What
is the slip in reciprocating pump?
Slip is the difference between the
theoretical discharge and actual discharge of the pump.
Slip= Qth-Qact.
What
is meant by Priming?
The
delivery valve is closed and the suction pipe, casing and portion of the
delivery pipe up to delivery valve are completely filled with the liquid so
that no air pocket is left. This is called as priming.
What is the main parts of reciprocating pump?
ü A cylinder
with a piston, Piston rod, connecting rod and a crank.
ü Suction
pipe, Delivery pipe.
ü Suction
valve and
ü Delivery
valve.
How will you classify
the reciprocating pump?
The reciprocating pump may be classified as,
1. According to the water in contact with one
side or both sides of the piston.
2. According to the number of cylinders
provided.
Classification according to the contact of
water is
According to the number of cylinders provided
they are classified as,
1. Single Cylinder pump.
2. Double cylinder pump.
3.
Triple cylinder pump.
Define
Mechanical efficiency.
It
is defined as the ratio of the power actually delivered by the impeller to the
power supplied to the shaft.
Define
overall efficiency.
It
is the ratio of power output of the pump to the power input to the pump.
Define
speed ratio, flow ratio.
Speed ratio: It is the ratio of peripheral speed at outlet
to the theoretical velocity of jet corresponding to manometric head.
Flow ratio: It is the ratio of the velocity of flow at
exit to the theoretical velocity of jet corresponding to manometric head.
Mention
main components of Reciprocating pump.
ü Piton
or Plunger
ü Suction
and delivery pipe
ü Crank
and Connecting rod
Define
Slip of reciprocating pump. When the negative slip does occur?
The
difference between the theoretical discharge and actual discharge is called
slip of the pump.
But in sometimes actual discharge may be higher then
theoretical discharge, in such a case coefficient of discharge is greater then
unity and the slip will be negative called as negative slip.
What are the
assumptions made in deriving Bernouillie’s equation?
1.The
fluid is ideal
2.The
flow is steady.
3.The
flow is incompressible.
4.The
flow is irrotational.
What is
bernouillie’s equation for real fluid?
(p1/pg)+(v12/2g)+z1=(p2/pg)+(v22/2g)+z2+hl
where
hl is the loss of energy (p/pg)-Pressure energy. (v2/2g)=Kinetic energy.
z-Datum
energy.
State the
application of Bernouillie’s equation ?
It
has the application on the following measuring devices.
1.Orifice
meter.
2.Venturimeter.
3.Pitot
tube.
State the methods of dimensional analysis.
1.
Rayleigh’s method
2.
Buckingham’s Π theorem
State Buckingham’s Π theorem
It
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 Π-terms.
State the limitations of dimensional analysis.
1.
Dimensional analysis does not give any due regarding the selection of
variables.
2.The
complete information is not provided by dimensional analysis.
3.The
values of coefficient and the nature of function can be obtained only by
experiments or from mathematical analysis.
Define Similitude
Similitude is defined
as the complete similarity between
the model and prototype.
State Froude’s model law
Only
Gravitational force is more predominant force. The law states ‘The Froude’s
number is same for both model and prototype’.
Define hydraulic machines.
Hydraulic machines which convert the energy of
flowing water into mechanical energy.
Give example for a low head,
medium head and high head turbine.
Low head turbine – Kaplan turbine
Medium head turbine – Modern Francis turbine
High head turbine – Pelton wheel
What is impulse turbine? Give
example.
In
impulse turbine all the energy converted into kinetic energy. From these the turbine
will develop high kinetic energy power. This turbine is called impulse
turbine. Example: Pelton turbine
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.
What is axial flow turbine?
In axial flow turbine water flows parallel to the
axis of the turbine shaft. Example: Kaplan turbine
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.
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.
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.
Define hydraulic efficiency.
It
is defined as the ratio of power developed by the runner to the power supplied
by the water jet.
Define mechanical efficiency.
It is defined as the ratio of power available at
the turbine shaft to the power developed by the turbine runner.
Define volumetric efficiency.
It
is defied as the volume of water actually striking the buckets to the total
water supplied by the jet.
Define over all efficiency.
It
is defined as the ratio of power available at the turbine shaft to the power
available from the water jet.
What
is Multistage centrifugal pumps?
A centrifugal pump containing two or more impellers
is called a multistage centrifugal pump. The impellers may be mounted on the
same shaft or on different shafts.
