Friday, 16 March 2018

FLUID MECHANICS & MACHINERY ki jankary gate ke liya

PROPERTIES OF FLUID

         Matter exists in three phase solid, liquid and gas. The phase of matter depends upon the inter-molecular attraction between two molecules. Solid is inter-molecular forces are very strong. Molecules very close to one another. Liquid is inter-molecular forces are weak. More space between the molecules. Gases is inter-molecular forces are very weak. More space between the molecules. Fluid is defined as substance which has capacity to flow. That deform continuously under the action of shear stress, no matter if it is small. NO definite shape of its own, but conforms to the shape of container. Fluid mechanic is branch of engineering science which is deals with the behaviors of the fluids at rest as well as in motion HYDRAULICS is topic in applied science and engineering dealing with the mechanical properties of liquids.


   
TYPES OF FLUID Ideal fluid, Real fluid, Newtonian fluid, Non-Newtonian fluid, Ideal plastic fluid. Ideal fluid is in compressible and having no viscosity, is known as ideal fluid. It is imaginary fluid. Fluid posses viscosity is known as real fluid. Shear stress is higher than yield value and shear stress is in proportion to stress rate.

Physical properties of fluid. Mass density or density or specific mass, weight density or specific weight, specific volume, specific gravity or relative density viscosity, surface tension and capillarity. Mass density or density or specific mass is a ratio of Mass per unit volume Mass density of water is a 1000 Kg/ cubic M. Where, M is a Mass, V is a volume. Weight density or specific weight is a Weight per unit volume at standard temperature and pressure, S.I. unit N/ cubic M. Specific weight of water is a 9810 N/ cubic M {9.81 KN/ Cubic M}, Where, W is a specific weight {N/cubic M}, e is a density {Kg/cubic M}, g is a Acceleration of gravity {m/ sq. sec}.specific volume is volume per unit weight. Specific gravity or relative density is density of fluid per unit density of standard fluid. Notes Water density is 998 kg/ cubic M-1atm  & 20 degree Celsius,1000 Kg/ cubic M-1atm & 4 degree Celsius, air density is a 1.2 Kg/cubic M -1atm & 20 degree Celsius, 0.84 Kg/ cubic M-1 atm & 20 degree Celsius            

Viscosity is a Resistant to flow shearing one layer of fluid over the adjacent layer. Reason of viscosity is molecular cohesive force. Reason of viscosity is, molecular momentum exchange or molecular momentum transfer. Viscosity of gas is increase with increase is temperature. Relative velocity of first layer of fluid particle with respect to stationary plate is zero {Vr=0} Velocity gradient in transverse direction. Rate of shear strain, Rate of angular deformation, Rate of shear deformation, Newton’s law of viscosity is shear stress is directly proportional to velocity gradient. Dynamic viscosity is a ratio of shear tress required to produce unit rate of shear strain. Kinematics viscosity is a ratio of dynamic viscosity to mass density.


Linearization of Newton law of viscosity We can assume linear velocity profile when h is very small. Effect of temperature on viscosity is a liquid:-With increase in temperature both dynamic and Kinematic viscosity of liquid decrease but rate of decrease is more for dynamic viscosity. Gases :-Dynamic viscosity is a Temperature increase Vrms increase,  Randomness increase,  molecular momentum exchange increase density increase Kinematic viscosity is with increase in temperature both dynamic and Kinematics viscosity of gases increase but rate of increase will be more for Kinematic viscosity.

Effect of pressure on viscosity:-In liquid Dynamic viscosity Pressure increase inter molecular spacing (no change )  Molecular cohesive force ( no change ) Pressure increase, Dynamic viscosity( no change) Kinematic viscosity:- Pressure increase  dynamic viscosity(no change) Pressure increase density ( no change) Pressure increase Kinematic viscosity (no change) Note :- Variation of pressure does not effect dynamic and Kinematic viscosity of liquid. Gases is Dynamic viscosity is a Pressure increase Vrms( No change )  dynamic viscosity( No change ), Kinematic viscosity is With increase in pressure Kinematic viscosity of gases decrease.

surface tension and capillarity:-Fluid which is enables to resist tensile stress Surface tension is a 0.073 N/m air- water interface surface tension  is a 0.480 N/m air- mercury interface Net force on molecule A is nonzero( Net inward pull) (Net cohesive force on molecule B is zero ) Analogy:-All molecules on the surface experience a net inward pull because of which there is tension in the liquid surface known surface tension. (Surface tension is depend on two liquids) Because of surface tension liquid try to minimize it's surface area this is reason why drops are spherical in shape ( for given volume sphere has minimum surface area) Due to surface tension liquid surface behaves like stretched elastic membrane because of which small needle can float on liquid surface. Insects can walk on liquid surface. One component of surface tension balances the weight of insect on liquid. Note:- value of surface tension depends on the combination of fluid at the interface the value of surface is constant.  It is a hypothesis. '6' represent amount of stretching work needed to increase surface area by unit amount. Let, E1 is a surface energy before stretching, E2 is a surface energy after stretching, A1 is a surface area before stretching, and A2 is a surface area after stretching

Effect of temperature on surface tension is With increase in temperature surface tension decrease and it's become zero at the critical point. Effect of pressure on surface tension is a Variation of pressure does not affect surface tension. Cohesion force is a Inter molecular forces. Attraction bet. Molecule of same liquid Adhesion force is the attraction forces between unlike molecular. Attraction between liquid and solid boundary

Capillarity is a rise or fall of liquid in glass tube. Adhesion > cohesion = liquid rise or Cohesion > adhesion = liquid fall. Capillarity is direction consequence of surface tension, where, h is a  capillary rise or drop, 6 is a surface tension, A is a  angle of contact, y is a specific weight of liquid is a  diameter of tube.

Compressibility is a volumetric strain to change in pressure. A diabetic compressibility it is Compression process is reversible adiabatic. Bulk modulus is a For perfectly in compressible fluid B is a 0 and Ba is a 2.5 x 10 rest to power -6 (It is easy compressible) Bb is a 3.7 x 10 rest to power -9 Ba >Bb A is more compressible than BOr B is more in compressible than A Higher the value of compressibility B more compressible fluid will be For perfectly in compressible fluid K is a oo. Ka is a 6.1 x 10 rest to power 9 pa, Kb is a 8.2 x 10 rest to power 8 pa. Ka> kb, A is more incompressible than B and B is max compressible than A.

Vapor pressure Initially, Rate of evaporation greater than rate of condensation (No.  Of molecules in given space will increase with time) with time rate of evaporation will decrease and rate of condensation will increase. Rate of evaporation = Rate of condensation. (No.  Of molecules in given space will not change with time) phase equilibrium. The pressure exert by Vapour molecules on the liquid surface when both area in phase equilibrium is known as Vapour pressure. Temperature increase Vapour pressure increase.

Rhelogy (Classification of fluid) is a 1) Dilatants Fluids n>1 and B is a 0 Ex. Butter, Quick sand. For Bingham plastic fluids: n=1 and B not = 0 Ex. sewage sludge, drilling mud,  tooth paste and gel. These fluids always have certain minimum shear before they yield.  For pseudo plastic fluid: n<1 and B=0 Ex. Paper pulp, rubber solution, lipsticks, paints, blood, polymeric solution etc. For Thyrotrophic Fluids: n<1 and B not = 0 Viscosity increase with time Ex. Printers, ink, and enamels. For Rheopectic fluids: n>1 and B not = 0 Viscosity decreases with time. Ex. Gypsum solution in water and betonies solution.


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