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

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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 KULIAH PENDAHULUAN Mengenal aplikasi Mekanika Fluida, Fluida dan propertiesnya FLUIDA STATIK Pressure, 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 PIPA Faktor 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 DIMENSI Kecepatan suara, Aliran stedi fritionless, nozzle choking, aliran dengan friksi dan pemanasan, nozzle-difusser INTERAKSI 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 incompressible Relatively 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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Density The density of a fluid is defined as its mass per unit volume. It is denoted by the Greek symbol, . = V m3m3 kgm -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 kg m

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Density Mass per unit volume 20 o C, 1 atm) Water water = 1000 kg/m 3 Mercury Hg = 13,500 kg/m 3 Air air = 1.22 kg/m 3 Densities of gasses increase with pressure Densities of liquids are nearly constant (incompressible) for constant temperature Specific volume = 1/density Temperature (C) Density (kg/m 3 )

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Specific Weight Weight per unit volume 20 o C, 1 atm) water = (998 kg/m 3 )(9.807 m 2 /s) = 9790 N/m 3 [= 62.4 lbf/ft 3 ] air = (1.205 kg/m 3 )(9.807 m 2 /s) = 11.8 N/m 3 [= lbf/ft 3 ]

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Specific Gravity Ratio of fluid density to density at STP 20 o C, 1 atm) WaterSG water = 1 MercurySG Hg = 13.6 AirSG air = 1

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States of Matter Fluid Solid 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 view Force F causes the top plate to have velocity U. Distance between plates (b) Area of plates (A) F b U Viscosity! What other parameters control how much force is required to get a desired velocity?

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Shear Stress change in velocity with repect to distance Tangential force per unit area Rate of deformation rate of shear F b v

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b v vbvb F Area A Friction force z Absolute Viscosity Shear stess (dyne/cm 2 ) Shear strain rate (s -1 ) Kinematic Viscosity Dyne-s/cm 2 =Poise N-s/m 2 =10 3 cP Dynamic and Kinematic Viscosity

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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 zero

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Perfect Gas Law PV = nRT R is the universal gas constant T is in Kelvin 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 _________ ______ __________ Temperature (C) Bulk Modulus of elasticity (GPa) sound water hammer Water speed of sound

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Vapor Pressure Temperature (C) Vapor pressure (Pa) liquid What is vapor pressure of water at 100°C? 101 kPa Connection forward to cavitation!

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p R 2 = 2 R Surface Tension Pressure increase in a spherical droplet pR2pR2 2R2R Surface molecules Temperature (C) Surface tension (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. R = 0.15 x m = N/m What is the difference between pressure in a water droplet and in an air bubble? Statics!

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Bagaimana mengukur viskositas ?

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GLASS CAPILLARY VISCOMETERS P = Pressure difference across capiller R = Radius of capiller L = Length od capiller V = Volume fluida = Viscosity ASTM D445

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A CALIBRATED HOLE IN THE BOTTOM. 2 1 xx zz V (Poiseuille Eq.) 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 cylinder Thin layer of water Inner cylinder

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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

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Viscosity Measurement: Solution Outer cylinder Thin layer of water Inner cylinder r = 5 cm t = 2 mm h = 10 cm P = 50 x W 10 rpm rr 2 rh FrFr

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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 L T M MLT -2

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Dimensions and Units QuantitySymbolDimensions Density ML -3 Specific Weight ML -2 T -2 Dynamic viscosity ML -1 T -1 Kinematic viscosity L 2 T -1 Surface tension MT -2 Bulk mod of elasticityE ML -1 T -2 These are _______ properties! fluid How many independent properties? _____ 4

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Units Unit: Particular dimension kg, m, s, o K(Systeme International) slug, ft, s, o R(British Gravitational) lbm, ft, s, o R(something else)

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What’s a SLUG?! Unit of mass in the BG system (~ kg, ~32.17 lbm) 1 lbf will accelerate a slug 1ft/s lb/14.59 kg = 2.2 lbm/kg

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Secondary Units Force N = kg-m/s 2 (Newton) lbf = slug-ft/s 2 (pound force) = 32.2 lbm-ft/s 2 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) hp550 ft-lb/s(horsepower)

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g c YANG SERING MEMBINGUNGKAN, W = mg W = mg /g c. FisikaEngineering (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.a H. Kekekalan Massa H. Kekekalan Energi (H.Termodinamika 1) H. Termodinamika 2 PERSAMAAN DASAR MEKANIKA FLUIDA Tujuan Pengajaran

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