PHYSICAL OF FLUID

OutlinePhysical of fluidDefinitionProperties of physical fluidClassification of fluidClassification of fluid flow

DEFINITIONS A simple way to classify matter is as either a solid or a fluid. Solids are objects with a definite size and shape.Fluids include liquids and gases - distinct from solids because of their abilities to flow and change shape.

MATTERFluidE.g.: liquids & gases Solid

What is fluid mechanics?It is a branch of physics that study the behavior of materials in fluid form (e.g.: water, oil).The study in fluid mechanics are classified into 2 different categories, that is :-Fluid statics :- study the behavior of fluid that is static, (not in motion) for example :- water in the tank reservoir, water inside the lake, air inside the balloon, etc. Fluid dynamics :- study the behavior of fluid that is in motion, for example :- water flowing in the river, wind blowing, water flowing inside the piping line, etc.

PROPERTIES OF PHYSICAL FLUIDSNot resisting deformation, or resisting it only lightly (viscosity)The ability to flow (also described as the ability to take on the shape of the container).

NO-SLIP CONDITIONWHAT IS NO-SLIP CONDITION?

Fluid in direct contact with a solid stick to the surface, and there is no slipThe fluid properties responsible for this - viscosity No slip condition responsible for development of velocity profileBoundary Layer The flow region adjacent to the wall in which the viscous effect are significantNo-slip condition also create surface drag/skin friction drag

VISCOSITYThe situation when a fluid moves relative to a solid or when two fluids move relative to each other.We move with relative ease in air but not so in water. Moving in oil would be more difficult.Slower downward of a glass ball dropped in tube filled with oil.The property that represent the internal resistance of a fluid to motion or the fluidity = Viscosity

VISCOSITYViscosity experiments

VISCOSITYTo obtain relation of viscosity, consider a fluid layer between two very large parallel plateConstant parallel force applied on the top plate while lower plate held fixThe fluid in contact with upper plates sticks to the plate surface and move with the same velocity.The Shear stress acting on the fluid layer is =F/A

VISCOSITYThus the velocity profile and velocity gradient isThe fluid contact with the lower plates assume the velocity of plate which is zero, The fluid velocity between the plates varies linearly

VISCOSITYThe side rotate trough angle B while the upper plate move da = V dtRe arranging

VISCOSITYKinematic viscosity = Coefficient of viscosity @ dynamic viscosityShear Stress(N/M2) Unit kg/m.s or equivalent N.s/m2 (poise) = 0.1 Pa.s Unit m2/s or stoke (1 stoke = 1 cm2/s = 0.0001 m2/s)Shear Force

VISCOSITYViscosity of a fluid depends both on temperature & pressure (weak)

For liquid both dynamic & kinematic viscosities independent of pressure (except extremely high pressure)

For gases same case for dynamic viscosity (at low to moderate pressure) but not for kinematic viscosity since density of gases proportional to pressure

The viscosity of fluid is a measure of resistance to deformation

Viscosity is due to the internal frictional force that develop between different layer of fluids as they are force to move relative to each other

VISCOSITYViscosity is caused by cohesive forces between molecules in liquids and the molecular collision in gases and its varies greatly with temperature

Viscosity of liquids decreases with temperature, whereas the viscosity of gases increases with temperature. WHY???Because in a liquid the liquid possess more energy at higher temperature and they can oppose the large cohesive intermolecular forces more strongly On the other hand, the intermolecular in gases is negligible, and the gas molecules at higher temperature moves randomly at higher velocities. This result in more molecular collisions per unit volume per unit time and therefore greater resistance.

Example 9-4Determine the viscosity of a fluid The viscosity of a fluid is to be measured by a viscometer constructed of twp 40-cm-long concentric cylinders. The outer diameter of the inner cylinder is 12 cm, and the gap between two cylinders is 0.15cm. The inner cylinder is rotated at 300rpm, and the torque is measured to be 1.8N.m. Determine the viscosity of the fluid

Solution The torque and the rpm of a double cylinder viscometer are given. The viscosity of the fluid is to be determined.

