giao trinh bom, quat, may nen vinamain

8/2/2019 Giao Trinh Bom, Quat, May Nen Vinamain

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T.S LE XUAN HOA Th.S NGUYEN TH BCH NGOC

GIAO TRNH

BM

QUATMAY NEN

TRNG AI HOC S PHAM KY THUAT TP HO CH MINH9/2004

Bo Tr Cng Nghip Vit Nam Vinamain.com


2/218

3

LI NOI AU

Bm, quat, may nen la mot trong nhng mon hoc chuyen nganh quantrong cua sinh vien nganh Cong nghe Nhiet ien lanh. Cuon sach nay c

bien soan nham ap ng yeu cau cua sinh vien Trng ai hoc S pham kythuat ve sach tai lieu chuyen nganh.

Sach Bm, quat, may nen gom 8 chng co noi dung e cap en cac ly

thuyet c ban ve cac loai may bm chat long va chat kh, cac loai may quat vamay nen kh dung trong cong nghiep va dan dung, lam c s cho sinh vienchuyen nganh Cong nghe Nhiet ien lanh hieu ro ve cac loai bm, quat,may nen thong dung dung trong cac nha may nhiet ien va trong thc te.

Sach se phuc vu tot cho viec giang day, hoc tap va nghien cu trong cactrng ai hoc ky thuat noi chung va Trng ai hoc S pham ky thuat thanhpho Ho Ch Minh noi rieng.



3/218

Muc luc 5

MUC LUCTrang

Li noi au 3Muc luc 5

Chng I : M au 9

1.1- Vai net ve lch s phat trien bm, quat, may nen 9

1.2- nh ngha va phan loai 10

1.3- Cac thong so lam viec c ban 12

Bai tap 15

Chng II: Khai niem chung ve bm 18

2.1- nh ngha va phan loai 18

2.2- Cac thong so lam viec c ban 19

Bai tap 26

Chng III: Bm canh dan 31

3.1- Khai niem chung ve bm canh dan 31

3.2- Bm ly tam 37

3.2.1- Khai niem chung 37

3.2.2- Phng trnh lam viec cua bm ly tam 38

3.2.3- Anh hng cua ket cau canh en cot ap cua bm ly tam 40

3.2.4- Lu lng va hieu suat lu lng 45

3.2.5- ng ac tnh cua bm ly tam 46

3.2.6- ng dung ong dang trong bm ly tam 50

3.2.7- So vong quay ac trng 53

3.2.8- Hien tng xam thc 54

3.2.9- Kiem tra bm 553.2.10- ieu chnh che o lam viec cua bm 56

3.2.11- Ghep bm ly tam 58

3.2.12- Lc doc truc trong bm ly tam - Cach khac phuc lc doc truc 60

3.3- Bm hng truc 65

3.3.1- Cau tao va pham vi s dung 65

3.3.2- Phng trnh lam viec 66

3.3.3- Hnh dang canh 67



4/218

Muc luc 6

3.3.4- ng ac tnh 69

3.3.5- ieu chnh cheo lam viec 70

Bai tap 70

Chng IV: Bm the tch 86

4.1- Khai niem chung ve bm the tch 86

4.1.1- Khai niem chung 86

4.1.2- Cac thong so lam viec c ban cua bm the tch 87

4.2- Bm piston 89

4.2.1- Cau tao, nguyen ly lam viec 89

4.2.2- Phan loai 90

4.2.3- Cach tnh lu lng cua bm piston 91

4.2.4- Chuyen ong khong on nh cua chat long trong bm. Phng trnhBecnuli, cach khac phuc 95

4.2.5- Ap suat cua bm trong qua trnh hut 98

4.2.6- Ap suat cua bm piston trong qua trnh ay 101

4.2.7- Vong quay gii han cua bm piston 103

4.2.8- ng ac tnh 103

4.3- Bm roto 105

4.3.1- Khai niem chung 1054.3.2- Bm banh rang 106

4.3.3- Bm truc vt 115

4.3.4- Bm canh gat 118

4.3.5- Bm chan khong vong nc 123

4.4- Bm piston-roto 125

4.4.1- Khai niem chung, u nhc iem, phan loai 125

4.4.2- Bm piston-roto hng knh 126

4.4.3- Bm piston-roto hng truc 133

Bai tap 136

Chng V: Quat 147

5.1- Khai niem chung ve quat 147

5.2- Quat ly tam 150

5.2.1- Ket cau va mot so chi tiet chnh 150

5.2.2- Cac thong so cua quat ly tam 151

5.2.3- ng ac tnh cua quat ly tam 155



5/218

Muc luc 7

5.2.4- ieu chnh quat 157

5.2.5- La chon quat theo ieu kien cho trc 160

5.2.6- Phan loai quat va mot so chi tiet chnh cua quat ly tam 1605.2.7- Anh hng cua tap chat kh en s lam viec cua quat 163

5.3- Quat truc 166

5.3.1- Nhng chu y ve quat truc 166

5.3.2 - Cac phng trnh c ban cua quat truc 168

5.3.3- Nhng thong so cua quat truc 173

5.3.4- Quat truc nhieu cap 176

5.3.5- ieu kien lam viec cua quat truc 177

5.3.6- ac tnh cua quat truc 177

5.3.7- ieu chnh lu lng 178

Chng VI: Khai niem chung may nen 180

6.1- Khai niem chung 180

6.2- Nhiet ong hoc may nen 183

Chng VII: May nen canh dan 195

7.1- May nen canh dan ly tam 195

7.1.1- Nguyen ly lam viec cua may nen ly tam 1957.1.2- Phng trnh lam viec cua cap may nen 196

7.1.3- Tnh toan lai ng ac tnh 198

7.2- May nen truc 201

7.2.1- Cau tao chung cua may nen truc, cau tao cap 201

7.2.2- Tnh chat, nhng thong so ac trng 202

Chng VIII: May nen the tch 208

8.1- May nen piston 2088.1.1- o th cong ( hay o th ch th) 208

8.1.2- Anh hng cua khoang khong chet 209

8.1.3- Cach bo tr may nen nhieu cap 210

8.2- May nen roto 213

8.2.1- Cau tao, nguyen ly lam viec 213

8.2.2- Cac thong so c ban 214

8.3- ieu chnh che o lam viec cua may nen 216



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Muc luc 8

8.3.1- Yeu cau 216

8.3.2- ieu chnh bang cach thay oi so vong quay 216

8.3.3- ieu chnh bang tiet lu ong nap 2178.3.4- ieu chnh bang cach m van nap 217

8.3.5- Thay oi the tch khoang khong chet 218

8.3.6- Mot so phng phap ieu chnh khac 219

Tai lieu tham khao 220



7/218

Chng I.M au 9

CHNG I: M AU

1.1- VAI NET VE LCH S PHAT TRIEN BM, QUAT, MAY NENBm, quat, may nen thuoc loai cac may thuy lc va may thuy kh.

May thuy lc tho s a co t thi co xa. Guong nc la may thuy lc au tien.Guong nc li dung nang lng cua nc e keo cac coi xay lng thc hoac a nc vaoong ruong, a c s dung khoang 3000 nam trc cong nguyen.

Cac may hut nc co s dung sc ngi va vat c s dung Ai Cap hang mayngan nam trc cong nguyen.

Bm piston c dung the ky th I trc cong nguyen. Bm piston co loai xch vocung c dung rong rai Cai-ro e lay nc o sau 91,5m vao the ky th 5-6 trc congnguyen.

Noi chung trc the ky th 17 may thuy kh rat tho s va t loai.

Bm piston:

Nam 1640 nha vat ly hoc ngi c la Otto Henrich a sang che ra bm piston autien e bm kh va nc dung trong cong nghiep.

Khoang nam 1805 nhabac hoc ngi Anh la Niu Kmen a phat minh ra bm pistone lay nc trong cac nha may khai thac mo, dung xilanh hi ngng tu e tao lccan thiet tren truc may nh ap suat kh quyen.

Nam 1840-1850 nhabac hoc ngi My laVortington a gia thiet c cau cua bm hima trong o piston cua bm va ong c hi c phan bo tren mot truc chung, schuyen ong cua piston c ieu chnh nh mot he thong phan bo hi ac biet.

May canh dan:

Trong nhng nam 1751-1754 nha bac hoc Euler a viet ve ly thuyet c ban cua tuabinnc noi rieng va cua may thuy kh canh dan noi chung, lam c s e hn 80 nam sau, vao

nam 1830 nha bac hoc ngi Phap la Phuoc-nay-ron a che tao thanh cong tuabin nc autien vavao nam 1831 nha bac hoc ngi Nga la Xablucop a sang che ra bm ly tam va quatly tam au tien. ay chnh la nhng bc nhay ln trong lch s phat trien cac may nanglng.

Bm nhieu cap:

Nha Bac hoc v ai ngi Anh la Reynolds khi nghien cu cau tao cua bm nhieu capa a vao nhng thiet b nh hng canh dan xuoi va ngc. Nam 1875 a phat minh raloai bm tng t nh loai bm nhieu cap hien ai ngay nay.



8/218

Chng I.M au 10

May nen:

Phat minh bm khong kh va dang n gian cua may nen hien ai vi mot chu kynen gan lien vi ten tuoi cua nha vat ly v ai ngi c la Gerike vao nam 1640.

S hoan thien may nen the ky 18-19 a thuc ay s phat trien cua cong nghiepquang mo va luyen kim.

Vao cuoi the ky 18 Anh nha bac hoc Vinkinsn a sang che ra may nen piston 2xilanh, nha bac hoc Uatt a che tao thanh cong may hut khong kh co truyen ongbang hi.

May nen nhieu cap co lam lanh trung gian xuat hien Phap vao khoang nhng nam30 cua the ky 19.

May nen nhieu cap co lam lanh trung gian gia cac cap nen xuat hien c vaonam 1849 do nha bac hoc Raten sang che ra.

Quat:

Vao nam 1831 nha bac hoc Nga Xablucop sang che ra quat ly tam au tien dung elam mat ham mo va lam sach may.

ac biet la 80 nam gan ay, ly thuyet ve thuy kh ong lc phat trien rat manh, conhieu thanh tu to ln trong viec ng dung cac phat minh ve lnh vc may thuy kh.

Ngay nay may thuy kh co rat nhieu loai vi nhieu kieu dang khac nhau c dungtrong moi lnh vc cua i song cung nh trong cong nghiep va nong nghiep. e ap ng nhu

cau ve nang lng ngay cang to ln cua cong nghiep hien ai, ngay nay ngi ta a che taoc cac tuabin c ln co cong suat en 500.000 kW hoac ln hn. So lng bm, quat, maynen cung nh tuabin cac chung loai khac nhau a c san xuat hang nam len en hang trieuchiec.

1.2- NH NGHA VA PHAN LOAI

1.2.1- nh ngha

Bm la may e di chuyen dong moi chat va tang nang lng cua dong moi chat. Khibm lam viec nang lng ma bm nhan c t ong c se chuyen hoa thanh the nang, ongnang va trong mot chng mc nhat nh thanh nhiet nang cua dong moi chat.

May e bm chat kh, tuy thuoc vao ap suat at c c goi la quat, may hut kh vamay nen kh.

Quat la may e di chuyen chat kh vi c so tang ap < 1,15 ( - ty so gia ap suatca ra va ap suat ca vao cua may) hay ap suat at c p < 1500 mmH2O.

May hut khla may lam viec vi > 1,15 hay ap suat at c p > 1500 mmH2Onhng khong co lam lanh nhan tao.



9/218

Chng I.M au 11

May nen khla may lam viec vi > 1,15 hay ap suat at c p > 1500 mmH2O vaco lam lanh nhan tao ni xay ra qua trnh nen kh.

