design and construction of an archimedes ......conveyor for grain (nagel 1968 p.8). the standard...
TRANSCRIPT
1
DESIGN AND CONSTRUCTION OF AN ARCHIMEDES
TURBINE FOR RURAL ELECTRIFICATION/LIGHTING IN
ZAMBIA
A Dissertation
Presented to
The Engineering Institute of Technology
by
Godfrey Mwansa
In Partial Fulfillment
of the Requirements for the Degree
Master of Engineering in
INDUSTRIAL AUTOMATION
SEPTEMBER 2017
COPYRIGHT Β© 2017 BY GODFREY MWANSA
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TABLE OF CONTENTS
List of Figures ................................................................................................................ 4
List of Tables ................................................................................................................. 6
Acknowledgement ......................................................................................................... 7
Abstract .......................................................................................................................... 8
Chapter 1. Motivation of Renewable Energy and Archimedes Turbine ........................ 9
1.1 What is the Archimedes Turbine?..................................................................... 9
1.2 Problem Formulation ...................................................................................... 14
1.3 Design and construction of a simplistic Archimedes turbine ......................... 15
1.4 Potential sites for Archimedes turbine installation in Zambia ........................ 17
Chapter 2. Literature Review of the Alternative Options to Archimedes Turbines .... 19
2.1 The Need for Renewable Energy .................................................................... 19
2.2 Renewable Energy Alternatives ...................................................................... 26
2.2.1 Solar Energy............................................................................................. 26
2.2.2 Wind Energy ............................................................................................ 30
2.2.3 Geothermal Energy .................................................................................. 31
2.2.4 Tidal Waves ............................................................................................. 32
2.2.5 Biomass .................................................................................................... 32
2.2.6 Hydro Power ............................................................................................ 33
Chapter 3 Methodology ............................................................................................... 42
3.1 Site Survey ...................................................................................................... 42
3.1.1 Site 1 Details ............................................................................................ 43
3.1.2 Site 2 Details ............................................................................................ 44
3.1.3 Site 3 Details ............................................................................................ 47
3.1.4 Site 4 Details ............................................................................................ 49
3.2 Design and Simulation of the Turbine. ........................................................... 51
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3.2.1 Turbine Parameters .................................................................................. 51
3.2.2 Simulation of the Turbine in Solid Works. .............................................. 62
3.3 Construction of the Turbine. ........................................................................... 66
3.3.1 Materials of construction ......................................................................... 66
3.3.2 Fabrication Process .................................................................................. 68
3.3.2.1 Construction of blades ................................................................... 68
3.3.2.2 Pulley Construction ........................................................................ 70
3.3.2.3 Machined members modification .................................................. 72
3.3.2.4 Completed assembly ...................................................................... 73
3.3.3 Electrical Assembly ................................................................................. 74
Chapter 4. Results and Analysis .................................................................................. 76
4.1 Power Available at the site ............................................................................. 76
4.2 Mechanical power of the screw Turbine. ........................................................ 80
4.2.1 Radius of gyration .................................................................................... 85
4.2.2 Rotational speed of screw ........................................................................ 85
4.2.3 Rotational Kinetic energy of the screw .................................................... 86
4.2.4 Mechanical efficiency of the screw turbine ............................................. 87
4.2.5 Electrical Output ...................................................................................... 87
4.2.6 AC Circuit and power Output .................................................................. 88
4.2.7 Circuit diagram ........................................................................................ 91
4.3 Discussion of Results ...................................................................................... 95
Chapter 5. Conclusion, Recommendations and Future works ..................................... 96
5.1 Conclusion. ..................................................................................................... 96
5.2 Recommendation ............................................................................................ 98
5.3 Future Works .................................................................................................. 99
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LIST OF FIGURES
Figure 1 Archimedes Screw Pump Diagram ............................................................... 10
Figure 2 Screw Parameters .......................................................................................... 10
Figure 3 Archimedes Screw Turbine ......................................................................... 122
Figure 4 Potential sites for Archimedes turbine installation in Zambia ...................... 17
Figure 5 Fossil Fuel Price over time ............................................................................ 20
Figure 6 Top ten World Energy Consumers ................................................................ 21
Figure 7 Global Energy Consumption ......................................................................... 21
Figure 8 Climate Change Perceptions.......................................................................... 22
Figure 9 CO2 Emissions from fuel combustion .......................................................... 23
Figure 10 Global Greenhouse Gas Emissions by Gas ................................................. 25
Figure 11 Solar Energy Creation ................................................................................. 27
Figure 12 Solar Thermal Electricity ............................................................................ 30
Figure 13 Geothermal Energy ...................................................................................... 32
Figure 14 Pelton and Francis Turbines ........................................................................ 38
Figure 15 Vertical shaft Francis Turbine ..................................................................... 39
Figure 16 Propeller turbine .......................................................................................... 40
Figure 17 Kaplan Turbine ............................................................................................ 41
Figure 18 Picture of Site 1 ........................................................................................... 43
Figure 19 Pictures of Site 2 .......................................................................................... 44
Figure 20 Pictures of Site 3 .......................................................................................... 47
Figure 21 Site 4 Pictures .............................................................................................. 49
Figure 22 Lathe Machine ............................................................................................. 69
Figure 23 Disk.............................................................................................................. 69
Figure 24 Shaft & blade construction .......................................................................... 71
Figure 25 Stock for the pulley ..................................................................................... 71
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Figure 26 Slotting Machine ......................................................................................... 72
Figure 27 Milling Machine .......................................................................................... 73
Figure 28 Completed Assembly................................................................................... 74
Figure 29 Mounting of the Dynamo ............................................................................ 75
Figure 30 Operating Archimedes Screw Generator ..................................................... 75
Figure 31 The turbine installed at the site .................................................................... 80
Figure 32 Electrical Operation ..................................................................................... 91
Figure 33 Brushed DC Motor ...................................................................................... 99
Figure 34 Single Phase Induction Generator ............................................................. 101
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LIST OF TABLES
Table 1 Classification of Hydro power plants ............................................................. 34
Table 2 Turbine types and their examples 1 ................................................................ 37
Table 3 Site 1 parameters ............................................................................................. 43
Table 4 Site 2 parameters ............................................................................................. 45
Table 5 Site 3 parameter .............................................................................................. 48
Table 6 Site 4 parameters ............................................................................................. 50
Table 1 Optimal Ratio Parameters of an Archimedes Screw ...................................... 52
Table 7 Alternator Pulley Dimensions 1 ...................................................................... 58
Table 8 Dimensions of turbine parts 1 ......................................................................... 66
Table 9 Site Dimensions. ............................................................................................. 76
Table 10 current flow time ........................................................................................... 77
Table 11 Trough Dimensions....................................................................................... 79
Table 12 Density of turbine parts................................................................................. 82
Table 13 rotational period of screw ............................................................................. 86
Table 14 Instrumentation devices used 1 ..................................................................... 95
Table 15 Project Budget 1............................................................................................ 97
Table 16 Bicycle dynamo pros and cons ..................................................................... 98
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ACKNOWLEDGMENT
I am grateful to the sovereign Lord of the Universe Jehovah for blessing
me with a very supportive mother who has been very instrumental in helping me
finance my Masterβs study. I am also grateful to have a great and most helpful
supervisor.
I would love to further extend my appreciation towards management and
machinists at Machine Masters who exhibited extraordinary patience and
endurance in trying to adapt their skill set to my requirements. I truly appreciate
the fatherly and patient approach of my supervisor. The lecturersβ untiring
tutoring have not only enhanced my knowledge but nurtured in me a desire to
continue learning - indeed all of you have had a very positive impact on my life.
God bless you all.
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ABSTRACT
Archimedes turbines have been used as electricity generating turbines for
over century in European countries. However this intermediate technology has
not been fully adopted in developing countries such as Zambia. The reason for
this gap could be a lack of a research culture in the country.
The site suitable for the installation of an Archimedes turbine is one with
a low head and a high flow. In this project, the researcher did not seek to produce
a novel design of the turbine but rather, to determine if the lack of
implementation of this technology in Zambia could have been as a result of a
lack of necessary skills in the country or a lack of suitable sites in the country.
Once the availability of suitable sites is established the turbine will be
designed on the basis of the site. The design process will be done using a
computer aided design software which enables the simulation of the complete
turbine. Solid Works will be used for this purpose as it can allow for the design
process and also the simulation of the turbine.
The parameters of the designed and simulated turbine will be the basis for
the construction of the turbine. A reputable machinist organisation will be used
to carry out the construction of the turbine so that the design parameters are
adhered to.
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CHAPTER 1. MOTIVATION OF RENEWABLE ENERGY
AND ARCHIMEDES TURBINE
1.1 What is the Archimedes Turbine?
The Archimedes turbine is one of the oldest machines in existence.
