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ME 101202 - Fluid Mechanics and Machinery

Nandha Engineering College, Erode - 52Department of Mechanical Engineering

Question Bank (Two Marks Questions and Answers)Year / Sem: II / III

UNIT- I BASIC CONCEPTS AND PROPERTIES

1. Define fluids.Fluid may be defined as a substance which is capable of flowing. It has no definite shape of its own, but confirms to the shape of the containing vessel.

2. Classify the different types of fluids.i) Ideal and real fluids ii) Newtonian and Non-Newtonian fluids

3. What are the properties of ideal fluid?Ideal fluids have following properties

i) It is incompressible ii) It has zero viscosity iii) Shear force is zero

4. What are the properties of real fluid? (or) What is a real fluid? The fluid which is having the following properties is known as real fluids.

i) It is compressible ii) They are viscous in nature iii) Some resistance is always offered by the fluid when it is in motion iv) Shear force exists always in such fluids.

5. Why are some fluids classified as Newtonian fluids? Give examples.In Newtonian fluids, a linear relationship exists between the magnitude of shear stress and resulting rate of deformation.Example: Water, Kerosene

6. What are Non-Newtonian fluids?In Non-Newtonian fluids, there is a non-linear between the magnitude of shear stress and resulting rate of deformation.

7. Define density and specific weight.Density is defined as mass per unit volume i.e., mass of the fluid contained in unit volume. It is also called mass density.

Density, ρ =mass

volume=m

V kg/m3

Specific weight is defined as weight possessed per unit volume. It is varies from place to place because of change in acceleration due to gravity.

Specific weight, w =

weightvolume

=WV N/m3

8. Define Specific volume and Specific Gravity.Specific volume is defined as volume of fluid occupied by unit mass (m3/kg)

Specific volume, v =

Volumemass

=Vm m3/kg

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Specific gravity is defined as the ratio of specific weight of fluid to the specific weight of standard fluid.

Specific gravity, S =

Specific weight of liquidSpecific weight of standard liquid

9. Define Surface tension and Capillarity.Surface tension is due to the force of cohesion between the liquid particles at the free surface.Capillary is a phenomenon of rise or fall of liquid surface relative to the adjacent general level of liquid.

10. Define Viscosity.It is defined as the property of a liquid due to which it offers resistance to the movement of one layer of liquid over another adjacent layer. (N-s/m2 or kg/m-s)

11. Define kinematic viscosity.It is defined as the ratio of dynamic viscosity to mass density.

i.e., γ = μ

ρ m²/sec

12. Define dynamic viscosity.The dynamic viscosity is defined as the shear stress required to produce unit rate of shear deformation.

13. Define Relative or Specific viscosity.It is the ratio of dynamic viscosity of fluid to dynamic viscosity of water at 20°C.

Relative of Specific viscosity, =

Dynamic viscosity of given fluid

Dynamic viscosity of water at 200 C

14. What is the effect of temperature on viscosity of water and that of air?When the temperature of water increases, the viscosity will decrease but it will increase with increase in temperature of air.

15. Define the term absolute temperature.The temperature measured from the absolute zero temperature is called as absolute temperature.

16. Define Compressibility.It is the property by virtue of which fluids undergoes a change in volume under the action of external pressure.

17. Define Newton’s law of Viscosity.According to Newton’s law of viscosity the shear force F acting between two layers of fluid is proportional to the difference in their velocities du and area A of the plate and inversely proportional to the distance between them.

18. What is cohesion and adhesion in fluids?Cohesion is due to the force of attraction between the molecules of the same liquid. The inner molecular attraction holds the liquid molecules together are known as cohesion.

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Adhesion is due to the force of attraction between the molecules of two different liquids or between the molecules of the liquid and molecules of the solid boundary surface. This property enables a liquid to stick over another body.

19. What is surface tension?Surface tension is due to the force of cohesion between the liquid particles at the free surface.

20. Write the equation of surface tension of liquid jet, liquid droplet and soap bubble.

Surface tension in liquid droplet, p =

4 σd

⇒σ=pd4

Surface tension in Soap Bubble, p =

8 σd

⇒σ=pd8

Surface tension in liquid jet, p =

2 σd

⇒σ=pd2

21. Define capillarity.Capillarity is a phenomenon of rise or fall of liquid surface relative to the adjacent general level of liquid. This phenomenon is due to the combined effect of cohesion and adhesion of liquid particles. The rise of liquid level is known as capillary rise where as the fall of liquid is known as capillary depression.

22. What are the parameters depends on magnitude of capillary?The magnitude of capillary is depends upon

i) Diameter of the tubeii) Specific weight of liquidiii) Surface tension of liquid

23. Explain the effect of property of capillarity.This phenomenon is due to the combined effect of cohesion and adhesion of liquid particle. So, the surface will act around the circumference of the tube.

24. Define the term fluid statics.Fluid statics is the study of a fluid at rest; the concept includes the situation where the fluids are either actually at rest or undergo uniform acceleration in a container or rotate as a solid mass.

25. How can we define vacuum pressure?The pressure below the atmospheric pressure is called as vacuum pressure.

26. State Pascal law?The intensity of pressure at any point in a static fluid is equal in all directionsPx= Py=Pz

27. State momentum of momentum equation?It states that the resulting torque acting on a rotating fluid is equal to the rate of change of moment of momentum

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28. What is momentum equationIt is based on the law of conservation of momentum or on the momentum principle It states that, the net force acting on a fluid mass is equal to the change in momentum of flow per unit time in that direction.

29 Give the Euler’s equation of motion?

( d p

p )+g dz + v dv = 0

30What are the assumptions made in deriving Bernouillie’s equation?a. The fluid is idealb. The flow is steady.c. The flow is incompressible.d. The flow is irrotational.

