Fourth Edition John Wiley & Sons, Inc.

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Oct 24, 2013 (3 years and 7 months ago)

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Introduction to Fluid Mechanics

Fourth Edition

John Wiley & Sons, Inc.


،ةلولحم نيرامتو حرش تاركذم


هاندأ داوملا نم ديدعلل ةقباس تاناحتما


نيروكذملا نيعقوملا ىلع

اناجم ةحاتم

عم فلتخت نأ تدرأ اذإ
هلمع بجي ام هل لق ناسنإ
.


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Chapter 1

Introduction

1
-
2 Definition of a Fluid.

1
-
3 Scope of Fluid Mechanics.

1
-
4 Basic Equations.

1
-
5 Methods & Analysis.

1
-
6 Dimensions and Units.


،ةلولحم نيرامتو حرش تاركذم


هاندأ داوملا نم ديدعلل ةقباس تاناحتما


نيروكذملا نيعقوملا ىلع

اناجم ةحاتم

ميكحلا ناسنلإا
دجي امم رثكأ

اصرف قلخي
.


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1
-
2
Definition

of a

Fluid



A

fluid

includes both liquids and gases.



A

fluid

is a a substance that deforms continuously under the application of a
shear stress no matter how small the shear stress may be.

ـلا فلاخب
solids

ريغتت يتلا
ةدحاو ةرمل

ـلا ةميق عم بسانتي
ً
اددحم
ً
اريغت ددحم نمز يفو
stress

قبطملا
نإف ،اهيلع
fluids

رطاب ريغتت

ً
اريغت نمزلا رورم عم دا

ً
ارمتسم

ـلا ةميق عم اضيأ بسانتي
stress

قبطملا
.اهيلع


ً
اقبط

نإف هلاعأ فيرعتلل
solids

لمحت عيطتست
stress

لكشب هبعوتستو اهيلع قبطملا
deformation

تباث
امأ ددحمو
fluids

يلأ
ً
اقبط رارمتساب لكشتت اهنإف
stress

فيرعت نكمي اذلو اهيلع قبطم
flu
ids

اضيأ
:يلاتلا فيرعتلاب



A

fluid

is a substance that cannot sustain a shear stress when at rest.

ريثكلا

نم

لمعلا

ديجلا

عيضي

ببسب

زجعلا

نع

لذب

ام

وه

رثكأ

لايلق
.



solid under constant shear

fluid under constant shear

liquid

لئاس

fluid

عئام

substance

هدام

deform

هلكش ريغتي

application

قيبطت

no matter

رظنلا ضغي

sustain

لمحتي


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1
-
3
Scope

of Fluid Mechanics



Many of industrials applications depends highly on the principles of fluid
mechanics including subsonic and
supersonic aircrafts, surface ships, submarines
and automobiles.


ولل
ه
ل
ـلل هتسارد ةدئاف نع لعفلاب جرخت سدنهم وأ بلاط يأ لأست امدنع ىلولأا ة
fluid mechanics


لا هنإف
ةيسدنهلا تاقيبطتلا نم يأ يف لماعت دق نكي مل اذإ صخلأاب كلذو هل ةدحاو ةدئاف ركذ عيطتسي داكي
دمتعت يتلا
ئدابم ىلع
ً
اريبك
ً
ادامتعا
fluid mechanics
.


لا ةسدنهلا تايلكب ابلاغ هسيردت متي يذلا سروكلا
ۥ


مي


ك
هب يفتكي نأ هتربخ تلاط امهم جرختم سدنهمل
ً
ادبأ ن
صصختلا اذه يف ةيلات تاسروكو ةصصختم ةساردل جاتحي هنكل ،ةرئاط وأ ةرايس لكيه وأ يئام دس ميمصتل
.

industrial

يعانص

principle

أدبم

subsonic

ةعرس تحت

ءوضلا

aircraft

هرئاط

submarine

هصاوغ


?•?«?‡
?
?•?©?-?ƒ
?
?å?ƒ
?
?°? ?è?—
?
?ü?ä?Ë
?
?ì?ª?ô?Ÿ??Þ?Ü?¸?‘
?
??ª? ?˜?´?Ó
?”?à?ô?³?í
?
?é?¯?Ž? ?ç?ù
?
?Ž?ä?ì?ã
?
?–?ç?Ž?Û
?
??Ñ?í?®?È?ß?•




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1
-
4
Basic

Equations



A
ll fluids must appreciate the following laws:

1.

The conservation of
mass.

2.

Newton's second law of motion.

3.

The principle of angular momentum.

4.

The first law of thermodynamics.

5.

The second law of thermodynamics.



I
n solving fluid problems, we may use one or more than one of the above laws,
we rarely use all of them in one single

problem.



W
e will need statics & dynamics as well as differential and integral calculus
.



E
xample of basic equations
:

I
deal gas equation
:

which relates the absolute pressure (
), to density (
), gas constant (
), and
absolute temperature (
).

Appreciate

مرتحي

Conservation

ظفح

M
omentum

كرحتلا ةيمك

Density

هفاثك

Relate

هقلاعب طبرت


عرزا

ةرذب

ةبغرلا

يف

فوسو كلقع

لكشت

ةاون

تاذ

بذجت ةوق

هيلإ

لك

ءيش

هجاتحي

قيقحتل

.كحاجن





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1
-
5
Methods

of Analysis



The first step in solving a problem is to define the system that you are attempting
to analyze. In basic mechanics, extensive use was made of the free
-
body
diagram. In thermodynamics closed
or open systems where considered. In this
text we use the terms system and control volume.