However, the machine has not always; existed as a turbine. Its first known form
was as a pump and was at the time called the Archimedes screw pump. The
Archimedes screw pump is a device for lifting water for irrigation and drainage
purposes (Chris Rorres 2000).
Archimedes of Syracuse is credited to be the inventor of the device, for
example the Greek historian Diodorus Siculus says of the device βmen easily
irrigate the whole of it [an island in the delta of the Nile] by means of a certain
instrument conceived by Archimedes of Syracuse, and which gets its name
[cochlias] because it has the form of a spiral or screwβ. (Chris Rorres 2000).
However, it is worth noting that Archimedes himself never made
reference to the screw pump in the extant of his works and it could be that he
may just have transmitted its knowledge from the actual or original inventors of
the pump who could have been the Egyptians while he was studying in
Alexandria in Egypt. In recent times, the screw has also been used as a screw
conveyor for grain (Nagel 1968 p.8).
The standard design and description of an Archimedes screw pump is that
it consists of a shaft to which is attached a series of blades. The physical
attributes associated with the screw are depicted in the figure below;
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Figure 1 Archimedes Screw Pump Diagram.
Pitch (Κ):
The pitch of the screw refers to the period of one blade, since the blades
on the screw form a spiral whose shape is best described by a sinusoidal curve.
The pitch refers to a linear length equivalent to a full oscillation of a sinusoidal
curve as is indicated in the figure below:
Figure 2 Screw Parameters. (Chris Rhores, 2000).
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Blades
Blades are the most significant part of the Archimedes screw, they are the
ones that form buckets through which water is hoisted upwards. To this end, the
number of blades will determine the amount of water that can be drawn by an
Archimedes screw.
Chute
The chute is the region of the screw bound by two adjacent blades, the
inner cylinder and the outer cylinder.
Bucket
This is the region occupied by water within any one chute. In the
operation of the screw as a pump each bucket is filled with water at the lower
reservoir and is emptied into the upper reservoir.
Other physical attributes of the screw which are significant include the
total length (L) of the screw measured from the lowest point of the screw along
the length of the screw to the highest point of screw near the upper reservoir.
The outer radius (R0) of the screw refers to the radius generated by the outer
cylinder created by the blades of the screw while the inner radius (Ri) is the one
created by the inner cylinder of the screw.
Though in the modern era the Archimedes screw is still finding its initial
application as a pump, the prominent use of it has now realised as is it being used
as a hydro power generating turbine. To use the screw as a turbine, one need
only reverse the direction of its operating mechanism. This means that instead of
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using motive mechanical power to drive the screw so that it may raise water from
a lower reservoir, water falling from a height will run down the spiral of the
turbine and as result of the kinetic energy carried by this water, it will
subsequently rotate the turbine.
The figure below gives a clear picture depicting the typical set up of an
Archimedes screw turbine, with water falling from a head driving the turbine
which in turn drives a generator
Figure 3 Archimedes Screw Turbine [William David Lubtiz, 2014].
In order to direct the flow of water and convert the maximum amount
kinetic energy carried by the water into rotational kinetic energy of the turbine, a
trough in which the turbine is inserted is also constructed. Depending on
available resources this trough can be constructed from concrete (onsite trough),
or steel. The Archimedes turbine is used for sites that have low heads but high
flows. The Archimedes turbine has shown efficiencies of between 78% and 83%
making it an excellent alternative low head hydro power generation. Typical
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large turbines rotate around 26 rpm thus the top of the screw connects to a
gearbox which increases the rotational speed to 750 and 1500 rpm making it
compatible for standard generator speeds. For the most cost effective
installations, the Archimedean screw turbines are often inclined at an angle of 22
degrees from the horizontal. (An introductory presentation of the Archimedean
screw as a low head hydro power generator, Christos 2015).
Advantages of the Archimedes screw turbine
Very cost effective as compared to water wheels and other turbines such
as the Kaplan or Pelton turbines.
They yield better efficiency even with partial loads as compared to
typical turbines like the Kaplan turbine or water wheels.
They are simple to use and install.
There is no complex civil works that must be done in order to necessitate
their installation.
The bearings used on Archimedes turbines are very durable.
Archimedes turbines are Robust, wear resistant and reliable.
They do no damage to fish and will only incur minimal environmental
impact upon their installation.
Archimedes turbines are the only turbines most suited for low water
heads.
Disadvantages of the Archimedes screw turbine
Changes in head during the year and the consequent changes in the power
generated.
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Requires high flow rates.
Maintenance of lower bearing is quite difficult.
Low rpm requires gearbox and this reduces efficiency.
For efficiency, the screw requires a variable speed drive in operation.
(An introductory presentation of the Archimedean screw as a low head
hydro power generator, Christos 2015).
1.2 Problem Formulation
At this stage, the researcher wishes to make it clear that this thesis is not
about an intention to try and produce a novel design of the Archimedes turbine,
but to, ascertain if the following questions and objectives can be answered and
realised respectively.
Does Zambia have the skill set and facilities that can construct and
reproduce an Archimedes turbine?
The researcher feels that this question deserves a decent answer in that in
the entire history of Zambia, right up to this point no Archimedes turbine has
ever been constructed.
So, could it be that Zambia perhaps just lacks the right kind of sites
where an Archimedes turbine can be installed?
Zambia has no lack of potential sites where an Archimedes turbine can be
installed, interestingly according to a World Bank report of 2015 conducted to
assess Zambiaβs potential to produce Hydro power, it was established that
Zambia has a potential to generate a staggering 6400 megawatts from its hydro
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systems and yet it only exploits 2400 megawatts from that amount. Thus, a lack
thereof of appropriate site where an Archimedes turbine can be installed may not
be the reason why Zambia has never reproduced and installed an Archimedes
turbine.
Perhaps it is expensive for the rural electrification authority of Zambia to
reproduce and construct such turbines?
Again, not really in that as the forgoing pages have indicated, one of the
advantages of using the Archimedes turbine is that it is more cost effective than
any other turbines such as the Kaplan and Pelton turbines, implying that it would
be much easier for such authorities to install and maintain such facilities and
actually live up to the task they have been charged by the government. The only
underlying reason remaining then is that maybe there is a lack of skills that can
carry out the construction of such a turbine.
Thus, the researcher deems it fit to establish if there is actually a lack of
individuals that could be presented with a drawing of the turbine and when asked
to reproduce it will either say it cannot be done or that they do not have the
machinery or facilities to carry out the design.
1.3 Design and construction of a simplistic Archimedes turbine
By simplistic, the researcher is referring to a design in which such
elements as the gear box are replaced with only a pulley and belt driving the
generator. Also, instead of using a typical generator, it is instead replaced with
easy to source devices such as brushed direct current motors, auto mobile
alternators and high rated (12V) bicycle dynamos to act as generators.
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This is not to override the importance of all those standard elements such
as a gearbox, generator and even a control panel with its corresponding
automation system. However a simplistic approach might just what may be
needed to relatively improve the lifestyle of people in Zambian rural areas.
Consider why that is the case, if anyone one keen on seeing a rural area
being electrified actually visited some rural establishments in Zambia such as
Chimbuka in chinsali northern Zambia, Malole of kasama, serenje in central
Zambia they would encounter what they would consider to be the paradox of the
century. The reality is that amidst these rural set ups are found hydro sites very
much suitable for electricity generation. Case in point is Chinsali which is home
of the Chipoma falls. This is a mini falls with very appropriate sites were
Archimedes turbines can be installed. Yes, turbines not turbine. Several turbines
can be installed in parallel and power the rural establishment. Yet people in that
area travel no less than 8km to gain access to electricity just to charge their
phones. To this effect the researcher feels that it would be in order to design and
construct a simplistic turbine which can easily be installed at such sites, with the
help of the rural electrification authority of Zambia the researcher would
recommend sensitizing rural establishments situated near to potential sites on the
design and construction of such simplistic turbines.
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1.4 Potential sites for Archimedes turbine installation in Zambia
Site name: Chipoma Falls
Location: 650 km north of the Zambian capital
Lusaka.
Volumetric flow rate: 2500 m3/sec
Average head of the falls: 5.3 m
Average flow velocity of water current: 30
m/sec.
Suitability for Archimedes turbine installation:
very suitable
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Figure 4 Potential sites for Archimedes turbine installation in Zambia.
The picture shows sites in Zambia
where an Archimedes turbine may be
potentially installed. With the
exclusion of the Victoria Falls, the
hydro power of the following sites
may be exploited by using an
Archimedes turbine;
Kalambo falls (Mbala,Zambia)
Ngonye falls (South, Zambia)
Lumangwe falls(Luapula)
Nkundalila
falls(serenje,Zambia)
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CHAPTER 2. LITERATURE REVIEW OF THE
ALTERNATIVE OPTIONS TO ARCHIMEDES TURBINES
2.1 The Need for Renewable Energy
Recently there has been a strong push towards the harnessing of green
energy all over the world due to the following reasons:
Depletion and increasing cost of non-renewable energy sources
For a long time the world has relied upon the use of fossil fuels especially
coal as the major source of energy, however no matter how bountiful such
resources can be it means that one day they will run out. Thus, if producing
electrical energy from coal is all the world has ever known it might just be that
the moment these reserves will be depleted the entire world will run out of ideas
on where the next reserves would come from.