31State Bernouillie’s Theorem as applicable to fluid flow.It states that an ideal incompressible fluid when the flow is steady and continuous, the sum of pressure energy, kinetic energy and potential energy is constant along the streamline

( pw )+ ( v2 )

2 g+ z = Constant

32 What is Bernouillie’s equation for real fluid?

( p1

p g )+ (v12 )

2 g+ z1=( p2

p g )+ (v22)

2 g+ z2+ h1

Where, hl - loss of energy, (p/pg) - Pressure energy, (v2/2g) - Kinetic energy andz - Datum energy

33 State the application of Bernouillie’s equation? Or Name the three flow measuring instruments.

It has the application on the following measuring devices.a. Orifice meter. b.Venturimeter. c.Pitot tube

34 What are the assumptions made on Bernoulli’s equation?a. The liquid is ideal and incompressibleb. The flow is steady and continuousc. The velocity is uniform over the cross section and is equal to mean velocityd. The only forces acting on the fluids are the gravity force and the pressure forcee. All the frictional forces are negligible

35 Write down the limitations of Bernoulli’s equation.a. Velocity of flow across the cross section is assumed to be constant whereas it is not so

in actual practice. The velocity of liquid particle is maximum at the center of the pipe and gradually decreases towards the wall of the pipe due to pipe friction

b. The equation has been derived under the assumption that no external force, except the gravity force, is acting on the liquid. But in actual practice the force such as pipe friction is acting on the liquid

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c. No loss of energy is assumed. But during turbulent flow, kinetic energy is converted into heat energy. Some energy is lost due to shear force in viscous flow. All these losses are considered.

36 Why large reduction of diameters from inlet throat is not allowed in venturimeter?Due to large reduction in diameters, the cavitation will occur. It will amaze and corrode the pipe. So, large reduction of diameters is not allowed.

37 Co-efficient of discharge of venturimeter is always greater than orifice meter, why?Loss of energy due to sudden enlargement is higher than loss of energy due to gradual contraction. So the coefficient of discharge is greater than orifice meter.

38 Write down the expression for discharge through a venturimeter explaining each term in it.

Q = Cd x a1 x a2

√a12−a2

2 x √2 g h

a1 - Area of inlet section pipe, a2 - Area of outlet section pipe, h - Manometric head difference, and g - Acceleration due to gravity

39 Why pressure difference is not measured between throat and exit?In exit portion of the venturimeter the flow separation takes place. So the pressure difference is measured between inlet and throat

40 What is venturimeter and explain its basic principles?A venturimeter is a device, which is used for measuring the rate of flow of fluid through pipes. The basic principle of venturimeter is that by reducing the cross sectional area along the pipe, a pressure difference is created from the pressure we can calculate the discharge through the pipe.

41 What are the various parts in venturimeter?a. Inlet section followed by convergent portion b. Throat partc.Divergent cone followed by outlet section

42 Why convergent portion is smaller than divergent portion?This is because of avoiding flow separation and consequent energy loss in that portion. But flow separation is occurring in divergent portion and therefore it is not used for flow measurement

43 What is cavitation in venturimeter and give its effects?Due to reduction in area the velocity of fluids increased and pressure decreased. When pressure comes below that of vapour pressure of the flowing fluid then the liquid will be vapourized. This phenomenon is called cavitation.Effects: Cavitation will very damage the pipe walls and also corrodes the pipes

44 What are the advantages of venturimeter?a. Loss of head is small and hence high Cd value and it may approach unity under

favorable conditionb. No wear and tear c. Less likelihood of becoming clogged with sediment

d. Well-established characteristics e. Suitable for large flow of water, process fluids, wastes gases and suspended solids

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45 What are the disadvantages of venturimeter?a. Long laying length b. More space requirementc. Quit expense in installation and replacementd. Possibility of cavitation

46 What is orifice meter and explain its basic principles?The orifice meter also a device used for measuring the discharge through pipes. The basic principle of orifice meter is that by reducing the cross sectional area of the pipe, a pressure difference is created from the pressure difference. We can calculate the discharge through the pipes.

47 What are the advantages of orifice meter?a. Low initial costb. Ease of installation and replacementc. Requires less space as compared with venturimeterd. Can be used in wide range of pipe sizes (0.01 m to 1.5 m)

48 What are the disadvantages of orifice meter?a. High loss of head b. Co-efficient of discharge has a low valuec. Susceptible to in accuracies resulting from erosion, corrosion and scaling

UNIT-II FLOW THROUGH CIRCULAR CONDUITS

49 Define fluid kinematics.Fluid kinematics is a science which deals with the geometry of motion in terms of displacement, velocity and acceleration and their distribution in space without considering any force or energy involved. Thus kinematics involves only the description of the motion of fluids in terms of space-time relationship.