1.2.2- Phan loai

a- Phan loai theo nguyen tac tac dung cua may vi dong moi chat trong qua trnh lamviec

Hnh 1.1 - S o phan loai theo nguyen tac tac dung cua may vi dong moi chat.

b- Phan loai theo tnh chat trao oi nang lng va cau tao

Bm co ba loai:

1. Bm canh dan: gom Bm ly tam Bm hng truc Bm hng cheo Bm xoay

2. Bm the tch: gom Bm piston Bm roto Bm piston-roto

3. Bm phun tiaQuat ch co loai canh dan gom:

1. Quat ly tam2. Quat truc

May nen co ba loai:1. May nen canh dan: gom

May e chuyen chat long va kh

May nenkh

Cho nc sachva dung dch

Cho hon hp at,tro va nc

Cho chat long coo nht cao

Phun tia

The tch

Phun tia

The tch

Canh dan

Phun tia

Canh dan

The tch

Canh danCanh dan



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11/218

Chng I.M au 13

g2

vvppzze

2AA

2BBAB

ABBA

Neu 0BAe - dong moi chat c may cap cho nang lng, vay may la bm (chat

long hoac kh).

Neu 0BAe - may c dong moi chat cap cho nang lng, vay may la ong c

thuy kh.

Vay cot ap cua may thuy kh la nang lng n v cua dong moi chat trao oi vi maythuy kh. Cot ap cua may thuy kh la:

g2

vvppzzH

2AA

2BBAB

AB

(1.1)

Thanh phan the nang n v goi la cot ap tnh, ky hieu Ht :

ABABt

ppzzH (1.2)

Thanh phan ong nang n v goi la cot ap ong, ky hieu H :

g2

vvH

2AA

2BB

(1.3)

Vay: t HHH (1.4)

1.3.2- Lu lng

nh ngha:

Lu lng la lng moi chat chuyen ong qua may trong mot n v thi gian. Tuythuoc n v o co lu lng the tch, lu lng khoi lng, lu lng trong lng.

Tnh bang n v the tch, ky hieu Q goi la lu lng the tch, co n v o la m3/s,m3/h, l/s.

Tnh bang n v khoi lng, ky hieu M goi la lu lng khoi lng, co n v o lakg/s, kg/h.

QM

Tnh bang n v trong lng, ky hieu G goi la lu lng trong lng, co n v ola N/s, N/h, kG/s.

gMgQQG (1.5)

1.3.3- Cong suat va hieu suat

Can phan biet ro hai loai cong suat:

Cong suat thuy lc



12/218

Chng I.M au 14

Cong suat tren truca- Cong suat thuy lc: ky hieu Ntl (co n v o la W) la c nang ma dong chat long

trao oi vi may thuy lc trong mot n v thi gian.

Cong suat thuy lc c tnh bang tch cua cot ap vi lu lng trong lng cua may.

QHGHN tl (1.6)

b- Cong suat lam viec: ky hieu N (co n v o laW) la cong suat tren truc cua maykhi may lam viec. Cong suat thuy lc khac cong suat tren truc. Qua trnh lam viec trong maycang hoan thien th N va Ntl cang t khac nhau.

oi vi bm: N > Ntl

QHNN tl

(1.7)

He so < 1 goi la hieu suat cua bm.

oi vi ong c: N < NtlQHNN tl (1.8)

He so < 1 goi la hieu suat cua ong c thuy lc.

c- Hieu suat cua may thuy lc, ky hieu ( o bang % hoac khong co n v o) dunge anh gia ton that nang lng trong qua trnh may trao oi nang lng vi dong moi chat.

T cong thc (1.7) va (1.8) ta co:

N

N tlB (1.9)

tl N

N (1.10)

Trong ieu kien lam viec, cac hieu suat phu thuoc vao rat nhieu yeu to: loai may,kch thc va cau tao cua may, loai moi chat chuyen ong trong may, che o lam viec cua

may, cac ac tnh cua mang ma may lam viec trong o.e anh gia hieu nang lng cua he thong chung gom co may va ong c cua no,

ngi ta con s dung hieu suat cua he thong ht:

tlht N

N

Trong o N cong suat ien e khi ong ong c.

e tnh hieu suat chung cua may thuy lc, ngi ta anh gia thong qua cac dang tonthat.



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Chng I.M au 15

e- Ton that nang lng trong may thuy lc: co 3 dang

Ton that cot ap cua dong moi chat chay qua may goi la ton that thuy lc, c anhgia bang hieu suat thuy lc, con goi la hieu suat cot ap, ky hieu H

Ton that do ma sat cua cac bo phan c kh trong may thuy lc goi la ton that c kh,c anh gia bang hieu suat c kh, ky hieu CK

Ton that do ro r moi chat lam giam lu lng lam viec cua may goi la ton that lulng c anh gia bang hieu suat lu lng, ky hieu Q

Hieu suat chung cua may thuy lc la:

= H.Q.CK (1.11)

BAI TAP

Bai I-1

Mot may thuy lc (bm nc) tieu hao cong suat tren truc N = 18,9 kW, hieu suat cuamay = 0,71. Xac nh cac thong so cua bm: lu lng, cot ap.

Biet ap suat d tai ca ra cua bm m8,50p2

va o chan khong ca vao

mpCK 3

, ng knh ong hut D1 = 100mm, ng knh ong ay D2 = 75mm,1 = 2 = 1 .

Hnh 1.3

Giai:

1) Cong thc tnh cot ap:

g

vvppH

2

21

2212

, bo qua o cao hnh hoc theo e bai

Hayg

vvppH CKAK

2

21

22



14/218

Chng I.M au 16

Van toc v1 , v2 c xac nh t phng trnh lien tuc: Q = v1S1 = v2S2

Ta co:2

11

1

4

d

Q

S

Qv

;

2

22

2

4

d

Q

S

Qv

Thay cac gia tr vao ta c phng trnh ng ac tnh li:

4242

2

4

1

2

2

4

2

2

2CKAK

1,0..81,9.2

16

075,0..81,9.2

16Q8,53

dg2

Q16

dg2

Q16ppH

233437853 Q,,H

2) Cong thc tnh cong suat tieu hao tren truc:

QHN

Hay Q

,

Q..,

,..,

Q

NH

3791

10819

710109183

3

Ket hp 2 phng trnh cot ap, ta thu c phng trnh bac 3 theo lu lng Q:

Q

,Q,,

379133437853 2 hay 0379185333437 3 ,Q,Q,

Giai phng trnh ta thu c: Q = 0,025 m3/s = 25 l/s

Vay cot ap se la: m,,.,,H 9555025033437853 2

ap so: Q = 25 l/s ; H = 55,95 mBai I-2

Mot may bm nc tieu hao cong suat tren truc N = 5,5 kW. Tnh cac thong so : cot

ap, lu lng va hieu suat cua bm. Biet ap suat d ca ra cua bm mp

202

(cot nc)

va ap suat chan khong tai ca vao cua bm mpCK 4

, toc o trong ng ong ay v = 4

m/s, ng knh ong ay d2 = 75mm, ng knh ong hut d1 = 100mm.

Hnh 1.4



15/218

Chng I.M au 17

ap so: Q = 17,65 l/s ; H = 24,56m ; N = 4,24kW ; = 0,75

Bai I-3

Mot may bm nc co ty so 014750,H

H

t

co ap suat ra mp

602

; ap suat vao

mpCK 31

ng knh ong hut D1 = 200mm, ng knh ong ay D2 = 150mm.

Xac nh cac thong so cua bm: H, Q, N. Biet hieu suat = 76% va z1-2 = 0.

ap so: H = 64m ; Q = 92 l/s ; N = 76kW

Bai I- 4

Mot bm nc at cach be hut A vi o cao hut zh = 1,36m. He so ton that trong

ng ong hut = 4.

Tnh cac thong so cua bm: lu lng , cot ap va cong suat tren truc. Biet ap suat d

ca ra cua bm m,p

86812

va chan khong ca vao bm m4HCK ;ng knh ong hut

va ay D1 = 300mm, D2 = 200mm; hieu suat cua bm = 76%.

Hnh 1.5

ap so: Q = 820 m3

/h ; H = 88m ; N = 259 kW.



16/218

Chng II.Khai niem chung ve bm 18

CHNG II : KHAI NIEM CHUNG VE BM

2.1- NH NGHA VA PHAN LOAI2.1.1- nh ngha

Bm la may e tao ra dong chat long. Hay noi cach khac, bm la may dung e dichuyen chat long va tang nang lng cua dong chat long. Khi bm lam viec nang lng mabm nhan c t ong c se chuyen hoa thanh the nang, ong nang va trong mot chngmc nhat nh thanh nhiet nang cua dong chat long.

Vay bm la loai may thuy lc dung e bien oi c nang cua ong c thanh nanglng e van chuyen chat long hoac tao nen ap suat can thiet trong he thong truyen dan thuy

lc.2.1.2- Pham vi s dung

Bm c s dung rong rai trong nhieu lanh vc:

Trong nong nghiep:bm la thiet b khong the thieu e thc hien thuy li hoa channuoi trong trot.

Trong cong nghiep: bm c s dung trong cac cong trnh khai thac mo, quang dauhay cac cong trnh xay dng.

Hien nay trong ky thuat van chuyen, phat trien xu hng dung bm va ng ong dane van chuyen cac san pham cua nganh khai thac mo ( quang dau), hoa chat, nguyenvat lieu xay dng, va o la phng tien van chuyen thuan li va kinh te.

Trong nganh che tao may, bm c s dung pho bien, no la mot trong nhng bophan chu yeu cua he thong ieu khien va truyen ong thuy lc trong may.

2.1.3- Phan loai

a. Theo nguyen ly lam viec va cau tao cua bm (tng t nh phan loai tren)

b. Theo cong dung:

Bm cap nc noi hi ( trong cac nha may nhiet ien) Bm dau ( trong cac he thong truyen ong thuy lc) Bm nhien lieu Bm cu hoa Bm hoa chat

c. Theo pham vi cot ap va lu lng s dung:

Ngi ta chia bm thanh cac loai: bm co cot ap cao, trung bnh hoac thap; bm colu lng ln, trung bnh hoac nho.



17/218


Trong ky thuat co 3 loai bm c s dung rong rai la bm ly tam, bm hng truc vabm piston. Bieu o phan bo pham vi s dung cua cac loai bm thong dung tren c thehien tren hnh 2.1

Hnh2.1 Pham vi s dung cua cac loai bm thong dung

2..2 - CAC THONG SO LAM VIEC C BAN

Hnh 2.2 S o he thong bm

H,m10000

100 1000 10000

10

100

Q, m3/h

Bm hng truc

Bm ly tam

Bmpiston

1000

1

P4

K2

zh

y

z

z

Be cha

ong ay

ong hut

p1= pa

Be hut

Bm

ong c

AKCK

K1

11

2

33

44



18/218


Bm bao gi cung lam viec trong mot he thong ng ong. e biet ro cong dung, quatrnh lam viec va cac thong so c ban cua bm, ta nghien cu s o thiet b cua mot bm lamviec trong he thong n gian tren hnh 2.2

Khi bm lam viec, chat long t be hut qua li chan rac theo ong hut i vao bm. Saukhi qua bm, chat long c bm cap cho nang lng chay vao ong ay e len be cha. Tbe cha chat long c phan phoi ve cac ni tieu thu. Trong he thong truyen ong thuy lc,

chat long sau khi ra khoi bm co ap suat cao, qua bo phan phan phoi i vao ong c thuy lce thc hien cac chuyen ong cua nhng c cau lam viec.

Bm co 5 thong so lam viec c ban: lu lng Q, cot ap H, cong suat N, hieu suat va cot ap hut cho phep [HCK]. Ta se lan lt nghien cu cac thong so nay.

2.2.1- Lu lng La lng chat long ma bm van chuyen c trong mot n v thi gian.

Tuy thuoc n v o co 3 loai lu lng: lu lng the tch Q co n v o la m 3/s, l/s,

m3 /h; lu lng khoi lng M co n v o la kg/s, kg/h, g/s; lu lng trong lng G con v o la N/s, N/h, kG/s,

Lu lng cua bm c xac nh bang cac dung cu o trung bnh lap tren ong aynh ong Venturi, lu lng ke kieu mang chan hoac cac dung cu o trung bnh bang thunglng hoac can at cuoi ong ay. Cac loai dung cu o nay ch xac nh c gia tr trung

bnh cua lu lng trong mot n v thi gian nao o.

