Fluid Mechanics Flashcards
The fluid property, due to which, mercury does not wet the glass is
surface tension
Laminar flow of a Newtonion fluid ceases to exist, when the Reynolds number exceeds
2100
When the momentum of one fluid is used for moving another fluid, such a device is called a/an
jet pump
The normal stress is the same in all directions at a point in a fluid, when the fluid is
having no motion of one fluid layer relative to the other.
Head developed by a centrifugal pump depends on its
both (a) and (b)
Hydraulic mean depth (Dm) for a circular pipe of diameter ‘D’ flowing full is 0.25 D. For a circular channel, at Dm = 0.3 D, gives the condition for the maximum
mean velocity
The head loss in turbulent flow in a pipe varies
as (velocity)2
Most commonly used joint in the underground pipe lines is the
sleevejoint
The net positive suction head (NPSH) of a centrifugal pump is defined as the sum of the velocity head and the pressure head at the
suction minus vapor pressure of the liquid at suction temperature.
With increasing flow rate, the hydraulic efficiency of a centrifugal pump
monotonically decreases.
The velocity profile for turbulent flow through a closed conduit is
logarithmic
In case of hydraulically smooth pipe, the resistance to flow depends only on the Reynolds number, whereas for a hydraulically rough pipe, the resistance to flow is governed by the relative roughness. Two pipes are said to have the same hydraulic roughness, when they have equal values of
friction co-efficient for flows at equal Reynold number.
Water hammer in a pipeline results from the
rapid pressure change due to a rapid change in the rate of flow.
Molten soap mass is transported by a __________ pump.
centrifugal
Which of the following denotes the effect of compressibility in fluid flow ?
Mach number
Nominal size of the discharge pipe of a pump is usually __________ the nominal size of the inlet pipe.
smaller than
The terminal velocity of a small sphere settling in a viscous fluid varies as the
inverse of the fluid viscosity.
If the discharge of a centrifugal pump is throttled, then its suction lift
increases
Foot valves provided in pumps are __________ valves.
directional control
At high Reynolds number
inertial forces control and viscous forces are unimportant.
Power loss in an orificemeter is __________ that in a venturimeter.
more than
The terminal velocity of a particle moving through a fluid varies as dpn. What is the value of n’ for Newton’s law regime ?
0.5
What is the normal range of exit cone angle of a venturimeter ?
7 to 15
A particle A of diameter 10 microns settles in an oil of specific gravity 0.9 and viscosity 10 poise under Stoke’s law. A particle B with diameter 20 microns settling in the same oil will have a settling velocity
one fourth as that of A.
The pitot static tube does not measure the __________ pressure.
all (a), (b) and (c)
The fluid in which the shearing stress within it is proportional to the velocity gradient across the sheared section, is called a __________ fluid.
Newtonion
In fluid flow, cavitation is caused, if the
flow pressure approaches its vapor pressure at the prevailing temperature.
The ratio of the depth of flow to the hydraulic radius for the most economical trapezoidal section, in open channel flow is
2
The drag co-efficient for a bacterium moving in water at 1 mm/s, will be of the following order of magnitude (assume size of the bacterium to be 1 micron and kinematic viscosity of water to be 10-6m2/s).
0.44
The maximum delivery pressure of compressors can be up to __________ atmospheres.
1000
Which of the following is not a dimension-less parameter ?
None of these
Co-efficient of velocity is __________ the coefficient of discharge.
more than
All pipes of a particular nominal size have the same
outside diameter
For the transfer of solution of thick slurry, the pump used is a __________ pump.
diaphragm
Which of the following is not concerned with the fluid-particle interaction ?
Weber number
Maximum theoretical suction lift for water at 15°C by a centrifugal pump is 34 ft. The same for water at 90°C will be __________ ft.
8
Pick out the wrong statement.
both (b) and (c)
Pressure drag does not depend upon the
all (a), (b) and (c)
__________ pumps are axial flow pumps.
Propeller
Brownian movement is prominent in the particle size range of __________ microns in case of settling of a particle in a fluid.
2 to 3
For a particle settling in water at its terminal settling velocity, which of the following is true ?
