S3 Chapter 1 Introduction of Fluid

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Semester 3
CB 306 HYDRAULIC
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Chapter 1 - Introduction of Fluid

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S3 Chapter 1 Introduction of Fluid

  1. 1. Chapter 1 -Chapter 1 - A PowerPoint Presentation byA PowerPoint Presentation by NOOR ASSIKIN BINTI ABD WAHABNOOR ASSIKIN BINTI ABD WAHAB © 2011
  2. 2. IntroductionIntroduction  This chapter will begin with several concepts,This chapter will begin with several concepts, definition, terminologies and approaches whichdefinition, terminologies and approaches which should be understood by the students beforeshould be understood by the students before continuing reading the rest of this module.continuing reading the rest of this module.  Then, it introduces the student with typicalThen, it introduces the student with typical properties of fluid and their dimensions which areproperties of fluid and their dimensions which are then being used extensively in the next chaptersthen being used extensively in the next chapters and units like pressure, velocity, density andand units like pressure, velocity, density and viscosity.viscosity.  Some of these can be used to classify type andSome of these can be used to classify type and characteristic of fluid, such as whether a fluid ischaracteristic of fluid, such as whether a fluid is incompressible or not or whether the fluid isincompressible or not or whether the fluid is Newtonian or non-NewtonianNewtonian or non-Newtonian..
  3. 3. Fluid ConceptFluid Concept • Fluid mechanics is a division inFluid mechanics is a division in appliedapplied mechanics related to the behaviour of liquidmechanics related to the behaviour of liquid or gas which is either in rest or in motion.or gas which is either in rest or in motion. • The study related to a fluid in rest orThe study related to a fluid in rest or stationary is referred tostationary is referred to fluid staticfluid static,, otherwise it is referred to asotherwise it is referred to as fluid dynamicfluid dynamic.. • Fluid can be defined as a substance whichFluid can be defined as a substance which can deform continuously when beingcan deform continuously when being subjected to shear stress at any magnitudesubjected to shear stress at any magnitude.. In other words, it can flow continuously asIn other words, it can flow continuously as a result of shearing action. This includesa result of shearing action. This includes any liquid or gas.any liquid or gas.
  4. 4. DEFINE FLUIDSDEFINE FLUIDS (a) Solid (b) Liquid (c) Gas k kk k Free surface
  5. 5.  For solid, imagine that the molecules can beFor solid, imagine that the molecules can be fictitiously linked to each other with springs.fictitiously linked to each other with springs. • In fluid, the molecules can move freely but areIn fluid, the molecules can move freely but are constrained through a traction force calledconstrained through a traction force called cohesioncohesion.. This force is interchangeable from oneThis force is interchangeable from one molecule to anothermolecule to another.. • For gases, it is very weak which enables the gas toFor gases, it is very weak which enables the gas to disintegrate and move away from its container.disintegrate and move away from its container.  For liquids, it is stronger which is sufficient enoughFor liquids, it is stronger which is sufficient enough to hold the molecule together and can withstandto hold the molecule together and can withstand high compression, which is suitable for applicationhigh compression, which is suitable for application as hydraulic fluid such as oil. On the surface, theas hydraulic fluid such as oil. On the surface, the cohesion forms a resultant force directed into thecohesion forms a resultant force directed into the liquid region and the combination of cohesionliquid region and the combination of cohesion forces between adjacent molecules from aforces between adjacent molecules from a tensioned membrane known astensioned membrane known as free surfacefree surface..
  6. 6. Definition of a FluidDefinition of a Fluid A fluid is a substance that flows under the action of shearing forces. 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 in which it is contained. A liquid is a fluid which is hard to compress. A given mass of liquid will occupy a fixed volume, irrespective of the size of the container. A free surface is formed as a boundary between a liquid and a gas above it.
