian o bieu dien he so lu lng ke Cm, Cv theo Re :He so lu lng ke khong thay oi oi vi mot loai lu lng ke nhat nh, khong phu thuoc vao che o dong chay trong khu vc Trong thc te, he so Cm, Cv dao ong quanh mot gia tr nhat nh Cm=0,5 Cv=0,8He so Cm, Cv dao ong do dong chay khong on nh, va lech kha nhieu so vi gia tr nhat nh a neu tren v :

Thay oi lu lng

Thay oi o m cua van 15.

C bieu th mc o ton that nang lng khi dong chay qua lu lng ke

Cau tao cua mang chan va venturi la khac nhau. Mang chan thay oi kch thc ot ngot hn nen ton that ap suat ln hn venturi Cm < Cv .

Ton that nang lng cua lu lng khi dong chay qua lu lng ke venturi nho hn ton that nang lng cua lu lng cua lu lng ke mang

Trong th nghim: vi ng knh lo va ng knh lo mang (venturi) bang nhau nen V2 va bang nhau. Do o C t le nghch vi .

Ket qua th nghiem cho thay ket luan tren la phu hp vi thc te.

S phu thuoc cua Cm va Cv theo Re :

Theo phng trnh tren, he so lu lng t le thuan vi van toc dong chay va t le nghch vi . (V) Re tang keo theo tang do o C tang hay giam phu thuoc vao mc o tang nhieu hay t cua Re va .

So sanh lu lng ke mang va venturi :S dng lu lng k mang va venturi u cho kt qu chnh xac. Tuy nhien, chnh xac ca lu lng k venturi co th tt hn, do kch thc co ng thay i t t, khong xy ra hin tng t ngt thay i, lc ma sat cc b s nh hn nhiu so vi lu lng k mang co s thay i ng knh t ngt.Nhng trong qua trnh th nghiem ta lai s dung lu lng ke mang chan do (Pm>(Pv nen khoang Q tra tren o th nhieu hn.3. Gian o bieu dien tha so ma sat f theo Re :Theo ly thuyet : Khu vc chay tang f=f1(Re) Khu vc chay roi thanh trn f=f2(Re) Khu vc qua o t chay roi thanh trn sang chay roi thanh nham: f=f3(Re,/d) Khu vc chay vi thanh nham hoan toan f=f4(/d)Theo thc nghiem : T gian o ta nhan thay cung mot o nham tng oi nhng s phu thuoc cua f theo Re khac nhau khi khao sat tren nhng chieu dai ong khac nhau s khac biet tren la do s khong ong nhat o m cua van 13 gia cac lan th nghiem , s ro r chat long doc ng ong , o nham cua ong khong ong eu doc theo ong (do g set)S phan chia cac khu vc che o chay phu thuoc vao o nham tng oi, ng knh cua ong va van toc lu chat trong ong do o vung Re chay tang cua ong nay co the la vung Re chay roi cua ong kiaT ket qua th nghiem ta thay:Ong 1": f thay oi theo Re chia lam hai khu vc :- f tang khi Re tang t 10000 35000 : Khoang Re nay the hien che o dong chay la chay tang. Ket qua khong phu hp vi ly thuyet.- f khong oi khi Re > 35000 : Khoang Re nay the hien che o dong chay qua o la chay roi thanh trn sang chay roi thanh nham, khi nay f at gia tr gan bang 0,027 .Ong 1/2": f thay oi theo Re chia lam hai khu vc :- f tang khi Re tang t 15000 76000 : Khoang Re nay the hien che o dong chay la chay tang- f khong oi khi Re > 76000 : Khoang Re nay the hien che o dong chay qua o la chay roi thanh trn sang chay roi thanh nham, khi nay f at gia tr gan bang 0,026.4. Gian o bieu dien lu lng Q theo o m cua van tai mot vai ap suat :T gian o ta nhan thay : Van cang m ln th lu lng qua van cang ln ng vi mot ton that cot ap cho trc.

Mc o ton that nang lng cung the hien chieu dai tng ng Le (bang so lieu cho th nghiem 3). o m cang ln th Le cang nho tc ton that cuc bo cang nho.5. ac tuyen rieng cua van tai cac o m khac nhau :

ng ac tuyen rieng cua van nam di ng 450 tc la van s dung la van ca.

o m cua van anh hng nhieu en ton that nang lng cua he thong, gian o cho thay ng vi cung mot tr so lu lng Q th ton that ap suat qua van m 1/4 la cao nhat va qua van m hoan toan la nho nhat do o e giam ton that ta phai m van hoan toan khi s dung.

Do ton that nang lng qua van nen ap suat au ra cua van giam. ieu nay c ng dung lam van tiet lu thay oi ap suat trong he thong dan kh .

6. Cac nguyen nhan gay sai so :

- S ro r chat long doc ng ong, lam ton that nang lng .

-S hoat ong khong on nh cua bm.

-S g set khong ong eu ben trong ong dan en o nham thanh ong khong eu, b ong can

-o m cua cac van khong ong nhat gia cac lan th nghiem .

-Cac gia tr ton that cot ap xac nh bang mat va dao ong lien tuc nen ket qua thu c co sai so.Mot vai so lieu xac nh c la do ket qua cua th nghiem trc nen se dan en hien tng sai so c lap lai nhieu lan.- S dung phng trnh e tra Q.7. PHU LUC7.1 oi n v : Nc 30oC : = 0.804.10-3Pa.s

= 996kg/m3.

Ong 1 D = 0.026m

Ong D = 0.0139m7.2 Xac nh lu lng Q:

(l/s)

7.3 Xac nh he so lu lng Cm va Cv :

0.6115

: mH2O

d = 0.0159m

Q : m3/s

7.4 Xac nh Re :

7.5 Xac nh he so ma sat f :

7.6 Xac nh chieu dai tng ng :

8. TAI LIEU THAM KHAO:[1]. Vu Van Tao va Nguyen Canh Cam, Thuy lc, Tap 1, NXB H va THCN, Ha Noi, 1968

[2]. o Van ai va cac tac gia, C s cac qua trnh va thiet b cong nghe hoa hoc, NXB H va THCN.

Mang chn

Ong Venturi

16

_1366804592.unknown

_1455034938.unknown

_1455077143.unknown

_1455077167.unknown

_1455077187.unknown

_1455077194.unknown

_1455077181.unknown

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