2.2.2- Cot ap: ky hieu H (m)

La nang lng n v ma bm truyen c cho chat long. T s o he thong lam vieccua bm (hnh 2.2), ta co:

H = era - evao = e3 - e2

g2

vpz

g2

vpyzH

222

h

233

h

g2

vvppyH

22

2323

(2.1)

Trong o: p2, p3 la cac ap suat tuyet oi

CKa2 ppp ;

AKa3 ppp

pCK, pAK la tr so ap suat oc c tren chan khong ke va ap ke.



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Do o:

CKAK23 pppp

Cong thc tnh cot ap cua bm se thanh:

g2

vvppyH

22

23CKAK

(2.2)

Trong he thong bm ta lay he so hieu chnh ong nang = 1 v dong chay trong hethong bm co tiet dien ong nho va van toc nc ln ngi ta thng coi la dong chay roi vac goi la dong chay roi kch thc be.

Neu ng knh ong hut va ng knh ong ay bang nhau va khong trch lu lngtren ng ong ay th v2 = v3 va khoang cach y co the bo qua ( y 0 ) th tr so cot ap co thexac nh bang cac tr so oc c cua ap ke va chan khong ke lap mieng vao va ra cua

bm:

CKAK

ppH (2.3)

Khi khong co cac so lieu o c cu the cua bm ang lam viec nh pCK, pAK mach co cac so lieu yeu cau cua he thong lam viec nh p1 , p4 , z ta co the tnh cot ap yeucau cua bm theo cac gia tr nang lng be hut va be cha nh sau:

Viet phng trnh nang lng Bernoulli cho mat cat (1-1) va (2-2):

wh

2

22h

2

11 hg2

vpzg2

vp

(2.4)

Hay

wh22

h

2112 h

g2

vz

g2

vpp(2.5)

hwh tong ton that nang lng ong hut.

T ay ta thay, neu p1 = pa va v1 nho th ap suat mieng vao cua bm p2 < pa tc la p2

phai c o bang chan khong ke.

Phng trnh nang lng Bernoulli cho mat cat (1-1) va (2-2) con c viet n gianla:

wh21 hee hay wh12 hee

Tng t ta viet phng trnh nang lng Bernoulli cho mat cat (3-3) va (4-4):

wd

244

d

233 h

g2

vpz

g2

vp

(2.6)

Hay

wd

24

d

2343 h

g2

vz

g2

vpp(2.7)

hw tong ton that nang lng ong ay.



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Ta thay, thngg2

v23 nho hn

wd

24

d hg2

vz rat nhieu nen p3 > p4; neu p4 = pa th

p3 > pa tc la ap suat mieng ra cua bm phai c o bang ap ke.

Phng trnh nang lng Bernoulli cho mat cat (3-3) va (4-4) con c viet n gianla: wd43 hee

Thay e2 va e3 vao phng trnh cot ap, ta co:

wh1wd423 heheeeH

w14wdwh14 heehhee

Hay w

21

2414

14 hg2

vvppzzH

w

21

2414 h

g2

vvppzH

(2.8)

hw = hwh + hw tong ton that nang lng trong he thong.

T cong thc (2.4) ta thay cot ap yeu cau cua bm dung e khac phuc:

Chenh lech o cao hnh hoc gia mat thoang be cha va be hut, con goi la o caodang z

o chenh ap suat tren mat thoang be cha va be hut 14 pp

o chenh ong nang gia be cha va be hutg2

vv 2124

Ton that nang lng trong he thong ng ong hw.Cot ap cua bm lam viec trong mot he thong cung chnh la cot ap cua he thong.

Cac thanh phan z va 14 pp la nhng ai lng khong thay oi oi vi mot he thong

cho trc, do o:

14t

ppzH goi la cot ap tnh cua he thong (2.9)

Con cac so hangg

vv

2

2

1

2

4 va hw la nhng ai lng thay oi theo lu lng cua he

thong, tc la phu thuoc van toc dong chat long trong ong, do o:

w

21

24

d h

g2

vvH

- goi la cot ap ong cua he thong (2.10)

Vay: H = Ht + H (2.11)



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Neu bieu dien bang o th phng trnh cot ap cua he thong (2.8) ta se c ngcong bieu th ac tnh lam viec cua he thong goi la ng ac tnh cua he thong hay con goila ng ac tnh li.

Hnh 2.3 ng ac tnh li

2.2.3- Cong suat va hieu suat

Theo (1.6) ta co cong thc tnh hieu suat thuy lc cua bm la:QHGHN tl (2.12)

- khoi lng rieng cua chat long, tnh bang N/m3

Q - lu lng cua bm, m3/s

H - cot ap toan phan cua bm, m

Muon tao c Ntl ( con goi la cong suat co ch) th truc bm phai co cong suat ln

hn, v trong khi lam viec bm phai tieu hao mot phan nang lng e bu vao cac ton that

thuy lc va ton that ma sat gia cac bo phan lam viec cua bm,

QHN

N tl (2.13)

< 1 la hieu suat toan phan cua bm, %

Hieu suat la:N

QH

N

N tl (2.14)

Khi chon ong c e keo bm, can phai chon cong suat cua ong c N c ln hn cong

suat tai truc N e e phong trng hp qua tai va bu vao ton that do truyen ong t ong c

en bm.

Nc = k.N (2.15)

H

0 Q

H,m

Q, m3/s

Ht

H = kQ2



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k > 1 he so an toan phu thuoc tng loai bm, ong c va cong suat lam viec.

2.2.4- Cot ap hut va chieu cao hut cho phep

Kha nang lam viec cua bm phu thuoc rat nhieu vao qua trnh hut cua bm. Trong

qua trnh bm hut chat long, banh cong tac phai tao c o chenh ap nhat nh gia mienghut cua bm va mat thoang cua be hut. o chenh ap nay goi la cot ap hutcua bm, nh noma chat long chay t be vao bm.

Hnh 2.4 S o li tren ng ong hut

21h ppH (2.16)

p1 , p2 - ap suat mat thoang cua be hut va loi vao cua bm

Neu p1 = pa ( ap suat kh tri) th cot ap hut bang cot ap chan khong tai loi vao cuabm.

2aCKh

ppHH (2.17)

Thay phng trnh (2.4) vao phng trnh tren ta co:

w

22

h21

h hg2

vz

ppH

(2.18)

Ta thay cot ap hut cua bm dung e khac phuc chieu cao hut zh , ton that tren ong huthw va tao nen ong nang can thiet cua dong chay mieng vao cua bm v 2

2/2g. Suy ra cot ap

hut tuy thuoc vao tr so ap suat tren mat thoang cua be hut ma ap suat nay lai co gii hannhat nh.

Trng hp p1 = pa theo cong thc (2.18) ta thay kha nang hut toi a cua bm ng vi

khi ap suat p2 = 0 la:

zh22pa

11



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OmH10p

HH 2a

maxCKmaxh

Vay ieu kien e bm lam viec c la:

maxCKw

22

hh Hhg2

vzH (2.19)

Thc te cot ap hut cua bm khi p1 = pa khong bao gi at c en 10 mH2O v apsuat mieng ra cua bm khi nho en mot mc nao o bang ap suat hi bao hoa cua chatlong tai nhiet o lam viec th se gay ra hien tng xam thc trong bm.

Hien tng xam thc

Khi chat long mot nhiet o nhat nh se soi va boc hi bao hoa di mot ap suatnhat nh. Ap suat nay goi la ap suat hi bao hoa pbh.

Bang ap suat hi bao hoa cua nc:

Nhiet o, toC 0 10 20 30 40 60 80 100 120

m,pbh

0,06 0,12 O,24 0,48 0,75 2,03 4,83 10,33 20,2

Nh vay mot nhiet o nao o, khi ap suat trong chat long bang ap suat hi bao hoapbh th chat long se soi, tao nen nhieu bot kh trong dong chay. Cac bot kh nay b dong chaycuon vao nhng vung co ap suat p > pbh , se ngng tu lai ot ngot thanh nhng giot chat longco the tch nho hn rat nhieu so vi the tch cua bot kh. Do o trong dong chay xuat hiennhng khoang trong cuc bo, thu nhng phan t chat long xung quanh xo ti vi van toc ratln, lam cho ap suat tai o ot ngot tang len rat cao, co khi ti hang ngan atmotphe. Ap suatcuc bo nay co the lam ro be mat kim loai, pha hong cac bo phan lam viec cua may. Hientng nay goi la hien tng xam thc, thng xay ra trong cac may thuy lc co ap suat nho,nhiet o cao. Nhat la ni chat long co van toc va ap suat thay oi ot ngot.

Khi hien tng xam thc xay ra, dong chay b gian oan, gay tieng ong bat thngva may b rung nhieu, lu lng, cot ap va hieu suat cua may b giam ot ngot. Hien tngxam thc keo dai se lam cac bo phan lam viec cua may b pha hong.

e tranh hien tng xam thc, can thoa man ieu kien:

bh2 pp

Cho nen e tranh hien tng xam thc, oi vi tng loai bm c san xuat ra, trongcac tai lieu ky thuat eu co ghi cot ap chan khong cho phep [HCK] ng vi pa = 1 at va

t = 20oC.

ieu kien e bm co ay u kha nang hut la:



24/218


CKw22

hh Hhg2

vzH (2.20)

Vay chieu cao hut cho phep cua bm la:

w22

CKh hg2

vHz (2.21)

Neu khong co gia tr [HCK] th [zh] phai c tnh theo ieu kien khong xay ra hientng xam thc.

Ta biet rang, ieu kien e khong xay ra hien tng xam thc la cot ap toan phan tailoi vao cua bm, ni co ap suat nho nhat, nguy hiem nhat phai ln hn ap suat hi bao hoacua chat long tai nhiet o lam viec.

Ta co: hpg2

vp bh2

22

(2.22)

h cot ap chong xam thc

Mat khac, t cong thc (2.4), ta co:

wha

222 hz

p

g2

vp

Thay vao bieu thc tren ta co chieu cao hut cho phep cua bm la:

w

bhah hhppz (2.23)

Cot ap chong xam thc h c xac nh bang thc nghiem, no phu thuoc vao sovong quay va lu lng cua bm. Theo Rutnhep, ta co:

3

4

C

Qn10h

(2.24)

n so vong quay trong mot phut cua banh cong tac

Q lu lng tnh bang m3/s

C he so phu thuoc vao ac iem ket cau cua bm, co gia tr thay oi trong khoang8001000. C lay gia tr cang ln th ieu kien chong xam thc cua bm cang tot.

BAI TAP

Bai II-1

Mot may bm nc tieu hao mot cong suat tren truc N = 66 kW, hieu suat = 81%,lu lng Q = 500m3/h va cot ap chan khong cho phep cua bm [HCK ] = 5,5 m



25/218


Tnh chieu cao hut cho phep cua bm [Zh ], biet he so ton that tren ng ong huth = 5 va ng knh ong hut va ong ay bang nhau D1 = D2 = 250mm.

Tnh cot ap va ap suat tai ca ra cua bm.

Hnh 2.5

Giai:

1) Chieu cao hut cho phep cua bm tnh theo cong thc:

g

v

g

vHZ hh

hCKh

22

22

; bo qua ton that doc ng va lay dau =

Van toc tren ng ong hut c tnh theo lu lng va van toc:2

4

h

hD

Qv

Vi Q = 500m3/h = 0,139 m3 /s ; Dh = D1 = 250mm = 0,25m thay vao:

s/m,,.

,.vh 832

250

139042

hay m,

,.

,

g

vh 408192

832

2

22

Vay chieu cao hut la: m,,.,,Zh 134054055

2) T cong thc tnh cong suat tren truc:

QHN hayQ

NH

Cot ap cua bm la: m2,39139,0.10.81,9

81,0.10.66H

3

3

3) Ap suat tai ca vao cua bm tnh t phng trnh Bernoulli tai mat cat tren matthoang cua be hut va mat cat tai loi vao bm:

g

v

g

vpZ

phh

a

22

2

2

2

22



26/218


Hay m,,.,,g

v

g

vZ

pphh

a 5440540131022

2

2

2

22

T cong thc:

23

2

2

2

323 pp

g2

vvpp

yH

Vay ap suat tai ca ra cua bm la:

m7,435,42,39p

Hp 23

ap so: [Zh] = 3,1m ; H = 39,2m ; m,p

7432

Bai II-2

Mot bm tieu hao mot cong suat tren truc N = 76 kW, bm nc t be kn A co ap

suat nho hn kh tri mpCK 4

len be kn B co ap suat ap ke mpAK 10

. o chenh gia 2

be z = 40m.