  7. 7. Fluid PropertiesFluid Properties • Define “characteristics” of a specific fluidDefine “characteristics” of a specific fluid •Properties expressed by basic “dimensions”Properties expressed by basic “dimensions” – length, mass (or force), time, temperaturelength, mass (or force), time, temperature • Dimensions quantified by basic “units”Dimensions quantified by basic “units” We will consider systems of units, important fluidWe will consider systems of units, important fluid properties (not all), and the dimensions associated withproperties (not all), and the dimensions associated with those properties.those properties.
  8. 8. System International (SI)System International (SI) • Length = meters (m)Length = meters (m) • Mass = kilograms (kg)Mass = kilograms (kg) • Time = second (s)Time = second (s) • Force = Newton (N)Force = Newton (N) – Force required to accelerate 1 kg @ 1 m/sForce required to accelerate 1 kg @ 1 m/s22 – Acceleration due to gravity (g) = 9.81 m/sAcceleration due to gravity (g) = 9.81 m/s22 – Weight of 1 kg at earth’s surface = W = mg = 1 kg (9.81Weight of 1 kg at earth’s surface = W = mg = 1 kg (9.81 m/sm/s22 ) = 9.81 kg-m/s) = 9.81 kg-m/s22 = 9.81 N= 9.81 N • Temperature = Kelvin (Temperature = Kelvin (oo K)K) – 273.15273.15 oo K = freezing point of waterK = freezing point of water – oo K = 273.15 +K = 273.15 + oo CC
  9. 9. System International (SI)System International (SI) • Work and energy = Joule (J)Work and energy = Joule (J) J = N*m = kg-m/sJ = N*m = kg-m/s22 * m = kg-m* m = kg-m22 /s/s22 • Power = watt (W) = J/sPower = watt (W) = J/s • SI prefixes:SI prefixes: G = giga = 10G = giga = 1099 c = centi = 10c = centi = 10-2-2 M = mega = 10M = mega = 1066 m = milli = 10m = milli = 10-3-3 k = kilo = 10k = kilo = 1033 µµ = micro = 10= micro = 10-6-6
  10. 10. DensityDensity • Mass per unit volume (e.g., @ 20Mass per unit volume (e.g., @ 20 oo C, 1 atm)C, 1 atm) – WaterWater ρρwaterwater = 1,000 kg/m= 1,000 kg/m33 (62.4 lbm/ft(62.4 lbm/ft33 )) – MercuryMercury ρρHgHg = 13,500 kg/m= 13,500 kg/m33 – AirAir ρρairair = 1.205 kg/m= 1.205 kg/m33 • Densities of gases = strong f (T,p) =compressibleDensities of gases = strong f (T,p) =compressible • Densities of liquids are nearly constantDensities of liquids are nearly constant (incompressible) for constant temperature(incompressible) for constant temperature • Specific volume = 1/density = volume/massSpecific volume = 1/density = volume/mass
  11. 11. DensityDensity The density of a fluid is defined as its mass per unit volume. It is denoted by the Greek symbol, ρ. ρ = V m3 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) ρ water= 998 kgm-3 ρair =1.2kgm-3 kg m
  12. 12. Mass DensityMass Density 2 kg, 4000 cm3 Wood 177 cm3 45.2 kg ; mass m Density volume V ρ= = Lead: 11,300 kg/mLead: 11,300 kg/m33 Wood: 500 kg/mWood: 500 kg/m33 4000 cm3 Lead Same volume 2 kg Lead Same mass
  13. 13. Example 1:Example 1: The density of steel isThe density of steel is 7800 kg/m7800 kg/m33 .. What is the volume of aWhat is the volume of a 4-kg4-kg block of steel?block of steel? 4 kg 3 4 kg ; 7800 kg/m m m V V ρ ρ = = = V = 5.13 x 10-4 m3V = 5.13 x 10-4 m3 What is the mass if the volume is 0.046 m3 ? 3 3 (7800 kg/m )(0.046 m );m Vρ= = m = 359 kgm = 359 kg