To that end, the international energy community is pushing towards a
much more permanent solution to this inevitable reality facing all non-renewable
energy sources such as coal. As shown in the figure below there was a price
spike in fossil fuels during the winter of 2000-2001 after which the cost of
petroleum and natural gas for electricity generation fell through early 2002.
However the beginning of 2002 saw a steady increase in both the nominal and
the real cost of natural gas and petroleum which peaked in the late 2005 and
early 2006. From October 2001 to January 2005, natural gas costs increased by
141%. The steady increase in the cost of fossil fuels is as a result of an increasing
demand for energy coupled with a steady depletion of the fossil fuels.
20
Figure 5 Fossil Fuel Price over time.
Growing demand for energy
The world population has been increasing steadily as the chart below
shows; a growth in the population entails that social and economic factors must
likewise evolve in order to be able to sustain the growing population. For any
meaningful evolution of the society and economy to take place energy is the core
driving element. For example an increase in population means that cities must
expand, food production must be scaled up, and economic drivers must also
function at a high rate to accommodate the expanding population. As a result the
21st century has seen the strongest growth in industrialisation which has been
characterised with a push for increased production and thus a subsequent
increase power consumption.
Clearly a growing population has a demand for more energy. The
implication of this has been that whatever energy sources the world has
previously relied upon have had to be expanded, or there has been a need to find
new sources of energy to close the gap between demand and the actual energy
21
being furnished to the world. Such new sources have included the harnessing of
energy from tidal waves, nuclear energy, wind energy, hydro power schemes and
solar power. Actually the demand for energy in relation to population increase is
growing exponentially.
Figure 6 Top ten World Energy Consumers. (www.energydata.net).
Figure 7 Global Energy Consumption. (www.energydata.net).
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From the bar graph it could be estimated that from 2000 to 2014 the
global consumption increased by 4000 Mt. It is no wonder why the world energy
outlook estimates the global energy requirement to grow by 37% by 2040.
To meet this growing demand the power sector also had to step up the
generation capacity. This they did. Different energy sources where exploited to
meet the growing demand but mostly exploited was generation using fossil fuels.
This put the power industry on the path to solve the power demand
problem but also created another problem. This is the emission of greenhouse
gases which has possibly led to the climate change problem being faced globally.
Climate change
Globally there has been an increase in the concern regarding the effects
of climate change, the figure below is an indication of the level of concern
expressed by different continents on the issue of climate change;
Figure 8 Climate Change Perceptions.
23
Climate change has mostly resulted from an increase in the emission of
greenhouse gases into the atmosphere, greenhouse gases are mainly carbon
dioxide and others. The chart below shows how carbon dioxide emissions have
increased from 1990 to 2014 in different countries;
Figure 9 CO2 Emissions from fuel combustion. (www.carbonbrief.org).
In just 24 years from 1990 to 2014, an increase of about 10 000 MtCO2
was released in the atmosphere. The adverse effects that have been associated
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with this increase in greenhouse gases namely global warming and climate
change are very conspicuous to all.
To bring that concern home to the researcherβs country Zambia, in the
past two years Zambia has faced extreme weather conditions ranging from
droughts to heavy downpours and flash floods. These extremes have negatively
impacted on the Zambian economy. During the 2015-2016 drought for example
Zambia faced massive power shortages which crippled production in the mining
sector on which its economy is largely dependent.
This year Zambia has faced flash floods which have damaged houses and
crops.
All these reasons are probably a result of an increase in greenhouse gases
in the atmosphere leading to a disruption in the climate. The increase in
greenhouse gases has been largely contributed to by the emission from different
sectors the major culprit being industrial carbon dioxide released by burning coal
in coal fired power plants. The pie chart below shows the emission rates from
different sectors;
25
Figure 10 Global Greenhouse Gas Emissions by Gas. (www.epa.gov).
Looking at the above figures indicates that mankind can still deviate from
the disastrous course they have embarked on and allow the environment or
atmosphere to heal.
The chart shows that 65% of the carbon dioxide is emitted from fossil
fuels and industrial processes. Fossil fuel usage ranges from its use in automobile
cars to its use in the industry as a fuel. Industrial processes that are major
contributor to carbon dioxide emissions are coal fire power plants. This means
that all that has to be done to get rid of those coal fired power plants is the
implementation of renewable energy systems.
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According to a World Bank report 59.08% of the Zambian population
live in rural areas, this means that majority of Zambians are living in rural areas.
It is interesting to note that for lighting and heating purposes people in rural areas
use wood fires and since the majority of Zambians live in such setups they
obviously contribute significantly to the 11% carbon dioxide emission from
forestry and land use. Thus, a project like the researcher has proposed would
shift that dependence to a much cleaner form of energy and a much more
versatile one in terms of its application.
Clearly as the forgoing indicates, there has never been a time in human
history when the need for renewable energy has been as overwhelmingly great, it
is somewhat an emergency, especially when this issue is perceived from the
stand point of the effect fossil fuels are having on climate change in that if
mankind continues going down this road they might just be killing themselves.
2.2 Renewable Energy Alternatives.
It is because of the reasons outlined above that the world at large has
turned its attention to renewable energy sources. Renewable energy or alternative
energy is energy that is produced from a source that cannot be completely
depleted. The following are the possible sources of renewable energy;
2.2.1 Solar Energy
Solar energy is generated from the core of the sun by a process called
fusion. The fusion process takes place when hydrogen atoms combine to
produces helium isotopes. However, during this process a significant amount of
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matter is also released which is transformed into energy as purported by the
Albert Einsteinβs equation;
πΈ = ππΆ2 (2.1)
Where E is the energy generated from a quantity of matter whose mass is
M and C is the speed of light.
Figure 11 Solar Energy Creation.
The radiant energy which the sun generates from this process in just one
day is more than the earth uses in on full year.
However, the sun is 93 million miles away from the earth and the photons
of energy travel at 186,000 miles/sec. It thus takes radiant energy 8 min to reach
the surface of the earth during which time a chunk of this energy will be
absorbed by different atoms and molecules within space and will be reflected
back into space by the atmosphere. The outcome is such that only a small
fraction of the energy emitted from the sun reaches the surface.
The amount of solar energy reaching the earth is only small in relation to
the initial radiated energy but in terms of how much the earth needs this small
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fraction when collected for a period of one hour has the capacity to meet the one
yearβs energy need for a nation like America. Solar energy is used mainly for
space heating, solar water heating and solar electricity.
Solar Space Heating
This finds its application in heating or warming up a room or an entire
house using solar radiation. The principle is less like that of a green house.
Which is to design a space in such a way that it allows in as much solar radiation
as possible.
Upon entry in into the space it is absorbed by various aspects of a room
such as walls and thus the wavelength of the waves reduces. The result is that the
radiation will fail to escape from the space but be trapped inside and thus
keeping the room warm.
Solar Water Heating
This has a solar collector which warms up water in a tank and the water is
distributed to different parts of the house like in a normal geyser household
heating system. The water is used for dishwashing, bathing and cooking.
Solar Electricity
There are two ways of converting solar energy to electric energy. Using
photovoltaic cell and solar thermal electricity:
29
Photovoltaic Cells
A photovoltaic cell is made of silicon and a platform to trap as much
solar energy as possible. The operation mechanism is such that when a photon
from the sun radiant energy strikes an atom of silica and the energy of the photon
given by the equation;
πΈ = βπ ( 2.2)
Where h is planks constant and f is the frequency of the photon. If this
energy is enough to excite an electron from one energy to another in the silicon
atoms, the result is that the transition of the electron will generate an electric
current which is subsequently used to power some electric device, such a clock,
calculator or if there is a large scale photovoltaic farm the generated power can
be used to power homes.
Solar Thermal Electricity
As for solar thermal electric energy, it is generated by concentrating solar
energy harvested from a large space toward a receiver. Circulating through the
receiver is water which will end up being superheated and the supersaturated
steam generated will expand against steam turbines and in turn generate
electricity. The schematic below is a representation of a concentrated solar power
system;
30
Figure 12 Solar Thermal Electricity.
2.2.2 Wind Energy
Wind energy is tapped from wind when the wind blows past a turbine, the
blade captures the energy and rotates. The rotation then spins an internal shaft.
The shaft is connected to a generator which finally generates the electrical
energy.