50 What stream lines?A streamline is an imaginary line drawn through a flowing fluid in such a way that the tangent at any point on it indicates the velocity at the point

51 Name the different forces present in fluid flow.a. Inertia force b.Viscous force c.Surface tension force d.Gravity force

52 Classify the different types of fluid flow.The fluid flow can be classified in several ways:

a. Steat flow and unsteady flowb. Uniform and non-uniform flowc. One-dimensional, two-dimensional and three-dimensional flowsd. Rotational and irrational flowe. Laminar and turbulent flowf. Compressible and incompressible flow

53 When in a fluid considered steady? Give an example for steady flow

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In steady flow, various characteristics of following fluids such as velocity, pressure, density, temperature etc at a point do not change with time. So it is called steady flowExample

a. Flow of water in a pipeline due to a centrifugal pump run at uniform speedb. Liquid efflux from a vessel in which constant level is maintained

54 When is the flow regarded as unsteady? Give an example for unsteady flow.The various characteristics of following fluids such as velocity, pressure, density, and temperature etc of a point change with respect to time.∂ v∂ t

≠0 ;∂ p∂ t

≠0

Example a. Liquid falling under gravity out of an opening in the bottom of a vesselb. Liquid flow in the suction and pressure pipes of a reciprocating pumpc. Wave movements in a sea

55 Define uniform and non-uniform flow.Uniform flow: It is a flow in which the velocity at any given instant does not change both in

magnitude and direction with respect to space. Mathematically

∂ v∂ s

=0

Non-uniform flow: The velocity of flow of fluid changes from one point to another point at any

instant. Mathematically

∂ v∂ s

≠0

56 What are one, two and three-dimensional flows?One-dimensional flow: In this type, various characteristics are function of time and one space co-ordinate onlyTwo-dimensional flow: In this type of flow, various characteristics are function of time and two space (rectangular) co-ordinates onlyThree-dimensional flow: In this type of flow, various characteristics are function of time and three space co-ordinates system

57 Distinguish between rotation and circularity in fluid flow.A rotational flow exists when the fluid particles rotate about their mass centers while moving along a streamlineCirculation is defined as the flow along a closed curve. Mathematically, the circulation is defined as the line integral of the tangential velocity about a closed curve.

58 Explain the terms rotational and irrotaional flow. Give examples.A rotational flow exists when the fluid particles rotate about their mass centres, while moving along a streamline. Example:

i. Liquid in a rotating tank where the velocity varies directly with a distance from centre.ii. Flow near the solid boundaries

An irrotaional flow exists when the fluid particles do not rotate about their mass centres while moving along a streamlineExample:

i. A vortex or whirlpool, which develops above a drain in the bottom of a stationary tankii. Flow above a drain hole of a washbasin.

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59 What is laminar and turbulent flow?A laminar flow is one in which the fluid particles move in layer with one layer of fluid sliding smoothly over an adjacent layerA turbulent flow is one in which the fluid particles move in an entirely haphazard or erratic manner

60 Mention the general characteristics of laminar flow.a. There is a shear stress between fluid layersb. ‘No slip’ at the boundaryc. The flow is rotationald. There is a continuous dissipation of energy due to viscous shear

61 What is compressible and incompressible flow?A flow is said to be compressible if the density changes from point to point due to pressure and temperature. Mathematically ρ ≠ constant A flow is said to be incompressible if the density is constant in flow field

62 What are streamline and path lines?A streamline is an imaginary line drawn through a flowing fluid in such a way that the tangent at any point on it indicates the velocity at that pointA path line is a line that is traced by a single fluid particle as it moves over a period of time. Path line shows the direction of velocity of the same fluid particles at successive instants of time

63 Explain the various characteristics of streamline.a. Streamlines do not cross to each otherb. There cannot be any movement of fluid mass across the streamlinesc. For steady flow the streamline pattern remains the same at different timesd. Streamline spacing varies inversely as the velocitye. The series of streamlines represent the flow pattern at an instant

64 What is stream tube?A stream tube is tube imagined to be formed by a group of neighboring streamlines passing through a small closed curve, which may or may not be circulate

65 What is streak line? Give examples.The streak line is a line that is traced by fluid particles passing through a fixed point in a flow field. It gives an instantaneous picture of the position of the fluid particles that have passed through a fixed point. Example:

a. The path traced by a smoke coming out of a man when smokingb. The path of the smoke coming out of the chimney

66 State and explain the basic principles of continuity equation.It states that the mass of fluid flowing through the pipe at all cross section remains constant

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

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68 Write the condition to satisfy the irrotational flow

∂2ψ∂ x2

+ ∂2ψ∂ y2

=0

69 Mention the few properties of stream function.a. If stream function exists, it is possible case of fluid flowb. If stream function satisfies Laplace equation it is possible case of an irrotational flow

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

71 Mention the few properties of potential function.a. If velocity potential exists, the slow should be irrotationalb. The velocity potential satisfies, the Laplace equation, it represents the possible steady

incompressible irrotational flow

72 Define fluid dynamics.The study of fluid motion considering the forces which cause acceleration and forces which resist acceleration is known as fluid dynamics

73 What is meant by equation of motion?The dynamic behavior of fluid motion is governed by a cup of equations, known as equations of motion

74 What is Hagen poiseuille’s formula?P1−P2

ρ g= h f=

32 μ U Lρ g d2

Hagen poiseuille formulaWhere

P1-P2 /ρg Loss of pressure head U Average velocityμ Coefficient of viscosity D Diameter of pipeL Length of pipe

75 What are the factors influencing the frictional loss in pipe flow?Frictional resistance for the turbulent flow is

i) Proportional to vn where v varies from 1.5 to 2.0.ii) Proportional to the density of fluid.iii) Proportional to the area of surface in contact.iv) Independent of pressure. v) Depend on the nature of the surface in contact.

76 What is the expression for head loss due to friction in Darcy formula?

h f=4 f L V2

2 g dWhere f - Coefficient of friction in pipe

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L - Length of the pipeD - Diameter of pipe, and V - Velocity of the fluid

77 Where the Darcy weishbach and Chezy’s formulas are used?Darcy weishbach equation is generally used for the flow through pipesChezy’s formula is generally used for the flow through open channels

78 What do you understand by the terms a) major energy losses, b) minor energy lossesMajor energy losses - This loss due to friction and it is calculated by Darcy weishbach formula and chezy’s formula.Minor energy losses - This is due to

i. Sudden expansion in pipe. ii. Sudden contraction in pipe.iii. Bend in pipe. iv. Due to obstruction in pipe.

