1 CTC 450 ► Bernoulli’s Equation ► EGL/HGL. Bernoulli’s Equation 2 .
Subject Hydraulics and Pneumatics Code...
Transcript of Subject Hydraulics and Pneumatics Code...
SJP POLYTECHNIC DAMLA
Branch – Mechanical Engineering
Semester – 4th
Subject – Hydraulics and Pneumatics
Code – 171741
Chapter-1 (INTRODUCTION)
Fluid
A Fluid is a substance which continuously deforms under the effect of shear stress.
OR
Fluid is a substance which does not resist a shear stress and deforms under it. It has
no definite shape but takes the shape of containing vessel. Its shape changes when
the shearing force is applied over. It flows, therefore under the effect of the
shearing force.
Examples of fluids are: water, oil, air, gases and vapours etc.
CLASSIFICATION OF FLUIDS:
Fluids are broadly classified in following two categories:
1. Liquids
2. Gases or Vapour
TYPES OF FLUIDS
The fluids may be classified into the following types:
[1] Ideal fluid
[2] Real fluid
[3] Newtonian fluid
[4] Non-Newtonian fluid
[5] Ideal plastic fluid
[6] Thixotropic substance.
Ideal Fluid
A fluid, which is incompressible, has no viscosity and no shearing resistance is
known as an ideal fluid or perfect fluid. Such fluids do not exist in nature and are,
therefore, only imaginary fluids, as all the fluids which exist, have some viscosity.
Real Fluids
Fluids which possess the properties such as viscosity, surface tension
and compressibility are referred as real or practical fluids.
All the fluids, in actual practice, are real fluids.
Newtonian Fluids
Fluid which do not obey the Newton’s law of viscosity is known as non-
Newtonian fluids.
OR
A real fluid in which the shear stress is not proportional to the rate of shear strain
is known as a non-Newtonian fluid.
Ideal Plastic Fluid Or Bingham Fluid
A fluid, in which shear stress is more than the yield value and proportional to the
rate of shear strain is known as ideal plastic fluid or Bingham fluid.
Thixotropic Substance
A substance, which is a non-Newtonian fluid, has a non-linear relationship
between the shear stress and the rate of angular deformation, beyond an initial
yield stress is called thixotropic substance.
HYDRAULICS
Hydraulics is that branch of engineering science which is based on experimental
observation of water flow.
CONCEPT OF CONTINUUM
A continuous and homogenous fluid medium is called continuum.
PROPERTIES OF FLUIDS
Density or Mass Density
Weight Density or Specific Weight
Specific Volume
Specific Gravity
Viscosity
Kinematic Viscosity
Surface Tension
DENSITY OR MASS DENSITY
Density of fluid is defined as the ratio of mass of fluid to its volume.
WEIGHT DENSITY OR SPECIFIC WEIGHT
Weight density or specific weight of fluid is defined as the weight per unit volume.
SPECIFIC VOLUME
Specific volume of a fluid is defined as the volume per unit mass of fluid.
SPECIFIC GRAVITY
Specific gravity is defined as the ratio of specific weight (or mass density) of the
fluid to the specific weight of standard fluid (or mass density of standard fluid).
VISCOSITY
Viscosity of fluid is defined as to be that property of fluid which determines its
resistance to shearing stress or shear deformation or angular deformation.
ADHESION
The property of a liquid which enables it to adhere to another body with which it
comes into contact is called adhesion.
Chapter-2 (PRESSURE AND ITS MEASUREMENT)
ATMOSPHERIC PRESSURE
Atmospheric pressure is the normal pressure exerted by atmospheric air on all
surfaces in contact with it.
GAUGE PRESSURE
If the pressure to be measured by gauge is above atmospheric pressure, it is
called positive gauge pressure.
Gauge pressure is defined as the pressure which is measured with the help of
pressure measuring instrument, in which the atmospheric pressure is taken as
datum i.e. atmospheric pressure on scale is marked as zero.
