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Bi T p Nhm Mn: Th y L c

Bi 6-3B m ng c th y l c

Cho N1 = 300 kw 03.0=

L = 1500 m Q = 0.2 m3

/sD = 400 m = 0.4 m

1. Tnh: NW2. Tnh: P1, P2

Gi i1.Ph ng trnh Becnuli cho m t c t 1-1 v 2-2 ( m t chu n 0-0 )

21

2

2

2

2

2

2

1

1

1

122

+++=++ tbh

g

VPZ

g

VPZ

(1)

Trong : Z1 = Z2 = 0V1 = V2 = 0

121 ==

T (1) Suy ra:g

v

D

lp

2..

2

=

V i 03,0= , l=1500 m, D= 0,4 m, Q= 0,2 m3/s

gD

Q

D

lhh dtb

..

.8

..42

2

21

==

= )(54,1481,9.4,0.

2,0.8.

4,0

1500.03,0

42

2

m=

T n th t cng su t trong ng ng

Ta c: Nw = .Q. ( Zg

VP++

2

2

)

Nhm:9 Trang: 1

N2

P2P1

N1

00

221 1

L,D

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V i: = 9810N/m3, D = 0.4m

Q = 0.2 m3/s ,

P= 14.54m

Z = 0

V y : Nw = . Q .

++ Zg

VP

2

2

=

++ ZgD

QPQ 42

28..

Nw = 9810 . 0,2

+

81,9.4,0.14,3

2,0.854.14

42

2

Nw =28781(W) = 28,781(Kw)

2. Tnh p su t P 1 do b m t o ra t i u ng ng v p su t P 2 tr c ng c th y l c cu i ng ng.

Ta c cng su t c a ng c th y l c: N2 = N1 Nw= 300 28,781 = 271,219(Kw)Cng su t c a b m:

++= Z

g

VPQN

2.

21

1

=

gD

Q

Q

NP

42

2

11

.8

..

V i Z= 0

)/(10.5,181,9.4,0.14,3

2,0.8

2,0.9810

10.3.9810 26

42

25

mN=

=

Cng su t c a ng c th y l c:

++= Z

g

VPQN

2.

2

12

(v i z=0)

=

gD

Q

Q

NP

42

2

22

.8

.

.

)/(10.35,181,9.4,0.14,3

2,0.8

2,0.9810

271219.9810 26

42

2

mN=

=

Nhm:9 Trang: 2

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BI 6.6L=20m ; D = 150mm = 2 ; = 0,03

l = 12m ; d = 150mm

r = 6 ; c = 0,2 , = 0,030

Q= ? ; Pck = 6mH2OZ =?

Gi i:

Bi Gi iPh ng trnh Becnuli cho m t c t 1 -1 v 2 2

1

0;0;0;

)1(

2121

2121

21222211

222

211

====

====

+++=++

a

tbg

Vp

g

VP

PPP

VVzzz

hzz

g.D.

Q.8.7

gD

Q8

DL

21g2V

DL

21tb 42

2

42

22

)()(h

=++=+=

415,0

15003,0

D

L.

32121

==

=+=+

Thay vo (1) ta c

)2(hZg.D

Q.8.7

21tb 42

2

==

Ph ng trnh Becnuli cho m t c t 2-2 v 3-3 (m t chu n 0-0)

z2=0 ; z3= h+z = 2+z ; p2= pa ; v2=0

2

4

3 d

QVV

== 132 ==

gd

Q

gd

Q

dl

crtbh 422

42

2 88

32 .6,8)( =++=

Thay vo (3) ta c:

3223

2332

++++= tbgVPP

hzh

gd

Q

gd

QPPZa 42

2

42

23 88 6,82

+++=

)6,81(26 422

8 +++= gd

QZ

)4(6,94 4228

gd

QZ

+=

Gi i (2) v (4) v i d=D=0,15(m) ta c :

Q=0,0384( m3/s) = 38,4 (l/s) Z=1,7 m

Nhm:9 Trang: 3

)3(322332222

332

22

+++=++ tbgVp

g

VPhzZ

B?

z

h

11

3

3

22

0 0

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Bi 6.7:

2

1 10 0

2

h

Pa

cho:

+

( ) ( )

( )( )

0 0 4 2

3

1

60 1

20 : 2 2.10

0, 92 0, 92.9810 9025, 2

Q v ph l s

t C St m s

N m

= =

= = == = =

+ ng ng: L = 5m ; d = 35mm + 0 00,1 ; 10 ; 1c dmm h h h m = = =

Tnh:

+ P t i m t c t vo c a b m. + V i 0 480 ; 1 10 ; 0,85t C St = = = = th P=?

Bi gi i:

1. Ph ng trnh becnuli cho m t c t 1-1 v 2-2: 2 2

1 1 2 21 1 2 2 1 2

2 2tb

P v P vZ Z h

g g

+ + = + + + (1)

V i:

1 2 1 2 2

4; 0; 0;

QZ h Z v v

d= = = =

Ta c:3

1 4

. 4. 4.10Re 182 2320

. . .0, 035.2.10

v D Q

d

= = = =

l ch y r i 1 = 2 = 1.Do Re nh nn tr ng thi dng ch y l ch y r i thnh tr n th y l c.

