FLUID PROPERTIES

Define fluid.A Fluid is a substance that deforms continuously when subjected to a shear stress no matter how small that shear stress may be.

Differentiate solid and fluid.FluidThe fluid deforms continuously when subjected to a shear stress.When the shear stress disappears the fluid never regain in to original shape. .SolidThe Solid deforms a definite amount when subjected to a shear stressWhen the shear stress disappears solids gain fully or partly their original shape. Define density.Density is defined as the mass of a substance per unit volume.If a fluid element enclosing a point P has a volume dV and dm , then the density is given by r = lim dV - 0 (dm / dV) = (dm / dV) The unit of density is kg/m3 .

Define specific volume,.Specific volume is defined as the reciprocal of density that is volume capacity per unit mass of fluidVs = ( 1 / r) = ( dV / dm ) The unit of sp. Volume is m3/kg

Define specific weight.Specific weight is the weight of the fluid per unit volume.g = ( weight / volume) = ( m g / v) = r g The unit of specific weight is N/m3.

Define specific gravity (SG).Specific gravity is the ratio of mass density (or) weight density of the fluid to the mass density (or) weight density of the standard fluid. For liquids, water at 4oc is considered as standard fluid.A liquid has a specific gravity of 1.527what are the values of specific weight and specific volume ?Specific gravity of a liquid (SG) = Sp. Weight (or) weight density of liquid / Sp. Weight (or) weight density of std liquid The standard liquid is water and its specific weight = r g = 1000 x 9.81 = 9810 N/m3The specific weight of the liquid = 9810 x 1.527 = 14979.8 N/m3.Density of the liquid ( r ) = 14979.8 / 9.81 = 1527 kg/ m3.Specific volume of liquid = 1 /r = 1 / 1527 = 6.54 x 10 4 m3/kg.

Define viscosity.The viscosity can be defined as the property of fluid which resist relative motion of its adjacent layers. It is the measure of internal fluid friction due to which there is resistance to flow, The unit of viscosity is Ns/m2.

State Newtons law of viscosity. (AU-MQP)The shear stress on a fluid element layer is directly proportional to the rate of strain (or) velocity gradient, the constant of proportionality being called the coefficient of viscosity.t a (du / dy) shear stress ( t ) = m (du / dy)

what is real fluid ? Give examples. (AU-M03).The fluids in reality have viscosity m > 0 hence they are termed as real fluids and their motion is known as viscous flow. (ex) Air , water, kerosene, blood, milk

Why are some fluids are classified as Newtonian fluid ? Give examples of Newtonian fluids. (AU-N02).The fluids, which obey Newtons law of viscosity are known as Newtonian fluids. For these fluids, there is a linear relationship between shear stress and velocity gradient. (ex) Air, water, kerosene.

What is a Tthyxotropic fluid ? (AU- N 03)If the viscosity increases with time the fluid is said to be a Thyxotropic fluid. (ex) Lipstick, paints enamels, crude oil.

What is a Rheopectic fluid ?If the viscosity decreases with time the fluid is said to be Rheopectic fluid. (ex) gypsum suspension, bentonite clay solution.

What is effect of temperature on viscosity of water and air ?*The viscosity of water decreases with increase in temperature.*The viscosity of air increases with increase in temperature.

Define kinematic viscosity and gives its uint.Kinematic viscosity is defined as the ratio of dynamic viscosity to density.n = m / r The unit of kinematic viscosity is m2/s

What is compressibility of fluid ?Compressibility of substance is the measure of its change in volume under the action of external forces, namely, the normal compressive forces. The measure of compressibility of the fluid is the bulk modulus of elasticity (K)K = lim DV - 0 (- DP) / (DV/V) The unit of compressibility is N/m2

Assuming the bulk modulus of elasticity of water is 2.07 x 106 kN/m2 at standard atmospheric condition. Determine the increase of pressure necessary to produce one percent reduction in volume at same temperature. (AU-N02)Bulk modulus of elasticity K = 2.07 x 106 kN/m2 - (dV/V) = 1% = 0.01K = - dP / (dV/V) \ Increase in pressure dP = -(dV/V) x K= 0.01 x 2.07 x 106 = 20700 kN/m2.

What is meant by vapor pressure of a liquid ?Liquids evaporate because of molecule s escaping from the liquid surface. These vapor molecules exert a partial pressure on the surface of the liquid known as vapour pressure.

What is cavitation ?In flowing fluid, if the pressure is equal to or less than the saturated vapor pressure, the liquid boil locally and produce vapor bubbles. These bubbles collapse in the high pressure region causing a partial vaccum. This phenomenon in known as cavitation.

Define surface tension and mention its unit.A free surface of the liquid is always under stretched condition implying the existence of tensile force on the surface. The magnitude of this force per unit length of an imaginary line drawn along the liquid surface is known as surface tension. The unit of surface tension is N/m.