79 What are the losses experienced by a fluid when it is passing through a pipe?a. Loss of energy due to sudden enlargementb. Loss of head due to sudden contractionc. Loss of energy at the exit from the piped. Loss of energy due to gradual contraction or enlargemente. Loss of energy due to an obstruction in pipef. Loss of energy at the entrance to a pipeg. Loss of energy in bendsh. Loss of energy in various pipe fittings

80 Give an expression for loss of head due to sudden enlargement of the pipe.

he=(V 1− V2)

2

2 gWhere he - Loss of head due to sudden enlargement of pipe.

V1 - Velocity of flow at section 1-1V2 - Velocity of flow at section 2-2

81 What are eddies and vena contracta in pipe minor losses?Due to sudden contraction, the streamline coverage to a minimum cross section is called vena contractaIn between vena-contracta and wall of the pipe a lot of eddies are formed. These eddies cause a considerable dissipation of energy.

82 Give an expression for loss of head due to sudden contraction.

hc=0 .5 V2

2 gWhere, hc - Loss of head due to sudden contraction & V - Velocity at outlet of pipe

83 Give an expression for loss of head at the entrance of the pipe.

hi=0 .5 V2

2 g

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Where, hi - Loss of head at entrance of pipe & V - Velocity of liquid at inlet and outlet of the pipe

84 Write the formula for loss of energy due to gradual enlargement and also bend in pipe.Loss of energy due to gradual enlargement

hL= k V

12− V22

2 gk – Co-efficient which depends on angle of convergenceLoss of head due to bend in pipe

hb= K V2

2 g

85 Define the terms a) Hydraulic gradient line [HGL] and b) Total Energy line [TEL]Hydraulic gradient line: Defined as the line which gives the sum of pressure head and datum head of a flowing fluid in apipe with respect the reference line.Total energy line: Defined as the line which gives the sum of pressure head, datum head and kinetic head of a flowing fluid in a pipe with respect to some reference line.

86 What is syphon? Where it is used?Syphon is along bend pipe which is used to transfer liquid from a reservoir at a higher elevation to another reservoir at a lower level.Uses of syphon:

i. To carry water from one reservoir to another reservoir separated by a hill ridge.ii. To empty a channel not provided with any outlet sluice.

87 What are the basic educations to solve the problems in flow through branched pipes?i. Continuity equation.ii. Bernoulli’s formula.iii. Darcy weisbach equation.

88 What is Dupuit’s equation ?L1

d15

+L2

d25

+L3

d35

= Ld5

WhereL1, d1 - Length and diameter of the pipe 1L2, d2 - Length and diameter of the pipe 2L3, d3 - Length and diameter of the pipe 3

89 What are the types of fluid flow?

i) Steady & unsteady fluid flowii) Uniform & Non-uniform flowiii) One dimensional, two-dimensional & three-dimensional flowsiv) Rotational & Irrotational flow

90 When in a fluid considered steady?In steady flow, various characteristics of following fluids such as velocity, pressure, density, temperature etc at a point do not change with time. So it is called steady flow.

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91 Define co-efficient of friction.It is the ratio of actual discharge to theoretical discharge of the pipe

92 What is co-efficient of velocity?

It is the ratio of actual velocity of fluid to theoretical velocity. Cv=

V act

V the

93 Define co-efficient of contractionIt is the ratio of area at vena contraction area to orifice area of the pipe

Coefficeint of contraction =Area at vena contractionArea at Orifice

94 How pressure can be measured in pitot tube?The velocity of flow can be determined by measuring the increase in pressure energy at this point

95 How the term dimensional analysis can be defined?Dimensional analysis is a mathematical tool or technique to study dimensions of several problems

96 Write down the Navier-Stokes equation.The equation of motion without considering force due to turbulence and considering the gravity, pressure and viscosity forces are known as Navier-Stokes equation.

Fx=(Fg )x+(F p )x+(Fv )xF y=(Fg )y +(F p) y

+( Fv ) y

F z=(F g)z+(F p)z+(Fv )z Where Fg - Gravity force, Fp - Pressure force & Fv - Viscous force

97 What are energy lines and hydraulic gradient lines?Energy line: If different sections of the pipe total energy is plotted to scale and joined by a line, the line is called energy grade lineHydraulic gradient line: The pressure head in a pipe decreased gradually from section to section of the pipe in the direction of the fluid flow due to loss of energy. If pressure heads at the different sections of the pipe are joined by a straight line. This line is called hydraulic gradient line or pressure line

98 What is hydraulic mean depth or hydraulic radius?

Hydraulic radius is the ratio of cross sectional area to perimeter of that section. m = A

P

99 What is pipe?Pipe is a closed conduit, which is used for carrying fluids under pressure

100 What are pipes in series?It is defined as the pipes of different diameters and lengths are connected with one another to form a single pipeline

101 What is equivalent pipe?

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A compound pipe consisting of several pipes of varying diameters and length may be replaced by a pipe of uniform diameter, which is known as equivalent pipe

102 What do you mean by flow through parallel pipes?When a main pipeline divides into two or more parallel pipes, which again join together to form a single pipe and continue as a main line. These pipes are said to be pipes in parllel

103 Define displacement thickness.It is defined as the distance measured perpendicular to the boundary by which the mainstream is displaced to on account of formation of boundary layer

104 Define momentum thickness.It is defined as the distance, measured perpendicular to the boundary, by which the boundary should be displaced to compensate for reduction in momentum of the flowing fluid on account of boundary layer formation

105 Define energy thickness.It is defined as the distance measured perpendicular to the boundary, by which the boundary should be displaced to compensate for reduction of kinetic energy of the flowing fluid on account of boundary layer formation

106 Define drag and lift.The component of the total force in the direction of flow of fluid is known as dragThe component of the total force in the direction perpendicular to the direction of flow is known as lift

UNIT III DIMENSIONAL ANALYSIS

1. State the methods of dimensional analysis.a. Rayleigh’s methodb. Buckingham’s theorem

2. State Buckingham’s theoremIt states that if there are ‘n’ variables in a dimensionally homogeneous equation and if these variables contain ‘m’ fundamental dimensions (M, L, T), then they are grouped into (n-m), dimensionless independent-terms.