Tnh lu lng va cot ap cua bm. Biet hieu suat cua bm %76 , ton that toan bo

trong he thong li mhw 10 , ng knh ong hut va ong ay bang nhau.

Hnh 2.6

Giai:

+ Phng trnh ng ac tnh li:

W

ABAB hg

vvppzH

2

22

mpppp CKAKAB 14

;



27/218


02

22

g

vv AB v ng knh ong hut va ong ay bang nhau.

mH 641001440

+ Lu lng:

T cong thc tnh cong suat:

QHN

Ta co: s/ls/m,..,

,..

H

NQ 920920

6410819

7601076 33

3

ap so: H = 64m ; Q = 92 l/s.

Bai II-3

Bm ly tam at vi o cao hut m,z h 7953 , ton that trong ong hut .m,hwh 5051

Ap suat toan phan mieng ra m7,74g2

vp2

33

.

Xac nh cot ap cua bm va ton that tren ng ong ay. Biet o cao gia 2 be chaHT = 68m; ng knh ong hut va ng knh ong ay bang nhau.

Hnh 2.7

ap so: H = 80m ; m,hwh 49510 .

Bai II-4

Xac nh cong suat cua mot ong c keo bm, lu lng Q = 400l/s co o cao hutz h = 3,5 m, ton that trong ong hut m,hwh 70 , o cao ong ay H = 50m, ton that trongng ong ay m,hw 85 , hieu suat cua bm = 80 %.



28/218


Hnh 2.8

Hng dan:Tnh cong suat cua ong c theo cong thc sau: Nc = k.NB, trong ok = 1,05.

ap so: Nc = 282 kW.



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Chng III. Bm canh dan 31

CHNG III: BM CANH DAN

3.1- KHAI NIEM CHUNG VE BM CANH DAN

3.1.1- Khai niem chung

Trong lch s phat trien cua may thuy lc th may thuy lc canh dan ra i tng oimuon so vi may thuy lc the tch. Nam 1640, bm piston au tien do nha bac hoc ngi csang che a ra i va c dung e bm nc va kh trong cong nghiep. Nhng mai en nam1830 nha bac hoc ngi Phap Phuocnayron mi che tao thanh cong tuabin nc. Sau o nam1831 va 1832 nha bac hoc ngi Nga Xablucop sang che ra bm va quat ly tam. o la nhngmay thuy lc canh dan au tien. Nhng hien nay may thuy lc canh dan c s dung phobien nhat va pham vi s dung ngay cang c m rong.

May thuy lc canh dan bao gom cac loai bm va ong c canh dan nh: bm ly tam,bm hng truc, cac loai tuabin nc

Trong may thuy lc canh dan viec trao oi nang lng gia may vi chat long cthc hien bang nang lng thuy ong cua dong chat long chay qua may.

3.1.2- Nguyen ly lam viec va cau tao chung

Bo phan quan trong va ien hnh nhat cua bm canh dan la banh cong tac. Banh congtac c cau tao t cac ban canh thng co dang mat cong goi la canh dan va cac bo phan conh chung. Trong banh cong tac cac canh dan c ghep chat vi truc, khi lam viec banh

cong tac quay trong moi trng chat long.Banh cong tac cua bm quay c la nh ong c keo ben ngoai va trong qua trnh

o, do co cac canh dan ma c nang cua ong c truyen c cho chat long, tao nen dongchay lien tuc qua banh cong tac. Chenh lech nang lng thuy ong cua chat long loi ra valoi vao cua banh cong tac chnh bang c nang cua bm a truyen cho chat long ( cha ke titon that).

3.1.3- Phan loai banh cong tac

Theo phng chuyen ong cua dong chat long t loi vao en loi ra cua canh dan,

banh cong tac canh dan c chia thanh bon loai sau: Banh cong tac ly tam hoac hng tam: chat long chuyen ong qua banh cong tac t

tam ra ngoai hoac t ngoai vao tam theo phng ban knh.

Banh cong tac hng truc: chat long chuyen ong qua banh cong tac theo phngsong song vi truc.

Banh cong tac tam truc hoac truc tam: chat long chuyen ong qua banh cong tac theohng tam roi chuyen sang hng truc hoac ngc lai.

Banh cong tac hng cheo: chat long chuyen ong qua banh cong tac khong theohng tam cung khong theo hng truc ma theo hng xien (cheo).



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3.1.4- Cac loai van toc ,tam giac van toc

Qu ao chuyen ong cua cac phan t chat long qua banh cong tac canh dan rat phctap nhng e n gian tnh toan, ngi ta gia thiet:

Dong chay qua banh cong tac bao gom cac dong nguyen to nh nhau

Qu ao chuyen ong tng oi cua cac phan t chat long trong banh cong tac theobien dang canh dan.

ieu kien e co dong chay nh gia thiet tren la:

Banh cong tac co so canh dan nhieu vo cung va moi canh dan mong vo cung ( canhdan khong co chieu day)

Chat long lam viec la chat long ly tng.Vi gia thiet tren, chuyen ong tuyet oi cua moi phan t chat long qua banh cong

tac co the phan tch thanh 2 chuyen ong ong thi: chuyen ong theo ( quay tron cung banhcong tac) va chuyen ong tng oi ( theo bien dang canh dan).

Chuyen ong cua cac phan t chat long qua banh cong tac c ac trng bang cacvan toc:

c - van toc tuyet oiu - van toc theo (cua chuyen ong theo), co phng thang goc vi ban knhv - van toc tng oi, co phng tiep tuyen vi bien dang canh dan.

vuc (3.1)

Hnh 3.1 Bieu dien cac loai van toc

Hnh 3.1 bieu th van toc cua cac phan t chat long loi vao va loi ra cua banh congtac bm ly tam.

Ch so (1) va (2) bieu th cho chat long bat au vao va ra khoi banh cong tac. e tienviec nghien cu cac thanh phan van toc cua dong chay, ta dung cac tam giac van toc thaycho cac hnh bnh hanh van toc. Ta co cac tam giac van toc loi vao va ra cua banh cong

tac:

c2

u

c1

w1

11

22u2w2

R2

R1



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Hnh 3.2 Tam giac van toc

Khi dung tam giac van toc e bieu th cac thong so ong hoc cua chat long ngoai cacky hieu c , u , w ta con a vao cac ky hieu sau:

- goc gia u va c - goc gia w va u theo hng ngc lai, bieu th goc bo tr canh dan

1 goi la goc vao , 2 goi la goc rauc -hnh chieu cua c len phng u ;

Rc - hnh chieu cua c len phng vuong goc vi u .

Trong cac banh cong tac ly tam hoac hng tam phng cua Rc bao gi cung i quatam cua banh cong tac goi la thanh phan van toc hng knh.

Trong banh cong tac hng truc Rc hng theo phng truc.

3.1.5- Phng trnh c ban cua may thuy lc canh dan

a- Phng trnh moment

Mat cat cua mot banh cong tac canh dan:

Hnh 3.3 Mat cat cua banh cong tac

1.Banh cong tac 2.a trc (a phu)

3.Canh dan 4.a sau (a chnh)

5.Ranh canh

u2

c1 R

c1u11

w1c1

u1

c2

c2R

c2u22

w2



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Hnh 3.4 Cac thanh phan van toc va tam giac van toc

ng dung nh ly c hoc ve bien thien moment ong lng, ta co the phat bieu oivi dong chat long chuyen ong qua banh cong tac nh sau:

Bien thien moment ong lng cua khoi chat long chuyen ong qua banh cong tactrong mot n v thi gian oi vi truc quay cua banh cong tac th bang tong moment ngoailc tac dung len khoi chat long o oi vi truc, tc la bang moment quay cua banh cong tac.

Xet mot dong nguyen to trong khoi chat long chuyen ong qua banh cong tac cuabm ly tam. Dong nguyen to co lu lng dQ, ong lng cua no tai mat cat (1-1) la:

111 c.dQ.c.mdKd

Tng t tai mat cat (2-2) la:

222 c.dQ.c.mdKd m, - khoi lng va khoi lng rieng cua chat long

c van toc thuyet oi.

Moment ong lng cua dong nguyen to oi vi truc quay cua banh cong tac tai matcat (1-1) va (2-2) la:

111111 cos.R.c.dQ.l.KdLd

222222 cos.R.c.dQ.l.KdLd

Bien thien moment ong lng cua dong nguyen to chat long trong mot n v thigian:

11122212 cosR.ccosR.c.dQ.dLdLL

V ta a gia thiet cac dong nguyen to chay qua banh cong tac la nh nhau, nen bienthien moment ong lng cua toan bo khoi chat long chuyen ong qua banh cong tac bang

tong bien thien moment ong lng cua cac dong nguyen to: 111222 cosR.ccosR.c.dQ.L

c2

l1l2R1

R2

22

11

u

c1

w1

11

22u2w2

R2

R1



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111222 cosR.ccosR.c.dQ.

111222l cosR.ccosR.c.Q.

Ql lu lng chay qua banh cong tac va chnh bang lu lng ly thuyet.

Goi M la moment do ngoai lc tac dung len truc quay, tc la moment quay cua tructh: LM

111222l cosR.ccosR.c.Q.M (3.2)

Vay phng trnh moment quay cua banh cong tac co dang tong quat la:

111222l cosR.ccosR.c.Q.M (3.4)

Hang dau tren cho may bm va hang dau di cho tuabin.

b- Phng trnh cot ap

Ta a biet, cot ap H cua may thuy lc canh dan la nang lng n v cua dong chatlong trao oi vi may thuy lc, no chnh la cong cua mot n v trong lng chat long traooi vi may.

Hn na, cong suat thuy lc cua may quan he vi cot ap la:

lllltl HgQHQN (3.5)

Hl - cot ap cua may ng vi trng hp dong chay qua may thoa man cac gia thieta neu, tc la khong co ton that va banh cong tac co so canh dan nhieu vo cung, con goi la

cot ap ly thuyet vo cung.Mat khac, cong suat tren truc quay la:

.MN (3.6)

Neu khong ke ti ton that, th cong suat thuy lc bang cong suat tren truc quay, do o:

.MHgQ ll

Thay tr so cua M theo cong thc (3.4) vao va bien oi, ta co:

g.cosRccosRc

H111222

l

(3.7)

Ta thay 11 uR , 22 uR

va u111 ccosR , u222 ccosR vao bieu thc tren, ta thu c:

g

cucuH u11u22l

(3.8)

ay laphng trnh c ban cua may thuy lc canh dan con goi laphng trnh Euler.

c- Y ngha nang lng cua phng trnh c ban



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T cac tam giac van toc ta co:

u1121

21111

21

21

21 cu2uccoscu2ucw

u2222

22222

22

22

22 cu2uccoscu2ucw

T ay ta rut ra:

212121u11 wuc21cu

222222u22 wuc21cu

Thay vao phng trnh c ban ta c:

oi vi bm:g2

cc

g2

ww

g2

uuH

21

22

22

21

21

22

l

oi vi ong c:g2

ccg2

wwg2

uuH

22

21

21

22

22

21

l

So hangg2

cc 2122 hay

g2cc 22

21 - la phan thay oi ong nang n v cua dong chay khi

i qua banh cong tac, no bieu th thanh phan cot ap ong H l.

So hang

g2

uu 2122 hay

g2

uu 2221 - ty le vi so vong quay va ng knh banh cong tac,

no bieu th thanh phan cot ap tnh tng oi c tao thanh do lc ly tam tac dung len dongchay. Trong trng hp bm hng truc R1 = R2, th so hang nay bang khong.

So hangg2ww 22

21 hay

g2ww 21

22 - phu thuoc o m rong mang dan cua banh cong tac,

oi vi bm 21 ww , chng to mot phan ong nang bien thanh ap nang.