Define capillarity. (AU-M04)Capillary implies the raise or depression of liquid in a capillary tube where it is held vertically or inclined in the liquid.

Define the pressure and mention its unit.If the fluid is stationary, then the force (dF) exerted by the fluid on the area is normal to the surface (dA). This normal force per unit area is called pressure..P = ( dF / dA) The unit of pressure is N/m2.

What should be the depth of oil of specific gravity 0.8, if it has exerted a pressure of 480N/m2 ?Specific gravity (SG) = 0.8 \ density = 800 kg/m3The pressure = r g z depth z = P/(r g) = 480 x 103 / (800 x 9.81) = 61.16 mExpress 3m of water head in cm of mercury.rm gm Hm = rw gw Hw 13600 x Hm = 1000 x 3 Hm = 0.22 m of Hg

Differentiate between absolute and gauge pressure.Absolute pressure is measured as a pressure above absolute zeroGauge pressure is measured as a pressure below atmospheric pressureGauge pressure = Absolute pressure - Atmospheric pressure

What do you mean by vacuum pressure ?If the pressure is less than the local atmospheric pressure it is called as vacuum pressure.Vacuum pressure = Atmospheric pressure - Absolute pressure

What is a manometer ? Name the common fluids used in it.A manometer is a transparent tube containing a liquid of known density used for the purpose of measuring the fluid pressure. The common fluids used are mercury, alcohol.

Differentiate between simple manometer and differential manometer.Simple manometerIn simple manometer, one end is connected to the point at which the pressure is to be measured and the other end is open to atmosphere.Differential manometerIn differential manometer, two ends are connected to the points whose difference of pressure is to be measured.

What is micro-manometer ? Where is it used ?In this manometer a large difference in meniscus levels are obtained for very small pressure difference. This manometer is useful for precise measurement of pressure difference.

Fluid Kinematics: - Lines of flow , velocity field and acceleration, Continuity Equation. (1D, 3D),Stream function and velocity potential function

Fluid Dynamics: - Bernoullis equation, Venturimeter, Orifice meter, Pitot tube.

What do you mean by dimension of flow?A fluid flow is said to be one, two or three dimensional depending upon the number of independent space coordinates.

When is a flow considered steady?A flow is considered steady when the dependent fluid variables at any point do not change with time.

When is the flow regarded as unsteady? Give an example for unsteady flow(AU MO3).When the fluid is regarded as unsteady if the dependent variable change with time at a position in the flow.The example for unsteady flow is flow at varying rates through a duct.

Differentiate uniform and non uniform flow.When velocity of fluid at any instant of time do not change from point to point in a flow field, the flow is said to be uniform.

What is the difference between laminar and turbulent flow.In the laminar flow the fluid particles move along smooth paths in laminar (or) layers with one layer gliding smoothly over the adjacent layer.In turbulent flow the fluid particles move in a very irregular path causing an exchange of momentum from one portion of the fluid to the another. The turbulence setup greater shear stress throughout the fluid and causes more irreversibility and losses.

Differentiate compressible and incompressible flow.Compressible flow is that type of flow in which the density of the fluid change from point to point. Incompressible flow is that type of flow in which the density is constant for the fluid flow. r = constant.

Distinguish rotational and irrotational flow.Rotational flow is that type of flow in which the fluid particles while flowing along stream lines also rotate about their axis. If the fluid particles while flowing along stream lines, do not rotate about their own axis that type of flow is called irrotational flow.

What are streamlines?A stream line at any instant can be defined as an stationary curve in the flow field so that at any point represents the direction of the instantaneous velocity at that point. The streamlines are defined by

What are path lines?A path line is the actual path traversed by given fluid particle with the passage of timefrom initial time to final time. The path lines are defined by

What are streak lines?A streak line at any instant of time is the locus of the temporary location of all particles that have passed through a fixed point in the flow field.

Define convective and local acceleration.Convective acceleration is the instantaneous space rate of change of velocity, Local acceleration is the local time rate change of velocity.

Write the one dimensional continuity equation for compressible fluid flow.Continuity equation for compressible fluid flow is mo = r1A1 u1 = r2A2 u2r1, r2 - density at section 1 & 2A1, A2 area at the section 1 & 2, u1, u2 - velocity at section 1 & 2.

Define stream function.It is defined as the scalar function of space and time, such that its partial derivative with respect to any direction gives the velocity component at right angles to that direction.

State the properties of stream function.i) If stream function exists , it is a possible case of fluid flow.ii) If stream function satisfies the laplace equation is a possible case of irrotational flow.

Define velocity potential function.It is defined as a scalar function of time and space such that its negative derivative with respect to any direction gives the fluid velocity in that direction.

State the properties of velocity potential function.*If the velocity potential function exists , it is a possible case of irrotational flow.*Lines of constant velocity potential function and lines of constant stream function are mutually orthogonal.

