Fluid Mechanics

1.A fluid is a substance that

a. permanently resists distortion

b. does not permanently resist distortion

c. has a definite density which is constant under all circumstances,

d. has a density which cannot be accurately determined.

2.The unit of pressure in SI system is

a. kg/m

^{2}
b. kg.m/s

^{2}
c. kg/m.s

^{2}
d. kg.m

^{2}/s
3.Pressure is a

a. vector

b. scalar

c. tensor

d. none of these

4.A fluid in equilibrium means

a. its viscosity is zero

b. shear stresses are acting on the fluid but no flow behavior is manifested

c. it is free from shear stresses

d. a hypothetical situation because fluids are never in equilibrium.

5.Two tubes of diameter 1 cm and 2 cm are filled with mercury to a height of 50 cm. Now pressure at the bottom of the mercury column will be --

a. higher for the tube of dia 1 cm

a. higher for the tube of dia 2 cm

b. the same for both the tubes

c. none of the above.

6.A manometer is used to measure

a. pressure difference

b. absolute pressure

c. both (a) and (b)

7.The flow of an incompressible fluid with no shear is known as

a. Potential flow

b. Laminar flow

c. Turbulent flow

d. Couette flow

8.A fluid is called Newtonian when the shear stress versus shear strain plot is

a. linear and passes through origin

b. linear but has an intercept

c. exponential and passes through the origin

d. is a rectangular hyperbola

9.When a fluid flows over a stationary solid surface, the fluid velocity at the fluid – solid interface is

a. Zero

b. equal to free – stream velocity

c. between zero and free – stream velocity

10.Liquid that does not flow at all until a threshold shear stress is attained is known as

a. Bingham Plastic

b. Pseudoplastic

c. Dilatant fluid

d. Newtonian liquid

11.The unit of viscosity in CGS system is commonly known as Poise. The dimension of Poise is

a. g/cm.s

^{2}
b. g.cm/s

c. g.cm

^{2}/s
d. g/cm.s

12.The unit of viscosity in SI system is

a. N.S

b. Pa. S

c. N. Pa

d. N.Pa/s

13.Viscosity of a gas

a. decreases with an increase in temperature

b. increases with an increase in temperature

c. remains unaffected with change in temperature.

14.Viscosity of a liquid

a. decreases with increasing temperature

b. increases with increasing temperature

c. remains unaffected with change in temperature

15.Kinematic viscosity is a ratio of

a. absolute viscosity to absolute pressure

b. absolute viscosity to absolute temperature

c. absolute viscosity to specific heat

d. none of the above

16.Kinematic viscosity has a unit of

a. m/s

b. m/s

^{2}
c. m

^{2}/s
d. kg.m/s

17.Reynolds number is a ratio of

a. momentum diffusivity to thermal diffusivity

b. momentum diffusivity to molecular diffusivity

c. inertial force to viscous force

d. average velocity to velocity of sound

18.Flow is laminar when Reynolds number is

a. less than 2100

b. less than 4000

c. less than 10000

d. less than 25000

19.Consider fluid flow over a flat plate. When flow in the boundary layer is completely laminar, the thickness of the boundary layer (d ) varies with the distance from the leading edge of the plate (x) in accordance with relation :

a. proportional to x

^{0.5}
b. proportional to x

^{0.8}
c. proportional to x

d. proportional to x

^{1.5}
20.The onset of turbulence is characterized by

a. a sudden rapid decrease in the thickness of the boundary layer

b. a sudden increase in velocity in the direction of flow

c. a sudden rapid increase in the thickness of boundary layer

d. a sudden decrease in velocity in the direction of flow

21.A turbulent boundary layer consists of three zones which are buffer layer, turbulent zone and

a. critical layer

b. stagnant zone

c. viscous sub layer

d. thin film zone

22.The equation of continuity applies to

a. incompressible fluids

b. compressible fluids

c. highly viscous fluids

d. both incompressible and compressible fluids

23.An incompressible fluid of density r flows through a tube of constant cross sectional area A at a flow rate of Q (vol/time). For this situation which of the following is /are correct?

a.

__Q/A__= constant
b. Q.r = constant

c. Q.r /A = constant

d. all (a), (b) and (c)

24.The unit of mass velocity in SI system is

a. kg/s

b. kg/

^{ }m^{3}. s
c. kg/m.s

d. kg/

^{ }m^{2}. s
25.For flow of incompressible fluids through tubes of constant cross-sectional area, mass velocity is

a. directly proportional to the absolute temperature

b. inversely proportional to the total pressure

c. directly proportional to the absolute temperature

d. independent of temperature and pressure

26.For laminar flow of Newtonian fluids in pipes, the ratio of average velocity to maximum velocity is equal to

a. 0.5

b. 1.0

c. 1.5

d. 2.0

27.The fully developed velocity profile for laminar flow of Newtonian fluids in pipes is

a. parabolic with the apex at the centerline of the pipe

b. parabolic with the apex at the pipe wall

c. rod-like

d. none of the above

28.For laminar flow in a pipe, the Fanning friction factor depends on Reynolds number according to the relation

a. f = 24/ Re

b. f = 18.5/ Re

c. f = 16/ Re

d. none of the above

29.A particle attains its terminal velocity when

a. gravity force + drag force=buoyancy force

b. gravity force - drag force=buoyancy force

c. buoyancy force = gravity force

d. drag force=buoyancy force

30.Consider steady flow of a viscous fluid at constant density through a horizontal pipe. The flow is fully developed. For such a situation, which one of the following equations describes the relation between wall shear stress, t

