Handout1 Pendahuluan

47
CHS220804 MEKANIKAFLUIDA (S1 Reguler) CHS220803E MEKANIKAFLUIDA (S1 Ekstensi) Departemen Teknik Kimia FT-UI Pengajar : Ir. SUKIRNO M.Eng/Ir. Diyan S M.Eng

Transcript of Handout1 Pendahuluan

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CHS220804 MEKANIKAFLUIDA (S1 Reguler)CHS220803E MEKANIKAFLUIDA (S1 Ekstensi)

Departemen Teknik Kimia FT-UI

Pengajar : Ir. SUKIRNO M.Eng/Ir. Diyan S M.Eng

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Periode 2009-2010

Lectures : Senin 19:00-21:30 K-204Selasa 10:00-12:30 K-106Kamis 10:00-12:30 K-210

Sbl Mid Test Pak Sukirno Stl Mid Test Pak Diyan S

Tutorials : Asisten

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Assessment

Pak Kirno 50% 25% : MidTest (2 jam) 10% : Kuis selama kelas/tutorial 15% : Tugas

Nilai P.Kirno x 50% + Nilai P.Diyan x 50%Nilai

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Books

Noel de Nevers Fluid Mechanics for Chemical Engineer, Second Ed.

Coulson & Richardson Chemical Engineering, Vol 1, 5e (1996) Butterworth-Heinemann

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GARIS BESAR KULIAHPENDAHULUAN

Mengenal aplikasi Mekanika Fluida, Fluida dan propertiesnya

FLUIDA STATIKPressure, Pascal’s Principle,Gravity and fluid pressure, Measurement of pressure, Archimedes’ Principle

FLUIDA MENGALIR (FLUID FLOW)Persamaan dasar: Pers. Kontinuitas (Neraca massa) Pers. Bernoulli (Neraca Energi) dan aplikasiBernoulli pada

flowmeter (orificemeter, venturimeter), alat transfer fluida (pompa)

KEHILANGAN FRIKSI (FRICTION LOSS) DALAM PIPAFaktor friksi, diagram Moody, Perhitungan friksi pada pipa sudden contraction/expansion fitting,

APLIKASI NERACA MOMENTUM UNTUK PERHITUNGAN GAYA PADA PIPA

Neraca momentum, perhitungan gaya pada belokan

ALIRAN GAS KECEPATAN TINGGI, SATU DIMENSIKecepatan suara, Aliran stedi fritionless, nozzle choking, aliran dengan friksi dan

pemanasan, nozzle-difusserINTERAKSI FLUIDA DAN PADATAN

Lapisan batas dan Gaya seret (drag force), Friksi fluida dalam media berpori, Pers. Blake-Kozeny, Ergun Darcy, Fluidisasi, Filtrasi,

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Fluid Mechanics

Engineering applications Oil /process fluid in pipelines Pumps, filters, rivers, etc Groundwater movement Blood in capillaries

Definition The study of liquids and gasses at rest

(statics) and in motion (dynamics)

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Industrial application …

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Storage

Valves

Pipe system

Pump

Flow Measurement

Process/Resistance

DIAGRAM SISTIM ALIRAN FLUIDA

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SUBDIVISI MEKANIKA FLUIDA

HYDRAULICS : the flow of water in rivers, pipes, canals, pump, turbines HYDROLOGY : the flow of water in the ground RESERVOIR MECHANICS : the flow of oil, gas and water in petroleum

reservoir

AERODYNAMICS : the flow of air around aeroplanes, rocket projectils METEOROLOGY : the flow of the atmosfeer

PARTICLE DYNAMICS : the flow of fluid around particles (dust settling, slurry, pneumatic transfort, fluidized be, air pollutant particles)

MULTIPLEPHASE FLOW oil well, carburetirs, fuel injector, combustion chamber, sprays.

COMBINATION OF FLUID FLOW with chemical reaction in combustion chamber, with mass transfer di distillation or drying

VISCOUS DOMINATED FLOW; lubrication, injection molding, wire coating, volcanoes, continental drift

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MENGENAL SIFAT FLUIDA Fluid Properties

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What is a Fluid?

… a substance which deforms continuously under the action of shearing forces however small.

… unable to retain any unsupported shape; it takes up the shape of any enclosing container.

... we assume it behaves as a continuum

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Liquids: Close packed, strong cohesive forces, retains volume, has free surface

Liquids and gasses – What’s the difference?

Liquid

Free Surface

Gas

Expands

Gasses: Widely spaced, weak cohesive forces, free to expand

Almost incompressibleRelatively easy to compress

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Common Fluids

Liquids: water, oil, mercury, gasoline, alcohol

Gasses: air, helium, hydrogen, steam

Borderline: jelly, asphalt, lead, toothpaste, paint,

pitch

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DensityThe density of a fluid is defined as its mass per unit volume. It is denoted by the Greek symbol, .

=V m3kgm-3

If the density is constant (most liquids), the flow is incompressible.

