Hidrolika I (IL-2101) Slide 2
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Transcript of Hidrolika I (IL-2101) Slide 2
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INTRODUCTION TOFLUID MECHANICS
Benno RahardyanMarisa HandajaniHaryo Satrio Tomo
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Fluids Properties Fluids vs. solids Density Compresibilty
Viscosity Surface Tension Pressure
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Motivasi
Pola, Perilaku, Interaksi?
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Definition of a Fluid
A fluid is a substance that flows under the action of shearingforces. If a fluid is at rest, we know that the forces on it are in
balance.
A gas is a fluid that is easily compressed. It fills any vessel inwhich it is contained.
A liquid is a fluid which is hard to compress. A given mass ofliquid will occupy a fixed volume, irrespective of the size ofthe container.
A free surface is formed as a boundary between a liquid and agas above it.
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Shear : A force acting in a direction parallel to a surface or to aplanar cross section of a body.
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Density
The density of a fluid is defined as its mass per unitvolume. It is denoted by the Greek symbol, .
=V m3 kgm -3
If the density is constant (most liquids), the flow is
incompressible .If the density varies significantly (eg some gasflows), 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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Exercise 1 The specific weight of water at ordinary pressure and
temperature is 9.81 kN/m3. The specific gravity of mercuryis 13.56. Compute the density of water and specific weightand density of mercury
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Compressibility
Compressibility :change in volume dueto change in pressure
For liquid is a functionof P, T
Liquid compressibility
is inverselyproportional to itsvolume modulus ofelasticity
dpd d
dp E
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Kompresibilitas
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Kompresibilitas
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Kompresibilitas
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Kompresibilitas Gas IdealE = np
Proses isotermal n = 1 E = p Proses isentropik n = k E = kp
Note: Gas ideal : gas yang memiliki panas spesifik yang konstan (Cp dan Cv) dan
mengikuti aturan:P/ = P = RT
=g = gP/RT R = 287 N.m/(kg.K) = 287 m 2/s 2.K
Gas real (non gas ideal): Panas spesifik bervariasi dalam perbedaan temperatur, sehingga:
P/ = P = zRTRo = zRM
z= faktor kemampuamampatan yang tergantung pada tekanan dan temperatur.
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Fluida Real
Memiliki gaya tangensial/geser pada saat ada gerakan relatifterhadap bidang FRIKSI
Gaya berlawanan dengan gerakan partikel
Gaya geser inilah yang menjadi prinsip sifat fluida :
viskositas/kekentalan
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Punya tegangan geser tertentu untuk dapat digerakan
berubah sejalan dengan laju deformasi
viskositas tidak berubah dengan laju deformasi
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Viskositas
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Viskositas
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Viskositas
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Viskositas
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Pressure
Pressure is the force per unit area, where the force is perpendicular to the area.
p= A m2
Nm -2
(Pa)
N F
This is the Absolute pressure , the pressure compared toa vacuum.
pa= 105
Nm-2
1psi = 6895Pa
The pressure measured in your tyres is the gauge pressure, p-p a.
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Measuring pressure (1)Manometers
h
p1 p2=p a
liquiddensity
x y
z
p1 = p x
px = p y
pz= p 2 = p a
(negligible pressurechange in a gas)
(since they are atthe same height)
py - p z = gh
p1 - p a = gh
So a manometer measures gauge pressure .
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Tegangan Permukaan
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Metode Pengukuran
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Metode Pengukuran
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Metode Pengukuran