chapter 1 fluid&properties

8/3/2019 Chapter 1 Fluid&Properties

1/82

BMCG 2172

FLUID MECHANICS


2/82

COURSE OBJECTIVES

This course is aimed to cover the basic

principles and equations of fluid mechanics, in

view of to develop students understanding of

how fluid mechanics is applied in engineering

practice.


3/82

LEARNING OUTCOMES

At the end of the course, students should be able to:

Define fluid and its properties.

Apply fluid mechanics equations in solving fluid statics

and dynamics problems.

Analyze stability of an object submersed in a fluid.


4/82

COURSE IMPLEMENTATIONS

Lectures: 28 hours of presenting the concepts, theory

and application (2 hours per week for 14weeks)

Tutorials: 14 hours of tutorials (1 hour per week for 14

weeks)


5/82

ASSESSMENT

NO ITEM QUANTITY %

1 Test 2 20 %

2 ProjectAssignment

1 20 %

3 Quiz 3 10 %

4 Exam 1 50 %

TOTAL 100%


6/82

CONTACT DETAILS

Name : Nurul Hilwa Binti Mohd Zini

Tel : 06-2346764

Room : 8/5/39, Tingkat 5, Bangunan MARS,

Kampus Industri UTeM

Email : [email protected]
mailto:[email protected]:[email protected]


7/82

References

Cheng, S. Y. (2006) Fluid Mechanics I, First KUTKM Edition. Prentice Hall,Malaysia

Cengel, Y. A. and Cimbala, J. M. (2006) Fluid Mechanics: Fundamentalsand Applications, International Edition. McGraw-Hill, Singapore.

Douglas, J. F., Gasiorek J. M. and Swaffield, J. A. (2001) Fluid Mechanics,

4th ed. Printice Hall, Spain.

Munson, B. R., Young D. F. and Okiishi, T. H. (2006) Fundamentals ofFluid Mechanics, 5th Edition. John Wiley & Sons, Inc, Asia.

Som, S. K. and Biswas, G. (2004) Introduction to Fluid Mechanics andFluid Machines, 2nd Edition. Tata McGraw-Hill, New Delhi.

Streeter, V. L. and Wylie, E. B. (1983) Fluid Mechanics, First SI MetricEdition. McGraw-Hill, Singapore.

Finnemore, E. J. and Franzini, J. B. (2002) Fluid Mechanics withEngineering Applications, International Edition. McGraw-Hill, New York.


8/82

INTRODUCTION

Mechanics the study of the effect of physical forces

on objects and their movements

Fluid Mechanics is the study of the

effect of forces generated by fluids or

fluid systems on objects of interest


9/82

Fluids

and their Properties


10/82

Fluids

3 states of matter = SOLID, LIQUID & GAS

Common characteristic of Liquids n gasses:

o Offer permanent resistance to a deforming force?

Noo Fluid flow under the action of shearing force? Yes

o Fluid body deforming continuously for as long asthe force is applied? Yes

o Can it retain any unsupported shape? No

o It can flows under its own weight? Yes

o Takes the shape of any solid body with which it

comes into contact? Yes

? ? ?

?

?

?

?

?

?


11/82

Shear Stress in a Moving Fluid


12/82

When flow past a solid boundary,the fluid in contactwith the

boundary adheresto it and will, Therefore, have the same velocity

as the boundary



13/82


Consider successive layers parallel tothe boundary, the velocityof the fluid will

very from layer to layeras y increases

y


14/82


Consider successive layers parallel tothe boundary, the velocity of the fluid will

very form layer to layeras y increases

y

Distance fromboundary, y

Velocity, u


15/82


Solid boundary


16/82


Solid boundary

A

B

D

C


17/82


Solid boundary

A

B B C C

D

x

y

E E. .

Shearingforce, F


18/82


Solid boundary

A

B B C C

D

x

y

E E. .

F

For small angles,

Shear strain,


19/82


Solid boundary

A

B B C C

D

x

y

E E. .

F

For small angles,

Shear strain,

Rate of shear strain

Where,

u =velocityof

the particle at E

Sh S i M i Fl id


20/82

Shear Stress in a Moving FluidAssuming that

shear stressis proportionaltou/y,i.e. t au/y

then,Shear Stress,

Whereu/yis the change of velocitywithyand may be written in differential formdu/dy

Theconstantis know as the dynamicviscosityof the fluid


21/82

Newtons law of viscosity

The value of dependsupon thefluidunder consideration


22/82

Newtons law of viscosity

There is wide variation of fluids

Fluids of has a constant valueareknow as Newtonian fluids


23/82

Picture from:

http://www.svce.ac.in/~msubbu/FM-WebBook/Unit-I/NonNewtonian.htm

dydu

t

Newtonian

fluid

A

B

C

D

E


24/82

Defination of fluid

A substance that deforms continuouslyunder the action of shearing forces, however

small they may be

If a fluid is at rest, there can be no

shearing forces acting and, therefore, allforces in the fluid must be perpendicular

to the planes upon which they act


25/82


Is there any shear stress in a fluid at rest? No

When is shear stress being developed?

If the particles of fluid move relative to each

other so that they have different velocities,causing the original shapeof the fluid to becomedistorted

If the velocity of the fluid is the sameat everypoint, noshear stresses will be produced, thefluid particle are at rest relativeto each other

?


26/82

Are the fluids in container A

and B in static?

