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

Departemen Teknik Kimia FT-UI

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

Periode 2009-2010Lectures : Senin 19:00-21:30 K-204Selasa 10:00-12:30 K-106Kamis 10:00-12:30 K-210

Sbl Mid Test Pak SukirnoStl Mid Test Pak Diyan S

Tutorials :Asisten

AssessmentPak Kirno 50%25% : MidTest (2 jam)10% : Kuis selama kelas/tutorial15% : Tugas

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

GARIS BESAR KULIAHPENDAHULUAN Mengenal aplikasi Mekanika Fluida, Fluida dan propertiesnya

FLUIDA STATIKPressure, Pascals 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 PIPANeraca 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 PADATANLapisan batas dan Gaya seret (drag force), Friksi fluida dalam media berpori, Pers. Blake-Kozeny, Ergun Darcy, Fluidisasi, Filtrasi,

Fluid MechanicsEngineering applicationsOil /process fluid in pipelinesPumps, filters, rivers, etc Groundwater movementBlood in capillaries

DefinitionThe study of liquids and gasses at rest (statics) and in motion (dynamics)

Industrial application

DIAGRAM SISTIM ALIRAN FLUIDAStorageValvesPipe systemPumpFlow MeasurementProcess/Resistance

SUBDIVISI MEKANIKA FLUIDA HYDRAULICS : the flow of water in rivers, pipes, canals, pump, turbinesHYDROLOGY : the flow of water in the groundRESERVOIR MECHANICS : the flow of oil, gas and water in petroleum reservoir

AERODYNAMICS : the flow of air around aeroplanes, rocket projectilsMETEOROLOGY : 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 dryingVISCOUS 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: Close packed, strong cohesive forces, retains volume, has free surfaceLiquids and gasses Whats the difference?Gasses: Widely spaced, weak cohesive forces, free to expandAlmost incompressibleRelatively easy to compress

Common FluidsLiquids:water, oil, mercury, gasoline, alcoholGasses: air, helium, hydrogen, steamBorderline: jelly, asphalt, lead, toothpaste, paint, pitch

DensityThe density of a fluid is defined as its mass per unit volume. It is denoted by the Greek symbol, . =Vm3kgm-3If 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-3air =1.2kgm-3kgm

DensityMass per unit volume (e.g., @ 20 oC, 1 atm)Waterrwater= 1000 kg/m3Mercury rHg= 13,500 kg/m3Air rair= 1.22 kg/m3

Densities of gasses increase with pressureDensities of liquids are nearly constant (incompressible) for constant temperatureSpecific volume = 1/density

Specific WeightWeight 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 GravityRatio of fluid density to density at STP(e.g., @ 20 oC, 1 atm)

WaterSGwater = 1MercurySGHg = 13.6AirSGair = 1

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

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

Shear Stresschange in velocity with repect to distanceTangential force per unit areaRate of deformationrate of shear

bvvbFArea AFriction forcezAbsolute ViscosityShear stess(dyne/cm2 )Shear strain rate(s-1)Kinematic ViscosityDyne-s/cm2=PoiseN-s/m2=103 cPDynamic and Kinematic Viscosity

Fluid classification by response to shear stress

Fluid ViscosityExamples of highly viscous fluids______________________Fundamental mechanismsGases - transfer of molecular momentumViscosity __________ as temperature increases.Viscosity __________ as pressure increases.Liquids - cohesion and momentum transferViscosity decreases as temperature increases.Relatively independent of pressure (incompressible)molasses, tar, 20w-50 oilincreases_______increases

Role of ViscosityStaticsFluids at rest have no relative motion between layers of fluid and thus du/dy = 0Therefore the shear stress is _____ and is independent of the fluid viscosityFlowsFluid viscosity is very important when the fluid is moving zero

Perfect Gas LawPV = nRTR is the universal gas constantT is in KelvinNote deviation from the text!Use absolute pressure for P and absolute temperature for T

Bulk Modulus of ElasticityRelates the change in volume to a change in pressurechanges in density at high pressurepressure waves_______________ __________soundwater hammerWaterspeed of sound

Vapor PressureliquidWhat is vapor pressure of water at 100C?101 kPaConnection forward to cavitation!

Surface TensionPressure increase in a spherical dropletDppR2 = 2pRsDppR22pRsSurface molecules

Example: Surface TensionEstimate the difference in pressure (in Pa) between the inside and outside of a bubble of air in 20C water. The air bubble is 0.3 mm in diameter.R = 0.15 x 10-3 ms = 0.073 N/mWhat is the difference between pressure in a water droplet and in an air bubble?Statics!

Bagaimana mengukur viskositas ?

GLASS CAPILLARY VISCOMETERSP = Pressure difference across capiller R = Radius of capillerL = Length od capiller V = Volume fluida = ViscosityASTM D445

A CALIBRATED HOLE IN THE BOTTOM. 21xzV(Poiseuille Eq.)cP = fluid density X cSt

ROTARY VISCOMETER

Example: Measure the viscosity of waterThe 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 SchemeRestate the goalIdentify the given parameters and represent the parameters using symbolsOutline your solution including the equations describing the physical constraints and any simplifying assumptionsSolve for the unknown symbolicallySubstitute numerical values with units and do the arithmeticCheck your units!Check the reasonableness of your answerolution

Outline the solutionRestate the goalIdentify the given parameters and represent the parameters using symbolsOutline your solution including the equations describing the physical constraints and any simplifying assumptions

Viscosity Measurement: Solutionr = 5 cmt = 2 mmh = 10 cmP = 50 x 10-6 W10 rpmwr2prhFwr

APPROXIMATE PHYSICAL PROPERTIES OF COMMON LIQUIDS AT ATMOSPHERIC PRESSURE

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

Dimensions and UnitsThe dimensions have to be the same for each term in an equationDimensions of mechanics arelengthtimemassforcetemperatureLTMMLT-2

Dimensions and UnitsQuantitySymbolDimensionsDensityr ML-3Specific Weightg ML-2T-2Dynamic viscositym ML-1T-1Kinematic viscosity L2T-1Surface tension MT-2Bulk mod of elasticityE ML-1T-2These are _______ properties!fluidHow many independent properties? _____4

UnitsUnit: Particular dimensionkg, m, s, oK(Systeme International)slug, ft, s, oR(British Gravitational)lbm, ft, s, oR(something else)

Whats a SLUG?!

Unit of mass in the BG system (~ 14.59 kg, ~32.17 lbm)1 lbf will accelerate a slug 1ft/s232.17 lb/14.59 kg = 2.2 lbm/kg

Secondary UnitsForceN = kg-m/s2(Newton)lbf = slug-ft/s2(pound force)= 32.2 lbm-ft/s2Work (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)

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

Conversion of Units

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 2PERSAMAAN DASAR MEKANIKA FLUIDATujuan Pengajaran

Internal and external flowsAir, sea-water oil & gas fresh water, mud, hydraulic oilDrilling, pumping, extraction, power generation, effluent disposal, fire systems, sanitationHome : water, heating, appliances fridge, washing / dish-washer machinesCar: engine cooling + car heater, fuel, oil, hydraulics, external aerodynamicsAeroplane: fuel, hydraulics, air-conditioning, cabin pressurization, oxygen, sanitation, external aerodynamics, gas turbines