TABLE OF CONTENTS
INTRODUCTION........................................................................................................................
OBJECTIVES...............................................................................................................................
THEORY......................................................................................................................................
APPARATUS...............................................................................................................................
PROCEDURES.............................................................................................................................
DATA AND RESULTS...............................................................................................................
DISCUSSIONS.............................................................................................................................
CONCLUSIONS...........................................................................................................................
REFFERENCES...........................................................................................................................
1
INTRODUCTION
Figures 1, 2 and 3 show the rotor and nozzle arrangements for the axial flow impulse turbine
(FM3O), the radial flow reaction turbine (FM31) and the Pelton turbine (FM32).
In an impulse turbine (Figure 1) the kinetic energy of a jet leaving a high pressure
stationary nozzle is converted on impact with the turbine blades to rotational mechanical
energy. As the water exiting the jet is at atmospheric pressure, the force exerted on the rotor is
entirely due to changes in the direction of the flow of water. The impulse turbine is therefore
associated with considerable changes of kinetic energy but little change in pressure energy. In
the case of the FM3O four independently controlled nozzles are installed around the rotor.
In a reaction turbine (Figure 2) the water is subject to a pressure drop as it flows
through the rotor. The reaction turbine is therefore associated with considerable changes in
2
Figure 1 : Rotor and nozzle arrangement of the impulse turbine
Figure 2 : Rotor and nozzle arrangement of the reaction turbine
Figure 3 : Rotor and nozzle arrangement of the Pelton turbine
pressure energy but little change in kinetic energy and is sometimes called a pressure turbine.
In the case of the FM31 water enters the rotor via a face seal and is discharged tangentially
through two nozzles at the periphery of the rotor. The nozzles therefore move with the rotor.
The Pelton turbine (Figure 3) is the most visually obvious example of an impulse
machine. A spear valve directs a jet of water at a series of buckets which are mounted on the
periphery of a rotor. As the water exiting the spear valve is at atmospheric pressure, the force
exerted on the rotor is entirely due to changes in the direction of the flow of water. The Pelton
turbine is therefore associated with considerable changes of kinetic energy but little change in
pressure energy.
The spear valve allows the jet diameter to be varied which allows the water flow rate
to be varied with a constant jet velocity. Large turbines may include more than one spear
valve around the periphery of the rotor. In the case of the FM32 a single spear valve is
installed.
The operating characteristics of a turbine are often conveniently shown by plotting
torque T, brake power Pb, and turbine efficiency Et against turbine rotational speed n for a
series of volume flow rates Qv, as shown in Figure 4. It is important to note that the efficiency
reaches a maximum and then falls, whilst the torque falls constantly and linearly. In most
cases a turbine is used to drive a generator in the production of electricity. The speed of the
generator is fixed to produce a given frequency of electricity. The optimum conditions for
operation occur when the maximum turbine efficiency coincides with the rotational speed of
the generator. As the load on the generator increases then the flow of water to the turbine
must increase to maintain the required operating speed.
This Armfield Capture unit is designed to allow students to determine the operating
characteristics of either an Axial Flow Turbine (FM3O), a Radial Flow Reaction Turbine
(FM31), or a Pelton Turbine (FM32), rapidly and meaningfully, using ‘on-line’ data
3
Figure 4 : Example characteristics of a turbine at different flow rates
acquisition and analysis. Test results may be displayed in tabular and graphical forms, and it
is a simple matter to repeat or add to the data to cover areas of the turbine performance of
particular interest.
OBJECTIVES
i. To observe and understand the operating characteristics of the turbines.
ii. To study the basic concept of impulse turbine.
iii. To relate the actual situation to the theoritical statement.
THEORY
Turbines are classified in two general categories : impulse and reaction. In both types the fluid
passes through a runner having blades. The momentum of the fluid in the tangential direction
is changed and so a tangential force on the runner is produced. The runner therefore rotates
and performs useful work, while the fluid leaves it with reduced energy. The important
feature of the impulse machine is taht there is no change in static pressure across the runner.
In the reaction machine, the static pressuredecreases as the fluid passes through runner.