VACUUM PRESSURE
When pressure to be recorded is below atmosphere, it is called vacuum pressure or
negative pressure this indicates the amount by which the recorded pressure is
below atmospheric pressure.
ABSOLUTE PRESSURE
Absolute pressure is defined as the pressure measured above absolute zero of
pressure. In other words, a pressure measured in a complete vacuum is called
absolute pressure.
PRESSURE MEASURING DEVICE
[A] Manometer
[B] Mechanical Gauges
MANOMETER
Manometers are of two types:
[1] Simple manometer or Open type manometers.
[2] Differential type of manometers.
SIMPLE MANOMETERS
The manometers which measure pressure at a point in a fluid contained in a
vessel or pipe are called simple manometers.
A simple manometer consists of a glass tube having one of its ends connected to
a point where pressure is to be measured and other end remains open to
atmosphere.
Simple manometers are of following types:
(i) Piezometer Tube
(ii) U-Tube Manometer or Double Column Manometer.
(iii) Micro manometer or Single Colum Manometer
PIEZOETER TUBE
It is the simplest types of manometer. It is directly fitted to the pipe or container.
Rise or height of liquid into the tube gives the pressure head of liquid.
U-TUBE MANOMETER
For measuring large gauge pressure, u-tube manometer is used. U-tube
manometer may be regarded as the modification of piezometer tube. Actually, u-
tube manometer consists of a glass tube bent in u-shape. One end of the tube is
connected to a pipe or container having a fluid (a) whose pressure is to be
measured while the other end is open to atmosphere.
Mechanical gauges
For pressure higher than two atmospheres, mechanical gauges are used in which
the liquid is counter balanced either by spring or dead weight.
Advantages:
1. Mechanical gauges are advantageous in the sense that they are portable.
2. Operation range is wider.
3. Direct reading is obtained. This is not the case with manometer.
4. Mechanical gauges are not fragile like manometer.
Types of mechanical gauges.
There are three types of mechanical gauges:
(i) Bourdon tube pressure gauge.
(ii) Diaphragm pressure gauge.
(iii) Dead weight pressure gauge.
Bourdon tube pressure gauge
Bourdon tube pressure gage is used to measure high as well as low pressures low
pressure measurement tubes, generally, are made of bronze while for high
pressure measurement nickel steel is generally used as tube material. (See figure).
Bourdon tube is a curved, elliptical-shaped, metallic tube. This tube is bent in the
form of segment of a circle and responds to pressure changes when one end of the
tube which is attached to gauge case, is connected to the pressure source, it tends
to expand as the fluid pressure in tube rises. Hence circumferential stress is set up
or we can say, hope tension is set up. As a result, free end of the tube moves. Free
end is connected by suitable levers to Rack which, then, engages with a small
pinion mounted on the same spindle as pointer. Thus, Rack and pinion move.
Pressure is indicated by the pointer over a printed dial.
Chapter-3 (FLOW OF FLUIDS)
TYPES OF FLOW
[1] Steady Flow
[2] Un-Steady Flow
[3] Uniform Flow
[4] Non-Uniform Flow
[5] Compressible Flow
[6] Incompressible Flow
[7] Laminar Flow
[8] Turbulent Flow
[9] Rotational Flow
[10] Irrotational Flow
Steady Flow
The flow in which fluid characteristics (fluid dependent variable) such as
velocity, pressure, density at any given point in the fluid, do not change with
time in the direction of any of the three coordinates is known as steady flow.
Unsteady Flow
When in flow, fluid characteristics such as velocity, temperature, density, pressure etc.
changes with time at a given point, it is called unsteady flow.
Uniform Flow
The flow in which fluid characteristics remain same throughout the flow field
at a given time, is called uniform flow.
Non-Uniform Flow
The flow in which the flow characteristics changes at various points along the
path is called non-uniform flow.
Laminar Flow
Laminar flow is called as that type of flow in which the fluid elements move along
well defined paths or stream lines and all the stream lines are straight and parallel.