3. State the limitations of dimensional analysis.a. Dimensional analysis does not give any due regarding the selection of variables.b. The complete information is not provided by dimensional analysis.c. The values of coefficient and the nature of function can be obtained only by

experiments or from mathematical analysis.

4. Define SimilitudeSimilitude is defined as the complete similarity between the model and prototype.

5. State Froude’s model lawOnly Gravitational force is more predominant force. The law states ‘The Froude’s number is same for both model and prototype’.

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6. Give the dimensions of the following physical quantities.(a) Pressure (b) Surface Tension (c) Dynamic viscosity (d) Kinematic viscosity

(a) Pressure ML-1T2 (b) Surface Tension ML-1T2 (c) Dynamic viscosity ML-1T-1 (d) Kinematic viscosity L2T-1

7. State the Fourier law of dimensional homogeneityThe law of Fourier principle of dimensional homogeneity states “an equation which expresses a physical phenomenon of fluid flow should be algebraically correct and dimensionally homogenous

8. What is dimensionally homogenous equation? Give examples.Dimensionally homogenous equations means, the dimensions of the terms of left hand side should be same as the dimensions of the terms on right hand side

9. What are the uses of dimensional homogeneity?a. To check the dimensional homogeneity of the given equationb. To determine the dimension of a physical variablec. To convert units from one system to another through dimensional homogeneityd. It is a step towards dimensional analysis

10. What are the points to be remembered while deriving expressions using dimensional analysis?a. First the variables controlling the phenomenon should be identified and expressed in

terms of primary dimensionsb. Any mathematical equation should be dimensionally homogenousc. In typical cases, a suitable mathematical model is constructed to simplify the problem

with suitable assumptions

11. How equations are derived in Raleigh’s method?The expression is determined for a variable depending upon maximum three or four variables only. If the number of independent variables becomes more than four, it is very difficult to find the expression for the dependent variables. So, a functional relationship between variables is expressed in exponential form of equations.

12. Describe briefly the selection of repeating variables in Buckingham Theorem.There is no separate rule for selecting repeating variables. But the number of repeating variables is equal to the fundamental dimensions of the problem. Generally, ρ, v, l or ρ, v, D are chosen as repeating variables. It means, one refers to fluid property (ρ) one refers to flow property (v) and the other one refers to geometric property (l or D). In addition to this, the following points should be kept in mind while selecting repeating variables.

1. No one variable should be dimensionless.2. The selected two repeating variables should not have the same dimensions.3. The selected repeating variables should be independent as far as possible.

13. Define weber number.It is the ratio of the square root of the inertia force to the surface tension force.

W e=√Inertia forceSurface Tension force

=√ρ L2 V 2

σ L=√ρ L V 2

σ

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14. Define Reynold’s number.It is defined as the ratio of the inertia force to the viscous force of a flowing fluid. Denoted by Re.

Re=Inertia forceViscous force

=ρ LVμ

(or ) LVυ ; (μ / ρ = ν = Kinematic viscosity)

15. Define Mach numberIt is defined as the square root of the inertia force of a flowing fluid to the elastic force

μ=√Inertia forceElastic force

=√ρ L2V 2

k L2=√ρ V 2

k

16. Mention the applications of model testing?a. Civil engineering structures such as dams, weirs, canals etcb. Design of harbour, ships and submarinesc. Aero planes, rockets and machines, missiles

17. What are the advantages of model testing?a. The model tests are quite economical and convenient and operation of a model may be

changed several times if necessary, without of increasing much expenditureb. With the use of models the performance of hydraulic structure/hydraulic machines can

be predicted in advancec. Model testing can be used to detect and rectify the defects of an existing structure,

which is not functioning properly

18. What are the similarities between model and prototype?a. Geometric similarity b. Kinematic similarityc. Dynamic similarity

19. What is meant by Kinematic similarity?Kinematic similarity is the similarity of motion. It corresponds to the points in the mode and in the prototype.

20. In fluid flow, what does dynamic similarity mean? What are the non-dimensional numbers associated with dynamic similarity?It is the similarity of forces. The flows in the model and prototype are of dynamic similar.Dimensional numbers are weight, force, dynamic viscosity, surface tension, capillarity etc

21. Mention the significance of Reynolds model lawa. Motion of air planes. b. Flow of incompressible fluid in closed pipes.c. Motion of submarines, andd. Flow around structures and other bodies immersed fully in moving fluids.

22. Write down the scale ratio for discharge, energy and momentumDischarge, Qr - Lr

5/2

Energy, Er - Lr4

Momentum, Mr - Lr7/2

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23. State the Euler model law and give its significanceOnly pressure for is more predominant force in addition to the inertia force. According to this law, the Euler number is same for both prototype and model.The Euler number itself is sufficient centerion in the following phenomena:

1. Where the gravity and surface tension forces are fully absent and the turbulence is fully developed with negligible viscous force.

2. It is applied in cavitation phenomena

24. Mention the types of modelsi) Undistorted models. ii) Distorted models

25. What is meant by undistorted models?The model which is geometrically similar to its prototype is known as undistorted models. In such models the conditions of similitude are fully satisfied.