Weight = buoyancy + drag
Pick out the correct statement.
A forced vortex occurs when fluid rotates as a solid about an axis.
Shear stress in a fluid flowing in a round pipe
is zero at the center and varies linearly with the radius.
The resistance wire used in a hot wire anemometer for conducting electrical current is made of
tungsten
Two dimensional stream function
is constant along a stream line.
What causes cavitation in centrifugal pump ?
Low suction pressure
Draining of shallow pits or sump is done by a sump pump, which is a __________ pump.
single stage vertical
A hydraulic ram acts as a/an __________ pump.
impulse
The line of action of the buoyant force passes through the centre of gravity of the
displaced volume of the fluid.
The friction factor for turbulent flow in a hydraulically smooth pipe
depends only on Reynolds number
The pressure at a point in a fluid is not the same in all directions, when the fluid is viscous and
moving
What causes convective acceleration in fluid flow ?
Non-uniformity of flow
The Stoke’s stream function applies to the
cases of axial symmetry.
Slugging in a fluidized bed can be avoided by using
shallow beds of solids and proper choice of particle size.
The ratio of width to depth for the most economical rectangular section in open channel flow is
2
The simple pitot tube measures the __________ pressure.
total
Capacity of a hydraulic accumulator is defined in terms of maximum
amount of energy stored.
With diminishing cross-sectional area in case of subsonic flow in a converging nozzle, the
both (a) & (b)
Manometers measure the __________ pressure.
difference in
Which of the following fluid forces are not considered in the Navier-Stoke’s equation?
Turbulent forces
Which of the following may be termed as a variable orifice flowmeter ?
Rotameter
In turbulent flow, a rough pipe has the same friction factor as a smooth pipe
when the roughness projections are much smaller than the thickness of the laminar film.
Air vessel provided in a reciprocating pump
none of these.
Bernoulli’s equation is dependent on the
none of these.
The capacity of an accumulator is the maximum
energy which it can store.
With increase in the temperature, viscosity of a liquid
decreases
The pump impeller and the turbine runner in a hydraulic torque converter
have different diameters.
Reciprocating pumps compared to centrifugal pumps
are not subject to air binding.
The fluid property which matters for falling rain drops to acquire spherical shape is its
surface tension
The simple pitot tube does not measure the
all a, b ,c
Boundary layer separation occurs when the
cross-section of the channel is reduced.
The head loss in turbulent flow in a pipe varies
approximately as the square of the velocity.
The ratio of the hydraulic radius to the diameter of the channel, for maximum mean velocity of flow in a circular channel, in open channel flow is
0.3
A centrifugal pump loses prime after starting. The reason of this trouble may be
all (a), (b), and (c)
Venturimeter and orificemeter measures the __________ of the fluid.
average velocity
Surge tanks are provided in high pressure water pipelines to
reduce the water hammer.
Working principle of manometer comprises of balancing a column of liquid against the pressure to be measured. Inclined tube manometer is especially used for the measurement of __________ pressure.
small differential
Isotropic turbulence occurs
where there is no velocity gradient.
The co-efficient of drag and lift for an incompressible fluid depends on the
Reynolds number
Euler’s equation of motion states, that at every point, the
force per unit mass equals acceleration.
The Navier-Stokes equation deals with the law of conservation of
momentum
Hydraulic intensifier is used for increasing the
intensity of pressure of the liquid.
Hydrometer measures the specific gravity of liquids based on the principles of buoyancy. Pycnometer is used to measure the specific gravity of
all ‘a’, ‘b’ & ‘c’
Euler’s equation of motion is a statement expressing
conservation of mass.
During ageing of fluid carrying pipes, the
absolute roughness increases linearly with time.
Pick out the wrong statement.
An ideal fluid is the one, which has negligible surface tension and obeys the Newton’s law of viscosity.
Mass velocity is independent of temperature & pressure, when the flow is
steady and the cross-section is unchanged.
Very small pressure difference (< 5 mm water coloumn) can be most conveniently measured by a/an __________ manometer.
inclined tube water.