Turbulent Flow
The type of flow in which the fluid particles do not move in layers and cross the
path of other particles is called a turbulent flow.
CONTINUITY EQUATION OF FLOW
The equation which represents that the weight of liquid remains same at all
sections provided no liquid is added or subtracted from the flowing liquid is
referred as continuity equation of flow.
BERNOULLI’S THEOREM
Bernoulli’s theorem is, actually, based on certain on certain assumptions these
assumptions are:
1. No work or heat interaction between a fluid element and the surrounding takes
place.
2. Flow is steady and continuous.
3. Fluid is incompressible and there is no friction.
4. The flow is one-dimensional i.e. it is along the stream line.
STATEMENT AND PROOF OF BERNOULLI’S THEOREM
“In a steady, continuous flow of an incompressible and ideal fluid, the sum of
potential head, pressure head and kinetic head along a stream line flow remains
same
VENA CONTRACTA
As a liquid approaches an opening, the liquid particles approaching it move along
converging stream lines. This stream of particles issuing from the orifice is called
jet this jet separates from the wall at the sharp edge and finally converges into a
section of minimum cross-sectional area. This section of minimum cross-sectional
area of a maximum contraction is called Vena contracta.
Chapter-4 (FLOW THROUGH PIPES)
INTRODUCTION
A pipe may be defined as closed conduit carrying a fluid under pressure
GEOMETRICAL TERMINOLOGIES
Depth of flow: depth of flow h is defined at a particular section of a
channels. This is so because it may vary from section to section. Thus,
depth of flow is the vertical distance of the bed of the channel from the
free surface at the section under consideration.
Top breadth: this is the breadth of channel section at the free surface.
The water area, A: The water area is the flow cross-sectional area
PERPENDICULAR TO THE direction of flow.
Wetted perimeter: wetted perimeter is the perimeter of solid boundary
in contact with the liquid. It is denoted by P.
LOSS OF ENERGY (OR HEAD) IN PIPE FLOW
ENERGY OR HEAD LOSSES pipe can be grouped; primarily,
into following categories:
Major energy loss.
Minor energy loss.
Major energy loss: this loss of energy is due to fraction in pipe can
be calculated using following formulae
(i) Darcy-Weishbach formulae
(ii) Chezy’s formulae
Minor energy losses: minor energy losses are attributed to the following
factors:
(i) Sudden expansion or contraction of pipe
(ii) Bend in pipe.
(iii) Pipe fitting or an obstruction in pipe.
HYDRAULIC GRADIENT AND TOTAL ENERGY LINE
Total energy line (T.E.L.) means line or contour obtained on plotting
total head at a section in flow direction while hydraulic gradient
(H.G.L.) means line obtained on plotting pressure head (potential +
pressure head of liquid at a section at against flow distance.
Chapter-5 (HYDRAULIC DEVICES)
INTRODUCTION
Devices which employ fluid or liquid in our case, as a medium for
transmitting a force and power by high pressures are called hydraulic
devices.
These are essentially based on the principle of fluid statics and fluid
kinetics. Hydraulic devices which are being discussed in this chapter
are:
1 Hydraulic ram
2 Hydraulic jack
3 Hydraulic accumulator
4 Hydraulic press
5 Hydraulic lift
HYDRAULIC RAM
Hydraulic ram is a device which can lift a small quantity of water to
a greater height when a large quantity of water is available at a
smaller height without using any external power, be it mechanical or
electrical.
Principle: It utilizes the water hammer principle to raise the pressure
energy of small quantity of water and can also be called an “impulse
pump”.
HYDRAULIC JACK
Hydraulic JACK IS A DEVICE USED TO LIFT HEAVY LOADS.
Principle of this device is Pascal’s law of transmission of pressure by
fluid combined with the operation of force pump.
