Fluid Mechanics Flashcards
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.
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
Most commonly used joint in the underground pipe lines is the
sleevejoint
Schedule number of a pipe, which is a measure of its wall thickness, is given by
1000 P’/S
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.
The velocity profile for turbulent flow through a closed conduit is
logarithmic
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
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
The pitot static tube does not measure the __________ pressure.
all (a), (b) and (c)
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 upto __________ atmospheres.
1000
Dimension of surface tension is(where, F = force, L = length)
FL^-1
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
__________ 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
A Bingham fluid of viscosity μ = 10 Pa.s and yield stress, τ0 = 10 KPa, is shared between flat parallel plates separated by a distance of 10-3 m. The top plate is moving with a velocity of 1 m/s. The shear stress on the plate is
20 kPa
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 centre and varies linearly with the radius.
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 ratio of average fluid velocity to the maximum velocity in case of laminar flow of a Newtonion fluid in a circular pipe is
0.5
The line of action of the buoyant force passes through the centre of gravity of the
displaced volume of the fluid.
Pick out the wrong statement.
With increase in the For ideally incompressible fluid, the Mach number will be
>0.6, the drag co-efficient decreases in case of compressible fluids.
What causes convective acceleration in fluid flow ?
Non-uniformity of flow
The Stoke’s stream function applies to the
cases of axial symmetry.
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
velocity increases and
pressure decreases
Boundary layer separation is characterised by one of the conditions given below, where ‘Re’ is the Reynolds number for the flow. Select the appropriate conditions.
Re»_space;1, decelerating flow
Manometers measure the __________ pressure.
difference in
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.
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 simple pitot tube does not measure the
static pressure.
dynamic pressure.
velocity at the stagnation point.
Boundary layer separation occurs when the
cross-section of the channel is reduced.
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
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.
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.
Very small pressure difference (< 5 mm water coloumn) can be most conveniently measured by a/an __________ manometer.
inclined tube water.
For pipe flows, head is proportional to __________ at constant capacity(where, D = pipe diameter).
1/D^5
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.
If more than two branches of pipes are to be connected at the same point, then use a/an
tee
In case of a centrifugal pump, the ratio of total delivered pressure to pressure developed with the impeller is called the __________ efficiency.
manometric
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
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
In case of isentropic flow, the speed of sound in an ideal gas is proportional to (where, T = absolute temperature )
sqrt T
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
Check valves are used
for unidirectional flow.
Velocity distribution for flow between two fixed parallel plates
varies parabolically across the section.
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
A mono pump is a __________ pump.
positive acting rotary
Higher specific speed (200-500) of a centrifugal pump indicates that the pump is of __________ flow type.
axial
The variable required to be known in correlations used for estimating the horse power of a centrifugal gas compressor and hence its cost are
P. Inlet pressure Q. Compressor rpm
R. Delivery pressure S. Volumetric flow rate at inlet.
P, Q and R
Boundary layer separation is caused by the
adverse pressure gradient.
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
The ratio of wall drag to total drag in the Stoke’s law range is
2/3
A pitched-blade turbine draws __________ a straight blade turbine.
less power than
The most suitable flow measuring device for the fluid flow measurement in a very large diameter pipeline is a
pitot tube
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
The centre of pressure is
a point on the line of action of the resultant force.
In a fluidised bed reactor
temperature is more or less uniform.
The flow of a liquid through tapering pipe at a constant rate is an example of __________ flow.
steady non uniform
A centrifugal pump designed for handling water (μ = 1 cp) will deliver __________ when pumping a thicker oil (μ = 30 cp).
less head & capacity
If ‘x’ is the depth of flow in an open channel of large width, then the hydraulic radius is equal to
x
In fluid flow, the boundary layer separation can not occur
none of these
For a given fluid flow rate, which of the following incurs maximum head loss ?
Orifice meter
Which of the following assumptions enables the Euler’s equation of motion to be integrated ?
The fluid is incompressible.
A fluid whose apparent viscosity increases with shear rate is termed as the __________ fluid.
dilatant
Which of the following is the most common pump for pumping either raw sewage or sludge ?