For any turbine, the energy held by the fluid is initially in the form of pressure, ie. a
high level reservoir in a hydro-electric scheme.
The impulse turbine has one or more fixed nozzles, in each of which this pressure is
converted to the kinetic energy of an unconfirmed jet. The jet of fluid then impinge on the
moving blades of the runner where they lose practically all their kinetic energy.
In a reaction machine, the changes from pressure to kinetic energy take place
gradually as the fluid moves through the runner, and for this gradual changes of pressure to be
possible the runners must be complete enclosed and the passages in it entirely full of the
working fluid.
4
The general relationship between the various forms of energy, based on the 1st Law of
Thermodynamics applied to a unit mass of fluid flowing through a ‘control volume’ is
expressed as :-
−W S=d ( v2/2 )+g .dz+∫ vol .dp+F
Where :
-Ws is the work performed by the fluid on the turbine
d(v2/2) is the change in kinetic energy of the fluid
g.dz is the change in potential energy of the fluid
∫ vol . dp is the change in pressure energy,where ‘vol’ is the volume per unit mass of the
fluid. For an incompressible fluid of constant density Rho, this term is equal to
∫ dp/ R ho or (p1-p2)/Rho where p2 refers to the turbine discharge outlet and
p1 to the turbine inlet
F is the frictional energy loss as heat to the surroundings or in heating the fluid
itself as it travels from inlet to outlet
The first three terms of the right hand side represent the useful work Wa ie.
−W a=( v12−v2
2
2 )+g ( z1−z2 )+(p1−p2
R ho)
Where subscript 2 refer to the turbine outlet and subscript to the inlet.
The term Wa represents the actual work produced in changing the energy stages of a unit mass
of
fluid. This may alternatively be presented as the total dynamic head H of the turbine, by
converting
the units from work per unit mass to head expressed as a length :-
H=( v12−v2
2
2 g )+( z1−z2 )+(p1−p2
R h o . g)
5
It can be assumed for the purposed of the following practical experiments that the fluid is
incompressible (i.e. is constant)
The variable obtained from the sensors on the equipment are :-
Symbol Term Units
dPo Orifice differential pressure Pa
P1 Turbine inlet pressure Pa
n Rotational speed of the pump Hz
Fb Brake force on turbine N
Constant used in the calculation are :-
Symbol Term Value Units
d Orifice diameter 0.009 m
Cd Discharge coefficient 0.63
r Pulley radius 0.024 m
Water density 998.2 kg/m3
Calculated variables are :-
Symbol Term Units
Qv Volume flowrate m3/s
Hi Input head to turbine m
Ph Hydraulic power available to turbine W
T Torque Nm
Pb Brake power W
Et Overall efficiency %
6
Formula used are :-
Qv=Cd . . d2 .√2 . p . dPo
4 p
H i=P 1g
Ph=g H i .Q v
T=Fb. r
Pb=2n . T
Et=Pb
Pe
×100
APPARATUS
7
Figure 5 : Turbine Service Unit Figure 6 : Armfield Controller
The unit consists of a clear acrylic reservoir (1), a circulating pump and associated pipe work
installed on a support plinth, which is bench mounted. The reservoir incorporates a drain
valve (2) at the base and a flange (3) at the top, to which the appropriate turbine is attached.
Water circulation is provided by a single stage centrifugal pump (5) driven by an
integral electric motor (4). The motor requires a single phase electricity supply.
The pump discharge pipe corporate a screwed connector which mates with the inlet pipe on
the appropriate turbine.
8
3
1
2
4
5
Figure 7 : Integrating Wattmeter Figure 8 : PC Turbine Domenstration Unit
The flow of water is measured using a differential pressure sensor SPW1 which is
connected across an orifice plate at the entrance to the pump inlet pipe. The pressure sensor is
connected between the tapping on the orifice plate and a tapping in the wall of the reservoir.
Additional tapping’s are provided for the connection of the appropriate instrumentation (not
supplied) to facilitate calibration of the differential pressure sensor.