Fig. shows the cross-section of simple hydraulic jack. It consists of a ram
which can raise the load as desired, a pump; a reservoir and small
cylinder containing plunger. Initially, as the handle is raised, plunger
moves up in its cylinder. At this moment, oil from the reservoir flows out
of hole and underside of plunger. Thereafter, plunger is pushed down
closing the hole through which oil entered into small cylinder, then
pushing the oil through a check valve into the large cylinder. Oil builds
up pressure in large cylinder gradually with each stroke of the pump
rising in the piston and load placed on it.
Hydraulic BREAK
ACCORDING TO METHOD OF actuation brakes are classified as
hydraulic brake, magnetic brake or eddy-current brakes. A hydraulic
braking system has been shown in fig. primarily, a hydraulic breaking
system is a liquid coupling between brake pedal and individual brake
shoe.
Chapter-6 (WATER TURBINES AND PUMPS)
CLASSIFICATION OF TURBINES
Broadly, turbines are classified on following two basis:
Hydraulic action of water or nature of energy head processed by water at
inlet.
Direction of flow of water in the runner or we can say direction of flow
along the vanes
HYDRAULIC ACTION OF WATER OR NATURE OF ENERGY
HEAD
On this basis, turbines are classified as under:
Impulse turbines
Reaction turbines
Impulse Turbines
Those turbine in which runner rotates by impulse action (impact) of
water are called impulse turbines.
Examples of impulse turbines are: Pelton Wheel, Girard Turbine.
Reaction Turbines
Those turbines in which the water entering the runner possesses
pressure as well as kinetic energy are called reaction turbines.
Examples: Francis Turbine, Kaplan Turbine.
CLASSIFICATION ACCORDING TO DIRECTION OF FLOW OF
WATER IN RUNNER
ON THE BASIS OF DIRECTION OF FLOW OF WATER, turbines
are classified as under:
(1) Tangential Flow Turbines
(2) Radial Flow Turbines
Comparison between Impulse and Reaction Turbines
S. No. Impulse Turbine Reaction Turbine
1. The total available head is converted into Only a part of available
velocity head by using a nozzle. head is converted into
velocity head rest of it
being converted into
pressure head. No
separate nozzle is used.
Both pressure and
2. Only the jet velocity changes in the process of velocity changes as fluid
fluid flow. flow through the runner.
Water must be admitted
over the entire
3. Water is admitted over part of circumstance. circumference of the
runner.
Water tight casing is must
Water tight casing is not required as the for enclosing the runner.
4. casing has no hydraulic function to perform
as such. It simply prevents splashing of water
and finally leads the water to tail race. It may be installed both
Turbine is always installed above tail race. above and below tail race.
Draft tube is used.
5. No draft tube is used. Air runner wheel always
Air has free access to vanes as the wheel run full.
does not run full.
Pelton Turbine
Invented by Pelton in 1890.
The Pelton turbine is a tangential flow impulse turbine.
The Pelton wheel is most efficient in high head applications.
Power plants with net heads ranging from 200 to 1,500 m.
The largest units can be up to 200 Megawatts.
Pelton turbines are best suited for high head and low flow sites.
Depending on water flow and design, Pelton wheels can operate with heads as
small as 15 meters and as high as 1800 meters.
As the height of fall increases, less volume of water can generate same power.
Horizontal arrangement is found only in medium and small sized turbines
with usually one or two jets. In some designs, up to four jets have been used.
The flow passes through the inlet bend to the nozzle outlet, where it flows out as a
compact jet through atmospheric air on to the wheel buckets. From the outlet of the
buckets the water falls through the pit down into the tail water canal.
Francis Turbine
The Francis turbine is a reaction turbine, which means that the working fluid
changes pressure as it moves through the turbine, giving up its energy.
The inlet is spiral shaped. The guide vanes direct the water tangentially to the
runner causing the runner to spin.
The guide vanes (or wicket gate) may be adjustable to allow efficient turbine
operation for a range of water flow conditions.
Power plants with net heads ranging from 20 to 750 m.
