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

Periode 2009-2010 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

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

Books Noel de Nevers Fluid Mechanics for Chemical Engineer, Second Ed. Coulson & Richardson Chemical Engineering, Vol 1, 5e (1996) Butterworth-Heinemann

ALIRAN GAS KECEPATAN TINGGI, SATU DIMENSI INTERAKSI FLUIDA DAN PADATAN 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, Internal and external flows Air, sea-water – oil & gas – fresh water, mud, hydraulic oil Drilling, pumping, extraction, power generation, effluent disposal, fire systems, sanitation

Fluid Mechanics Definition Engineering applications The study of liquids and gasses at rest (statics) and in motion (dynamics) Engineering applications Oil /process fluid in pipelines Pumps, filters, rivers, etc Groundwater movement Blood in capillaries

Industrial application … Home : water, heating, appliances – fridge, washing / dish-washer machines Car: engine cooling + car heater, fuel, oil, hydraulics, external aerodynamics Aeroplane: fuel, hydraulics, air-conditioning, cabin pressurization, oxygen, sanitation, external aerodynamics, gas turbines

DIAGRAM SISTIM ALIRAN FLUIDA Storage Pipe system Valves Flow Measurement Pump Process/Resistance

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

MENGENAL SIFAT FLUIDA Fluid Properties

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

Liquids and gasses – What’s the difference? Expands Liquid Free Surface Liquids: Close packed, strong cohesive forces, retains volume, has free surface Gasses: Widely spaced, weak cohesive forces, free to expand Almost incompressible Relatively easy to compress

Common Fluids Liquids: Gasses: Borderline: water, oil, mercury, gasoline, alcohol Gasses: air, helium, hydrogen, steam Borderline: jelly, asphalt, lead, toothpaste, paint, pitch

Density The density of a fluid is defined as its mass per unit volume. It is denoted by the Greek symbol, . kg  water= 998 kgm-3 m  = V air =1.2kgm-3 kgm-3 m3 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)

Density Mass per unit volume (e.g., @ 20 oC, 1 atm) Water rwater = 1000 kg/m3 Mercury rHg = 13,500 kg/m3 Air rair = 1.22 kg/m3 Densities of gasses increase with pressure Densities of liquids are nearly constant (incompressible) for constant temperature Specific volume = 1/density 950 960 970 980 990 1000 50 100 Temperature (C) Density (kg/m3)

Specific Weight Weight per unit volume (e.g., @ 20 oC, 1 atm) gwater = (998 kg/m3)(9.807 m2/s) = 9790 N/m3 [= 62.4 lbf/ft3] gair = (1.205 kg/m3)(9.807 m2/s) = 11.8 N/m3 [= 0.0752 lbf/ft3]

Specific Gravity Ratio of fluid density to density at STP (e.g., @ 20 oC, 1 atm) Water SGwater = 1 Mercury SGHg = 13.6 Air SGair = 1

States of Matter “a fluid, such as water or air, deforms continuously when acted on by shearing stresses of any magnitude.” - Munson, Young, Okiishi Solid Shear Stress t Fluid

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

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

Dynamic and Kinematic Viscosity Area A Friction force F vb b v z Absolute Viscosity Kinematic Viscosity Shear stess (dyne/cm2 ) Shear strain rate (s-1) Dyne-s/cm2=Poise N-s/m2=103 cP

Fluid classification by response to shear stress

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 _______

Role of Viscosity Statics Flows zero 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

Perfect Gas Law Note deviation from the text! PV = nRT R is the universal gas constant T is in Kelvin Use absolute pressure for P and absolute temperature for T

Bulk Modulus of Elasticity Relates the change in volume to a change in pressure changes in density at high pressure pressure waves _________ ______ __________ 2.00 2.05 2.10 2.15 2.20 2.25 2.30 2.35 20 40 60 80 100 Temperature (C) Bulk Modulus of elasticity (GPa) sound Water water hammer speed of sound

Vapor Pressure 101 kPa liquid 1000 2000 3000 4000 5000 6000 7000 8000 10 20 30 40 Temperature (C) Vapor pressure (Pa) liquid What is vapor pressure of water at 100°C? 101 kPa Connection forward to cavitation!

Surface Tension Pressure increase in a spherical droplet DppR2 2pRs 0.050 0.055 0.060 0.065 0.070 0.075 0.080 20 40 60 80 100 Temperature (C) Surface tension (N/m) Pressure increase in a spherical droplet DppR2 2pRs Surface molecules DppR2 = 2pRs

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. s = 0.073 N/m R = 0.15 x 10-3 m Statics! What is the difference between pressure in a water droplet and in an air bubble?

Bagaimana mengukur viskositas ?

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

A CALIBRATED HOLE IN THE BOTTOM. (Poiseuille Eq.) 1 V x z cP = fluid density X cSt 2

ROTARY VISCOMETER

Example: Measure the viscosity of water Outer cylinder Thin layer of water Inner cylinder 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?

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

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

Viscosity Measurement: Solution Outer cylinder Thin layer of water Inner cylinder wr 2prh Fwr r = 5 cm t = 2 mm h = 10 cm P = 50 x 10-6 W 10 rpm

APPROXIMATE PHYSICAL PROPERTIES OF COMMON LIQUIDS AT ATMOSPHERIC PRESSURE

Dimensions & Units Tujuan : mereview satuan untuk menghilangkan kebingunan konversi satuan SI dan Engineering

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 

Dimensions and Units Quantity Symbol Dimensions Density r ML-3 Specific Weight g ML-2T-2 Dynamic viscosity m ML-1T-1 Kinematic viscosity  L2T-1 Surface tension  MT-2 Bulk mod of elasticity E ML-1T-2 These are _______ properties! fluid 4 How many independent properties? _____

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

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

Secondary Units Force N = 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)

gc YANG SERING MEMBINGUNGKAN, Fisika Engineering W = mg W = mg /gc. (g: gravitational acceleration).

Conversion of Units

MEKANIKA FLUIDA Tujuan Pengajaran 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. PERSAMAAN DASAR MEKANIKA FLUIDA H. Newton F= m.a H. Kekekalan Massa H. Kekekalan Energi (H.Termodinamika 1) H. Termodinamika 2