handout1 pendahuluan
TRANSCRIPT
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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