For a given Reynold number as d/D for an orifice increases, Cd will (where, d & D are orifice & pipe diameters respectively).
increase
A differential pressure cell is used for
remote recording of pressure difference.
In case of a centrifugal pump, the ratio of total delivered pressure to pressure developed with the impeller is called the __________ efficiency.
manometric
If more than two branches of pipes are to be connected at the same point, then use a/an
tee
Acceleration head in a reciprocating pump
does not change the work requirement of the pump.
The ratio of inertial forces to elastic forces is called the __________ number.
Mach
Fluid flow at increasing rate through a diverging pipe is an example of __________ flow.
non-steady non-uniform
The temperature in isentropic flow
depends on Mach number only.
Check in a centrifugal pump is
all (a), (b) and (c).
Drag force acting on a body does not depend upon the
density of the body.
Centrifugal pump is normally classified on the basis of the
type of casing.
Where does the maximum stress occur in case of laminar flow of incompressible fluid in a closed conduit of diameter ‘d’?
At the wall
Applying a pressure drop across a capillary results in a volumetric flow rate ‘Q’ under laminar flow conditions. The flow rate for the same pressure drop, in a capillary of the same length but half the radius is
Q/16
In an incompressible fluid, the density is
not affected with moderate change in temperature & pressure.
Check valves are used
for unidirectional flow.
Velocity distribution for flow between two fixed parallel plates
varies parabolically across the section.
Priming is needed in a __________ pump.
centrifugal
An ideal nozzle design aims at
both (a) & (b)
Which of the fluid forces are not considered in the Reynold’s equation of flow ?
Compressibility forces
For ideally incompressible fluid, the Mach number will be
1
Theoretical head developed by a centrifugal pump does not depend upon the __________ the impeller.
none of these
Higher specific speed (200-500) of a centrifugal pump indicates that the pump is of __________ flow type
axial
A mono pump is a __________ pump
positive acting rotary
An ideal fluid is
both (a) & (b)
Boundary layer separation is caused by the
adverse pressure gradient.
With increase in temperature, the vapor pressure of liquids
increases
The ratio of wall drag to total drag in the Stoke’s law range is
2/3
A mercury (specific gravity = 13.6) manometer connected across an orificemeter fitted in a pipe shows a manometer reading of 2 cms. If the manometer liquid is changed to carbon tetrachloride (specific gravity = 1.6), then for the same flow rate of water the new manometer reading will be __________ cms.
17
Rotary vacuum pumps can reduce the absolute pressure to as low as __________ mm Hg.
0.01
The most suitable flow measuring device for the fluid flow measurement in a very large diameter pipeline is a
pitot tube
A pitched-blade turbine draws __________ a straight blade turbine.
less power than
A centrifugal pump is called a turbine pump, if it is having a
vaned diffusion casing.
Remote control valve is a __________ valve.
butterfly
Centre of pressure in an immersed body is __________ the centre of gravity.
below
Which of the following quantities are computed by using the hydraulic radius for non-circular ducts ?
Reynold number, relative roughness and head loss.
The centre of pressure is
a point on the line of action of the resultant force.
Stoke’s law is valid, when the particle Reynolds number is
< 1
Which of the following is not a dimension-less parameter ?
Kinematic viscosity
The blades of a centrifugal impeller are said to be curved forward, if the __________ of the motion of impeller blades.
outlet tip of a blade is towards the direction
In which of the following cases, it is possible for flow to occur from low pressure to high pressure ?
Flow through a converging section.
For the same terminal conditions and fitting size, the least friction loss is incurred in a/an
union
The uniformity of a gas fluidised bed depends upon the __________ of the solid particles.
both (a) and (b)
The continuity equation of fluid mechanics utilizes the principle of conservation of
mass
The co-efficient of discharge of an orificemeter is a function of
both (a) and (b).
A floating/submerged body is always stable, if its centre of gravity
lies below its centre of buoyancy.
Critical velocity in a pipe flow
increases as pipe diameter increases.
A centrifugal pump designed to pump water is employed to pump a more viscous oil. In the later case, the pump
all (a), (b) and (c).
The ratio of maximum to average velocity in case of streamline flow between parallel plates is
1.5
In an incompressible flow of fluid, the fluid
density does not change with pressure & temperature.