Draft Tube
In a reaction turbine, water leaves the runner with remaining kinetic energy. To
recover as much of this energy as possible, the runner outlet is connected to a
diffuser, called draft tube. The draft tube converts the dynamic pressure (kinetic
energy) into static pressure.
Draft tube permits a suction head to be established at the runner exit, thus making
it possible for placing the wheel and connecting machinery at a level above that of
water in the tail race under high water flow conditions of river, without loss of
head.
To operate properly, reaction turbines must have a submerged discharge.
The water after passing through the runner enters the draft tube, which directs the
water to the point of discharge.
The aim of the draft tube is also to convert the main part of the kinetic energy at
the runner outlet to pressure energy at the draft tube outlet.
Cavitation
Cavitation is a term used to describe a process, which includes nucleation, growth
and implosion of vapour or gas filled cavities. These cavities are formed into a
liquid when the static pressure of the liquid for one reason or another is reduced
below its vapour pressure at the prevailing temperature. When cavities are carried
to high-pressure region, they implode violently.
Cavitation is an undesirable effect that results in pitting, mechanical vibration and
loss of efficiency.
If the nozzle and buckets are not properly shaped in impulse turbines, flow
separation from the boundaries may occur at some operating conditions that may
cause regions of low pressure and result in cavitation.
The turbine parts exposed to cavitation are the runners, draft tube cones for the
Francis and Kaplan turbines and the needles, nozzles and the runner buckets of the
Pelton turbines.
Measures for combating erosion and damage under cavitation conditions include
improvements in hydraulic design and production of components with erosion
resistant materials and arrangement of the turbines for operations within good
range of acceptable cavitation conditions.
Specific Speed
It is defined as the speed of a turbine which is identical in shape, geometrical
dimensions, blade angles, gate opening etc., with the actual turbine but of such a
size that it will develop unit power when working under unit head
This is the speed at which the runner of a particular diameter will develop 1 kW (1
hp) power under 1 m (1 ft) head.
Ns = N 5P
H 4
The specific speed is an important factor governing the selection of the type of
runner best suited for a given operating range. The impulse (Pelton) turbines have
very low specific speeds relative to Kaplan turbines. The specific speed of a
Francis turbine lies between the impulse and Kaplan turbine.
Selection of Turbines
Turbine Head Specific Speed
(SI)
Pelton Wheel >300 m 8.5-30 (Single Jet)
30-51 (2 or More)
Francis Turbine 50-450 m 51-255
Kaplan Turbine Up to 60 m 255-860
Hydraulic pump
Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or
hydrodynamic. A hydraulic pump is a mechanical source of power that converts
mechanical power into hydraulic energy (hydrostatic energy i.e. flow, pressure). It
generates flow with enough power to overcome pressure induced by the load at the
pump outlet. When a hydraulic pump operates, it creates a vacuum at the pump
inlet, which forces liquid from the reservoir into the inlet line to the pump and by
mechanical action delivers this liquid to the pump outlet and forces it into the
hydraulic system. Hydrostatic pumps are positive displacement pumps while
hydrodynamic pumps can be fixed displacement pumps, in which the displacement
(flow through the pump per rotation of the pump) cannot be adjusted, or variable
displacement pumps, which have a more complicated construction that allows the
displacement to be adjusted. Hydrodynamic pumps are more frequent in day-to-
day life. Hydrostatic pumps of various types all work on the principle of Pascal's
law.
Gear pumps
These pumps create pressure through the meshing of the gear teeth, which forces
fluid around the gears to pressurize the outlet side. For lubrication, the gear pump
uses a small amount of oil from the pressurized side of the gears, bleeds this
through the (typically) hydrodynamic bearings, and vents the same oil either to the
low pressure side of the gears, or through a dedicated drain port on the pump
housing. Some gear pumps can be quite noisy, compared to other types, but
modern gear pumps are highly reliable and much quieter than older models. This is
in part due to designs incorporating split gears, helical gear teeth and higher
precision/quality tooth profiles that mesh and un mesh more smoothly, reducing
pressure ripple and related detrimental problems. Another positive attribute of the
gear pump, is that catastrophic breakdown is a lot less common than in most other
types of hydraulic pumps. This is because the gears gradually wear down the
housing and/or main bushings, reducing the volumetric efficiency of the pump
gradually until it is all but useless. This often happens long before wear causes the
unit to seize or break down.