Do o, cot ap tnh la:

g2

ww

g2

uuH

22

21

21

22

tl

Vay: tldll HHH (3.9)

3.2 - BM LY TAM



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3.2.1- khai niem chung

u iem c ban cua bm ly tam:

Bm c nhieu loai chat long nh nc, dau, nhien lieu, hoa chat, ke ca cac honhp cua chat long va chat ran.

Pham vi s dung ln va nang suat cao, cu the:- Cot ap H t 10 mH2O en hang ngan mH2O- Lu lng Q t 2 70.000 m3/h- Cong suat t 1 6000 kW- So vong quay t 730 6000 v/ph.

Ket cau nho gon, chac chan, lam viec tin cay. Hieu suat cua bm tng oi cao so vi cac loai bm khac: = 0,65 0,90. Ch tieu kinh te tot ( gia thanh tng oi re).

S o ket cau cua mot bm ly tam n gian bieu th tren hnh 3.5

Hnh 3.5 S o ket cau cua bm ly tam

Bm ly tam gom cac bo phan chu yeu sau:

1 - Banh cong tac 2 - Truc bm

3 - Bo phan dan hng vao 4 - Bo phan dan hng ra ( con goi la buong xoan oc)

5 - Ong hut 6 -Ong ay

Trc khi cho bm lam viec can phai lam cho than bm trong o co banh cong tac vaong hut c ien ay chat long, goi la qua trnh moi bm.

6

42

1

3

5



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Qua trnh lam viec:

Khi bm lam viec, banh cong tac quay, cac phan t chat long trong banh cong tacdi anh hng cua lc ly tam b don t trong ra ngoai chuyen ong theo cac mang dan va ivao ong ay vi ap suat cao hn, o la qua trnh ay cua bm. ong thi loi vao cua banh

cong tac tao nen mot vung co ap suat chan khong, va di tac dung cua ap suat be chaln hn ap suat loi vao cua bm, chat long be hut lien tuc b hut vao bm theo ong hut.o la qua trnh hut cua bm. Qua trnh hut va ay cua bm la cac qua trnh lien tuc, tao nendong chay lien tuc qua bm.

Bo phan dan hng ra, co dang xoan oc nen goi la buong xoan oc la e dan chat longt banh cong tac ra ong ay c ieu hoa, on nh va con co tac dung bien mot phan ongnang cua dong chat long thanh ap nang can thiet.

3.2.2- Phng trnh lam viec cua bm ly tam

a- Phng trnh c ban cua bm ly tam (phng trnh cot ap):

Bm ly tam la mot dang cua bm canh dan, t phng trnh c ban cua may thuy lccanh dan , ap dung cho bm canh dan ta co:

g

cucuH u11u22l

(3.10)

Trong cac bm ly tam hien ai, a so cac banh cong tac co ket cau loi vao hoac bophan dan hng vao sao cho dong chat long loi vao cua mang dan chuyen ong theo hngknh, ngha la c vuong goc vi u tc la 1 = 90o, e cot ap cua bm co li nhat (c1u = 0).

Tam giac van toc loi vao la tam giac vuong, ta co:

Hnh 3.6 Tam giac van toc loi vao cua banh cong tac

Khi o phng trnh c ban cua bm ly tam co dang la:

gcu

H u22l (3.11)

b- Cot ap thc te:

Ta a biet, phng trnh c ban cua bm ly tam c lap t ieu kien gia thiet lythuyet:

- Canh dan nhieu vo cung va mong vo cung- Chat long la ly tng.

u1

c1 w1

11= 90o



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Vi gia thiet th nhat ta co van toc phan bo eu tren cac mat cat cua dong chay quacac mang dan. Vi gia thiet th hai ta bo qua ton that cua dong chay trong cac mang dan. Vthe nen cot ap tnh theo phng trnh c ban goi la cot ap ly thuyet ng vi so canh dannhieu vo cung (Hl).

Thc te, canh dan co chieu day nhat nh t 2 20mm va so canh dan hu han t6 12 canh gay nen s phan bo van toc khong eu tren cac mat cat cua dong chay, tao nencac dong xoay cac dong quan trong mang dan. ieu nay the hien tren hnh (3.7)

Hnh 3.7 Phan bo van toc trong mang dan

Mat khac, chat long co o nht do o gay nen ton that trong dong chay. V vay cot apthc te nho hn cot ap Hl .

Cot ap thc te cua bm ly tam H c tnh theo cong thc sau:

lHZ H..H (3.12)

Z he so ke ti anh hng cua so canh dan hu han en cot ap, goi la he so cot ap;bang ly thuyet ve dong xoay va thc nghiem, nam 1931 vien s Protskua a xac nh Z oivi bm ly tam theo cong thc sau:

2Z sinZ1 (3.13)

Z so canh dan cua banh cong tac.Vi Z va 2 thong thng th tr so trung bnh cua he so cot ap 8,0Z .

H he so ke ti ton that nang lng cua dong chat long chuyen ong qua banh congtac, no phu thuoc vao rat nhieu yeu to nh kch thc, ket cau cua banh cong tac va bo phanhng dong goi la hieu suat cot ap cua banh cong tac.

Vi bm ly tam: 9,07,0H .

Trng hp ke ti anh hng cua so canh dan hu han en cot ap, ta co cot ap ly

thuyet ng vi so canh dan hu han la: lZl H.H (3.14)

wmax

wmin



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Cot ap thc te cua bm ly tam la:

gcu

..H u22HZ (3.15)

oi vi bm co ket cau va so vong quay thong thng th:

2u

.cosc..c.. 222HZu2HZ

Vay trong tnh toan gan ung, co the xac nh cot ap thc te cua bm ly tam theo bieuthc:

g2u.

H22 (3.16)

- he so cot ap thc te.3.2.3 Anh hng cua ket cau canh en cot ap cua bm ly tam

Hnh dang bo tr ket cau cua canh dan chu yeu phu thuoc vao goc 1 va 2 tc la gocvao va ra cua canh dan. Ta xet anh hng cua cac goc nay en cot ap cua bm ly tam.

a- Anh hng cua goc1

Goc vao 1 la goc bo tr canh dan cung la goc bieu th phng cua van toc tng oi loi vao cua banh cong tac. Trng hp co li nhat ve cot ap cua bm th tam giac van toc loi vao la tam giac vuong co 1 = 90o. T hnh (3.6), ta thay 1 ch phu thuoc vao u1 va c1, ta

co:

1

11 u

ctg (3.17)

Theo phng trnh c ban cua bm ly tamgcu

H u22l ta thay goc 1 khong anh

hng trc tiep en cot ap cua bm ly tam. Nhng neu 1 khong thch hp se gay ra va apdong chay vi canh dan loi vao banh cong tac anh hng xau en hieu suat va cot ap cuabm.

Ngi ta thng chon 1 = 15o 30o.

b- Anh hng cua goc 2

Ly thuyet va thc nghiem chng to rang tr so cua 2 co anh hng trc tiep enphng va gia tr cua cac thanh phan van toc cua dong chay trong mang dan, do o co anhhng quyet nh en cot ap toan phan H va cac cot ap thanh phan Ht va H cua bm. V vayoi vi banh cong tac bm ly tam, goc 2 co y ngha ac biet quan trong.

Tuy theo tr so cua 2, banh cong tac co 3 cach bo tr canh dan:

2 < 90

o

: canh dan cong ve pha sau ( so vi u) goi la banh cong tac co canh dan ngoatsau ( a) loai a thng gap bm e bm cac chat long nh nc, dau,

2 = 90o : canh dan hng knh loi ra goi la banh cong tac co canh dan hng knh (b).



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2 > 90o : canh dan cong ve pha trc goi la banh cong tac co canh dan ngoat trc ( c) loai b,c thng gap quat va may nen e bm cac chat kh

Hnh 3.8 Cac cach bo tr canh dan

Hnh 3.9 Hnh dang canh dan cua banh cong tac

Ngoai ra trong thc te, ngi ta con che tao hnh dang canh dan cua banh cong tac rata dang, hnh 3.9 bieu dien mot so loai canh dan co goc ra 2 khac nhau:

e hieu ro vai tro cua 2 oi vi cot ap cua bm ta xet 3 banh cong tac ly tam co:

- kch thc nh nhau- goc vao 1 nh nhau- so vong quay lam viec nh nhau- goc ra2 khac nhau.

w2

a) 2 < 90o

c2

b) 2 = 90o

c) 2 > 90o

2

c2

u2

u12

w2

u2

u12

2u2

u1

w2

c2



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Ta khao sat cot ap do tng loai banh cong tac tao nen vi cac kieu canh dan noi tren.Khi ve cac tam giac van toc cho kieu banh cong tac nay ta can chu y:

Cac banh cong tac co 1, kch thc loi vao, lu lng va so vong quay lam viec nhnhau nen co tam giac van toc loi vao nh nhau.

Cac banh cong tac co ng knh ngoai D2 va vong quay lam viec nh nhau nenchung co van toc vong u2 bang nhau.

Ta co cac tam giac van toc la:

Hnh 3.10 Tam giac van toc loi vao

Hnh 3.11 Tam giac van toc loi ra

T phng trnh c ban cua bm ly tamgcu

H u22l , ta thay trong ca 3 trng hp co

u2 nh nhau nen Hl ch phu thuoc vao c2u. Ta xet s thay oi cua cot ap Hl trong ca 3trng hp tren.

* Khi 2 < 90o

T tam giac van toc bieu th tren hnh a, ta co:

2R22u2 gcotcuc (3.18)

Thay vao phng trnh c ban (3.11) ta c:

ggcotcuu

H 2R2222

l

(3.19)

Ta thay, khi 0gcotcuc 2R22u2 tc la:

R2

22 c

ugcot hoac2

R22 u

carctg

u1

c1 w1

1

1= 90o

c1R= c2R

c2 c2 c2

c2u < u2

c2R

a) b) c)

w2w2

u2 u2 u2

c2u = u2 c2u = 2u2

c2R

w2

c2R

2 < 90o 2 = 90o 2 > 90

o



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th Hl = 0 ngha la bm lam viec khong co cot ap.

Vay muon bm lam viec tao c cot ap th canh dan cua banh cong tac phai co

2 > 2min =2

R2

uc

arctg . Va ta nhan thay Hl tang theo ty le thuan vi 2.

* Khi 2 = 90o

Luc nay tam giac van toc loi ra la tam giac vuong c bieu th tren hnh b, nen2u2 uc do o ta co:

gu

gc.u

H22u22

l

Thng trong bm ly tam tr so cua cR thay oi rat t t loi vao en loi ra cua banhcong tac nen ta co:

c2R = c1R = c1

Khi o cot ap ong la:

g2cc

g2cc

H2

R222

21

22

dl

T hnh b, ta co: 222

R222 ucc , nen:

g2

uH

22

dl (3.20)

Ma cot ap tnh la : dlltl HHH nen ta thu c:

g2u

g2u

gu

H22

22

22

tl

Tc la:g2

u2

HHH

22l

tldl

(3.21)

Ta tiep tuc tang 2 len na ta thay:

* Khi 2 > 90oT hnh c, ta co c2u > u2. ta khao sat trng hp khi c2u = 2u2 , luc o:

gu2

gu2u

gc.u

H2222u22

l

Nh vay Hl = Hl va do o Hlt = 0 tc la khong co cot ap tnh.

Neu ta tiep tuc tang 2 len na th c2u > 2u2 luc o Hl > Hl tc la cot ap ong lnhn cot ap toan phan hay noi cach khac cot ap tnh co tr so am.