A weir is used to measure the large water discharge rate from a river or from an open channel. A weir is not of __________ shape.
circular
Pressure co-efficient is the ratio of pressure forces to __________ forces.
inertial
Which of the following conditions must be satisfied for lift force to be developed ?
Circulation around the body is essentially required.
The Reynolds number for an ideal fluid flow is
∞
Curve III in the above diagram represents a/an
pseudo plastic fluid
What is the ratio of total kinetic energy of fluid passing per second to the value obtained on the basis of average velocity (for laminar flow through a circular pipe)?
2
The line traced by a single fluid particle as it moves over a period of time is called __________ line.
path
The pressure head on sudden contraction in a horizontal pipe is converted into the __________ head.
velocity
The unit of velocity head is
ft-lbf/lb
A stream tube is that, which has __________ cross-section entirely bounded by stream lines.
any convenient
Which of the following properties of a fluid is responsible for offering resistance to shear ?
Viscosity.
Erosion and pits formation on the impeller of a centrifugal pump may be due to
cavitation.
The velocity profile exhibited by laminar flow of Newtonian fluids is such that the velocity distribution w.r.t. radius of the circular pipe is a/an __________ with the apex at the centre line of the pipe.
parabola
A rotameter works on the principle of __________ pressure drop.
constant
The effect of solid boundary on the fluid flow is confined to the boundary layer, except for fluids
both (a) & (b)
The excess of the sum of pressure & velocity heads over the vapor pressure of the liquid at the suction is called the
net positive suction head (NPSH).
The head developed by a centrifugal pump is largely determined by the
Angle of the vanes and the speed of the tip of the impeller.
Up to what value of ‘Mach number’, a fluid may be considered as incompressible ?
0.3
Pick out the wrong statement:
Friction losses in pipe fittings are generally expressed in terms of velocity heads.
Flow rate of high velocity flue gas discharged through a stack to the atmosphere can be most conveniently measured by a
pitot tube
Potential flow is the flow of
incompressible fluids with no shear.
The value of critical Reynolds number for pipe flow is
1300
Mach number is important in a fluid flow problem, when the inertia and __________ forces predominate.
elastic
In case of coutte flow, the fluid flow is between two large flat parallel plates with
top plate moving and the bottom plate fixed.
Piezometric head is the sum of the __________ heads.
elevation & pressure
Propellers are
axial flow mixers.
Which of the following is not an advantage of fluidization from transfer operation point of view
Lower fluid pumping power requirement.
The component of acceleration resulting due to unsteady nature of flow is called __________ acceleration
local
In a stabilized soap bubble, pressure inside it compared to external pressure is
more
Multistage compressors are used in industry, because they
resemble closely to isothermal compression.
Power required for mixing Newtonian fluids is a function of the
none of these.
The hydrodynamic and thermal boundary layers will merge, when
Prandtl number is one.
Differential manometer measures the
pressure difference between two points.
With increase in the ratio of orifice diameter to pipe diameter in case of an orificemeter, the overall pressure loss
remains constant
The vent valve provided in a liquid handling centrifugal pump is
all (a), and (b) and (c).
The discharge through a semi-circular weir varies as (where, H = Head of liquid.)
H^2
The Mach number for hypersonic flow of compressible fluid is
> 4
Mass velocity in case of steady flow and through a constant cross-section conduit is independent of the
both (a) & (b)
The valve used for very remote and accurate control of fluid is a __________ valve.
needle
A mixed flow centrifugal pump
employs such an impeller, through which the flow is a combination of radial & axial flow.
In centrifugal pump operation, the cavitation can be eliminated by maintaining suction pressure __________ the vapor pressure of the liquid at the suction temperature.
higher than
One dimensional flow implies
a flow which does not account for changes in transverse direction.
A rectangular surface 3’ x 4’, has the lower 3 edge horizontal and 6’ below a free oil surface (sp. gr. 0.8). The surface inclination is 300 with the horizontal. The force on one side of the surface is(where, y = specific weight of water)
48y
Centrifugal compressors compared to reciprocating compressors
all (a), (b) and (c).