_{w}, and shear stress, t , at any radial position in the pipe ?
a. [t /t

_{w}]=[r /R ]
b. [t /t

_{w}]=[R/r ]
c. [t /t

_{w}]=1-[r /R ]^{2}
d. [t /t

_{w}]=[r /R ]^{2}
31.Water flows laminarly through a tube of dia 1 cm. The average water velocity is u

_{av}and the maximum velocity is u_{max}. Then
a. u

_{max }= 1.5 u_{av}
b. u

_{max}= 2 u_{av}
c. u

_{max }= 2.5 u_{av}
d. u

_{max }= 3 u_{av}
32.The Fanning equation relating pressure drop and friction factor is given by

a. - D p

_{s}= 2fLu^{2}/ r g_{c}D
b. - D p

_{s}= 2Lr u^{2}/ fg_{c}D
c. - D p

_{s}= 2fLr u^{2}/ g_{c}D
d. - D p

_{s}= 2fDr u^{2}/ g_{c}L
( L : length of the pipe; D : diameter ; f : friction factor ; u : average velocity; r : density)

33.For an ideal fluid flow the Reynolds number is

a. 2100

b. >4000

c. 0

d. infinity

34.For turbulent fluid flow through pipes, the kinetic energy and momentum correction factors are practically equal to

a. 0.5

b. 1

c. 2

d. 4

35.Under otherwise uniform conditions Fanning friction factor for a rough pipe is

a. smaller than that for a smooth pipe

b. greater than that for a smooth pipe

c. equal to that for a smooth pipe

36.Water flows turbulently through a smooth pipe. At the centre line the velocity gradient is

a. infinity

b. zero

c. between zero and one

d. none of the above

37.Consider turbulent flow of a fluid in a smooth pipe. At the centre line the turbulence is

a. isotropic

b. anisotropic

38.Velocity distribution in turbulent flow is customarily expressed in terms of dimensionless parameters : u + = u/u*, where u* = Ö t

_{w}g_{c}/r (friction velocity), and y + = y/m Ö t wg_{c}r . Now which of the following equation represents velocity distribution in the laminar sublayer ?
a. u

^{+}= 5 ln y^{+}- 3.05
b. u

^{+}= 2.457 ln y^{+}+ 5.67
c. u

^{+}= y^{+}
d. u

^{+}. y^{+}= 1
39.The logarithmic velocity law for the turbulent core was proposed by

a. Reynolds

b. Nikuradse

c. Von Karman

d. Prandtl

40.Stokes’ law is valid (strictly theoretically) when particle Reynolds number is N

_{Re,p}is
a. much less than one

b. equal to one

c. much greater than one

d. none of the foregoing

41.As predicted by stokes’ law, the drag coefficient, C

_{D }, is given by
a. 16/ N

_{Re},p
b. 8/ N

_{Re},p
c. 24/ N

_{Re},p
d. 32/ N

_{Re},p
42.In potential flow, wall drag is

a. infinite

b. zero

c. finite and non-zero

d. none of the foregoing.

43.At the stagnation point,

a. pressure is zero

b. both pressure and velocity is zero

c. velocity is zero

d. neither pressure non velocity is zero.

44.A sphere settles freely through a pool of liquid and the settling is in stokes’ law range. The terminal velocity of the sphere will

a. be independent of the liquid viscosity

b. increase linearly with viscosity

c. decrease inversely with viscosity

d. decrease inversely with the square of viscosity.

45.In a laboratory experiment spheres of different sizes are allowed to settle freely through a pool of liquid and terminal velocities are calculated. It is found that terminal velocity increases with the square root of the particle diameter. It appears that the settling conforms to

a. Stokes’ low range regime

b. intermediate regime

c. Newton’s law regime

d. Any one of the above, more data needed for correct prediction.

46.Two spherical particles, one of dia d

_{1}and the other of dia d_{2}, settle freely through a pool of liquid and the settling is in accordance with Stoke's law. d_{1}:d_{2}= 1 : 2. Therefore, u_{1}: u_{2}is equal to
a. 1 : 2

b. 2 : 1

c. 4 : 1

d. 1 : 4

47.For free settling in intermediate range, terminal velocity of a particle varies as

a. particle dia, dp

b. dp

^{0.5}
c. dp

^{2}
d. dp

^{1.14}
48.The drag coefficient in hindered settling is

a. equal to that in free settling

b. grater than in free settling

c. less than in free settling.