For higher pressures at the outlet impellers can be
connected in series. For higher flow output impellers can be connected in
parallel.
A common application of the multistage centrifugal
pump is the boiler feedwater pump. For example, a 350 MW unit would require two
feedpumps in parallel. Each feedpump is a multistage centrifugal pump producing
150 l/s at 21 MPa.
All energy transferred to the fluid is derived from
the mechanical energy driving the impeller. This can be measured at isentropic
compression, resulting in a slight temperature increase (in addition to the
pressure increase).
Define
Compressibility.
It is the property by virtue of which fluids
undergoes a change in volume under the action of external pressure.
What
are the names of the principle parts of a centrifugal pump?
The principle parts of a centrifugal pump are the
pump casing, also called a volute, and the impeller. The other parts are the
pump shaft, bearing(s), shaft seal, the wear rings, and the inlet and
outlet.The impeller is mounted on the pump shaft. The pump shaft is coupled to an
external power source like a motor. The motor turns the shaft, the shaft makes
the impeller turn and the fluid being pumped is put in motion.The volute causes
a change in pressure in the fluid.The shaft seal stops the fluid from leaking
out of the casing (volute).The wear rings separate the high and low pressure
areas inside the casing.The bearing(s) make the shaft turn easier.The inlet and
outlet parts of the casing connect to the fluid piping system.
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.
What
types of error mostly encountered with centrifugal pump?
The fact of
the matter is that there are three types of problems mostly encountered
with
centrifugal pumps:
-design
errors
-poor
operation
-poor
maintenance practices
What is
cohesion and adhesion in fluids?
Cohesion is due to the force of attraction between
the molecules of the same liquid.
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.
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
Why
centrifugal pump is not called a positive displacement type of pump?
A positive displacement pump causes a fluid to move
by trapping a fixed amount of it then forcing (displacing) that trapped volume
into the discharge pipe. Centrifugal pumps impart pressure to the fluid, to
cause a pressure differential and cause flow, but even if the outlet is sealed,
the pump can continue to run because it hasn't trapped the fluid. When no flow
is occuring, a centrifugal pump acts like a propeller spinning in the water. If
flow is stopped on a line that a positive displacement pump is supplying flow
to, the pump is forced to stop since the trapped fluid prevents it from moving
any more fluid.
What is momentum equation?
It 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.
What is the effect of temperature on
Viscosity?
When temperature increases the
distance between molecules increases and the cohesive force decreases. So,
viscosity of liquids decrease when temperature increases. In the case of gases,
the contribution to viscosity is more due to momentum transfer. As temperature
increases, more molecules cross over with higher momentum differences. Hence,
in the case of gases, viscosity increases with temperature.
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.
What
causes radial thrust in a centrifugal pump?
When a centrifugal pump operates at its best
efficiency point (BEP), the flow angles match with the impeller vane angles. At
the BEP, the flow velocity in the volute is uniform around the volute (i.e.,
there is not acceleration of the fluid in the volute). Therefore, the pressure
around the volute is uniform. The uniform pressure around the circumference
results in a net zero radial force on the impeller (or the shaft). Note this is
theoretical. In practice even at BEP, there is a small radial load because the
pressure is not uniform.
If the pump is operated away from the BEP, the flow
velocities in the volute are non-uniform which results in a non-uniform
pressure field and a net radial load (can be obtained by integrating the
pressure around the circumference of the volute or the impeller).
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
Comparison
between centrifugal pump and gear pump?
Basic difference is generally centrifugal pumps are
non positive displacement type where as gear pumps are positive displacement
type. This means, gear pump discharges a fixed volume of fluid for every
rotation of shaft.
What are the
properties of real fluid?
Real fluids have following properties
i) It is
compressible
ii) They are viscous in nature
iii) Shear force exists always in such fluids.
What
are different types of vanes used in centrifugal pump?
there are three major types vanes are used for a
centrifugal pumps those are
1.forward curved vanes
2.backward curved vanes
3.flat vanes
Define
density and specific weight.
Density is defined as mass per unit volume (kg/m3)
Specific weight is defined as weight possessed per
unit volume (N/m3)
What
is the difference between a pd pump and centrifugal pump?
PD or positive displacement pump has a piston which
directly contacts the fluid. In a centrifugal pump the impeller creates a partial
vacuum inside the casing due to which suction takes place. Discharge takes
place by the rotation of the impeller.