Slugging occurs in a fluidized bed, if the bed is
both (a) & (b)
The terminal velocity of a solid spherical particle falling through a stationary fluid mass in the Stoke’s law range is proportional to the
all (a), (b) and (c).
Nominal size of a pipe is an indication of its __________ diameter.
approximate
Fluidized beds are formed, when the
gravity force is less than the fluid friction
A fluid is pumped at the rate of 10 lb/sec to a height of 55 ft. The horse power required is __________ hp.
1
Pick out the wrong statement:
The point at which the resultant pressure on an immersed surface acts, is known as the center of gravity.
Medium viscosity lubricating oil can be most ideally pumped by a __________ pump.
vane
Pump used for the transportation of molten sodium in a fast breader reactor is a/an __________ pump.
electromagnetic
Small pressure differences in liquids is measured using a/an
inclined tube manometer.
With increase in pump speed, its NPSH requirement
increases
In the Newton’s law range, the terminal velocity of a solid spherical particle falling through a stationary fluid mass is __________ the fluid viscosity.
inversely proportional to
Gear pump
is a positive displacement pump.
Most of the centrifugal pumps used in chemical plants are usually __________ driven.
electric motor
Check valve provided in the discharge line of a centrifugal pump serves the purpose of controlling the
back flow of fluid in the event of stoppage of pump.
Venturimeters, orificemeters and nozzles are used to measure the fluid discharge from a pipeline. The average fluid velocity in a pipeline can be measured by a/an
hot wire anemometer
The time taken for gravity flow of a fixed volume of liquid (as in Redwood viscometer) is directly proportional to its
ratio of absolute viscosity to density.
The exit cone angle in case of a standard venturimeter is __________ the entrance cone angle.
smaller than
Sewage sludge is __________ type of non-Newtonian fluid
Bingham plastic
Ratio of pressure and inertia force gives __________ number.
Euler
Permanent loss in a venturimeter is about __________ percent of the pressure drop in theupstream cone.
10
Volume of liquid displaced by a floating body is equivalent to its
own weight
What is the pipe called which lifts water from a reservoir to a greater height than the initial level in the supply reservoir ?
Siphon
Steady uniform flow is represented by flow through a/an
long pipe at constant rate.
The __________ is measured by a piezometric opening.
total pressure
Pick out the correct statement pertaining to the flow through a converging-diverging tube.
No shock wave develops in the tube when the Mach number at exit is greater than unity.
Cavitation can be prevented by
maintaining the suction head sufficiently greater than the vapor pressure.
Assuming flow to be laminar, if the diameter of the pipe is halved, then the pressure drop will
increase
Steady flow occurs, when the
conditions do not change with time at any point
With increase in the ratio of orifice diameter to pipe diameter, the fraction of the orifice pressure differential that is permanently lost
decreases
Which of the following two quantities when same, makes one pipe system equivalent to another pipe system ?
Head & discharge
The kinetic energy correction factor for velocity distribution of laminar flow is
1.66
Priming of a centrifugal pump is done to
avoid chances of separation inside the impeller.
For pipes that must be broken at intervals for maintenance, the connector used should be a/an
union
A fluid is the one, which
cannot remain at rest under the action of shear force.
One horsepower is equal to
550 lbf.ft/second
Fluid flow in a/an __________ is an example of pressure flow.
pipe
Absolute viscosity of a fluid is a function of the __________ of the fluid.
both(b)&(c)
Select the wrong statement pertaining to flow of an incompressible fluid through a venturimeter.
Venturimeter occupies less space than an orificemeter.
Reynolds number for water flow through a tube of I.D. 5 cm is 1500. If a liquid of 5 centipoise viscosity and 0.8 specific gravity flows in the same pipe at the same velocity, then the pressure drop will
increase
Cocks are used to control
any liquid
Pick out the correct statement.
Mach number is given by the ratio of the speed of the fluid to that of sound in the fluid under conditions of flow.
The bulk modulus of elasticity of a liquid
increases with pressure.
The friction factor is
none of these.