49.Under otherwise uniform conditions, as the drag coefficient increases, the terminal velocity of a particle

a. increases

b. remains unaffected

c. decreases

50.Brownian movement predominates over the gravity force for particles of size

a. 100 m m

b. 10 m m

c. 0.1m m

d. none of the foregoing

51.For free settling of spherical particles in accordance with Newton’s law, the drag coefficient is

a. constant

b. directly proportional to the particle

c. Reynolds number inversely proportional to the particle Reynolds number.

d. Inversely proportional to the 0.6 power of the particle Reynolds number.

52.A fluidized bed is formed when

a. Fluid friction is zero

b. Gravity force is less than fluid friction

c. Pressure force is equal but acts in opposite direction to the gravity force

d. Sum of fluid friction and pressure force is equal but opposite to gravity force

53.Under otherwise uniform conditions, as the gas density is reduced (e.g. by increasing the temperature), the pressure drop per unit length of the fluidized bed

a. increases

b. decreases

c. remains unaltered.

54.Consider flow of a compressible fluid through a converging nozzle. Mach number for flow is less than 1 at the inlet to the nozzle. Then

a. du/dz > 0

b. du/dz < 0

55.For steady, isentropic flow of a compressible fluid through a convergent-divergent nozzle, sonic conditions can occur

a. only at the throat

b. anywhere between the inlet of the converging section and the throat.

c. anywhere between the throat and the outlet of the diverging section.

d. only at the outlet of the diverging section.

56.Stokes equation is valid in the Reynolds number range

a. 0.01- 0.1

b. 0.1-2

c. 2-10

d. 10-100

57.Consider a convergent divergent nozzle; a compressible fluid flows through the nozzle. The process-taking place in the divergent section may be described as an isentropic expansion. For this case, the stagnation temperature

a. is constant

b. changes linearly in the direction of flow

c. is maximum at the throat

d. is minimum at the throat

58.Consider a convergent divergent nozzle through which flows a compressible fluid. The conditions and flowrate are such that Mach no. is unity at the throat. The flow in the divergent section

a. is sonic

b. is definitely subsonic

c. is definitely supersonic

d. may be subsonic or supersonic, depending on the pressure in the downstream side.

59.Which of the following statements is/are correct about valves ?

a. Gate valves are so designed as to cause fluids to change in direction of flow of fluids.

b. Globe valves do not cause any change in direction of flow of fluids.

c. Under otherwise uniform conditions, pressure drop in a gate valve is larger than that in a globe valve.

d. None of the above statements is correct.

60.In a certain process, one needs fluid flow in a given direction and the valve is to open or close by the fluid pressure. Which of the following valves permits fluid flow in one direction only ?

a. gate valve

b. globe valve

c. check valve

d. any of the above

61.Safety valve is basically

a. a gate valve

b. a globe valve

c. a check valve

d. none of the foregoing

62.Consider pumping of a liquid at ambient temperature and conditions are such that no cavitation occurs. If the fluid temperature is now increased, chance for cavitation will

a. decrease

b. increase

c. remain unaffected

63.Cavitation will not occur if the sum of the velocity and pressure heads at the suction is

a. zero

b. much larger than the vapour pressure of the liquid

c. much smaller than the vapour pressure of the liquid

d. equal to the vapour pressure of the liquid.

64.In SI system, net positive suction head (NPSH) has a unit of

a. kg/ m

^{2}
b. N/ m

^{2}
c. J/ m

d. J/kg

65.The maximum discharge pressure for commercial piston pumps is around

a. 10 atm

b. 50 atm

c. 200 atm

d. 500 atm

66.The mechanical efficiency for large piston pumps varies from

a. 10 to 20%

b. 40 to 50%

c. 70 to 90%

d. 97 to 99%

67.The volumetric efficiency for a reciprocating pump varies from

a. 10 to 20%

b. 40 to 50%

c. 90 to 100%

68.As the discharge pressure increases, the volumetric efficiency of a positive displacement

a. decreases

b. remain practically constant

c. increases

d. may decrease or increase, depending on the size of the pump.

69.Which of the following is/are example(s) of rotary positive displacement pump(s) ?

a. gear pump

b. vane pump

c. screw pump

d. all of the foregoing

70.A non-newtonian fluid obeying power law equation and having n=0.5 flows laminarly through a pipe of circular cross-section. For this case, the ratio of average velocity to the maximum (centre-line) velocity is

a. ½ as in Newtonian liquids

b. 1/3

c. 2/5

d. 3/5

71.For a given volumetric flowrate of a Newtonian liquid in laminar flow, the pressure drop is inversely proportional to the fourth power of the pipe diameter. For a very pseudoplastic liquid for which n – o, the pressure drop is more nearly

a. inversely proportional to the pipe diameter

b. inversely proportional to the square of the pipe diameter

c. inversely proportional to the cube of the pipe diameter

d. inversely proportional to the square root of the pipe diameter.

72.Dilute solutions of polymeric molecules flowing through a conduct exhibit a phenomenon called "drag reduction". Drag reduction is basically

a. sudden reduction is Reynolds number at some location in the conduit.

b. reduction in friction factor (as compared to what might be expected at the prevailing Reynolds no.)

c. reduction in fluid viscosity at some location in the conduit

d. None of the foregoing.

73. In the figure given below, which one is the stagnation point?

a. A

b. B

c. C

d. D