A B


27/82

A B


28/82

Solid


29/82

Solid


30/82

MASS DENSITY


31/82

2 containers of same volume

Samevolume


32/82

Fill the containers with: - Sands and Stones (sand and stone are same material of different size)

Sands Stones


33/82

Which one is heavier?

Sands Stones


34/82

Sands

Stones

Heavier!

Air space


35/82

This suggested that for the same volume,the heavier material is denser(higher massdensity) than the lighter material

Sands

Stones

Denser!


36/82

And so mass density is (can be define as): -

Sands(denser)

Stones

As mass is measure in the unit of kg

and volume is measure in the unit of m3,

so the unit of density is kg/m3

- units


37/82

The value of mass density canvary widely between fluids

Sands(denser)

Stones


38/82

Sands(denser)

Stones

i.e. density of mercury is higher than the density ofwater, where,

Density of mercury = 13.56 Mg/m3

Density of water = 1 Mg/m3

Atoms in mercury are about 13 times denser thanthe molecules in water


39/82

Specific Weight

A result of,m(kg) x g(m/s2) = W(N)

Therefore,

gravitational

accelerationWeightmass

gravitational

acceleration

Weight

Per

volume

Mass

Pervolume


40/82

Specific Weight

Therefore, Specific weight is defined asthe weight per unit volume

wwill very from point to point,

according to the local value of gravitationalacceleration


41/82

Relative Density/Specific Gravity

The ratio of the mass density of asubstance to some standard mass density

Standard mass density is the

maximum density of water at 4 deg. Celsius


42/82

Relative Density/Specific Gravity

i. e. The relative density of oil is0.84;

In other words, the density of oil is0.84 times that of water


43/82

Specific Volume

being used to mean volume per unitmass


44/82

VISCOSITY

S S


45/82

Shearing force, F


Solid boundary

Sh S i M i Fl id


46/82


X

Shearing force, F

Solid boundary

Sh S i M i Fl id


47/82


X

Shearing force, F

Solid boundary

Sh S i M i Fl id


48/82

X

Shearing force, F

Shear stress (x direction),

A


Solid boundary

Sh S i M i Fl id


49/82

F


Shear stress (x direction),

C ffi i t f d i i it


50/82

Coefficient of dynamic viscosity

X

Shearing force, F

A

- Units

Solid boundary

C ffi i t f d i i it


51/82

Coefficient of dynamic viscosity

X

Shearing force, F

A

Shear force per unit area (shear stress)

require to drag one layer of fluid with unit velocitypast another layer a unit distance away from it

Solid boundary

Ki ti i it


52/82

Kinematic viscosity

- Units

Ratio of dynamic viscosityto mass density

Kinematic viscosity,

Often measured in stokes (St)

Where,


53/82

SURFACE

TENSION


54/82

Oxygen Atom

CHENGS SHOW

+


55/82

Oxygen Atom

CHENGS SHOW

+ 2

88


56/82

CHENGS SHOW

Hydrogen Atom

2

88


57/82

Water Molecule

Covalent bonding

(strong primarybond)

+

CHENGS SHOW


58/82

Weak secondary bond

Cohesive force

CHENGS SHOW

+


59/82

Bonding of molecules in water


60/82

The cohesive forcesbetween moleculesdown into a liquid are

shared with allneighboring molecules

No neighboring moleculesabove,

Enhancement of the

intermolecular attractiveforces occurred

(called surfacetension)


61/82

Water Molecule

Orderly arranged

Effect of Surface Tension


62/82

Effect of Surface Tension

To reduce the surface

of a liquid to aminimum

Free Surface

ReducedFree Surface


63/82

Drop of liquid tends totake a spherical shape in

order to minimize surfacearea


64/82

Free surface

Liquid

Liquid

Intermolecularattractive forces,

F


65/82

Liquid

Intermolecularattractive forces,

F

Surface tension,

L


66/82

Needle


67/82

L

s

q

s

q

Express the needle weight Win term of the given

parameters, i.e. s,q and L

Assume the needle diameter isnegligible

W


68/82

L

s

q

s

q

Express the needle weight Win term of the given

parameters, i.e. s,q and L

Assume the needle diameter isnegligible

W

W = F

= s(2L) sinq (Answer)


69/82

Air

Water

Air

Mercury

s = 0.073 N/m s = 0.5 N/m


70/82

CAPILLARITY


71/82

Angle of contact


72/82

Angle of contactbetween liquid and solid

Solid boundary Solid boundary

Liquid wets a surfaceand spreads out

Small contact angle

Large contact angle

Adhesion> cohesion

Adhesion


73/82

Capillary action is theresult of adhesion andsurface tension

Adhesion of water tothe walls of a vessel willcause an upward force

on the liquid at theedges and result in ameniscus which turnsupward


74/82

The surface tensionacts to hold the surface

intact, so instead of justthe edges movingupward, the wholeliquid surface isdragged upward.


75/82

hd

Upward surface tension force = Weight of the column in thetube

h


76/82

hd

For water and glass,


77/82


78/82

Capillary action is negligible forwater and mercury for tubediameters of 1 cm or more


79/82

VAPOUR PRESSURE


80/82

V P


81/82

Vapour Pressure

By increasing the water temperature to 100 oC,we increase the vapour pressure to the pointat which it is equal to the atmosphericpressure (1 atm abs), so that boiling occurs

Can boiling of water occur < 100 oC?

V P


82/82

Vapour Pressure

Water boils at 60 oC at 0.2 bar (0.2 atm)

chapter 1 fluid&properties

Documents