Define
Specific volume and Specific Gravity.
Specific volume is defined as volume of fluid
occupied by unit mass (m3/kg)
Specific gravity is defined as the ratio of
specific weight of fluid to the specific weight of standard fluid.
Why
the centrifugal pump is called high discharge pump?
for a simple reason because it has high discharge
than any other available pump.
the centrifugal pump uses the centrifugal force to
push out the fluid
centrifugal force = (mass *velocity2)/radius.
hence centrifugal force is directly proportional to
the square of the velocity, in this case being the velocity of the fluid.
power provided to pump proportional to the force
exerted by the impeller. Hence higher the power results in higher centrifugal
force implying square of the velocity of the fluid. higher the velocity of the
fluid higher the discharge of the pump.
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.
What
are the spare parts of centrifugal pump?
It depends on the specific pump.For most: the
impeller, the wear ring & mechanical seal.In a pump with a packed stuffing
box, the packing.In some pumps, the shaft coupling.
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.
Define
kinematic viscosity.
It is defined as the ratio of dynamic viscosity to
mass density. (m²/sec)
Define
Relative or Specific viscosity.
It is the ratio of dynamic viscosity of fluid to
dynamic viscosity of water at
20°C.
What is the expression for head loss due to
friction in Darcy formula?
hf = 4fLV2 / 2gD
Where
f = Coefficient of friction in pipe L
= Length of the pipe
D = Diameter of pipe V
= velocity of the fluid
What do you
understand by the terms a) major energy losses, b) minor energy losses
Major energy losses: -
This loss due to friction
and it is calculated by Darcy weis bach 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 .
How Centrifugal force generate by the centrifugal pump?
The process liquid enters the suction nozzle
and then into eye (center) of a revolving device known as an impeller. When the
impeller rotates, it spins the liquid sitting in the cavities between the vanes
outward and provides centrifugal acceleration.
As liquid leaves the eye of the impeller a
low-pressure area is created causing more liquid to flow toward the inlet.
Because the impeller blades are curved, the fluid is pushed in a tangential and
radial direction by the centrifugal force. This force acting inside the pump is
the same one that keeps water inside a bucket that is rotating at the end of a
string.
Give an expression for loss of
head due to sudden enlargement of the pipe:
he = (V1-V2)2
/2g
Where
he = Loss of head due to
sudden enlargement of pipe .
V1 = Velocity of flow at
section 1-1
V2 = Velocity of flow at
section 2-2
Give an
expression for loss of head due to sudden contraction:
hc =0.5 V2/2g
here,
c = Loss of head due to sudden contraction.
V = Velocity
at outlet of pipe.
Give an
expression for loss of head at the entrance of the pipe:
hi =0.5V2/2g
Where,
hi = Loss of head at
entrance of pipe.
V = Velocity of liquid at inlet and outlet
of the pipe.
Define the
terms a) Hydraulic gradient line [HGL], b) Total Energy line [TEL]
a) Hydraulic gradient line:
Hydraulic gradient line
is 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.
b) Total energy line:
Total energy line is 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.
What is
sypon ? Where it is used:
Sypon 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 sypon : -
1. To carry water from
one reservoir to another reservoir separated by a hill ridge.
2. To empty a channel not
provided with any outlet sluice.
How kinetic energy is converted in to pressure
energy by centrifugal pump?
The energy created by the centrifugal
force is kinetic energy. The amount of energy given to the liquid is
proportional to the velocity at the edge or vane tip of the impeller. The
faster the impeller revolves or the bigger the impeller is, then the higher
will be the velocity of the liquid at the vane tip and the greater the energy
imparted to the liquid.
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.
What is
Dupuit’s equation?
L1/d15+L2/d25 +L3/d35 = L / d5
Where
L1, d1 = Length and
diameter of the pipe 1
L2, d2 = Length and
diameter of the pipe 2
L3, d3 = Length and
diameter of the pipe 3
What are
the types of fluid flow?
Steady & unsteady fluid flow
Uniform & Non-uniform flow
One dimensional, two-dimensional &
three-dimensional flows
Rotational & Irrotational flow
Name the different forces present in fluid flow
Inertia force
Viscous force
Surface tension force
Gravity force
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.
Give the Euler’s equation of motion?
(dp/p)+gdz+vdv=0