A wind turbine mainly consists of a steel tubular tower which stands up
to 325 feet tall. This tower supports the hub which secures the wind turbine
blades it also consists of a nacelle which houses the turbines shaft, gearbox,
generator and controls. Modern turbines are also equipped with wind assessment
control systems which enables the turbine to automatically start rotating after
sensing wind.
The generated electrical energy is then fed to power transmission system
and finally delivered to a home, ranch or farm. Often there are many such
generators on a very large space called a wind farm. Depending upon the height
31
of the turbine, one turbine can have the capacity to power one home or hundreds
of houses.
2.2.3 Geothermal Energy
As the name suggest this form of energy is heat tapped from the earth. It
is a clean and sustainable form of energy.
Below the surface of the earth is a sea of high temperature magma whose
high temperature in geothermal power generation is utilised by sinking a well
through which water is pumped. When the water becomes supersaturated steam,
it moves upwards and drives a special turbine that in turn runs a generator which
produces electrical energy.
After expanding in the turbines the steam condenses and becomes water
which is again pumped back to the earthβs core to be heated so as to be converted
into supersaturated steam again. There could be one or more of such wells. The
more there are the higher the generated electrical energy.
A geothermal power plant is required to be located at the source of the
well obviously for the purpose of reducing energy losses that would occur had
the well and the turbines being located at two different places. This ensures that
the enthalpy of the steam is fully utilised. Below is a general schematic
representation of a geothermal power plant.
32
Figure 13 Geothermal Energy.
2.2.4 Tidal Waves
The cyclic movements of the seas caused by the gravitational effects of
the sun and the moon on the sea causes sea tides. The energy of these tides is
harnessed in order to produce electrical energy.
2.2.5 Biomass
Any decaying organic substances or objects could be classified as
biomass. Electrical energy is generated in two ways from biofuels as they are
commonly called:
The first is to gather all the organic waste and take them to a furnace
where they are burnt and the heat energy generated is then used to heat water
33
which produces steam that expands against steam turbines more or less like in a
coal fired power plant to generate electrical energy.
The second option is to ferment the waste in a landfill and collect all the
escaping methane which can then be used as natural gas to fire gas powered
power plant.
2.2.6 Hydro Power
Hydro power is electrical energy generated from water in motion, this is
achieved in two possible ways:
Exploitation of the kinetic energy of fast moving water
Fast moving water possesses kinetic energy which can be harnessed and
converted to electrical energy. Fast moving water can exist in the form of a rapid
stream or run off water from a river.
Exploitation of the potential energy of water stored behind a dam
The other of harnessing the energy of water in motion is by enclosing it
behind a massive wall. A dam is in most cases built across a river, implying that
instead of allowing the water to continue with the free flow, the water ends up
collecting behind the wall and thus elevating the water.
Elevating the water means giving it more head which in turn gives the
mass of water more potential energy. Once this has been achieved all that has to
be done is converting the massive potential energy now possessed by the water
into kinetic energy. The kinetic energy of the water will in turn be converted into
34
rotational kinetic energy of a turbine which will drive a generator and in turn
generate electricity.
Classification of Hydro power plants
The table below shows how hydro power plants are classified;
Table 1 Classification of Hydro power plants.
LARGE
HYDRO
MORE THAN 100MW AND OFTEN FEEDING INTO A
LARGE ELECTRICITY GRID.
Medium
hydro
15-100MW β usually feeding a grid
Small hydro 1-15MW- Usually feeding into a grid
Mini-Hydro Above 100KW,but below 1MW; either standalone schemes or
more often feeding into the grid
Micro-Hydro From 5KW up to 100KW; usually provides power for a small
community or rural industry in remote areas away from the
grid.
Pico-Hydro From a few hundred watts, up to 5KW
It is worth noting that many sites that are suitable for the development of
both large and medium hydro power plants have already been exploited. Coupled
to this is the fact that projects of this magnitude have the following downsides:
35
Considerable environmental impact
The environmental impacts and consequences of large dams are quite
numerous and varied, listed below are some of them:
Dam wall blocks fish migration, for example in the year 2002 low flows
below dams killed thousands of salmon fish in Klamath.
Entrapment of sediments critical for maintaining physical processes and
habitats downstream of the dam.
Transformation of a freely flowing river into an arterial lake. This leads
to changes in the physical and chemical makeup of the water body which
may not be suitable for aquatic life that had existed therein previous
conditions.
Expensive to construct and often takes long
Building a wall across river is an endeavour that not only can take a very
long period of time but one which is also very expensive.
Due to the forgoing reasons and perhaps a couple more, the attention has
now been turned to micro, mini and pico-hydro schemes to enhance the
availability of electrical energy especially in rural set ups.
Hydro Turbines
Hydraulic turbines may be defined as prime movers that transform the
kinetic energy of falling water into mechanical energy of rotation and whose
prime function is to drive an electric generator. (Q.H Nagpurwala)
36
There are two ways of classifying hydro turbines, the first is the
classification based on the way a turbine interacts with water. When turbines are
classified in this manner two groups of turbines emerge as described below:
Impulse turbines
Flow energy is completely converted to kinetic energy before
transformation in the runner.
The impulse forces being transferred by the direction changes of the flow
velocity vectors when passing the buckets create the energy converted to
mechanical energy on the turbine shaft.
The flow enters the runner from jets spaced around the rim of the runners.
The jet hits momentarily only a part of the circumference of the runner.
Reaction turbines
There are two effects that cause the energy transfer from the flow to the
mechanical energy on the turbine shaft:
Firstly, it follows from a drop in pressure from inlet to outlet of the
runner. This is denoted as the reaction part of the energy conversion.
Secondly, the changes in the directions of the flow velocity vectors
through the runner blade channels transfer impulse forces. This is denoted as the
impulse part of the energy conversion.
Examples of turbines
37
Table 2 Turbine types and their examples 2.
REACTION TURBINES IMPULSE TURBINES
Francis turbine Pelton turbine
Kaplan Turbine Turgo turbine
Propeller turbine
Pelton Turbine
Invented by Pelton in 1890
It is a tangential flow impulse turbine.
Most efficient in high head applications.
Most applicable for power plants whose net heads are in the range of 200
to 1500m
Largest unit can generate up to 200 Megawatts.
These kind of turbines are best suited for high head low flow sites.
Depending on water flow and head, Pelton turbines can operate with
heads as low as 15m and as high as 1800m.
As height of fall increases, less volume of water can generate same
power.
38
Figure 14 Pelton and Francis Turbines.
Reaction turbine in which the working fluid changes pressure as it moves
through the turbine and in turn giving up its energy. Pelton and Francis turbines
are examples of reaction turbines.
The inlet of the Francis turbine is spiral shaped with guide vanes which
direct the water tangentially to the runner causing the runner to spin.
In order to allow for efficient operation even under varied a wide range of
flow conditions, the guide vanes are designed and constructed in such a way that
they are adjustable.
They are used in power plants whose net heads range from 20 to 750m.
39
Figure 15 Vertical shaft Francis Turbine.
Propeller Turbine
Runner only has a few blades radially oriented on the hub and without an
outer rim.
The water flows axially through the runner of the turbine.
The runner blades have a slight curvature and thus cause relatively low
flow losses. This allows for higher flow velocities without great loss of
efficiency.
The runner diameter is smaller and thus the rotational speed is more than
twice that of the Francis turbine of a corresponding head and discharge.
The comparatively high efficiencies at partial loads and the ability of
overloading is obtained by a coordinated regulation of the guide vanes and the
runner blades to obtain optimal efficiency for all operations.
40
Figure 16 Propeller turbine.
Kaplan Turbine
Kaplan turbines have adjustable runner blades, that offers significant
advantage to give high efficiency even in the range of partial load, and there is
little drop in efficiency due to head variation or load.
The runner blade operating mechanism consists of a pressure oil head, a
runner servomotor and the blade operating rod inside the shaft, etc.
The Diagonal flow turbine has runner blade-stems constructed at a certain
diagonal angle to the vertical centre line of the machine.
41
Figure 17 Kaplan Turbine.
Archimedes Turbine
However, the turbine on which this Thesis is based does not explicitly fit
in any of these two categories. That turbine is called the Archimedes turbine.
Here are two reasons why the turbine might not be strictly or explicitly be a
reaction or impulse turbine;
In a Reaction turbine, the blades (runners) are fully immersed in water
and are enclosed in a pressure casing. The blades are angled so that pressure
differences across them cause them to rotate. The Archimedes screw is probably
closest to this type of turbine but it is not enclosed in pressure casing. Like the
Archimedes screw, reaction turbines are generally used on low head applications.
Impulse turbine runners operate in air and are turned by jets of water
hitting the runners. The Archimedes screw bears no resemblance to this type of
turbine. Impulse Turbines are used with high head systems and use nozzles to
produce the high velocity jets.
