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第二章 液压油与液压流体力学基础 PowerPoint PPT Presentation


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液压传动是以液体作为工作介质进行能量传递的,因此,了解液体的物理性质,掌握液体在静止和运动过程中的基本力学规律,对于正确理解液压传动的基本原理,合理设计和使用液压系统都是非常必要的。. 第二章 液压油与液压流体力学基础. 一、液体的密度 单位体积液体的质量称为液体的密度,通常用“ ρ” 表示 式中: V —— 液体的体积,单位为 m 3 ; m —— 液体的质量,单位为 kg 。. §2-1 液体的物理性质. 二、液体的可压缩性 液体受压力作用而使体积减小的性质称为液体的可压缩性。通常用体积压缩系数来表示: 式中 k —— 液体的体积压缩系数;

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第二章 液压油与液压流体力学基础

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Vm3

mkg

2-1


k

V

V

p


kK

K=1.42.0109Pa

KK=0.71.4109Pa



1


1

  • Ns/Pas

  • /s

  • 1/s=1042/s =104St=106mm2/s =106cSt


N324032mm2/scSt205020mm2/scSt


200 ml2.8t120t2t2=52s


  • mm2/scst


  • E1E2E1E2

  • E

  • aba+ b=100

  • c2-1


2-1c

a

10

20

30

40

50

60

70

80

90

b

90

80

70

60

50

40

30

20

10

c

6.7

13.1

17.9

22.1

25.5

27.9

28.2

25

17

  • 3

  • 4



1



+

+



2

1

2


a.

b.

c.


1

1

2

3


2

1

2

3


3

1

2

3

4


2-2

  • pPaMpa


1

2



poghpa



=+

=-

PaN/MPaN/bar

1MPa=106 Pa1bar=105 Pa



dFx=dFcos=pdAcos=plrcosd


2-3

1.



2.



3.

qm/sL/min


dAu

dq=udA

A


Re

4.


Re

RecReRec


Re=4Rv/

RR=A/

A


1v1A1=2v2A2

1=2

v1A1=v2A2

q =vA=



1



W=p1dA1ds1-p2dA2ds2

= p1dA1 u 1 dt -p2dA2 u 2 dt

dA1 u 1 =dA2 u 2=dq

W= dqdt(p1-p2)

(2)

Ek=dqdtu22/2-dqdt u12/2

Ep=gdqdth2-gdqdth1

E=Ek+Ep


E=W


hw

1 2

12

2


  • 12

  • =1

  • =4/3




1.

2-4


Ff=-2rldu/dr

ur

p=p1-p2Ff

p1- p2r=Ff


rdrdA=2rdr



=64/Re

=75/Re

=80/Re

2.

  • =fRe/d

  • =0.3164Re-0.25

  • Re/d


qn

pnqn

q



l/d0.5

l/d4

0.5l/d4

2-5



hwhw1hw2

Ae A2


A1=A2v1=v21=2h1=h2


=

mm=0.5

m=1

K


1

pbdy++dbdx=p+dpbdy+bdx


C1C 2y=0u=0y=u=0

dp/dx


2.

u0v=u0/2



e

=e/


1

1

2

3

2-6


p

2

p

Allt1


t1

cKEdc

c= l/t 1

c9001400m/s


tctc=2l/cttc

ttcp

1


mtA

3



p1/p23.5


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