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11 PropertiesofLiquidsPropertiesofLiquids

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11DifferencebetweenFluids&Solids

Fluids may be liquids (definite volume;freesurface) or gases (expand to fill anycontainer).

Fluid

is

a

body

of

matter

that

canflow;

i.e.

continuestodeformunderashearingforce.

Solid hasacertainvolumeandshape

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Fluids

Liquid Gas

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12Propertiesofaliquid

121 Density

Massperunitvolume

Units

gmmass/cm

3

Kgmass/m3

3L

M

Volume

Mass

=

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122SpecificWeight

Specificweightisdefinedastheweightofthe

substanceperunitvolume

Unitsgm/cm3 ,N/m3 ,Kg/cm3 ,ton/m3

gL

gM

L

F

Volume

Weight=

=

33

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1221Units

Nkgmkgkg

mKgNcmgmgm

ggmgmgmassWeight

onacceleratimassF

mass

mass

mass

mass

81.91sec/81.911

sec/111sec/9811

11

2

2

2

=

=

=

=

=

=

=

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123Specificweight&specificGravity

RelativeDensityS SpecificGravityG

Cowater

liquidG4@

=

Cowater

liquid

S4@

=

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124Viscosity

Viscosityisthepropertyofliquidthatindicates

theresistanceofliquidagainstmotion.Viscositycanbedescribedeitherby

dynamicviscosity

kineticviscosity

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DynamicViscosity

dyduVelocity

Shear

/ydepthatgradient

ydepthaatstress

==

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Where

is the shear stress at depth y is the dynamic viscosity of the liquiddu/dy is the velocity gradient at depth y

dydu/

=

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1241Dynamicviscosityunits

2

211

sec/sec// cmgmcmgm

FTLTML

mass

1 poise = 0.1 N sec/m2

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1242KineticViscosity

sec/212 cmTL

=

1 stoke = 1 cm2/sec

The kinetic viscosity is affected by temperature

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125Vaporpressure

Thevaporpressureisdefinedas thepressureof

theatmosphereadjoiningtheliquidatwhichtheliquidstartstoevaporate

Allliquidspossesatendencytovaporizewhenexposedtogaseousatmosphere.

Thevaporpressuredependson:

i.Theliquidtemperature.

ii.Atmosphericpressureadjoiningtheliquid.

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126Compressibility

A fluid is comprisable when its density

changeswithchangeofpressureactingonit.

Inreality allfluidsarecompressible.

The compressibility of liquid is measured by

BULKMODULUSOFELASTISITYK

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1261BulkModulusofElasticityK

VV

PK

=

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Continue BulkModulusofElasticityK

The water compressibility increase with the

increase of temperature up to 50oC, then it

startstodecrease.

Themodulusofelasticityforfreshwaterat20oC

istoosmallthatitconsideredasincompressible

fluid

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127SurfaceTension

Molecules of liquid held together by force

attraction.Theyareequallyattracted. The resultant of these forces at the solid

boundary containing the liquid surface

tension

Surface Tension is a force in the liquid

surface and acts normal to the line of unit

lengthdrawnimaginaryonthesurface.