Trong thc te, bm khong the lam viec c vi H lt 0 v khi o bm khong co khanang ay chat long. Vay muon cho bm lam viec c th goc ra 2 cua canh dan trong banhcong tac khong c ln qua mot gia tr gii han nao o, tc la:



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2 2max

Vay e cho bm lam viec c th tr so cua goc 2 phai thoa man ieu kien:

2min < 2 < 2max (3.22)

Quan he gia cot ap ly thuyet cua bm va tr so cua goc 2 c bieu th tren hnh 4.8.ng EK ch s thay oi cua cot ap toan phan theo phng trnh:

ggcotcuu

H 2R2222

l

(3.23)

ng EI ch s thay oi cua cot ap tnh theo phng trnh:

g2gcotc

g2u

H2

2R222

tl

(3.24)

Hnh 3.12 - Quan he gia cot ap ly thuyet cua bm va tr so cua goc 2

Qua o th ta thay, goc 2 cang ln th cot ap ly thuyet cua bm cang ln, bm co khanang truyen c nang cho chat long cang nhieu. Nhng trong ky thuat can giai quyet sao choc nang ma bm truyen cho chat long la co li nhat, ngha la co hieu qua cao nhat va apng c cac yeu cau lam viec khac nhau ve cot ap ong va cot ap tnh. Tuy kha nang lamviec khac nhau cua bm ma chon 2 thch hp.

Bm ly tam lam viec trong pham vi:

Hlt = ( 0,7 0,8 )Hl

Hl = ( 0,2 0,3 )Hl

Tc la ng vi 2 = 15o 30o.

90o2 = 2min 2 = 2max

Hl

Hl = u22/g

Hl = 2u22/g

Hlt

Hl

2

Hl = u22/2g

Hlt = u22/2gE I

K

D



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Trong trng hp ac biet 2 = 50o.

3.2.4- Lu lng va hieu suat lu lng

Hnh 3.13 Lu lng chat long trong banh cong tac

Lu lng chat long chay qua banh cong tac cua may thuy lc canh dan noi chung vabm ly tam noi rieng c xac nh theo cong thc:

b.D..cQ Rl (3.25)

b chieu rong mang dan ng vi ng knh D cua banh cong tac (thng la tai loira)

D - ng knh D cua banh cong tac

cR hnh chieu van toc tuyet oi len phng vuong goc vi u.

Lu lng qua banh cong tac xem nh lu lng ly thuyet Ql cua bm. Lu lng thcte Q qua ong ay nho hn Q l v khong phai tat ca chat long sau khi ra khoi banh cong tac eui vao ong ay ma co mot phan nho Q chay tr ve loi vao banh cong tac hoac ro r ra ngoaiqua cac khe h cua cac bo phan lot kn A va B c bieu th tren hnh ve (3.13)

Vay: Ql = Q + Q

e anh gia ton that lu lng cua bm ngi ta dung hieu suat lu lng Q :

QQQ

QQ

lQ

(3.26)

Q < 1 phu thuoc vao ket cau va chat lng lam viec cua cac bo phan lot kn.Thng oi vi bm ly tam:

Q = 0,95 0,98

Bm co lu lng cang ln th Q cang cao.

3.2.5- ng ac tnh cua bm ly tam

Cac thong so cua bm nh H, Q, N, thay oi theo cac che o lam viec cua bm viso vong quay n khong oi hoac thay oi.

Q

Q

Ql

A

B



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Hnh 3.15 ng ac tnh ly thuyet va ng ac tnh tnh toan

Neu 2 < 90o th cotg 2 > 0, ta co ng AD Neu 2 = 90o th cotg 2 = 0, ta co ng AC Neu 2 > 90o th cotg 2 < 0, ta co ng AB

oi vi bm ly tam, ta co 2 < 90o do o ng ac tnh cua bm ly tam la ng

nghch bien bac nhat AD. ay la ng ac tnh c ban ly thuyet cua bm ly tam khi cha keti so canh dan hu han va ton that.

Neu ke ti so canh dan hu han, ng ac tnh tr thanh ng A/D/, bieu dien:Hl = Z.Hl

Trong o Z < 1 - la he so ke ti so canh dan hu han.

Neu ke ti ton that lu lng Q, ng ac tnh tr thanh ng A/D1/ Neu ke ti cac loai ton that thuy lc cua dong chat long qua banh cong tac, ta biet cac

loai ton that thuy lc nay eu ty le vi bnh phng cua van toc, tc cung la bnhphng cua lu lng th ng ac tnh tr thanh ng cong bac hai A//D//:

- Khi Q = Qkte (ng vi lu lng thch hp nhat) th hw co gia tr nho nhat (hw 0 ) :

H = 1.

- Khi Q > Qkte hay Q < Qkte th ton that hw eu tang.

Neu ke ti ton that c kh th ng ac tnh dch ve pha trai va thap hn A//D// motchut, o la ng A///D/// - ay chnh la ng ac tnh c ban tnh toan cua bm lytam.

b- ng ac tnh thc nghiem

H

Ql

AA/

A//

A///

u22/g

Qkte

B

C

DD/D1/

D//

D

///

QH

2 > 90o

2 = 90o

2 < 90o ( Z )



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Viec xay dng ng ac tnh tnh toan rat phc tap kho khan, bi vay trong ky thuatthng xay dng cac ng ac tnh bang cac so lieu o c khi khao nghiem tren cac maycu the o la ng ac tnh thc nghiem.

S o he thong th nghiem bm ly tam bieu th tren hnh (3.16).

Hnh 3.16 - S o he thong th nghiem bm ly tam

Muon xay dng c cac ng ac tnh thc nghiem cua bm ly tam th phai chobm lam viec trong mot he thong th nghiem nh hnh ve.

Trnh t tien hanh th nghiem e xay dng ng ac tnh gom cac bc sau:

1. M khoa 2 ong hut va cho bm lam viec cho en khi so vong quay cua truc bm atti tr so yeu cau, trong khi o khoa 4 ong ay van ong ( Q = 0 ). T cac tr so oc luc nay ap ke A va chan khong ke C, ta suy ra cot ap H cua bm che okhong tai

2. M dan khoa 4 ong ay e tang lu lng cua bm cho en khi at ti tr so ccai. Trong qua trnh thay oi lu lng, so vong quay lam viec khong oi. Tai moi vtr m cua khoa 4, ta o c cac so lieu th nghiem cua bm va ong c ien e tnhra lu lng Q, cot ap H va cong suat cua ong c ien Nc.

Tai moi iem lam viec ta tnh c cong suat thuy lc cua bm. So sanh cong suatthuy lc va cong suat o c tren truc cua bm ta suy ra c hieu suat cua bm.

Nh vay, t cac so lieu th nghiem, ta co the xay dng c cac ng ac tnh thcnghiem cua bm ly tam H-Q, N-Q, -Q. Cac ng ac tnh thc nghiem cua bm ve hnhdang noi chung cung giong nh ng ac tnh tnh toan, nhng khong trung nhau ( do co motso loai ton that ma trong khi tnh toan ta khong anh gia het c).

oi vi bm ly tam, ngoai 3 ng ac tnh tren con co them ng bieu dien quanhe cot ap chan khong cho phep vi lu lng [HCK] = f(Q).

ng ac tnh thc nghiem co dang nh sau:

1

2

3

4

5

C A

1- Be hut2, 4- Khoa3- Bm5- Lu lng keC- Chan khong keA- Ap ke



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Hnh 3.17 - ng ac tnh thc nghiem

Cong dung cua ng ac tnh lam viec cua bm: Qua cac ng ac tnh H-Q, -Q, N-Q ta thay c khu vc lam viec co li nhat ng

vi hieu suat cao nhat [ max hoac = (max 7%)]

Qua hnh dang cua ng ac tnh ta biet c tnh nang lam viec cua bm e sdung bm cho hp ly.

ng ac tnh [HCK] = f(Q) e tnh toan ong hut va xac nh v tr at bm mot cachhp ly.

c- ng ac tnh tong hpMoi ng ac tnh lam viec c xay dng vi mot so vong quay lam viec khong

oi cua bm. Neu thay oi vong quay lam viec th ng ac tnh lam viec cung thay oitheo. e biet c nhanh chong cac thong so Q, H, N, cua bm thay oi nh the nao khi nthay oi, ngi ta dng ng ac tnh tong hp.

ng ac tnh tong hp cua bm la ng bieu dien cac quan he Q-H, N-H vi cacso vong quay lam viec khac nhau, tren o cac iem lam viec cung hieu suat c noi vinhau thanh nhng ng cong goi la ng cung hieu suat.



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Hnh 3.18 - ng ac tnh tong hp cua bm

3.2.6 ng dung ong dang trong bm ly tam

Ta biet rang, khi so vong quay lam viec n cua bm thay oi th cac thong so lam vieckhac cua bm cung thay oi theo.

Thc nghiem chng to rang, khi mot bm ly tam vi so vong quay thay oi t (di50% so vi so vong quay nh mc) th hieu suat cua bm thay oi tng oi t, co the xem

nh khong oi = const. Mat khac cac tam giac van toc eu ty le vi so vong quay, nen cactam giac van toc se ong dang vi nhau. Do o cac che o lam viec khac nhau cua bmtrong trng hp nay xem nh cac trng hp tng t.

Theo ly thuyet ve tng t, hai che o lam viec goi la tng t nhau khi chung thoaman 3 ieu kien tng t:

Ta xet mot may mo hnh va mot may nguyen hnh, ky hieu: ch so M - mo hnh,N - nguyen hnh.

1. Tieu chuan tng t hnh hoc:

constbb

DD L

N

M

N

M

2. Tieu chuan tng t ong hoc:

constww

cc

uu

vN

M

N

M

N

M

3. Tieu chuan tng t ong lc:

const

F

F

P

PF

N

M

N

M



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Ta co the van dung cac quan he tng t nay e tm moi quan he gia Q, H, N theo sovong quay n.

Goi HM, QM, NM la cot ap, lu lng va cong suat ng vi so vong quay n M;

HN, QN, NN la cot ap, lu lng va cong suat ng vi so vong quay nN.a - Phng trnh ong dang lu lng

Ta co phng trnh lu lng cua bm ly tam:

b.D..cQ R

Theo ket cau cua banh cong tac, b ty le vi D nen co the viet:

b = k1.D

k1 he so ty le

CR cung ty le vi van toc u, nen:

nD60

u.cR

- he so ty le

Thay vao bieu thc cua Q ta c:

n60

D.kQ32

1

hay kk60nD

Q1

2

3

Khi ta co tng t hnh hoc th k = const, co tng t ong hoc th = const, do o:

constnD

Q3

hay:N

M

3

N

M

N

M

nn

DD

QQ

N

M

DD

= L - la tieu chuan tng t hnh hoc

Luc o ta co: N

M3

LN

M

n

n

Q

Q (3.28)

Khi ta tnh cho cac che o lam viec cua cung mot bm th L = 1, phng trnh codang:

N

M

N

M

nn

QQ

(3.29)

b- Phng trnh ong dang cot ap

Theo phng trnh c ban cua bm ly tam ta co:

2

u2222

2

u222

u22l u

cnD60g

1ucu

g1

gcuH



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hay: constuc

60g1

nDH

2

u22

22l

v

const

u

cconst

u

c

u

cconst

c

c

u

u

2

u2

N

N

M

M

N

M

N

M

Nh vay ta c:2

N

M2L

2

N

M

2

N

M

Nl

Ml

nn

nn

DD

HH

(3.30)

Khi L = 12

N

M

Nl

Ml

nn

HH

(3.31)

c- Phng trnh ong dang cong suat

Ta co: N = QHl

Vay:3

N

M5L

N

M

3

N

M

5

N

M

N

M

Nl

Ml

N

M

N

M

N

M

nn

nn

DD

HH

QQ

NN

Khi vi cung mot chat long lam viec, ta co:3

N

M5

L

N

M

n

n

N

N

(3.32)

Khi L = 1 :3

N

M

N

M

nn

NN

(3.33)

Trong thc te, ngoai so vong quay lam viec thay oi con co the gap trng hp tronglng rieng cua chat long thay oi, ng knh ngoai D cua banh cong tac thay oi. e apng yeu cau s dung, thng khi can giam cot ap va tang lu lng so vi nh mc, ngi taco the got bt ng knh D ( ch trong pham vi 10%) th hieu suat cua bm coi nh khongoi. Ta co the xem cac che o lam viec cua bm trong trng hp nay la cac che o lam viectng t.

Goi Q1, H1, N1 la lu lng, cot ap va cong suat ng vi D, 1 va n1Q2, H2, N2 la lu lng, cot ap va cong suat ng vi D, 2 va n2.