42
CHAPTER 3. METHODOLOGY
3.1 Site Survey
The first stage towards the design and construction of any turbine is the
site where the turbine is going to be installed. Subsequently the turbine was
constructed in such a way that it suited the conditions that were studied at the
site:
To achieve this several sites were inspected in order to determine which
one would best fit in the budget and one which would accommodate the
operating characteristics of a screw turbine namely:
High flow
Low head.
For all the sites that were surveyed, the following parameters were
calculated:
Head from which water was falling
The volumetric flow rate of the water at the site.
Canal diameter from which water was falling
43
3.1.1 Site 1 Details
Figure 18 Picture of Site 1.
Parameters associated with site 1:
Table 3 Site 1 parameters.
PARAMETER VALUE
Breadth of canal 0.7m
Depth of canal 0.6m
Head from which water falling 1m
Length of canal over which the flow
velocity of the canal was taken
3.5m
Average Time taken by a floater to
cover the length of the canal over
which velocity was measured
4.08sec
44
Pros of site 1
Already existing head means there would be no need for modifying the
site by building a temporary dam to elevate the water level to produce a
realistic head.
Easy installation of turbine.
Would require a low budget to tailor design a turbine according to this
site parameters.
Cons of site 1
Flow velocity is low and this yields a low volumetric flow rate of the
stream which would in turn affect the power output of the screw turbine.
The site is too cramped and tight, this can make manoeuvring around
during site installation somewhat difficult.
3.1.2 Site 2 Details
45
Figure 19 Pictures of Site 2.
Parameters associated with site 2:
Table 4 Site 2 parameters.
PARAMETERS VALUE
Breadth of canal 0.8m
Depth of canal 0.21m
Head from which water falls 1.76m
Length of canal over which the flow
velocity of the canal was taken
13m
Average Time taken by a floater to
cover the length of the canal over
which velocity was measured
5.7sec
46
Pros of site 2
Flow velocity is very high and thus this site would yield higher power
outputs if the turbine is installed here.
Site 2 also already existing head thus there would be no need of installing
an artificial wall to raise the head somewhat.
Cons of site 2
The site is located in a very unsafe section of the stream.
The terrain is very bad and as such to do the installation of the turbine it
would cost more than the budget can handle.
Space is too tight for free movement, this can affect the installation
process of the turbine, making it a very difficult ordeal.
47
3.1.3 Site 3 Details
Figure 20 Pictures of Site 3.
48
Parameters associated with site 3:
Table 5 Site 3 parameters.
PARAMETER VALUE
Breadth of canal 1.51m
Depth of flowing water in the canal 0.21m
Head from which water falls 3.5m
Length of canal over which the flow
velocity of the water was taken
13mΝΝΝΝ
Average Time taken by a floater to
cover the length of the canal over
which velocity was measured
5.7sec
As can be noted, the canal length over which the flow velocity of the
water was taken and the average time taken to cover the length of the canal over
which the velocity of the water was measured for site 3 is the same as that for
site 2 in that site 2 is downstream of site 3.
Pros of site 3
Of all the sites surveyed this site gave the best and highest head.
The flow velocity is very high and thus coupled with the high this spot
would yield the highest power output.
49
Enough space for manoeuvring during turbine installation.
Cons of site 3
Presence of a deep hole at the point where the water hits the surface
would make the endeavour of installing the turbine a very dangerous one.
The site would require a budget much higher than what is available to
fully construct and install a screw turbine which would sit at the site.
3.1.4 Site 4 Details
Figure 21 Site 4 Pictures.
50
Table 6 Site 4 parameters.
PARAMETERS VALUE
Breadth of canal 2.2m
Depth of flowing water in the canal 0.15m
Head from which water falls 0.93m
Length of canal over which the flow
velocity of the water was taken
5m
Average Time taken by a floater to
cover the length of the canal over which
velocity was measured
2.3sec
Advantages of this site
Availability of an already existing head makes it easy to deal with the
site.
Enough space for manoeuvre during installation.
High velocity of the stream means a considerably high volumetric flow
rate of the stream is available which would result is a high-power output
from the turbine.
This site offered more flexibility than the other three sites surveyed by
the researcher and such it was selected to be the one on which the turbine was to
be installed.
51
The entire site has a width of 2.2m hence it is feasible that this entire
width could be exploited by designing and constructing a turbine which would
cover the entire width of the canal at this point. Such an approach would offer
the following advantages:
Maximum volumetric flow rate of the water could be trapped from the
stream.
The turbine would be subjected to dimension of velocity vector that the
flow could offer.
Ultimately the above stated advantages would result in having a turbine
which would yield the highest power output. However exploiting the entire width
of the stream would prove to be costly as this would require that a turbine with
an outer diameter 2.2m be constructed.
To this effect, the researcher will only use 120mm of diameter for this
project due to the limitations imposed by the available budget.
3.2 Design and Simulation of the Turbine.
The second stage in the process was the design of the turbine, this stage
basically involved the following two sub-stages;
Determination of the turbine design parameters.
Simulation of the turbine using Solid Works.
3.2.1 Turbine Parameters
The design parameters of the Archimedes turbine are dictated by the site
conditions on which it will be installed. However balance must always be sought
52
between performances and cost. This is especially true considering that this kind
of project is expected to be executed for rural set ups in which people might not
necessarily have the means to finance such a project.
To this end the researcher sought to produce design parameters which
would both be optimal but also cost effective.
Optimal design of the screw:
Table 2 Optimal Ratio Parameters of an Archimedes Screw (Chris Rorres,
2000).
Turbine length (L):
The site parameters which dictate the length of the turbine are the optimal
angle of inclination and the head available at the site. The angle of inclination of
53
the turbine which has been discovered to yield reasonable results is 23.80 (Cfd of
a Screw Blade for Standalone Micro Hydro Generator, Suga Ganeshan 2013).
The head available at the preferred site i.e. site 4 is 0.93m, with this head
coupled with the optimal angle of inclination, the optimal length for this site
would have to be:
Turbine Length
Head = 0.93m
Optimal turbine length = 0.93 / sin 23.80 =2.304m.
This length is optimum for the site, however given the scale of the project
and the duration during which it was expected to be completed, compounded
with a lack of monetary resources, the researcher adopted a length of 1.20m to
construct the turbine.
With adjustment, the angle of inclination of the turbine came to
β = π ππβ1 (0.93
1.2)
β = 50.80
(3.1)
ΙΈ=23.80
ΙΈ=23.80
54
While it is true that the optimal inclination angle will give reasonable
results Murray Lyons asserted that an increase in the angle of inclination
improves the efficiency of the turbine. The horizontal distance which the turbine
will thus span from the foot of the wall will be:
βππππ§πππ‘ππ πππ π‘ππππ =0.93π
π‘ππ 50.8
βππππ§πππ‘ππ πππ π‘ππππ = 0.758π
(3.2)
Thus the slope of the screw (K):
πππππ ππ π ππππ€(πΎ) =0.93
0.758= 1.23
(3.3)
Number of Blades (N);
The number of blades selected to be used in the construction of an
Archimedes turbine is based on the principle that the efficiency of the turbine
increases with an increase in the number of helical flights. (Lab Testing and
Modelling of Archimedes Screw Turbines, Murray William Keith Lyons 2014).
To this end the number flights selected was 14 for the turbine to strive
towards turbine efficiency.
Diameter of the outer cylinder (D0):
The outer cylinder refers to the cylinder created by the circumference of
the blades of the screw. For a 14 bladed screw, the optimal radius ratio according
55
to the analytical analysis conducted by Chris Rorres is 0.5360. (Chris Rorres,
2000).
πππππ’π πππ‘ππ =πππ‘πππππ πππππ’π
ππ₯π‘πππππ πππππ’π =
π πΌ
π 0=
π·πΌ
π·0
πΈπ₯π‘πππππ ππππππ‘ππ(π·0) =πΌππ‘πππππ ππππππ‘ππ
πππ‘ππππ πππππ’π πππ‘ππ
ππ₯π‘πππππ πππππ‘ππ(π·0) =65
0.5360
ππ₯π‘πππππ ππππππ‘ππ = 121.27ππ β 121ππ
(3.4)
Pitch (β);
The pitch refers to the period of the blade. The optimal pitch ratio for a
screw turbine with 14 blades as extracted from the table of optimal values is
0.3270.
The pitch ratio is given by the formula below;
πβ =πΎπ¬
2ππ 0
π¬ = (2ππ 0πβ)/πΎ
π 0 = ππ’π‘ππ πππππ’π =121
2= 60.5ππ
πβ = πππ‘ππππ πππππ’π πππ‘ππ = 0.3270
πΎ = π ππππ ππ π‘βπ π ππππ€ = 1.23
56
πππ‘πππ’π ππ‘ππβ =6.28 Γ 60.5 Γ 0.3270
1.23= 101ππ
(3.5)
Thus for the screw turbine under construction the optimum pitch or
period of the blades ought to be 101mm, However a lack of facilities to facilitate
a robust bending of the blades made it very difficult to produce a screw with that
given pitch and as such, the pitch was adjusted to 70mm.That pitch was adopted
after one week of struggling to maintain a pitch of 101mm on the shaft.