26. Define the term scale effectIt is impossible to product the exact behaviour of the prototype by model testing alone. The two models of same prototype behaviour with different. Solve ratios will not be same. So discrepancy between models and prototype will always occur. It is known as scale effect.

27. Obtain scale ratio of discharge for distorted models.

Discharge scale ratio, Qr=( Lr )H x [ (Lr )V ]32

UNIT-IV ROTODYNAMIC MACHINES

1. Define fluid machines.The device in which the fluid is in continuous motion and imparts energy conversion is known as fluid machines.

2. Define hydraulic machines / turbine.Hydraulic machines which convert the energy of flowing water into mechanical energy

3. What is hydroelectric power?The turbine converts hydraulic energy into mechanical energy. This mechanical energy is converted into electrical energy. So conversion of energy from hydraulic to electric is called hydroelectric power.

4. What is the basis of classification of turbines?a) According to the action of the water flowingb) According to the main direction of flow of waterc) According to head and quantity of water requiredd) According to the specific speed

5. Classify the different types of turbinea) Action of the water flowing

i. Impulse turbine ii. Reaction turbine

b) Main direction of water flow

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i. Tangential flow turbine ii. Radial flow turbine iii. Axial flow turbine iv. Mixed flow turbine

c) Head and quantity basisi. High head turbine ii.Medium head turbine

iii.Low head turbined) Specific speed basis

i. Low specific speed ii.Medium specific speediii. High specific speed

6. Give example for a low head, medium head and high head turbine.Low head turbine – Kaplan turbineMedium head turbine – Modern Francis turbineHigh head turbine – Pelton wheel

7. Write the Euler’s equation for turbo machines.The force exerted by the water in the direction of motion is given byF=ρ a V1(V w1+ V w2)

Hence the momentum of the water or impulse = F x u = ρ a V1(V w1+ V w2)× u

8. What are the components of energy transfer in turbo machines?a) Whirl velocity b) Flow velocity c) Relative velocity

9. Define degree of reaction.The ratio between the kinetic energy change in the moving blade to the kinetic energy in the stage. Or it is the ratio between increase in relative kinetic energy in moving blade to the stage work output.

Degree of reaction, R=Increase in relative kinetic energy in moving blade

Stage work outpu

10. What is impulse turbine? Give example.In impulse turbine all potential energy converted into kinetic energy. From these the turbine will develop high kinetic energy power. This turbine is called impulse turbine. Example: Pelton turbine

11. What is reaction turbine? Give example. In a reaction turbine, the runner utilizes both potential and kinetic energies. Here portion of potential energy is converted into kinetic energy before entering into the turbine. Example: Francis and Kaplan turbine.

12. Differentiate the impulse and reaction turbine.

S.No. Impulse turbine Reaction turbine

1All the potential energy is converted into kinetic energy by nozzle before entering to turbine runner

Only a portion of the fluid energy is transferred into kinetic energy before the fluid enters the turbine

2 Flow regulation is possible without loss Flow regulation is possible with loss

3Blades are only in action when they are i.e. infront of nozzle

Blades are in action at all the time

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4Water may be allowed to enter a part or whole of the wheel circumference

Water is admitted over the wheel circumference

5Wheel does not run full and air has free access to the bucket

Water completely fills the vane passages throughout the operation of the turbine

6 Unit is installed above the tailraceUnit is kept entirely submerged in water below tailrace

7Flow is regulated by means of a needle valve fitted into the nozzle

Flow is regulated by means of a guide-vane assembly

13. What is tangential flow turbine?The water flows along the tangent to the path of rotation of the runner.Example: Pelton wheel

14. What is radial flow turbine?In the turbine, water flows along the radial direction and mainly in the plane normal to the axis of the rotation as is passes through the runner. It may be either inward radial flow type or outward radial type.

15. What is axial flow turbine?In axial flow turbine water flows parallel to the axis of the turbine shaft.Example: Kaplan turbine, propeller turbine

16. What is mixed flow turbine?In mixed flow water enters the blades radially and comes out axially, parallel to the turbine shaft. Example: Modern Francis turbine.

17. Differentiate the inward flow reaction turbine and outward flow reaction turbine.

S.No. Inward flow reaction turbine Outward flow reaction turbine

1

Water enters at the outer periphery, flows inward and towards the centre of the turbine and discharges at the outer periphery

Water enters at the outer periphery flows outward and discharges at the outer periphery

2 The discharge does not increase The discharge increases3 Easy and effective speed control Very difficult to speed control

4Good for medium and high heads and suitable for large outputs and units

Good for medium or low heads

5 Commonly used for power projects Practically obsolete

18. Differentiate the Francis and Kaplan turbine.

S.No. Francis turbine Kaplan turbine

1Correct disposition of the guide and moving vanes is obtained at full load only

Correct disposition of the guide and moving vanes is obtained at any load

2System may have one or two servomotors depending on the size of the unit

Two servomotors respective of the size of the unit always do governing

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3Since only the guide vanes are controlled high efficiency is obtained

Both guide and runner vanes high efficiency is obtained even at partial loads

4Servomotors are kept outside the turbine shaft

Both servomotors are kept inside the hollow shaft of the turbine runner

19. What are the main parts of pelton wheel?a) Penstock b) Spear and nozzlec) Runner and buckets d) Break nozzle

e) Outer casing f) Governing mechanism

20. What is penstock in pelton wheel?Penstock is a large sized pipe, which conveys water from the high level reservoir to the turbine. Depending upon low head or high head installations, a penstock is made of wood, concrete or steel. In order to control the water flow penstocks have different control valves at different sections.