  14. 14. Specific WeightSpecific Weight ]/[]/[ 33 ftlbformNgργ = • Weight per unit volume (e.g., @ 20Weight per unit volume (e.g., @ 20 oo C, 1 atm)C, 1 atm) γγwaterwater = (998 kg/m= (998 kg/m33 )(9.807 m)(9.807 m22 /s)/s) = 9,790 N/m= 9,790 N/m33 [= 62.4 lbf/ft[= 62.4 lbf/ft33 ]] γγairair = (1.205 kg/m= (1.205 kg/m33 )(9.807 m)(9.807 m22 /s)/s) = 11.8 N/m= 11.8 N/m33 [= 0.0752 lbf/ft[= 0.0752 lbf/ft33 ]]
  15. 15. Specific GravitySpecific Gravity Ratio of fluid density to density of water @ 4o C 3 /1000 mkg SG liquid water liquid liquid ρ ρ ρ == Water SGwater = 1 Mercury SGHg = 13.55 Note: SG is dimensionless and independent of system of units
  16. 16. Specific GravitySpecific Gravity The specific gravity (or relative density) of a material is the ratio of its density to the density of water (1000 kg/m3 ). Steel (7800 kg/m3 ) ρr = 7.80 Brass (8700 kg/m3 ) ρr = 8.70 Wood (500 kg/m3 ) ρr = 0.500 Steel (7800 kg/m3 ) ρr = 7.80 Brass (8700 kg/m3 ) ρr = 8.70 Wood (500 kg/m3 ) ρr = 0.500 Examples:Examples: 3 1000 kg/m x r ρ ρ =
  17. 17. viscosity in fluid flowsviscosity in fluid flows
  18. 18. ViscosityViscosity • Viscosity,Viscosity, µµ,, is a measure of resistance to fluid flow as ais a measure of resistance to fluid flow as a result of intermolecular cohesion. In other words, viscosityresult of intermolecular cohesion. In other words, viscosity can be seen as internal friction to fluid motion which cancan be seen as internal friction to fluid motion which can then lead to energy loss.then lead to energy loss. • Different fluids deform at different rates under the sameDifferent fluids deform at different rates under the same shear stress. The ease with which a fluid pours is anshear stress. The ease with which a fluid pours is an indication of its viscosity. Fluid with a high viscosity such asindication of its viscosity. Fluid with a high viscosity such as syrup deforms more slowly than fluid with a low viscositysyrup deforms more slowly than fluid with a low viscosity such as water. The viscosity is also known as dynamicsuch as water. The viscosity is also known as dynamic viscosity.viscosity.  Units:Units: N.s/m2 or kg/m/sN.s/m2 or kg/m/s  Typical values:Typical values: Water = 1.14x10-3 kg/m/s; Air = 1.78x10-5 kg/m/sWater = 1.14x10-3 kg/m/s; Air = 1.78x10-5 kg/m/s
  19. 19. ViscosityViscosity • Proportionality constant = dynamic (absolute)Proportionality constant = dynamic (absolute) viscosityviscosity • Newton’s Law of ViscosityNewton’s Law of Viscosity • ViscosityViscosity • UnitsUnits • Water (@ 20Water (@ 20oo C):C): µµ = 1= 1xx1010-3-3 N-s/mN-s/m22 • Air (@ 20Air (@ 20oo C):C): µµ = 1.8= 1.8xx1010-5-5 N-s/mN-s/m22 • Kinematic viscosityKinematic viscosity V V+d v dy dV µτ = dydV / τ µ = 2 2 // / m sN msm mN ⋅ = ρ µ ν = Kinematic viscosity: m2 /s 1 poise = 0.1 N-s/m2 1 centipoises = 10-2 poise = 10-3 N-s/m2
  20. 20. Newtonian and Non-NewtonianNewtonian and Non-Newtonian FluidFluid Example: Air Water Oil Gasoline Alcohol Kerosene Benzene Glycerine Newton’s’ law of viscosity is given by; dy du µ=τ (1.1) τ = shear stress µ = viscosity of fluid du/dy = shear rate, rate of strain or velocity gradient • The viscosity µ is a function only of the condition of the fluid, particularly its temperature. • The magnitude of the velocity gradient (du/dy) has no effect on the magnitude of µ.

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