Angle of incline (Ξ²):
This is the angle of incline of spiral intersection of blade and inner
cylinder with respect to the axis of screw. In order to determine this angle we
need the radius of the inner cylinder and a length along the screw axis which
each blade covers before is joined to the next blade.
π½ =π‘ππβ1(πππππ’π ππ πππ‘πππππ ππ¦ππππππ)
(ππππππ πππππ‘β πππππ π‘βπ π ππππ€)= π‘ππβ1 (
30.5
40) = 37.30
(3.6)
Angle of incline (Ξ±):
This is the angle of incline of spiral intersection of a blade and the outer
cylinder of the blade with respect to the screw axis. It was also determined in a
manner similar to Ξ² but this time with reference to the radius of the outer
cylinder.
57
πΌ =π‘ππβ1(πππππ’π ππ π‘βπ ππ’π‘ππ ππ¦ππππππ)
πππππ‘β πππππ π‘βπ π ππππ€=
π‘ππβ1 (121
2)
40= 56.50
(3.7)
These two angles were closely adhered to during the construction
process.
The group of design parameters:
Length of the turbine.
Angle of incline for the screw on site.
Number of blades.
Diameter of outer cylinder
Inclination angles of the blades with respect to the screw axis
Fully describes the screw and as such the screw was constructed on the
basis of the values given.
58
Pulley Design:
The design parameters of the pulley where largely influenced by the
physical dimensions of the alternator (generator) especially those of its pulley
since this the part of the alternator which was to be interacting with the pulley.
Alternator pulley dimensions
Table 7 Alternator Pulley Dimensions 2.
PARAMETER VALUE
Pulley diameter 38mm
Width of fan belt groove 10mm
Depth of fan belt groove 10mm
This set up is called a drive and driven assembly in which the alternator
pulley was to be driven by the fabricated pulley using a fan belt. The diameter of
the pulley was thus governed by the velocity ratios equation (Machine Design,
R.S Khrumi)
π2
π1=
π·1
π·2
π1 = π ππ‘ππ‘πππππ π ππππ ππ π‘βπ ππ’ππππ¦(ππππ£ππ)
π2 = π ππ‘ππ‘πππππ π ππππ ππ π‘βπ πππ‘ππππ‘ππ ππ’ππππ¦(ππππππ€ππ)
π·1 = π·πππππ‘ππ ππ π‘βπ ππ’ππππ¦(ππππ£ππ)
59
π·2 = π·πππππ‘ππ ππ π‘βπ πππ‘πππππ‘ππ ππ’ππππ¦(ππππππ€ππ)
(3.8)
The researcher initially sought to increase the rotational speed of the
alternator pulley by 40 times that of the screw pulley. This would have meant
that the pulley would have had a diameter of;
ππ’ππππ¦ πππππ‘ππ π‘π πππππππ π πππ‘πππππ‘ππ ππ’ππππ¦ π ππππ ππ¦ 40 = 40 Γ 38 = 1520ππ
(3.9)
This was not realistic and there was no stock which could make a pulley
that big. The available stock had a diameter of 190mm meaning that the speed
ratio would be;
π2
π1=
190
38= 5
(3.10)
This is reasonable for a project of this scale. Thus the pulley was made
with diameter of 190mm. The belt grooves dimensions were adopted from the
alternator pulley. The schematic below shows the arrangement of the layout.
60
Machined members:
The machined members are the mild steel cylindrical bars which were
welded to both ends of the shaft so that it may fit in the ball bearings. Thus, the
design parameters of these two pieces were largely influenced by the diameter of
the ball bearings and the internal diameter of the shaft in which they were to be
fitted.
Diameter of the end to fit in the shaft = 58mm.
Diameter of end to fit in the ball bearing and the pulley = 30mm
Ball bearing diameter = 30mm
Machined member to which the pulley was attached.
61
The machined member to be welded to the side of the screw that was to
be submerged in the water was designed the same as the layout above, the only
difference being the length of the 30mm protruding member which was left at
30mm.
Trough design parameters:
The design of the trough is governed by the equation an equation which
determines the gap between the screw and the trough given by Nagel (Nagel
1968):
πππ = 4.5 Γ βπ·
πΊππ = 4.5 Γ β121
πππ = 49.5 β 50ππ
(3.11)
62
Guided by this design parameter and of course the length of the screw,
the trough was designed with the following parameters with screw being
centrally aligned in the trough:
ππππ π‘βπ πππ π π‘π π‘βπ π‘ππ = 121 + 50 + 50 = 221ππ
(3.12)
The arc length of the trough is 0.67 m and its length determined by the
length of the screw is to be 1.22m.
This was all the information that was necessary to design the screw
turbine and after having fully determined each of these parameters it was now
necessary to produce the design in Solid Works.
3.2.2 Simulation of the Turbine in Solid Works.
Before a simulation of the turbine could be carried out the first step was
to reproduce the turbine in Solid Works. The following steps were followed to
reproduce the design in Solid Works;
Select any plane from the planes pane on the left-hand side of the screen.
63
Sketch tab on the top left corner was then selected and then the icon for
sketching a circle was selected in order to reproduce a circle whose
diameter is equal to the inner diameter of the screw.
Within the sketch tab, there is an item labelled offset entities which
enables the addition of the outer diameter of the screw to be added to the
sketch since the thickness of the shaft of the turbine is 2mm the offset
parameter was set at 2mm to reproduce the outer diameter of the turbine.
The sketch tab was exited and the features tab was selected and the
extruded boss/base tab was selected, which gave the sketch a three-
dimensional view. On the left side of the screen a pane which allowed for
the addition of the length of the screw popped and the length of the screw
to which blades were to be attached was entered (1000mm).
64
Once the turbine shaft had been produced the thickness of the shaft was
selected and subsequently the sketch tab which appears was selected and
then the sketch tab was exited from the top left corner of the screen. Then
the features tab was selected to reveal the curves item. The curves drop
down menu was selected to reveal the different types of curves and the
helix curve was selected. Once it was selected the parameters reflective
the turbine up for construction were entered. i.e. pitch=70mm, clockwise
direction with a start angle of zero degrees.
Once the helix had been produced a reference plane to produce the three-
dimension view of the helix was selected and a sketch was made at the
starting point of the helix curve. The sketch was basically a rectangle
65
with a breadth equivalent to the thickness of the blades (3mm) and a
height equal to the height of the blades measured from the top of the
shaft. At the top left corner is tab named swept boss/base. It was selected
in order to reproduce a 3D sweep of the helix and thus generating the 14-
bladed screw shown below. (Colour change is as a result of changing the
material from brass to mild steel).
After the turbine had been designed in Solid Works, the trough was
designed after. This was achieved by selecting a front plane from the
planes pane, selecting the sketch tab and from the drop-down menu of the
arcs, a three point curve was selected which was offset by 3mm to reflect
the thickness of the trough. The resulting arc was then extruded by
1200m which is the length of the trough.
66
3.3 Construction of the Turbine.
3.3.1 Materials of construction
Once the design parameters had been produced, the construction stage of
the turbine was initiated by sourcing the construction materials. All the materials
used in this project were bought expect a few that were improvised.
The improvised aspects of the project includes the support for the
generator and the flat mild steel bars used to support the turbine in the trough.
The table below shows the turbine parts, the material from which they are
constructed and the dimensions of each part;
Table 8 Dimensions of turbine parts 2.
PART MATERIAL DIMENSIONS
Turbine shaft Galvanised steel
pipe
Length 1000mm
Inner diameter 56mm
Outer diameter 58mm
Thickness of pipe 2mm
blades
Mild steel
length 2400mm
thickness 3mm
width 1200mm
Ball bearingsΓ2 Stainless steel Internal diameter 30mm
67
PART MATERIAL DIMENSIONS
Machined
membersΓ2
Stainless steel
machined
member on
submerged
end
Diameter
of
protrudin
g end
30mm
Length of
protrudin
g end
30mm
Outer
diameter
58mm
Machined
member to
which
pulley is
attached
Diameter
of
protrudin
g end
30mm
Length of
protrudin
g end
175mm
Outer
diameter
55mm
Trough Mild steel
Length
thickness
arc
68
PART MATERIAL DIMENSIONS
length
1220mm
3mm
670mm
Pulley Mild steel
Diameter
Hole
diameter
thickness
190mm 30mm 20mm
3.3.2 Fabrication Process
3.3.2.1 Construction of blades
The turbine blades were made by cutting square plates from the
rectangular mild steel sheet using a grinder. A pipe was then tacked to each steel
plate by welding so that clamping can be done easily when the edges of each
plates were being evened out on the lathe machine.