21. What is the function of spear and nozzle?The nozzle is used to convert whole hydraulic energy into kinetic energy. Thus the nozzle delivers high speed jet. To regulate the water flow through the nozzle and to obtain a good jet of water spear or nozzle is arranged.

22. What is function of outer casing?A casing is made of cast iron or fabricated steel plate. It is used to prevent the splacing of water and discharge of water to tailstock. It is also act as a safeguard against accidents.

23. What is break nozzle and mention its function?If the spear nozzle set was closed the runner will revolve long time due to inertia. To stop the runner in a short time a small nozzle provided which directs a jet of water on the backside of the buckets.

24. What is the function of governing mechanism in pelton wheel?Governing mechanism is used to regulate the water flow to the turbine at constant level so that the speed of the turbine kept constant. This automatically regulates the quantity of water flowing through the runner in accordance with any variation of load.

25. Define gross head and net or effective head.Gross Head: The gross head is the difference between the water level at the reservoir and the level at the tailstock. Effective Head: The head available at the inlet of the turbine.

26. Define water and bucket power.Water power: The power supplied by water jetBucket power: The power developed by the bucket wheel

27. Define hydraulic efficiency.It is defined as the ratio of power developed by the runner to the power supplied by the water

jet. ηh=

Power developed by the runnerPower supplied by the water jet

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28. Define mechanical efficiency.It is defined as the ratio of power available at the turbine shaft to the power developed by the turbine runner.

ηm=Power available the turbine shaftPower developed by the turbine runner

=Shaft powerWater power

29. Define volumetric efficiency.It is defined as the volume of water actually striking the buckets to the total water supplied by the jet.

ηv=Qa

Q=Q - q

Q ; ηv lies between 0.97 to 0.99

30. Define overall efficiency.It is defined as the ratio of power available at the turbine shaft to the power available from the water jet.

ηo=Shaft powerWater power

= Pw Q H

31. What is scroll or spiral casing?The water from the penstock enters the scroll casing which completely surrounds by the runner. The cross sectional area of the scroll casing decreases along the flow of direction, area is maximum at inlet and nearly zero at exit.

32. What is speed rings or stay ring?The speed rings consists of an upper and lower ring held together by series of fixed vanes called stay vanes. The number of stay vanes is usually taken as half to direct the water from the scroll casing to the guide vanes and also it resists the load imposed upon it.

33. What is the function of guide vanes or wicket gates in Francis turbine?The guide vanes direct the water on to the runner at appropriate angles as per design. Also it is used to regulate the quantity of water supplied to the runner the guide vanes are airfoil shaped and they may be made of cast steel, stainless steel or plate steel.

34. What are draft tube and its function?After passing through the runner, the water is discharged to the tailrace through a gradually expanding tube called draft tube.The pressure at the exit of the runner of a reaction turbine is generally less than atmospheric pressure. By passing reduced through draft tube, the outer velocity of water is reduced and gain in useful pressure head is activated to increase the output of turbine.

35. What are the main components in Kaplan turbine?The Kaplan turbine consists of the following main components

a) Scroll casing b) Stay ringc) Guide vanes d)Draft tube e) Runner

36. What are the significant of unit quantities and specific quantities?a) To predict the behavior of a turbine working under different conditions

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b) Make comparison between the performances of turbine of same types of different sizesc) Compare the performance

37. Define unit speed (Nu) of turbine.

Unit speed is defines as the speed of turbine when working under a unit head. Nu=

N

√H

38. Define unit discharge.It is the theoretical discharge of a turbine when working under unit head

Unit discharge, Qu=Q

√H

39. Define unit power.It is the theoretical power of a turbine when working under unit head

Unit power, Pu=P

H32

40. Define the specific speed of a turbine.Specific speed is the speed of a geometrically similar turbine, which will develop unit power when working under unit head.

41. Give the range of specific speed values for Kaplan turbine and pelton wheel.a) Range of speed for Kaplan turbine = 257 to 858b) Range of specific speed for pelton wheel = 10 to 30-single jet

= 17 to 50-two jets= 24 to 70-with four jets

42. What is meant by surge tank?A surge tank is small reservoir or tank in which the water level rises or falls to reduce

43. What are the purposes of providing surge tank?a) When sudden closure of valve, sudden reduction of flow in the penstock will occur. To

avoid this reduction of rate of flow, surge tanks are provided in the upstream of the pipeline

b) To reduce the rapid velocity fluctuation in pipeline during starts and shut down of a turbine

44. What are the different types of surge tanks?a) Simple surge tank b) Incline surge tankc) Differential surge tank

45. A turbine develops 5 MW under a head of 20 m at 125 rpm. What is the specific speed?

Given: P = 5 MW, H = 20 m; N = 125 rpm Solution: N s=

N √PH5/4

= 208.98 (Ans)

46. What is draft tube? In which type of turbine it is mostly used?-21-


The tube which increases the outlet velocity of turbines is known as draft tube. So, head is saved by fitting draft tube.

47. Write the function of draft tube in turbine outlet.a) It allows the turbine to set above tail-water level without loss of head for doing

inspection and maintenance.b) It regains the major portion of the kinetic energy delivered from the runner by diffuse

action.

UNIT-V POSITIVE DISPLACEMENT PUMPS

1. What is meant by Pump?A pump is device which converts mechanical energy into hydraulic energy.

2. State the important classification of centrifugal pump.According to number of stages

i) Single stage pump ii. Multi-stage pump

3. Mention main components of Centrifugal pump. i. Impeller ii. Casing

iii.Suction pipe, strainer & Foot valve iv. Delivery pipe & Delivery valve

4. What are the purposes of providing casing on the centrifugal pump?i) To guide water to and from the impeller, andii) To partially convert the kinetic energy into pressure energy

5. What are the various types of casing?i. Volute casing ii. Vortex casingiii.Volute casing with guide blades

6. Where the suction pipe is placed? For what?It is provided with a strainer at its lower en so as to prevent the entry of solid particles, debris etc into the pump.