0,25 0,25

0, 3164 0, 31640, 04

3460e

R = = =

Nh v y: 2 2

22 2 4 2 4

8 8. . .

aP P Q l Qh d g d d g

= +

2

22 4

8.

Q lh

d g d

= +

3 2

2 4

8(10 ) 51 1 0, 04.

.(0, 035) .9, 81 0, 035

= +

0, 62duP

= (m c t d u)

V i 32 0, 85.9810 8338, 5( )N

m = =

0, 62.8338, 50, 05( )

0, 98.105duP at = =

Nhm:9 Trang: 5

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BI:6-8.

D

1 2

2

0

1

0

- Vi t ph ng trnh Becnuli cho cc m t c t 1-1, 2-2 (m t chu n O-O).

21

2

2

2

2

2

2

1

1

1

1 22 +++=++ tbdd hgvp

zg

vp

z

Trong : z1 = z2 = 0

v1 = v2 = v =83,2

)10.2

150.(

10.50

23

3

==

S

Q

(m/s).

V ng ng c chi u di l n nn ta c th b qua t n th t c c b .

g

v

D

lhh dtb

2

..2

21==

* Khi t = 100C tra bi u hnh 6-8 trang 171(BT th y l c v my th y l c) ta c:

9,0

)(10.3)(3

1

24

2

1

=

==

s

m

s

cm

)(88299810.9,031 m

N==

Suy ra: 2320141510.3

10.150.83,2.Re

4

3

1

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* Khi t = 200C tra bi u ta c:

894,0

)(10.25,1)(25,1

2

24

2

2

=

==

s

m

s

cm

)(87709810.894,0 32 m

N==

Suy ra: 2320339610.25,1

10.150.83,2.Re

4

3

2 >===

Dv

L dng ch y r i: 121 ===

- Do Re2 nh nn tr ng thi dng ch y l ch y r i thnh tr n th y l c.

041,0)3396(

3164,0

Re

3164,0

25,025,02

===

Nh v y: 87,55781,9.2

83,2.

10.150

10.5.041,0

2..

2

3

32

2121 =====

g

v

D

lhh

ppdtb

d

m c t

d u.

21 ppp = = 557,87 . 8770 = 4,9 . 106 (N/m2)

* Khi t = 300C tra bi u ta c:

889,0

)(10.5,0)(5,0

3

2

4

2

3

===

s

m

s

cm

)(87219810.889,033 m

N==

Suy ra: 2320849010.5,0

10.150.83,2.Re

4

3

3 >===

Dv

L dng ch y r i: 121 ===

- Do Re3 nh nn tr ng thi dng ch y l ch y r i thnh tr n th y l c.

033,0)8490(

3164,0

Re

3164,025,025,0

2

===

Nh v y: 44981,9.2

83,2.

10.150

10.5.033,0

2..

2

3

32

2121 =====

g

v

D

lhh

ppdtb

d

m c t d u.

Nhm:9 Trang: 7

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21 ppp = = 449 . 8721 = 3,9 . 106 (N/m2)

Bi 4-15:

Cho: P =760mmHg

=9,8.104(N/m2)

to = 200C 273= T 0KD = 0,2m , 95,0=

Gi i1.Tnh l u l ng khng kh khi c t p c a r i dng trong chn khng k

h=0,25(m) 2/800 mNr =

Ch n m t c t 1-1, 2-2 nh hnh v ch n mt ph ng i qua tr c qu t, lm m t chu n. Ta c ph ng trnh Becnuli t i 2 m t c t l:

=++ gVPZ 2

2

11

11

21

2

22

22

2+++ whgVPZ (1)

Ta c: Z1 = Z2 =0121 ==

V1= 0Hw1-2 = 0 o n dng ch y ng n khng c ch ng ng i v t.

(1)g

VPPa

2

2

22 +=

2PPh ack

=

cka h

PP=

2

(2)

Th (2) vo ( ) ta c:g

Vh

PPck

a

2

2

22+=

Nhm:9 Trang: 8

D

1

1h

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g

Vhck

2

2

2= (3)

Ta c p su t chn khng t i c t n c ph i b ng p su t khng kh. Pck = Pkk kkkkrck hh = .

V i: ( )34

akk m/N82,11

293.27,29.750

10.8,9.760

RT

P ===

( )m2,1694,11

8000.25,0

.hh

kk

rckkk ==

=

Th vo (3) ta c:

)s/m(62,57175.81,9.2h.g.2v kk2 ===

)s/m(8,1

4

5,62,57.2,0.14,3v.

4

d.Q 3

2

2

2

ttkk ==

=

V i ( )smQ kk /71,195,0.8,195,03===

2, V i Q kk-tt = 1,8 (m3/s), T= 273 20 = 2530kV hkk = 169,2 (m) khng kh

Pkk = 405(mmHg) = 0,54.105 (N/m2)

V i ( )35

kk m/N3,7287.253

10.54,0.81,9

RT

P.g.g ====

C t p c a r u l:

hck-r = hck-kk. ( ) ( )mm154m154,08000

3,7.2,169

r

kk ===

Nhm:9 Trang: 9

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