69
Figure 22 Lathe Machine.
The lathe process led to a formation of disks evenly smoothened out at
the circumference. Once the disks had their circumference smoothened by the
lathe machine, the same machine was use to bore out a hole of 70mm diameter at
the centre of each plate to produce a disk like the one shown below:
Figure 23 Disk.
Once all the disks had been produced they had to be fitted onto the shaft
spaced by a pitch of 70mm, to achieve this each disk was cut from the outer
70
circumference to the inner circumference of the bored hole using an angle
grinder.
Finally, by employing arch welding all the 14 blades were fitted to the
shaft to produce a complete spiral with 14 blades each spaced by 70mm from
each other;
3.3.2.2 Pulley Construction
A stock of mild steel was first cut out from an already available long and
large mild steel stock using an angle grinder. The cut stock was then set
on the lathe machine.
Centers were made or marked on the cut stock as it was set to the lathe
machine in order that it runs true or straight.
To achieve the 120mm outer diameter of the pulley, it was machined
down while on the lathe machine.
71
Afterwards grooves were made in the stock.
Since the pulley was not to be attached to the machined member by
welding, the constructed pulley was inserted on the slotting machine in
order to make a key way through which the machined member was to be
locked to the pulley.
Figure 24 Shaft & blade construction.
Figure 25 Stock for the pulley.
72
Figure 26 Slotting Machine.
3.3.2.3 Machined members modification
Stock members were cut using an angle grinder.
Centres were made on both sides of each of the stock members to ensure
that it runs true and or straight.
The stocks were both machined down to a diameter of 55mm so that they
can all fit inside the pipe/shaft of the turbine.
Once the 55mm machining down had been conducted it was now
necessary to machine down the opposite side of each of these members to
a diameter of 30mm to fit in the bearings and the pulley, this was done
by unclamping the work and clamping it on the finished side i.e the
55mm side.
73
The shaft to which the pulley was to be inserted was then taken to the
milling machine in order to make a key slot.
Using a dividing head and the tail stock, the shaft was the clamped on the
milling machine and the machining process was initiated.
A trough in which the turbine was to sit was constructed by rolling a
3mm sheet of mild steel plate on a rolling machine.
Finally, the screw was then fitted on the trough using the bearings which
were fitted on the two shafts.
Figure 27 Milling Machine.
3.3.2.4 Completed assembly
The picture below shows the completed assembly of the turbine, trough
and the pulley mechanism. The protruding metal bars are the ones to which the
generator is to be attached.
74
Figure 28 Completed Assembly.
3.3.3 Electrical Assembly
Once the turbine, trough, pulley had been assembled together the next
phase of the assembly was the mounting of a generator to the turbine. The
researcher used a bicycle dynamo to act as a generator.
75
Figure 30 Mounting of the Dynamo.
The dynamo was mounted above the pulley using bolts and screws right
above the pulley and the fan belt was inserted so that it ran along the pulley
mounted to the screw and the pulley of the dynamo as shown below:
Figure 29 Operating Archimedes Screw Generator.
76
CHAPTER 4. RESULTS AND ANALYSIS
4.1 Power Available at the site
The maximum power available at any site being considered for a hydro
turbine installation is given by the equation ;( Archimedes Screw for Micro
hydro power generation, William Lubtiz)
πππ΄π = ππ»ππ
(4.1)
Q is the total volumetric flow rate of the water at the site.
H is the maximum head or the height from which the water falls.
Ο is the density of the water (1000kg/m3)
G is the acceleration due to gravity (9.81m/s2)
Volumetric flow rate data collection.
Table 9 Site Dimensions.
PARAMETER VALUE
length of canal over which the velocity of the
flowing stream was determined
5m
width of canal 2.20m
Depth of water flowing in the canal 0.15m
77
Trials runs for the time taken for a floater to cover 5m.
Table 10 current flow time.
TRIAL TIMES(sec)
1 2.33
2 2.29
3 2.47
4 2.12
25 2.04
6 2.37
7 2.17
8 2.11
9 2.31
10 2.47
π£πππ’πππ‘πππ ππππ€ πππ‘π(π) = πΆπππ π π πππ‘πππππ ππππ ππ πππππ Γ π£ππππππ‘π¦ ππ π€ππ‘ππ
ππππ π π πππ‘πππππ ππππ = π€πππ‘β ππ πππππ Γ ππππ‘β ππ π€ππ‘ππ ππ πππππ
= 2.2 Γ 0.15 = 0.33π2
78
Velocity of the flowing water in the canal.
π£ππππππ‘π¦ ππ π€ππ‘ππ ππ πππππ =(πππ π‘ππππ πππ£ππππ)
π‘πππ π‘ππππ
(4.2)
Average time taken for the floater to cover a distance of 5m;
aπ£πππππ π‘πππ π‘ππππ
=2.33 + 2.29 + 2.47 + 2.12 + 2.04 + 2.37 + 2.17 + 2.11 + 2.31 + 2.47
10
ππ£πππππ π‘πππ π‘ππππ =22.68
10= 2.268π ππ
(4.3)
Thus the velocity of the water flowing in the canal is;
π£ππππππ‘π¦ =5
2.268= 2.205π/π ππ
(4.4)
The volumetric flow rate of the water in the canal and therefore the flow
rate from the site where the turbine is installed is:
π£πππ’πππ‘πππ ππππ€ πππ‘π = 0.33 Γ 2.205 = 0.728π3/π ππ
(4.5)
79
Power available at the site:
πππ€ππ ππ£πππππππ ππ‘ π‘βπ π ππ‘π = 0.728 Γ 1000 Γ 0.93 Γ 9.81
πππ€ππ π£πππππππ ππ‘ π ππ‘π = 6641.8π€ππ‘π‘π = 6.641πΎπ
(4.6)
Power made available to the turbine.
This all power is not being made available to the turbine because the
turbine does not have a diameter of 2.2m so it can be subjected to the entire
volume of water having that power.
Therefore the amount of power made available to the turbine depends on
the dimensions of the trough since it is the one through which the water is
flowing before contacting the turbine.
Table 11 Trough Dimensions.
TROUGH PARAMETER
(ASSUMING A SEMI CYLINDER)
VALUE
Diameter of trough 0.323m
Length of the trough 1.22m
Volume of water passing through the trough every second= volume of
partially filled cylinder.
80
π£πππ’ππ ππ π€ππ‘ππ ππππ€πππ ππ π‘βπ π‘πππ’πβ ππ£πππ¦ π πππππ = 1/2 Γ π Γ π 2 Γ π»
(4.7)
The total power made available to the turbine will be calculated on the
basis of this volumetric flow rate.
Vπππ’ππ ππ π€ππ‘ππ ππππ€πππ π‘βπππ’πβ π‘βπ π‘π’πππππ = 0.5 Γ 3.142 Γ 0.16152 Γ 1.22
= 0.05π3/π
πππ€ππ ππππ ππ£ππππππ π‘π π‘βπ π‘π’πππππ = ππ‘ Γ π Γ π Γ β
πππ€ππ ππππ ππ£πππππππ π‘π π‘βπ π‘π’πππππ = 0.05 Γ 1000 Γ 9.81 Γ 0.93 = 456.2πππ‘π‘π
(4.8)
4.2 Mechanical power of the screw Turbine.
The mechanical power of the turbine manifests itself as the rotational
kinetic energy of the turbine as shown in the picture below the splashes of the
water are as a result of the rotation of the blades of the turbine.
Figure 30 The turbine installed at the site.
81
The mechanical power of the turbine is given by the equation below:
mππβππππππ πππ€ππ ππ π‘βπ π‘π’πππππ
= π‘ππππ’π Γ πππ‘ππ‘πππππ π ππππ ππ π‘βπ π‘π’πππππ(ππππ
π )
πππΈπΆπ» = π Γ π
(4.9)
(Theory of machines, RS KHURMI).
In order to determine the values of both the torque generated by the screw
and the rotational speed of the screw sophisticated and costly instruments are
required. A load cell attached to circuitry using the Hall Effect could be used to
determine the torque of the screw and tachometer can be used to determine the
rotational speed of the turbine.
However, none of the above mentioned instruments are at the disposal of
the researcher thus making it impossible to determine the mechanical power
output using the formula.
But since the mechanical power manifests itself as the rotational kinetic
energy, the researcher used the rotational kinetic energy formula to determine the
mechanical power of the turbine.
πππ‘ππ‘πππππ πππππ‘ππ ππππππ¦ = 1/2 Γ πΌ Γ π2
(4.10)
82
I is called the moment of inertia of a rotating object in this case the
rotating object is the turbine.
The moment of inertia is the product of the mass of a rotating body and
the square of its radius of gyration.