7. What is meant by Priming?The delivery valve is closed and the suction pipe, casing and portion of the delivery pipe upto delivery valve are completely filled with the liquid so that no air pocket is left. This is called as priming.

8. Define Manometric head.It is the head against which a centrifugal pump works.

9. Write down the formula for manometric efficiency.

ηmano=Manometric headHead impartes by impeller to liquid

=Output of the pumpPower imparted by the impeller

10. Define volumetric efficiency.It is defines as the ratio of quantity of liquid discharged per second from the pump to the quantity passing per second through the impeller.

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11. Write down the relationship between overall efficiency, manometric efficiency, volumetric efficiency and mechanical efficiency.

ηo= ηmano x ηv x ηmech

12. Define Mechanical efficiency.It is defined as the ratio of the power actually delivered by the impeller to the power supplied to the shaft.

ηmech=Power at the impellerPower at the shaft

13. Define overall efficiency.It is the ratio of power output of the pump to the power input to the pump.

ηo=Power output of the pumpPower input of the pump

14. What are backward curved vanes?When the outlet tip of blade curves in a direction opposite to that of motion, then it is called backward curved vanes

15. Define radial vane.The liquid leaves the vane with relative velocity in a radial direction.

16. What are forward curved vanes?When the outlet tip of blade curves in the direction of motion, then it is called forward curved vanes

17. Write down the formula for specific speed of a pump.

N s=N √QHm

3/4= N √P

Hm5/4

18. Define speed ratio, flow ratio.Speed ratio: It is the ratio of peripheral speed at outlet (u2) to the theoretical velocity of jet corresponding to manometric head (Hm).

Ku=u2

√2gHm Ku varies from 0.95 to 1.25Flow ratio: It is the ratio of the velocity of flow at exit (Vf2) to the theoretical velocity of jet corresponding to manometric head (Hm).

K f=V f2

√2gHm Kf varies from 0.1 to 0.25

19. How can we obtain a high head in a pump network?A number of impellers are mounted on the same shaft in series to obtain a high head.H total= n x H

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20. What will be the effect of arranging the pumps in parallel?A number of pumps are arranged in parallel for obtaining high discharge.Q total= n x Q

21. What are the characteristics curves?i) Main characteristics curvesii) Operating characteristics curvesiii) Constant efficiency or Muschel curvesiv) Constant head and constant discharge curves.

22. What is the principle of reciprocating pumps? And state its displacement type.It operates on a principle of actual displacement of liquid by a piston or plunger, which reciprocates in a closely fitting cylinder.

23. State the main classification of reciprocating pump. According to the liquid being in contact with piston or plunger. According to the number of cylinders provided.

24. Mention main components of Reciprocating pump.i) Piton or Plunger ii) Suction and delivery pipe

iii) Crank and Connecting rod

25. What is the main difference between single acting and double acting reciprocating pump?In single acting reciprocating pump, the liquids acts on one side of the piston only whereas in double acting reciprocating pump, the liquid acts on both sides of the piston.

26. Write down the formula for discharge, work done and power required for double acting pump.

Discharge, Q=2 A L N60

Workdone, WD=2 w A L N60

(hs+ hd )

Power required to drive the pump, P=2 w A L N60

(hs+ hd )

27. Define Slip of reciprocating pump. When does the negative slip does occur?The difference between the theoretical discharge and actual discharge is called slip of the pump. Slip= Q th - Qact

Percentage Slip=Q th - Qact

Qth

x 100 =(1 - Qact

Qth) x 100 =(1 - Cd ) x 100

But in sometimes actual discharge may be higher than theoretical discharge, in such a case coefficient of discharge is greater than unity and the slip will be negative called as negative slip. It is possible when the delivery pipe is shorter than the suction pipe with higher running speed.

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28. What is indicator diagram?Indicator diagram is nothing but a graph plotted between the pressure head in the cylinder and the distance traveled by the piston from inner dead center for one complete revolution of the crank.

29. Write down the formula for work done by the pump in an indicator diagram.Work done = K x Area of indicator diagram

=w A N60

x Area of indicator diagram for single acting pump

=2 w A N60

x Area of indicator diagram for double acting pump

30. Define suction head.It is the vertical height of the centre line of the pump shaft above the liquid surface in the sump from which the liquid is being raised.

31. Write down the formula for saving in work by fitting air vessels.

Work saved=W 1 - W2

W 1

x 100

32. What is meant by Cavitations?It is defined phenomenon of formation of vapor bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure and the sudden collapsing of theses vapor bubbles in a region of high pressure.

33. What is the effect of cavitations in pumps?Breakdown of the machine itself due to severe pitting and erosion of blade surface

34. How can we identify the cavitation in pumps?i) Sudden drop in efficiency ii) Head falls suddenly

iii) More power requirement iv) Noise and vibration v) Pitting and erosion of surface

35. State any precautions against cavitations.i) The pressure should not be allowed to fall below its vapour pressureii) Special material coatings can be given to the surfaces where the cavitation occurs

36. What are rotary pumps? Give various types.Rotary pumps resemble like a centrifugal pumps in appearance. But the working method differs. Uniform discharge and positive displacement can be obtained by using these rotary pumps; it has the combined advantages of both centrifugal and reciprocating pumps.The various types are: External and Internal gear pump, Lobe pump and Vane pump.

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