Reciprocating pump
Transition length for a turbulent fluid entering into a pipe is around __________ times the pipe diameter.
50
Which of the following pipe bends will incur the largest head loss ?
U-bend
A centrifugal pump has the following specifications:
Power = 4 H.P.; Speed = 800 rpm
Head = 8 metres
Flow = 1000 litres/minutes.
If its speed is halved, the new discharge will be __________ litres/minute.
500
Lower BWG means __________ of the tube.
lower cross-section
For laminar flow of Newtonion fluid in a circular pipe, the velocity distribution is a function of the distance ‘d’ measured from the centre line of the pipe, and it follows a __________ relationship.
parabolic
N2Re/NFr is called the __________ number.
Galileo
As the velocity V and thus the Reynolds number of a flow past a sphere increases from very low value, the drag force for Re «_space;1
increases linearly with V.
Pascal’s law is valid, only when the fluid is
at rest
A double acting reciprocating pump compared to a single acting pump (of almost same size working under same pressure levels) would give almost double
discharge
Which of the following is used for very accurate measurement of flow of gas at low velocity ?
Hot wire annemometer
The rate of shear versus the shear stress curves are time dependent for __________ fluid.
thixotropic
rheopectic
A pressure of 10 m head of water is equivalent to __________ kN/m2.
98
A pressure head of 320 metres of water in meters of CCl4 (sp.gr = 1.6) will be
200
The ratio of the wall drag to the form drag in the Stoke’s law range (for motion of spherical particles in a stationary fluid) is
2
Choking in case of pipe flow means that a
specified mass flow rate can not be achieved.
Velocity of liquid hydrocarbon fuels in a pipeline can not be measured by magnetic flowmeters, because their __________ is very low/small.
electrical conductivity
The nominal size of a hose pipe is specified by its
I.D.
For flow of fluids through packed bed, the superficial velocity is
less than the average velocity through channels.
Cd is always __________ Cc.
greater than
Which of the following is an undesirable property of a manometric liquid ?
High vapour pressure.
Liquid delivery by centrifugal pump starts, only when the head developed by it is equal to the __________ head.
manometric
The maximum head that can be developed by a single impeller is __________ ft.
250-300
Foot valve provided in the pump is a __________ valve.
back pressure
What is the ratio of the velocity at the axis of the pipe to the mean velocity of flow in case of pipe flow under viscous condition ?
2
Which of the following options will facilitate the achievement of a very high head (say 30 metres) in case of a centrifugal pump?
Mounting of two or more impellers in series on a single shaft.
An equipotential line is __________ to the velocity vector at every point.
normal
Efficiency of power transmission (η) through a circular pipe is given by (ht - hf)/ht, which has a maximum value of __________ percent.
66.6
One dimensional fluid flow implies the
flow in which transverse components are zero.
Power requirement of fans having constant wheel diameter varies __________ fan speed.
as cube of
In the low Reynolds number region, the drag force on a sphere is proportional to
V
Each term in Bernaulli’s equation represents the __________ of the fluid.
energy per unit weight
If the head over the triangular notch is doubled, the discharge will increase by __________ times.
5.657
Friction factor for a hydraulically smooth pipe at NRe = 2100 is f1. If the pipe is further smoothened (i.e., roughness is reduced), the friction factor at the same value of NRe, will
increase
The discharge through a venturimeter depends upon
pressure drop only.
For a given Reynolds number, in a hydraulically smooth pipe, further smoothening __________ the friction factor.
brings about no further reduction of
The momentum correction factor for the velocity distribution of laminar flow is
none of these
For the same flow rate of a fluid, the pressure drop is the least for
venturimeter
In area meter (e.g., rotameter), with increase in the fluid flow rate, the
pressure drop is almost constant.
In case of end to end connection of two or more pipes in series, the __________ each pipe.
same rate of flow passes through
Which of the following equations applies to the fluid flow through a packed bed for very large Reynolds number ?