System

and control volume
:



A
system

is defined as a fixed, identifiable quantity of mass; the system
boundaries separate the system from the surroundings.



The boun
daries of the system may be fixed or movable.

However, there is no
mass transfer across the system boundaries.



In the familiar piston
-
cylinder assembly from thermodynamics, Fig. 1.2, the gas
in the cylinder is the system. If a high
-
temperature source is brought in contact
with the left end of the cylinder, the piston will move to the right; the boundary
of the syst
em thus moves.



Heat and work may cross the boundaries of the system, but the quantity of matter
within the system boundaries remains fixed.



There is no mass transfer across the system boundaries.




Fig. 1.2 Piston
-
cylinder assembly


extensive

فثكم

consider

ربتعي

separate

لصفي

surrounding

طيحم

remain

ىقبي , لظي

boundary

دودح


ريثكلا

نم

لمعلا

ديجلا

عيضي

ببسب

زجعلا

نع

لذب

ام

وه

رثكأ

لايلق
.



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A
control volume

is an arbitrary volume in space through which fluid flows. The
geometric boundary of the control volume is called the control surface. The
control surface may be real or imaginary; it may be at rest or in motion.



Figure 1.3 shows a possible control surfa
ce for analysis of flow through a pipe.
Here the inside surface of the pipe. a real physical boundary, comprises part of
the control surface. However, the vertical portions of the control surface are
imaginary.











arbitrary

يئاوشع

imaginary

يليخت

comprise

فلؤي ، لكشي

portion

ءزج


بهذت نيأ ملعت مل اذإ
،

ضرغلاب يفت قرطلا لكف
.





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1
-
6

Dimensions

and Units

Physical

units
:

1)

Mass

(M).

2)

Length

(L).

3)

Time

(t).

4)

Temperature

(T).

Common

systems of dimensions
:

a.

System International units (SI).

Mass

is measured in
kg

Length

is measured in
m

Time

is measured in
sec

Temperature

is measured in
K

(
Kelvin
)

Force

is measured in
N
=
kg.
m / sce
2

(
)

b.

British Gravitational system of units (FLtT)
:

Force

is measured in

lbf

Length

is measured in
ft

Time

is measured in
sec

Temperature

is measured in
K

(
Kelvin
)

Mass

is measured in
slug

=
ib.
sec
2
/ ft (
)

dimensions

داعبأ

units

تادحو

measure

سيقي

Kelvin

ةرارح سايق ةدحو

slug

هلتك سايق ةدحو


ىتح أرقاو كريرس راوجب

اباتك عض
!مانتل كسفن دهجت لاو مونلا كبلغي






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Examples

of units
:

Each

of the following quantities is expressed using MltT and FLtT systems
.

quantity

formula

MLtT

FLtT

density

هفاثكلا




Spesfic weight

يعونلا نزولا




Pressure

طغضلا




Torque

يلكلا مزع




shear stress

صقلا داهجا




surface tension

يحطسلا رتوتلا


























momentum































viscosity


































specific heat
























































نم
نأ مهملا

هلجأ نم ظقيتست ام كيدل نوكي
.







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Appendix A

FLUID PROPERTY DATA














Water

(
For

liquids)

Air

(
For

gases)

نأ لبق

أدبت

ةجاح يف تنأ كفده قيقحتل يعسلا يف
.








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ةياغلل ةعضاوتم كفادهأ لعجت لا
.







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A
-
1

SURFACE TENSION

The values of surface tension,

, for most organic compounds are remarkably
similar at room temperature;
the typical range is 25 to 40 mN/m. Water is higher, at
about 73 mN/m at 20 C. Liquid metals have values in the range between 300 and
600 mN/m; liquid mercury has a value of about 480 mN/m at 20 C. Surface tension
decreases with temperature; the decrease i
s nearly linear with absolute temperature.
Surface tension at the critical temperature is zero.

Values of
𝛔

are usually reported for surface in contact with the pure vapor of the
liquid being studied or with air. At low pressure both values are about the

same.















يه كراكفأ نم ةركف لك نإ
امإ ةنبل
رصق ىلإ اهفيضت
كعيراشم ربق ىلإ وأ كملاحأ
.








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2010

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A
-
2

TH
E PHYSECAL NATURE OF VISCOSITY

Viscosity is a measure of internal fluid friction, i.e., resistance to deformation. The
mechanism of gas
viscosity is reasonably well understood, but the theory is poorly
developed for liquids. We can gain some insight into the physical nature of viscous
flow by discussing these mechanisms briefly.

The viscosity of a Newtonian fluid is fixed by the state of
the material. Thus



(



)
.

Temperature is the more important variable.












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A
-
2.2
Effect of pressure on Viscosity

a.

Gases

The viscosity of gases is essentially independent of pressure between a few
hundredths of an atmosphere and a few atmospheres. However, viscosity at high
pressures increases with pressure (or density).

b.

Liquids

The viscosities of most liquids are not affected by moderate pressures, but large
increases have been found at very high p
ressure. For example, the viscosity of
water at 10,000 atm is twice that at 1 atm.


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October

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Appendix G

SI UNITS, PREFIXES, AND CONVERSION FACTORS




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