If the density varies significantly (eg some gas flows), the flow is compressible.

(Although gases are easy to compress, the flow may be treated as incompressible if there are no large pressure fluctuations)

water= 998 kgm-3

air =1.2kgm-3

kgm

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Density Mass per unit volume (e.g., @

20 oC, 1 atm) Water water = 1000 kg/m3

Mercury Hg = 13,500 kg/m3

Air air = 1.22 kg/m3

Densities of gasses increase with pressure

Densities of liquids are nearly constant (incompressible) for constant temperature

Specific volume = 1/density950960970980990

1000

0 50 100Temperature (C)

Den

sity

(kg

/m3 )

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Specific Weight

Weight per unit volume (e.g., @ 20 oC, 1 atm)

water = (998 kg/m3)(9.807 m2/s)

= 9790 N/m3

[= 62.4 lbf/ft3]air = (1.205 kg/m3)(9.807 m2/s)

= 11.8 N/m3

[= 0.0752 lbf/ft3]

]/[]/[ 33 ftlbformNg

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Specific Gravity Ratio of fluid density to density at STP

(e.g., @ 20 oC, 1 atm)

3/9790 mkgSG

liquid

water

liquidliquid

Water SGwater = 1 Mercury SGHg = 13.6 Air SGair = 1

3/205.1 mkgSG

gas

air

gasgas

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States of Matter

FluidSolid

Shear Stress

“a fluid, such as water or air, deforms continuously when acted on by shearing stresses of any magnitude.” - Munson, Young, Okiishi

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Fluid Deformation between Parallel Plates

Side viewSide viewForce F causes the top plate to have velocity U.Force F causes the top plate to have velocity U.

Distance between plates (b)Distance between plates (b)Area of plates (A)Area of plates (A)

F

b

U

Viscosity!Viscosity!

What other What other parameters control parameters control how much force is how much force is required to get a required to get a desired velocity?desired velocity?

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Shear Stress

change in velocity with repect to distancechange in velocity with repect to distance

AFAF

2m

N

2m

N v

b

v

b

v

b

v

b

dv

dy

dv

dy

AvF

b

AvF

b F v

A b

F v

A b

s

1

s

1

Tangential force per unit area

Rate of deformation

rate of shear

F

b

v

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bv

vbF

Area AFriction force

z

Absolute Viscosity

b

FA

vb

Shear stess(dyne/cm2 )

Shear strain rate(s-1)

Stokes

cm

/cms-dyne

s/cmdyne

density

viscosityabsolute

2

42

2

Kinematic Viscosity

Dyne-s/cm2=PoiseN-s/m2=103 cP

Dynamic and Kinematic Viscosity

2m

sN

2m

sN

2s

mkgN

2s

mkgN

3mkg

smkg

3mkg

smkg

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ssds

Fluid classification by response to shear stress

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Fluid Viscosity Examples of highly viscous fluids

______________________ Fundamental mechanisms

Gases - transfer of molecular momentum Viscosity __________ as temperature increases. Viscosity __________ as pressure increases.

Liquids - cohesion and momentum transfer Viscosity decreases as temperature increases. Relatively independent of pressure

(incompressible)

molasses, tar, 20w-50 oil

increases

_______

increases

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Role of Viscosity

Statics Fluids at rest have no relative motion

between layers of fluid and thus du/dy = 0

Therefore the shear stress is _____ and is independent of the fluid viscosity

Flows Fluid viscosity is very important when the

fluid is moving

zerozero

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Perfect Gas Law

PV = nRT R is the universal

gas constant T is in Kelvin

Note deviation from the text!Note deviation from the text!

Use absolute pressure for P and absolute temperature for T

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Bulk Modulus of Elasticity Relates the change

in volume to a change in pressure changes in density at

high pressure pressure waves

_________ ______ __________

VdV

dpEv

2.00

2.05

2.10

2.15

2.20

2.25

2.30

2.35

0 20 40 60 80 100

Temperature (C)

Bul

k M

odul

us o

f el

asti

city

(G

Pa)

soundsoundwater hammerwater hammer

Water

vE

a

vEa speed of soundspeed of sound

d

dpEv

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Vapor Pressure

0

1000

2000

3000

4000

5000

6000

7000

8000

0 10 20 30 40

Temperature (C)

Vap

or p

ress

ure

(Pa)

liquid

What is vapor pressure of water at 100°C?101 kPa

Connection forward to cavitation!

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pR2 = 2R

Surface Tension Pressure

increase in a spherical droplet

Rp

2R

p2

pR2

2RSurface moleculesSurface molecules

0.0500.0550.0600.0650.0700.0750.080

0 20 40 60 80 100

Temperature (C)

Sur

face

tens

ion

(N/m

)

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Example: Surface Tension Estimate the difference in pressure (in

Pa) between the inside and outside of a bubble of air in 20ºC water. The air bubble is 0.3 mm in diameter.