Blake-Pllummer equation
The flow of gas along a pipe in the direction of decreasing pressure causes decrease in its
specific volume
Centrifugal pump can’t be used to pump
thick molten soap at 80°C.
A stream line is
fixed in space in steady flow.
Quicksand is an example of a __________ fluid.
dilatent
Differential manometer measures the
pressure difference
Gradually varied flow in open channel is a/an __________ flow.
steady non-uniform
The line of action of the buoyant force acts through the
centroid of the displaced volume of fluid.
Cavitation in a centrifugal pump can be avoided by keeping the
inlet pressure high
The peripherial velocity at inlet of a centrifugal pump having inlet diameter of 25 cms and rotating at 950 rpm is __________ m/sec.
12.4
Select the correct practical example of steady non-uniform flow.
Steadily decreasing flow through a reducing section.
Which of the following must be followed by the flow of a fluid (real or ideal)?
(I) Newton’s law of viscosity.
(II) Newton’s second law of motion.
(III) The continuity equation.
(IV) Velocity of boundary layer must be zero relative to boundary.
(V) Fluid cannot penetrate a boundary.
II, III, V
Mach number is defined as the ratio of the local flow velocity to the sonic velocity in the fluid. For what value of Mach number, the gases are considered incompressible ?
< 0.3
The frictional resistance in laminar flow does not depend on the
area of surface in contact.
A venturimeter measures the
none of these
Gradually varying fluid flow is an example of __________ flow.
non-steady uniform
The discharge through a V-notch weir varies as
H5/2
Water flow rate in a pipe of 3.5 metres diameter can be most economically and conveniently measured by a/an
pitot tube
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.
In case of venturimeters, friction losses are about __________ percent of maximum velocity head.
2
Friction produced by the formation of wakes is called the __________ friction.
form
With a constant diameter impeller of a centrifugal pump
head varies as the square of speed.
At low Reynolds number
viscous forces control and inertial forces are unimportant.
In Newton’s law range, the terminal velocity of a solid spherical particle falling through a stationary fluid mass varies as the __________ of its diameter.
square root
Unsteady uniform flow is represented by flow through a/an
long pipe at decreasing rate.
While starting a centrifugal pump, its delivery valve should be kept
closed
In case of a rotameter, the density of the float material is __________ that of the liquid it replaces.
more than
Multistage centrifugal pumps are generally used for
high head.
For a specific centrifugal air blower operating at constant speed & capacity, the power requirement and pressure vary
directly as gas density.
It is possible to integrate an automatic flow controller to a
rotameter
For liquid flow through a packed bed, the superficial velocity as compared to average velocity through the channel in the bed is
less
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
Which of the following can be used for the direct measurement of volumetric flow rate of slurry ?
Rotameter
A Pitot tube indicates 5 cm of water (manometer) when it is being used for measuring velocity of air. The velocity of air in m/sec is
28.2
Purpose of relief valve in a reciprocating pump is to
protect the pump against developing excessive pressure.
Select the correct statement.
The discharge through a venturimeter depends upon Δp only and is independent of orientation of the meter.
Function of air vessel provided in a reciprocating pump is to
reduce discharge fluctuation.
Pressure drop in packed bed for turbulent flow is given by the __________ equation.
Blake-Plummer
In the complete turbulence zone (in rough pipes), the
friction factor is independent of the relative roughness.
Which of the following has the minimum compressibility ?
Water at room temperature
In case of centrifugal fan or blower, the gas capacity varies as
speed
Pick out the wrong statement.
Newton’s law of viscosity is not applicable to the turbulent flow of fluid with linear velocity distribution.
The velocity profile for a Bingham plastic fluid flowing (under laminar conditions) in a pipe is
parabolic near the wall and flat in the middle.
Pick out the wrong statement.
In a static mass of liquid, the pressure at a point is the same for all liquids.
A piezometer opening measures the __________ fluid pressure.
undisturbed
The pressure co-efficient is the ratio of pressure forces to __________ forces.
viscous
Drag force on the float of a rotameter is(where Q = flow rate of the )
constant