The differential pressure sensor is connected to channel 1 on the IFD interface
console.
PROCEDURES
The laboratory equipment was set up by the lab session facilitator as follows.
a) The Turbine Service Unit FM3SU was placed in a suitable location adjacent to a
compatible microcomputer.
b) The drain valve (2) at the base of the reservoir was ensured is fully closed.
c) The Differential Pressure Sensor SPW1 (9) is checked so it is connected to the two
tappings at the front of the reservoir. P1 LOW on SPW1 must be connected to the
tapping on the orifice plate and HIGH P2 must be connected to the tapping in the wall
of the reservoir.
d) The reservoir (3) was filled with clean water until the level is approximately 100mm
below the top.
e) The flexible tubing connecting differential pressure sensor SPW1 to the orifice plate
should be primed with water using the priming syringe supplied.
f) The syringe was filled with clean water. Each flexible tube was disconnected from the
tapping on the reservoir.
g) The syringe and back-fill the flexible tube were inserted with water. When all air
bubbles have been expelled the tubing was reconnected to the reservoir.
h) The required turbine (FM3O FM31 or FM32) was placed on top of the reservoir,
ensuring that the O-ring seal is located in the recess in the top flange of the reservoir.
Loosely attach the pipe connector from the service unit to the turbine, then, the base
plate of the turbine was fastened to the top flange of the reservoir by tightening the
thumb screws. Finally tighten the pipe connector.
i) The interface console IFD was placed alongside the computer.
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j) The mains supply lead from an appropriate electrical supply was connected to the
MAINS INPUT socket on lED ensuring that the electrical supply is compatible with
the console (indicated on the rear of the console).
k) Water was checked either it circulates through the turbine. The pump was then turned
off.
l) Each of the sensor conditioning boxes was connected to the appropriate SENSOR
SOCKETS on the front of IFD, using the numbered connecting leads, as follows:
Channel 1 to sensor SPWI on the Turbine Service Unit (FM3SU)
Channel 2 to sensor SPH2 on the base plate of the appropriate Turbine
Channel 3 to sensor SSO2 on the base plate of the appropriate Turbine
Channel 4 to sensor SLRI on the base plate of the appropriate Turbine
Brake Belt Removal And Refitting
The position of the slave pulley was adjusted by sliding the slave pulley bracket (3)
back and forth, so that the bracket is upright when the belt is lightly tensioned between the
turbine pulley and slave pulley.
As equipment was fully set up, the student was needed to carry out these following
procedures:
a) The brake force at the software interface was adjusted, starting from initial value of
zero.
b) The stable reading was then recorded by pressing the ‘record’ function from the
software. The data then shows up at the table of data which is automatically generated
by the software.
c) The brake force is then adjusted by a small increment of 0.1 to 0.9 N up to total of 5 N
brake force. Thus, this process was repeated by simply repetition of steps 1 and 2.
d) The collected data is then used for the software to generate graphs as the result. This is
again automatically generated by using the software.
10
DATA AND RESULTS
11
Sample calculation:
Sample data from Sample number 8 from the table
g=9.81m/ s2
d=0.009 m
C d=0.63
ρ=998.2kg
m2 d Po=26.284 kPa
Volume flow rate, Qv,
Qv=Cd π d2√2 ρ d Po
4 ρ¿ 0.63 × π× 0.0092 ×√2× 998.2 ×26.284 k
4 (998.2 ) ¿0 .291 dm3/ s
Impact head, Hi,
H i=P1
ρg¿ 248.828 k
998.2× 9.81¿25 . 41 m
Hydraulic Input Power,Ph,
Ph= ρgQ v H 1¿998.2 ×9.81 × 0.291× 10−3 ×25.41¿72 . 41W
Torque,T
12
T=Fbr¿1.9 ×0.024¿0 .0456 Nm
Brake power,Pb
Pb=2πnT¿2 ×227
×76 × 0.0456¿22 W
Turbine efficiencies,
Egr=Pb
Ph
×100 %¿ 2272.41
×100 %¿30 . 5 %
DISCUSSION
13
CONCLUSION
14