Rotary vane pumps
Rotary vane pumps (fixed and simple adjustable displacement) have higher
efficiencies than gear pumps, but are also used for mid pressures up to 180 bar
(18,000 kPa) in general. Modern units can exceed 300 bar (30,000 kPa) in
continuous operation, although vane pumps are not regarded as "high pressure"
components. Some types of vane pumps can change the centre of the vane body, so
that a simple adjustable pump is obtained. These adjustable vane pumps are in
general constant pressure or constant power pumps: the displacement is increased
until the required pressure or power is reached and subsequently the displacement
or swept volume is decreased until an equilibrium is reached. A critical element in
vane pump design is how the vanes are pushed into contact with the pump housing,
and how the vane tips are machined at this very point. Several type of "lip" designs
are used, and the main objective is to provide a tight seal between the inside of the
housing and the vane, and at the same time to minimize wear and metal-to-metal
contact. Forcing the vane out of the rotating centre and towards the pump housing
is accomplished using spring-loaded vanes, or more traditionally, vanes loaded
hydrodynamically.
Screw pumps
Principle of screw pump
Screw pumps (fixed displacement) consist of two Archimedes' screws that
intermesh and are enclosed within the same chamber. These pumps are used for
high flows at relatively low pressure (max 100 bars (10,000 kPa). They were used
on board ships where a constant pressure hydraulic system extended through the
whole ship, especially to control ball valves but also to help drive the steering gear
and other systems. The advantage of the screw pumps is the low sound level of
these pumps; however, the efficiency is not high.
The major problem of screw pumps is that the hydraulic reaction force is
transmitted in a direction that's axially opposed to the direction of the flow.
There are two ways to overcome this problem:
1. put a thrust bearing beneath each rotor;
2. create a hydraulic balance by directing a hydraulic force to a piston under
the rotor.
Types of screw pumps:
1. single end
2. double end
3. single rotor
4. multi rotor timed
5. multi rotor untimed.
Reciprocating pump
A reciprocating pump is a class of positive-displacement pumps which includes
the piston pump, plunger pump and diaphragm pump. When well maintained,
reciprocating pumps will last for years or even decades; however, left untouched,
they can undergo rigorous wear and tear. It is often used where a relatively small
quantity of liquid is to be handled and where delivery pressure is quite large. In
reciprocating pumps, the chamber in which the liquid is trapped, is a stationary
cylinder that contains the piston or plunger
Centrifugal pumps
These are a sub-class of dynamic ax symmetric work-absorbing turbo
machinery. Centrifugal pumps are used to transport fluids by the conversion of
rotational kinetic energy to the hydrodynamic energy of the fluid flow. The
rotational energy typically comes from an engine or electric motor. The fluid enters
the pump impeller along or near to the rotating axis and is accelerated by the
impeller, flowing
radially outward into a diffuser or volute chamber (casing), from which it exits.
Common uses include water, sewage, agriculture, petroleum and petrochemical
pumping. Centrifugal pumps are often chosen for their high flow rate capabilities,
abrasive solution compatibility, mixing potential, as well as their relatively simple
engineering. A centrifugal fan is commonly used to implement a vacuum cleaner.
The reverse function of the centrifugal pump is a water turbine converting potential
energy of water pressure into mechanical rotational energy.
Priming
If the pump casing becomes filled with vapors or gases, the pump impeller
becomes gas-bound and incapable of pumping. To ensure that a centrifugal pump
remains primed and does not become gas-bound, most centrifugal pumps are
located below the level of the source from which the pump is to take its suction.
The same effect can be gained by supplying liquid to the pump suction under
pressure supplied by another pump placed in the suction line.