Rubber latex is an example of a __________ .fluid.
pseudoplastic
The phenomenon occuring during pumping of a liquid solution containing dissolved gases, which may come out of the solution giving rise to gas pockets, is termed as
cavitation
Working of a __________ pump characterizes mixed flow.
turbine
The rate of change of moment of momentum represents the __________ by the fluid.
torque applied
Water flow rate in a pipe of 3.5 metres diameter can be most economically and conveniently measured by a/an
pitot tube
In case of venturimeters, friction losses are about __________ percent of maximum velocity head.
2
The specific speed of a pump is defined as the speed of a unit of such a size, that it
delivers unit discharge at unit head.
For a reciprocating pump, the indicator diagram is the graph between the
volume swept by piston for one complete revolution and the pressure in the cylinder.
The most important factor, which determines the maximum height to which water can be lifted by a pump at standard temperature is the
barometric pressure
High specific speed of a pump implies that, it is a/an __________ pump.
axial flow
Glass pipes can be joined by
bell and spigot joint
The range of a particular rotameter can be increased by
use of floats of different densities.
Weber number is the ratio of inertial force to __________ force
surface tension
The curve of metacenter for a floating body __________ the curve of buoyancy.
is the evolute of
At what value of crank angle (roughly), no flow of water from or into the air vessel takes place in case of a double acting reciprocating pump ?
40° and 140°
Which of the following is dimensionless ?
Fanning friction factor
Prandtl number is a measure of the
heat conduction to viscosity of a fluid
A compressor that takes suction at a pressure below atmospheric and discharge against atmospheric pressure is called a __________ pump.
vacuum
Unsteady non-uniform flow is represented by flow through a/an
expanding tube at increasing rate.
In hindered settling, the particles are
near each other,
Out of the following flow measuring devices, which one incurs the maximum installation cost as well as pressure loss ?
Venturimeter
Which of the following has the maximum compression ratio ?
Vacuum pump
An ideal plastic substance indicates no deformation, when stressed upto yield stress, but behaves like a Newtonion fluid beyond yield stress. Which of the following is an ideal plastic ?
Sewage sludge
The capacity of a centrifugal pump Can be increased by increasing the
all (a), (b) and (c).
Scale up of agitator design requires
all geometrical, dynamic and kinematic similarity.
Which law is followed by the velocity distribution in the turbulent boundary layer?
Logarithmic law
Forces acting on a particle settling in fluid are __________ forces.
gravitational or centrifugal buoyant drag
For a fluid rotating at constant angular velocity about vertical axis as a rigid body, the pressure intensity varies as the
square of the radial distance.
Navier-Stokes equation is useful in the analysis of __________ fluid flow problems.
viscous
Specific speed of a centrifugal pump depends upon the __________ head.
none of these
Two fluids are flowing through two similar pipes of the same diameter. The Reynold’s number is same. For the same flow rate if the viscosity of a fluid is reduced to half the value of the first fluid, the pressure drop will
decrease
When the head pumped against is less than the head of the fluid used for pumping, the usual device is a/an
airlift
A pump operating under specific conditions delivers insufficient quantity of liquid. This may be set right by
both (b) and (c).
Two liquids manometer is used for measuring small pressure differences in
gases
Minimum fluidization velocity for a specific system depends upon the
all (a), (b) and (c).
A piezometer provided in the pipe measures
static pressure
For the production of very high vacuum, a __________ pump is normally used.
diffusion
Potential flow is characterized by the
irrotational and frictionless flow.
In parallel pipe problems, the
head loss is the same through each pipe.
Fluid flow through a packed bed is represented by the __________ equation
Ergun’s
For pumping slurry, one can use a __________ pump.
diaphargm
Bernoulli’s equation describes the
mechanical energy balance in potential flow.
When larger particles e.g., grains are subjected to fluidization, the corresponding bed produced is termed as the __________ bed.
spouted
With increase in molecular weight of the gas, the head developed by a centrifugal compressor will
Which law/principle of solid mechanics is similar/equivalent to Newton’s law of viscosity in fluid mechanics ?
Hooke’s law.
The losses in open channel flow generally vary as the
first power of the roughness.
Rise of liquid in a capillary tube is due to
both (a) & (b)