Rp

2R

p2

R = 0.15 x 10-3 mR = 0.15 x 10-3 m

= 0.073 N/m = 0.073 N/m

m1015.0

N/m 073.023

p

m1015.0

N/m 073.023

p

970 Pap =970 Pap =

What is the difference between pressure in a water droplet and in an air bubble?

hp hp waterm 1.0/9806

9743

mN

Paph

waterm 1.0

/9806

9743

mN

Paph

Statics!

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Bagaimana mengukur viskositas ?

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GLASS CAPILLARY VISCOMETERS

P = Pressure difference across capiller R = Radius of capillerL = Length od capiller V = Volume fluida = Viscosity

LV

t

8

Pr 4

ASTM D445

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A CALIBRATED HOLE IN THE BOTTOM.

2

1

txV

Dzg o

128

4 )(

xz

xQ

Dzg o

128

4 )(V

tk

(Poiseuille Eq.)

tk

cP = fluid density X cSt

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ROTARY VISCOMETER

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Example: Measure the viscosity of water

The inner cylinder is 10 cm in diameter and rotates at 10 rpm. The fluid layer is 2 mm thick and 10 cm high. The power required to turn the inner cylinder is 50x10-6 watts. What is the dynamic viscosity of the fluid?

Outer Outer cylindercylinder

Thin layer of waterThin layer of water

Inner Inner cylindercylinder

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Solution Scheme Restate the goal Identify the given parameters and represent

the parameters using symbols Outline your solution including the equations

describing the physical constraints and any simplifying assumptions

Solve for the unknown symbolically Substitute numerical values with units and

do the arithmetic Check your units! Check the reasonableness of your answer

olution

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Outline the solution Restate the goal Identify the given parameters and

represent the parameters using symbols

Outline your solution including the equations describing the physical constraints and any simplifying assumptions

23- s/mN 1.16x10

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Viscosity Measurement: Solution

hrPt

322

hrPt

322

23-32

6-

s/mN 1.16x10m) (0.1m) (0.05(1.047/s)2

m) (0.002 W)10(50

x 23-32

6-

s/mN 1.16x10m) (0.1m) (0.05(1.047/s)2

m) (0.002 W)10(50

x

tAU

F t

AUF

U UA A

thr

F22

thr

F22 P P

thr

P322

thr

P322

Outer Outer cylindercylinder

Thin layer of waterThin layer of water

Inner Inner cylindercylinder

r = 5 cmt = 2 mmh = 10 cmP = 50 x 10-6 W10 rpm

r2rh

Fr

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APPROXIMATE PHYSICAL PROPERTIES OF COMMON LIQUIDS AT ATMOSPHERIC PRESSURE

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Dimensions & Units

Tujuan : mereview satuan untuk menghilangkan kebingunan konversi satuan SI dan Engineering

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Dimensions and Units

The dimensions have to be the same for each term in an equation

Dimensions of mechanics are length time mass force temperature

aF m aF m

L

T

MMLT-2

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Dimensions and UnitsQuantity SymbolDimensionsDensity ML-3

Specific Weight ML-2T-2

Dynamic viscosity ML-1T-1

Kinematic viscosity L2T-1

Surface tension MT-2

Bulk mod of elasticity E ML-1T-2

These are _______ properties!fluid

How many independent properties? _____4

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Units Unit: Particular dimension

kg, m, s, oK (Systeme International)

slug, ft, s, oR (British Gravitational) lbm, ft, s, oR (something else)

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What’s a SLUG?!

Unit of mass in the BG system (~ 14.59 kg, ~32.17 lbm)

1 lbf will accelerate a slug 1ft/s2

32.17 lb/14.59 kg = 2.2 lbm/kg

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Secondary Units

ForceN = kg-m/s2 (Newton)lbf = slug-ft/s2 (pound force)

= 32.2 lbm-ft/s2

Work (Force through a distance)J = N-m (Joule)ft-lbf (foot pound)

Energy (Work per time)W = J/s (Watt)ft-lbf/s (foot pound per sec)hp 550 ft-lb/s (horsepower)

22 T

LM

T

ML

maF

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gc YANG SERING MEMBINGUNGKAN,

W = mgW = mg /gc.

Fisika Engineering

(g: gravitational acceleration).

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Conversion of Units

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Memahami fenomena/konsepnya dan mampu mengaplikasikan PERSAMAAN DASAR fluida statik maupun fluida mengalir, untuk mendapatkan solusi persoalan praktis, yang sering dijumpai dalam enjinering terutama yang berkaitan dengan operasi teknik kimia seperti transportasi fluida, pengontakkan fluida-padatan, pemisahan fluida padatan.

MEKANIKA FLUIDA

H. Newton F= m.aH. Kekekalan MassaH. Kekekalan Energi (H.Termodinamika 1)H. Termodinamika 2

PERSAMAAN DASAR MEKANIKA FLUIDA

Tujuan Pengajaran