Ta co quan he tng t cua mot bm ly tam nh bang sau:

Cac thong Khi thay oi Khi n thay oi Khi D thay oi Khi , n, D thay oi



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so

Lu lngQ

12 QQ 1

1

22 Qn

nQ

1

3

2 Q'D''DQ

13

1

22 Q'D

''Dnn

Q

Cot ap H1

2

12 HH

1

2

1

22 Hn

nH

1

2

2 H'D''DH

122

1

2

2

12 H'D

''Dnn

H

Cong suatN 11

22 NN

1

3

1

22 Nn

nN

1

3

2 N'D''DN

153

1

2

1

22 N'D

''Dnn

N

3.2.7- So vong quay ac trng

e ac trng cho mot he thong, ngi ta dung mot may mau tng trng ( may mohnh). Quy nh cua may bm mo hnh co cac thong so sau:

HS = 1 m cot chat long

QS = 0,075 m3/s

NS = 0,736 kW ( tng ng 1 ma lc)

S hieu suat co li nhat

nS so vong quay ac trng, v/ph.

Bat ky may thuy lc nao c che tao ra cung phai tng t vi may mo hnh cung hethong, cac thong so lam viec cua may o va cua may mo hnh quan he vi nhau theo luattng t, tc la:

n

nQ

Q S3L

S (1)

2

S2

LS

n

n

H

H

(2)

3S5

LS

nn

NN

(3)

Ket hp cong thc (1) va (2), rut L va cho bang nhau, ta thu c cong thc:

43

21

SH

Q.n.65,3n (3.34)

n so vong quay, v/ph

Q lu lng, m3/s

H cot ap, m

Ket hp cong thc (2) va (3), rut L tng t nh tren, ta thu c cong thc:



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4

5

21

SH

N.n.167,1n (3.35)

N cong suat , kW

Neu n tnh theo ma lc, ta co:

45

21

SH

N.nn (3.36)

Muon biet mot may thuy lc canh dan nao thuoc he thong cua may mo hnh nao,ngi ta dung so vong quay ac trng nS tnh theo cac cong thc tren e phan biet, nen nSc goi la so vong quay ac trng.

V du: nS = 40 80 v/ph bm ly tam ty toc cham 5,3

D

D

o

2

nS = 140 300 v/ph bm ly tam ty toc nhanh 1,13,1DD

o

2

nS = 600 1800 v/ph bm hng truc 6,08,0DD

o

2

3.2.8- Hien tng xam thc

Ap suat dong chat long chay qua bm luon luon thay oi va khong bang nhau trong

tng iem rieng re tren mat cat cua dong chay.Trong nhng bm thong thng, ap suat nho nhat la gan loi vao cua banh cong tac

pha lom cua canh dan, tc la cho nao van toc tng oi W va ong nang ng vi noW2/2 at c gia tr ln nhat (vung A tren hnh).

Hnh 3.19 Vung xay ra xam thc

Neu vung A ap suat bang hay nho hn ap suat hi bao hoa cua chat long trong bm,th se xuat hien hien tng xam thc. Hien tng nay se lan rong ra cac vung lan can cua

dong chay.

R1AR2

w2

w1



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Hien tng xam thc co hai khong ch v no huy hoai kim loai ma con v may lamviec khi co xam thc se lam giam rat ln hieu suat.

Bm lam viec khi co xam thc rat on, rung manh va khi cng o xam thc len caoxuat hien s va ap se rat co hai cho bm.

Bien phap khac phuc:

Han che van toc chat long trong dong chay cua bm ng dung hnh dang tien li cho dong chay va cho mat cat cua banh cong tac S dung bm che o gan vi che o a tnh toan trc Mot bien phap quan trong trong viec chong xam thc cua bat ky loai bm nao o la

can co o cao hut thch hp, ma vi o cao hut nay khong xay ra xam thc goi la ocao hut cho phep (a c tnh toan phan bm canh dan).

3.2.9 Kiem tra bm

1. Chon bm ung yeu cau ky thuat, da vao ng ac tnh cua bm, trong o ac bietchu y ng ac tnh c ban (H-Q).

2. Cac thiet b va ong ho o ap suat, o chan khong, o ien can co ay u. Can lapvan mot chieu ong hut va ong ay e de dang khi moi va khi ong bm.

3. Trc khi cho bm lam viec phai moi bm4. Trc khi bm khi ong phai kiem tra dau m trong bm va ong c, cac moi ghep

bulong, he thong ien.5. Khi khi ong bm, cho ong c quay on nh roi mi t t m khoa ong ay

(nhng vi bm ap suat thap th ngc lai, m khoa ong ay roi mi khi ong neukhong ong c kho khi ong va de b qua tai).

6. Khi bm lam viec, can theo doi ong ho o, chu y nghe tieng may e kp thi phathien nhng bat thng e x ly kp thi.

7. Khi chuan b tat may, lam th t ong tac ngc vi khi cho may chay: ong van ong ay trc, tat may sau.

8. Khi bm lam viec chat long khong len hoac len t, can dng may va kiem tra lai: Cac van hoac khoa ong ay va ong hut. Li chan rac co b lap kn hoac mieng ong hut khong ung o sau can thiet

cach mat thoang cua be hut.

Banh cong tac quay ngc (bm ien co the b au day ngc pha).

3.2.10 ieu chnh che o lam viec cua bm



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Hnh 3.20 iem lam viec

iem lam vieccua bm la giao iem cua hai ng ac tnh cua bm va cua he thongtrong cung mot he toa o.

Qua trnh thay oi iem lam viec cua bm theo mot yeu cau nao o goi la qua trnhieu chnh.

Co hai phng phap ieu chnh:

a- ieu chnh bang khoa

Hnh 3.21 - ieu chnh bang khoa

ieu chnh bang khoa tao nen s thay oi ng ac tnh li bang cach ieu chnh(ong hoac m) khoa ong ay e thay oi lu lng cua he thong (khong ieu chnh onghut v de gay ra hien tng xam thc).

Khi m khoa hoan toan ta co iem lam viec A (HA, QA). Khi ong bt khoa lai th ton that khoa se tang len (AB), lu lng cua he

thong giam, ngha la ng ac tnh li se thay oi doc hn, trong khi ac

tnh bm khong oi. Do o iem lam viec t A chuyen en B (H B, QB).Phng phap nay n gian, thuan tien nhng khong kinh te v gay them ton that.

H

HA

QA Q

A

Hl - Q

HB - Q

H

HA

QA Q

A

Hl - Q (A)

HB - Q

BHB

QB

Hl - Q (B)



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b- ieu chnh bang thay oi so vong quay cua truc bm

Hnh 3.22 - ieu chnh bang thay oi so vong quay

Noi dung cua phng phap nay la thay oi ng ac tnh rieng cua bm bang cachthay oi so vong quay cua truc bm.

iem lam viec A(HA,QA) ng vi so vong quay lam viec nA. Khi tang so vong quayen nB > nA th ng ac tnh cua bm se khac i trong khi o ng ac tnh li khongthay oi, iem lam viec t A chuyen en B (HB, QB).

Phng phap nay dung cho bm co thiet b thay oi so vong quay. Phng phap naykinh te hn so vi phng phap tren. Nhng oi vi bm khong co thiet b thay oi so vongquay lam viec th phng phap tren thong dung hn.

oi khi ngi ta ket hp ca hai phng phap tren.c- Khu vc ieu chnh

Ta thay rang muon ieu chnh bm th phai thay oi ng ac tnh li hoac thay oing ac tnh bm. Nhng thc te khong phai co the ieu chnh iem lam viec ve bat ciem nao tren ng ac tnh cua bm.

Hnh 3.23 - Khu vc ieu chnh

V du: Tren hnh ve, co mot bm lam viec trong he thong vi cac ng ac tnh nha c the hien, trong o ng ac tnh cua bm co dang loi. iem T la iem gii han chia

H

HA

QA Q

A

Hl - Q

HB Q (nA)

BHB

QB

CHB Q (nB >nA)

HB Q (nC < nA)

QC

HC

H

Q

Hl - Q

HB - Q

iemg/han

T

K/vcK/vckhong O O



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ng ac tnh ra lam hai khu vc: ben phai iem T la khu vc lam viec on nh, con bentrai iem T tuy theo v tr cua ng ac tnh li, bm co the lam viec khong on nh goi lakhu vc lam viec khong on nh cua bm.

Thc nghiem chng to rang:

Khong the ieu chnh bm trong khu vc khong on nh. Khi khi ong bm, can ha thap H li e iem lam viec cua bm khong ri vao

khu vc khong on nh.

oi vi cac bm quan trong nh bm cao ap cap nc cho noi hi (nha may nhietien), yeu cau ve ng ac tnh cua bm la khong co vung lam viec khong on nh, tc lang ac tnh co dang doc ng hoac thoai.

V tr cua iem gii han T phu thuoc vao goc 2. Goc 2 cang nho th khu vc lam

viec khong on nh cang nho.3.2.11 - Ghep bm ly tam

Co hai cach ghep bm: ghep song song va ghep noi tiep.

a- Ghep song song: (khi he thong co yeu cau lu lng ln hn lu lng cua motbm)

ieu kien e cac bm ghep co the lam viec c la:

Cac bm phai lam viec vi cung cot ap: H1 = H2 = = Hi e xac nh lu lng cua bm ghep song song lam viec trong mot he thong, ta canxay dng ng ac tnh chung cua cac bm ghep (H-QC) va biet ng ac tnh li

(Hli-Q).

ng ac tnh chung cua cac bm ghep song song (H-QC) trong he thong c xaydng bang cach cong cac lu lng vi cung mot cot ap (cong cac hoanh o tren cung tungo).

V du: Khao sat hai bm co ng ac tnh khac nhau: (H1-Q) va (H2-Q) ghep songsong, ta thay vi moi cot ap H > HB trong he thong ch co bm 2 lam viec. Khi H = HB ca haibm eu cung lam viec nhng lu lng cua he thong ch bang lu lng cua bm 2 ng vi

iem B (QB = Q2) (hnh 3.24)

iem C la iem lam viec cua cac bm ghep trong he thong. Khi o bm 1 lam viecvi C1Q , bm 2 lam viec vi

C2Q . Vay: Tong lu lng cua hai bm ghep song song trong he

thong nho hn tong lu lng cua hai bm o khi lam viec rieng re cung trong he thong o.

21C2

C1C QQQQQ

(v he thong lam viec vi nhieu bm ghep song song co cot ap ln hn do lu lng trong hethong tang len so vi khi tng bm rieng re lam viec trong he thong).



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Hnh 3.24 - Ghep song songNhan xet:

ieu chnh he thong co cac bm ghep song song tng oi phc tap khi cac bm ghepco ng ac tnh khac nhau nhieu Do vay can ghep cac bm co ng ac tnhgan giong nhau.

Ghep bm song song co hieu qua ln khi ng ac tnh cua chung thoai (co o docnho) va ng ac tnh cua li khong doc lam Ta can ng dung ghep song songtrong cac he thong bm can co cot ap thay oi t khi lu lng thay oi nhieu.

So lng bm ghep song song e tang lu lng co gii han nhat nh, c xac nhbi ng ac tnh chung va ng ac tnh li.

b- Ghep noi tiep: (khi he thong co yeu cau cot ap ln hn cot ap cua mot bm)

Hnh 3.25 Ghep noi tiep

HB

H

Q1

Q

Hl-Q

HB1-Q

B

Q2HB2-Q

HC -Q

12

QC < Q1+Q2

QB = Q2

Q1CQ2C

HB1 - Q

HB2 - Q

HC - QHC = H1C + H2C

Q

HHli - Q

A

1

2

H1CH2C

QC

12



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ieu kien ghep noi tiep:

Cac bm ghep phai lam viec vi lu lng nh nhau: i21 QQQ Cot ap lam viec khi Q = const:

i21C HHHH

ng ac tnh chung cua cac bm ghep (HC - Q) c xay dng bang cach cong caccot ap cua rieng tng bm vi cung mot lu lng (cong cac tung o tren cung mothoanh o)

Khao sat hai bm 1, 2 co ng ac tnh khac nhau ghep noi tiep lam viec trong mothe thong.

iem A (giao iem cua ng ac tnh chung va ng ac tnh li) la iem lamviec cua cac bm ghep trong he thong, xac nh lu lng Q va cot ap H cua hai bm ghep.