Assumption

The inner cylinder is completely submerged in the fluidThe viscous effects on the two end of the cylinder are negligible

Example 9-4 (Continues)Analysis The velocity profile is linear only when curvature effects are negligible, and the profile can be approximated as being linear in this case since l/R = 0.025

CLASSIFICATION OF FLUIDNewtonian FluidNon-Newtonian Fluid Pseudoplastic (Shear Thinning)Dilatant (Shear Thickening)Bingham Plastic

CLASSIFICATION OF FLUID

CLASSIFICATION OF FLUIDNewtonian Fluid The rate of deformation is proportional to the shear stressE.g. water, air, gasoline, oil

Non- Newtonian FluidPseudoplastic (Shear Thinning)The apparent viscosity is decrease with the rate of deformation (The fluid becoming less viscous as it is sheared harder)E.g. Some paints, Polymer solutions, fluids with suspended solutionsDilatant (Shear Thickening)The apparent viscosity is increase with the rate of deformationE.g. Starch, SandBingham PlasticMaterial can resist a finite shear stress and thus behave like solid but deform continuously when the shear stress exceed the yield stress.E.g. toothpaste

CLASSIFICATION OF FLUID FLOWViscous VS Inviscid regionInternal VS External FlowCompressible VS IncompressibleLaminar VS TurbulentNatural VS ForcedSteady VS Unsteady

CLASSIFICATION OF FLUID FLOWViscous VS Inviscid regionViscous Flow Flow which frictional effects are significantInviscid region Viscous flow are negligibly small compared to inertia/ pressure forces

CLASSIFICATION OF FLUID FLOWInternal VS External FlowInternal Fluid flow in confining spaceFlow in pipe, duct fluid is completely bounded by a solid surfacesExternal Fluid flow over a surfaceFlow an unbounded over a surface plate, wire

CLASSIFICATION OF FLUID FLOWCompressible VS IncompressibleDepending on the level of variation of density during flowIncompressible If density remain nearly constant throughoutThe volume fluid remain unchanged

CLASSIFICATION OF FLUID FLOWCompressible VS IncompressibleFlow speed is often expressed in dimensionless No. - Mach Number

Speed of sound = 346 m/sSonic Ma = 1Subsonic Ma < 1Supersonic > 1, Hypersonic >>1

CLASSIFICATION OF FLUID FLOWCompressible VS IncompressibleLiquid flows are incompressible to a high level of accuracyApproximation of incompressible of gases is depend on the Mach No. Gas flow can be approximated incompressible if the density change

CLASSIFICATION OF FLUID FLOWLaminar VS TurbulentLaminar highly ordered fluid motion characteristic by smooth layers of fluidThe flow of high viscosity fluids such as oil at low velocities typically laminar

Turbulent - highly disordered fluid motion typically at high velocities & is characterized by velocity fluctuations.The flow of low viscosity fluids such as air at high velocities typically turbulent

Transitional- The flow of low viscosity alternates between laminar and turbulent.

CLASSIFICATION OF FLUID FLOWLaminar VS TurbulentFigure of (a) Laminar flow (b) Turbulent flow(b)(a)

CLASSIFICATION OF FLUID FLOWNatural VS ForcedForced flow is force to flow by external means such as pump or fanNatural Fluid flow is due to natural means such as buoyancy effect.

CLASSIFICATION OF FLUID FLOWSteady VS UnsteadySteady No change at a point with timeUnsteady Opposite of steadyUniform- No change with location over a specific regionTransient- typically used for developing flowSteady flow condition devices that are intended for continuous operation

CLASSIFICATION OF FLUID FLOWDimensional FlowsA flow is best characterized by its velocity distributionA typical fluid flow in 3-D V(x,y,z) (rectangular)/ or V(r,, z) (cylindrical) coordinates.

Assignment 1Define internal, external and open-channel flowsDefine incompressible flow and incompressible fluidWhat is the non-slip condition? What causes it?What is forced flow? How does it differ from natural flow?What is viscosity? What is the cause of it in liquids and in gases? Do Liquids or gases have higher dynamic viscosities?What is Newtonian fluid? Is water a Newtonian fluid?How does the dynamic viscosity of (a) Liquid (b) gases varies with temperature?

Assignment 22.The viscosity of a fluid is to be measured by a viscometer constructed of two-75-cm long concentric cylinders. The outer diameter of the inner cylinder is 15cm, and the gap between the two cylinders is 0.12cm. The inner cylinder is rotated at 200rpm, and the torque is measured to be 0.8N.m. Determine the viscosity of the fluid