What is a flow net?A mesh or net work of stream lines and equipotential lines is called a flow net.

Write the applications and limitation of flow net?*It is used to determine the direction of flow and velocity at any point in the closed system*To determine the pressure distribution for given boundaries of flow.

Define circulation.Circulation is defined as the flow along a closed curve. Mathematically circulation is obtained if the product of the velocity component at any point and the length of small element containing that point is integrated around the curve.

State Bernoullis theorem.Bernoullis theorem states that in a steady flow of ideal incompressible fluid, the sum of pressure head, velocity head and potential head is constant along a stream line provided no energy is added or taken out by external source.

What are all the assumptions taken when deriving the Bernoullis equation. Write the Bernoullis equation and explain the terms.i. Fluid is ideal and incompressible.ii. flow is steadyiii. Flow is along the stream line ie. One dimensional.iv. The velocity is uniform over the section and is equal to mean velocity.v. The only forces acting on the fluid are the gravity forces and pressure forces.

Write the Bernoullis equation and explain the terms.Bernoullis equation is (p/density*g)+(U2/2g)+Z=constantThe first term is the flow energy per unit weight (or) pressure head .The second term is the kinetic energy per unit weight (or) kinetic head. The third term Z is the potential energy per unit weight (or) potential head. The sum of these terms is known as total head.

Water if flowing through a pipe of 10 cm diameter under a pressure of 19.62 N/cm2 with mean velocity of 3m/s. Find the total head of water at a cross section, which is 8m above the datum line.The pressure (p) = 19.62 N/cm2 = 19.62 x 104 N/m2 ; velocity U = 3m/sDatum head Z = 8 m density of water r = 1000 kg /m3Total head = (p/rg) + (U2/2g) + Z = [(19.62x104)/(100x9.81)] + [32/(2x9.81)] + 8 = 28.46 m of water.

Write few applications of Bernoullis equation.*flow through venturimeter* flow through orifice meter*flow through orfices & mouth pieces*flow over notches & weirs

What is venturimeter and name the parts of venturimeter?A venturimeter is a device used for measuring the rate of a flow of fluid through a pipe. It consists of three parts i) short converging part ii) throat iii) Diverging part. It is based on the principle of Bernoullis theorem.

What is a pitot tube and write its principle.Pitot tube is a glass tube bent at right angle . When it is placed in a flow, the liquid raises up in the tube due to conversion of kinetic energy into pressure energy. This raise is used to measure the velocity of flow at a point in the pipe or channel.Dimensional analysis, Models & SimilitudeGive the dimensions of the following quantities, a) Pressure b) Surface tension c) dynamic viscosity d) kinematic viscosity.a) Pressure M L-1 T-2 b) surface tension M T-2c) dynamic viscosity M L-1 T-1 d) Kinematic viscosity L2 T-1State the Buckinghams-p theorem.Buckinghams-p theorem states n quantities with in base dimensions can generally be arranged to provide only (n-m) independent dimensionless parameters also referred as p terms.what do you mean by repeating variables? How are the repeating variables selected for dimensional analysis ?In dimensional analysis, it is necessary to recognize the common variables for grouping. These common variables are known as repeating variables. The repeating variables should be chosen in such a way that one variable contain geometric property, other variable contains flow property and third contains fluid property. Normally the characteristic length (L), the velocity (u) and the density are chosen.Show that the ratio of inertia force to viscous force gives Reynolds number,Inertia force = mass x acceleration = r L3 u /t = r L2 (ut) u /t= r L2 u2Viscous force = shear stress x surface area = m (u/L) L2= m uLratio = (r L2 u2) / (m uL) = r u L / m = Reynolds Number.What is a Mach number? Mention its field of use.The Mach number is the square root of ratio of inertia force to the elastic forceFor surface tension and capillarity studies which dimensionless number is used?The surface tension forces are associated with Weber numberWeber Number = inertia force/surface tention forceSo for surface tension and capillarity studies Weber number is used.Mention any two applications of Eulers number.i) flow through hydraulic turbines and pumpsii) flow over submerged bodies iii) flow through penstocks.Name the three types of similarity.a) geometric similarity b) Kinematic similarity c) Dynamic similarity.What is geometric similarity?Geometric similarity concerns the length dimensions. A model and prototype are geometrically similar if and only if all body dimensions in all three coordinates have the same linear scale ratio. scale ratio = Lm/LpIn fluid flow , what does dynamic similarity mean ?Dynamic similarity exists when the model and prototype have the same length scale ratio, time scale ratio and force scale ratio. So the forces at homogeneous points are related through a constant called the force ratio.Estimate the speed of rotation of a 3m diameter propeller to cruise at 10m/s if a 1/16 scale model provided the following results.U = 5m/s N = 750rpmThe dynamic similitude requires (Nd)/U to e equated for model and the prototypeThe speed of rotation = Np = (150 x 10 )/(5 x 10) = 150 rpm.