Khi ghep noi tiep nen chon bm va he thong co ng ac tnh doc nhieu mi co hieuqua cao, v khi thay oi lu lng t a tang c cot ap theo yeu cau.

Chu y: Khi ghep hai bm 1 va 2 noi tiep lien nhau can chu y la bm 2 phai lam viecvi ap suat cao hn bm 1, v vay neu khong u sc ben bm se b hong. Do o phai chontren ng ong ay cua bm 1 iem nao co ap suat khong gay nguy hiem cho bm 2 eghep.

3.2.12 Lc doc truc trong bm ly tam cach khac phuc lc doc truc

Khi bm lam viec, banh cong tac cua bm chu tac dung cua cac ap lc theo hngtruc. Ta se khao sat cac lc nay.

Hnh 3.26 - Lc doc truc trong bm ly tam

Khi bm lam viec, chat long bong hut A chuyen ong theo phng song song vitruc vao banh cong tac di ap suat kha nho p1. Sau khi vao banh cong tac, dong chat longngoat 90o va tr thanh thang goc vi truc. Ap suat chat long tang dan en tr so p2 loi ra, p1


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ung ap suat trong cac khe o bang p2. Do o ap lc hng truc tac dung len a sau cuabanh cong tac hng ve pha trai la:

2222tr rR..pP

Va ap lc hng truc tac dung len a trc banh cong tac, hng ve ben phai la: 221121222ph rR..pRR..pP

V p2 >> p1 Ptr >> Pph. Do o ap lc doc truc co xu hng ay banh cong tac vepha ngc vi hng chuyen ong cua chat long vao banh cong tac.

22112phtrI rR.pp.PPP

Hoac: 221tI rR.H..P

Trong thc te, do s quay cua chat long theo cac a cua banh cong tac trong cac kheh B va C nen ap suat trong cac khe giam dan t ngoai vao trong (t R2 R1) theo cacng parabol.

Ngoai PI ra, con co lc hng truc PII tac dung len banh cong tac theo hng cua dongchay (ngc vi PI), PII xuat hien do chat long thay oi phng chuyen ong loi vao cuabanh cong tac (t hng truc sang hng knh), co the tnh theo nh luat ong lng:

ol

oII CgQ.

C.mP

m khoi lng chat long chuyen ong qua banh cong tac, gQ.

m l

Co van toc chat long bong hut cua banh cong tac.

Vay ap lc tong cong ap dung tren mot banh cong tac cua bm la:

III PPP

oi vi bm nhieu cap co so banh cong tac la i th tong ap lc hng truc la:

A = iP

* Neu roto cua bm bo tr thang ng (bm truc ng) th cong thc tnh tong ap lchng truc A tren can bo sung them thanh phan trong lng cua roto G:

GP.iA

Dau tuy thuoc vao s bo tr mieng vao va ra cua bm, gay nen cac ap lc hngtruc cung hay ngc chieu vi trong lng G cua roto.

Tac hai cua lc hng truc

Lc hng truc trong bm lam mon cac o chan tao nen s sai lech cac khe h trongbm va lam cho roto co vao than bm khi lam viec gay anh hng xau en hieu suat va lamhong bm.

Cach khac phuc



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1. oi vi bm co mot banh cong tac:

Dung banh cong tac co hai mieng hut.

Hnh 3.27 Banh cong tac hai mieng hut

Cau tao vanh lot kn th hai chia khe h gia than bm va a sau cua banh cong tacthanh hai phan. Phan tren thong vi bong ay co ap suat 2pp , phan di thong vibong hut bang cac lo khoan tren a sau banh cong tac. Nhc iem cua phng phapnay la lam giam hieu suat lu lng Q .

Hnh 3.28 - Cau tao vanh lot kn th hai gia than bm va a sau

2. oi vi bm co nhieu banh cong tac:

Bo tr banh cong tac thanh cac cap oi xng nhau.



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Hnh 3.29 - Bo tr banh cong tac thanh cac cap oi xng

Dung piston can bang. Dung a can bang.

Hnh 3.30 a can bang



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Chon bm theo ieu kien cho trc

Hnh 3.31 Chon bm theo lu lng va cot ap cho trc



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3.3- BM HNG TRUC

3.2.1- Cau tao va pham vi s dung

a- Pham vi s dung

Bm hng truc co pham vi s dung rat rong rai khi can lu lng ln va cot ap thap,cu the:

Lu lng : Q = 0,1 25 m3/s Cot ap: H = 4 10 mH20

ac biet co khi H = 22 m.

b- Cau tao va nguyen ly

Hnh 3.32 - S o ket cau bm hng trucS o ket cau bm hng truc

1.Bo phan dan hng vao 2.Than bm

3.Banh cong tac 4.Mc chat long 5.Truc bm

Ket cau cua bm hng truc n gian va chac chan. No gom co phan ong va phantnh.

Phan quay (phan ong) gom banh cong tac gan lien vi truc. Banh cong tac hnh khoi

tru co gan cac canh dan mat cong phan bo eu xung quanh. Thng so canh dan cua banhcong tac t 3 6 canh. Phan ng yen (phan tnh) la vo bm co dang hnh tru rong, pha



64/218


trong co cac canh dan hng va bo phan truc. Pha tren bo phan dan hng than bm uoncong e tien bo tr cac bo phan dan ong truc bm.

Truc cua bm hng truc thng c noi trc tiep vi ong c ien. Khi bm lamviec, banh cong tac quay trong moi trng chat long va do co cac canh dan mat cong dang

cong xon (cong theo khong gian 3 chieu) nen chat long c hut vao bm va di chuyen theophng song song vi truc vi lu lng ln.

3.3.2- Phng trnh lam viec

Tng t nh bm ly tam, ta co the ve tam giac van toc loi vao va loi ra cua banhcong tac bm hng truc theo hnh ve di ay. Trong o u2 = u1 = u; c1R = c2R

Hnh 3.33 - Tam giac van toc

Ta biet phng trnh c ban oi vi bm canh dan noi chung la:

g

cucuH u11u22l

(3.37)

Ap dung cho bm hng truc, ta co:

u1 = u2 = u

c1u = 0 (v loi vao banh cong tac, dong chat long cha co chuyen ong quay)

Vay phng trnh c ban viet cho bm hng truc la:

gc.uHu2

l (3.38)

Hoac:g2

ccg2

wwH

21

22

22

21

l

(3.39)

Hai phng trnh (3.37) va (3.38) la cac phng trnh c ban cua bm hng truc. Vaycot ap cua bm hng truc tao nen do s chenh lech ve tr so cua cac thanh phan van toctng oi va tuyet oi loi ra va loi vao cua banh cong tac.

121 2

w1 w2

c2R

u1 = u2 = uc2u

c2

c1 = c1R



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So sanh phng trnh lam viec cua bm ly tam va bm hng truc, ta thay cot ap cua

bm hng truc khong co thanh phan lc ly tamg2uu 21

22 tham d, ma thanh phan nay oi

vi bm ly tam rat quan trong v la thanh phan chu yeu e tao nen cot ap cua bm.

Cot ap thc te cua bm hng truc:

g2u

K1H

2

2H

(3.40)

32

SH n.0244,0K - he so cot ap thc te

nS so vong quay ac trng, v/ph.

3.3.3- Hnh dang canh

Do tnh chat a neu tren ma bm hng truc co nhng ac iem sau: Cot ap cua bm hng truc khong the ln bang cot ap cua bm ly tam. Cot ap tnh cua bm hng truc ch do o m rong cac mang dan cua banh cong tac

tao nen (w1 > w2).

g2ww

H22

21

tl

(3.41)

Do vay cac mang dan cua banh cong tac phai co o m rong thch ang e tao

nen cot ap tnh can thiet cho bm (w1 >> w2). ieu nay gay nen cac ton that phuthem, v lc quan tnh cua dong chay qua mang dan co van toc thay oi ln. e giamton that phu them nay, cac mang dan cua bm hng truc can c gia cong chnhxac va co o nhan be mat cao ( 5 7).

T (3.38) ta thay, muon dong chat long qua banh cong tac cua bm hng truc ccan bang on nh th canh dan phai co ket cau sao cho cot ap cua moi dong nguyen tochat long c tao nen bi canh dan moi v tr phai nh nhau, ngha la:

constgc.u

H u2l vi moi ban knh R (3.42)

Muon vay, constc.u u2 (3.43)

Tc la, neu u tang dan t trong ra ngoai th c2u cung phai giam dan t trong ra ngoaitheo hng knh cua banh cong tac.

T tam giac van toc:

2Ru2 gcotcuc

1R gcotcu

Suy ra 21Ru2 gcotgcotcc (3.44)Thay (3.44) vao (3.38) ta co:



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21Rl gcotgcotcguH (3.45)

Hoac 21R

l gcotgcotRg30c.n.

H

(3.46)

Trong o constg30c.n. R

( oi vi mot bm nhat nh n = const, cR = const )

T bieu thc (3.46) ta thay:

1. Banh cong tac cua bm hng truc ch tao c cot ap khi canh dan co cac goc raln hn goc vao ( 2 > 1) tc la mat canh dan khong the la mat phang ma la matcong. Tr so cua 1 va 2 cang khac nhau nhieu th o cong cua canh dan cang ln.

2. Neu hai bm lam viec co cot ap nh nhau, bm nao co so vong quay lam viec thn th canh dan cua banh cong tac cua bm o phai co o cong ln hn.

3. ieu kien (3.43) c am bao khi: constgcotgcot.R 21

Hnh 3.34 - Thiet dien mat cat canh dan

Do o cac cap tr so (1, 2) khong co nh ma thay oi theo ban knh R, ngha la ocong canh dan khong ong eu moi ni, ma pha trong sat bau o cong canh dan se lnnhat va giam dan t trong ra ngoai theo hng knh. o cong canh dan nho nhat ng vi banknh ln nhat. V o cong thay oi nh vay nen mat canh dan la mat cong theo 3 chieu khong

gian, tc dang xoan vo o.3.3.4- ng ac tnh



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Hnh 3.35 - ng ac tnh thc nghiem

ng ac tnh thc nghiem cua bm hng truc co nhng net khac vi bm ly tam.

Tren hnh (3.35) the hien ng ac tnh lam viec cua bm hng truc co canh dan conh vi so vong quay khong oi.

Trong cac bm hng truc c ln thng gap trng hp canh dan cua banh cong tacco the thay oi c goc o bang cac c cau c kh bo tr ben trong bau banh cong tac eieu chnh lu lng bm. Banh cong tac nh vay goi la banh cong tac co canh dan ieuchnh c. oi vi loai bm nay ng ac tnh lam viec c xay dng vi cac goc okhac nhau cua canh dan.

So sanh ng ac tnh lam viec cua bm hng truc vi bm ly tam ta thay co nhngiem khac nhau:

1. ng ac tnh H Q co o doc ln hn, nhat la 2 au. khoang gia co the coiem uon hoac iem gay. Cot ap cang tang khi lu lng cang giam va ln nhatkhi ong khoa hoan toan tren ong ay ( Q = 0), Hmax = HQ = 0.

2. ng ac tnh N Q cung co hnh dang tng t nh H Q. Khi Q = 0 thN = Nmax. Cong suat Nmax co the vt t 1,5 2 lan cong suat lam viec bnhthng cua bm.

ng ac tnh H Q va N Q co hai ac iem noi tren v khi lu lng trong banhcong tac nho th xuat hien dong chay hng knh t trong ra ngoai tao nen dong xoay vong

buong cha banh cong tac, dong xoay nay co cng o ln nhat khi Q = 0. Do anh hng cuadong xoay ma cot ap va cong suat tang khi lu lng giam.

3. Pham vi lam viec toi u cua bm hng truc tng oi hep. Neu bm lam viec vilu lng khac lu lng nh mc khong nhieu lam ve ca hai pha ( ln hn hoacnho hn) th hieu suat bm eu giam rat nhieu.

ng ac tnh tong hp cua bm hng truc the hien tren hnh 3.36

giao trinh bom, quat, may nen vinamain

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