πππ π ππππππ‘ ππ πππππ‘ππ = πππ π ππ ππππππ‘ Γ πππππ’π ππ ππ¦πππ‘πππ2
πΌ = π Γ πΎ2
(4.11)
(Theory of machines, RS KHURMI).
The radius of gyration is defined as the distance from a given reference,
where the whole body is assumed to be concentrated give the same value of I.
Mass of the screw.
The following data was utilized to determine the mass of the screw:
Table 12 Density of turbine parts.
NAME OF
SCREW
PART
DIMENSIONS OF PART DENSITY OF
MATERIAL USED
Blades Radius of disk 0.0605m Mild steel 7850kg/m3
Thickness 0.003m
Radius of cut out 0.035m
83
disk
Pipe/shaft on
which blades
are welded
thickness 0.002m Galvanized
steel
7900kg/m3
circumference 0.182m
length 1m
Machined
member
attached to the
pulley.
Cylinder 1
(30mm)
Cylinder 2
(58mm)
Stainless
steel
8030kg/m3
radius 0.015m radius 0.029m
height 0.175m height 0.1m
Machined
member
submerged in
water
Cylinder
1(30mm)
Cylinder
2(58mm)
Stainless
steel
8030kg/m3
Radius 0.015m Radius 0.029m
height 0.03m Height 0.14m
Mass of the 14 blades;
πππ π ππ π‘βπ ππππππ = 14 Γ πππ π ππ π π πππππ πππππ.
πππ π ππ π π πππππ πππππ = π Γ ππππ’ππ = ππ‘π[(π 2) β (π2)]
πππ π ππ π π πππππ πππππ = (7850 Γ 0.003 Γ 3.142)[0.06052 β 0.0352]
πππ π ππ π π πππππ πππππ = 0.18ππ
84
πππ π ππ 14 ππππππ = 14 Γ 0.18ππ = 2.52ππ
(4.12)
Mass of the shaft:
π βπππ‘ πππ π = π Γ ππππ’ππ ππ π βπππ‘
π βπππ‘ πππ π = π Γ ππππ’πππππππ ππ π βπππ‘ Γ π‘βππππππ π Γ πππππ‘β
π βπππ‘ πππ π = 7900 Γ 0.182 Γ 0.002 Γ 1 = 2.88ππ
(4.13)
Mass of machined member attached to pulley:
πππ’ππππ¦ = ππ[(π 2 Γ β1) + (π2 Γ β2)]
πππ’ππππ¦ = 8030 Γ 3.142[(0.0292 Γ 0.1) + (0.0152 Γ 0.175)] = 3.12ππ
(4.14)
Mass of machined member submerged in water:
ππ π’πππππππ = ππ[(π 2 Γ β1) + (π2 Γ β2)]
πππ’ππππ¦ = 8030 Γ 3.142[(0.0292 Γ 0.14) + (0.0152 Γ 0.03)] = 3.14ππ
(4.15)
Total mass of screw:
π‘ππ‘ππ πππ π ππ π‘βπ π ππππ€ = 2.52 + 2.88 + 3.12 + 3.14 = 11.66ππ
(4.16)
85
4.2.1 Radius of gyration
Since the axis of rotation of the turbine is at the centre of the screw along
the length of the screw, then the researcher used as the radius of gyration the
length from the centre of the screw to the tip of the blade of a turbine.
dππ π‘ππππ ππππ ππππ‘ππ π‘ππ ππ πππππ = πππππ’π ππ ππ¦πππ‘πππ = 0.15π
(4.17)
Mass moment of inertia of the screw
πππ π ππππππ‘ ππ πππππ‘ππ = πππΆπ πΈπ Γ π ππππ’π ππ ππ¦πππ‘πππ2
(4.18)
(Theory of machines, RS KHURMI).
πΌπ ππππ€ = 11.66 Γ 0.152
πΌπ ππππ€ = 0.262πππ2
(4.19)
4.2.2 Rotational speed of screw
The following data was gathered towards the determination of the
screwβs rotational speed in radians/sec.
86
Table 13 rotational period of screw.
TRIAL 1 2 3 4 5 6 7 8 9 10 11 12
Time taken
to complete
one
oscillation(
sec)
0.1
2
0.1
2
0.1
2
0.1
2
0.1
1
0.1
2
0.1
2
0.1
2
0.1
1
0.1
0
0.1
1
0.1
2
ππππππ =(0.11) Γ 4 + 8(0.12)
12
ππππππ = 0.12π ππ
πππ‘ππ‘πππππ π ππππ = π =2π
ππππππ
π =6.28
0.12= 52.3ππππ /π ππ
4.2.3 Rotational Kinetic energy of the screw
πππ‘ππ‘πππππ πππππ‘ππ ππππππ¦ = 1/2 Γ πΌ Γ π2
(4.20)
(Theory of machines, RS KHURMI).
rππ‘ππ‘πππππ πππππ‘ππ ππππππ¦ =1
2Γ 0.262 Γ 52.32
πππ‘ππ‘πππππ πππππ‘ππ ππππππ¦ ππ π‘βπ π ππππ€ = 358.8π€ππ‘π‘π
(4.21)
87
4.2.4 Mechanical efficiency of the screw turbine
The mechanical efficiency of the screw turbine refers to the ratio of the
mechanical power which manifests itself as the rotational kinetic energy of the
turbine to the power made power input made available by the flowing water.
πππβππππππ πππππππππ¦ = ππππβ =πππ‘ππ‘πππππ πππππ‘ππ ππππππ¦ ππ π ππππ€
πππ€ππ ππππ ππ£ππππππ ππ¦ π€ππ‘ππΓ 100
(4.22)
(Power systems, V.K Mehta)
ππππβ =358.8
456.2= 0.786
(4.23)
4.2.5 Electrical Output
Rotational speed of the pulley attached to the bicycle dynamo:
π2
π1=
190
38= 5
(4.24)
Where N1 is the rotational speed of the pulley attached to the screw
turbine. Thus the rotational speed of the pulley attached to the dynamo is:
(π2) = 5 Γ 52.3ππππ
π ππ= 261.5ππππ /π ππ
(4.25)
88
The frequency of the alternating induced voltage in the dynamo is the
same as the frequency of the pulley. Thus:
πππππ’ππππ¦ ππ π‘βπ ππ’ππππ¦ =π
2π=
261.5
6.28= 41.6π»π§
πππππ’ππππ¦ ππ ππππ’πππ π£ππππ‘ππ = 41.6π»π§
(4.26)
4.2.6 AC Circuit and power Output
Data collection:
Internal resistance of the coil:
The internal resistance of the coil was measured directly using an
electrical multi meter. Value indicated was 7.5Ξ©.
Internal inductance of the coil
The internal inductance of the coil is given by the equation below:
πΏ =π0 Γ π2 Γ π΄
π
(4.27)
(Electrical Technology, Theraja)
π0 = πππππππππππ‘π¦ ππ ππππ π ππππ = (1.25663706 Γ 10β6ππππ β2π΄β2)
π = ππ’ππππ ππ π‘π’πππ ππ π‘βπ ππππ ππ π‘βπ ππ¦ππππ
π΄ = πΌππππ ππππ ππππ = ππ2/4
89
π = πππππ‘β ππ π‘βπ ππππ ππ πππ‘πππ .
(4.28)
It is worth noting that the inducatance of the coil could have easily been
determined by using an LCR meter but in the absense of such, the hard
painstaking way of counting the number of coils followed by a measurment of
the length of the coil and its diameter was adopted.
Number of turns of the coil.
Dynamo was dissmantled and the number of turns of the coil were
counted.
ππ’ππππ ππ π‘π’πππ = π = 631
(4.29)
Length of the coil
πππππ‘β ππ π‘βπ ππππ = π = 0.048π
(4.30)
Area of the coil.
ππππ = ππ2/4
ππππππ‘ππ ππ π‘βπ ππππ = 0.04π
ππππ =3.142 Γ 0.042
4= (1.2568 Γ 10β3)π2
(4.31)
90
Thus the inductance of the coil:
πΏ = ππππ’ππ‘ππππ =π0 Γ π2 Γ π΄
π
πΏ = ππππ’πππ‘πππ =(1.25663706 Γ 10β6) Γ (6312) Γ (1.2568 Γ 10β3)
0.048
πΏ = ππππ’ππ‘ππππ = 0.0131βππππ¦π = 13.1ππ»
(4.32)
Internal reactance of the coil:
πππ‘πππππ πππππ‘ππππ ππ π‘βπ ππππ = ππππ‘ = 2πππΏ
πΉππππ’ππππ¦ ππ ππππ’πππ π£πππ‘πππ = πππππ’ππππ¦ ππ π‘βπ ππ’ππππ¦ = 41.6βπ§
πππ‘πππππ ππππ’ππ‘ππππ = ππππ‘ = (2 Γ 3.142 Γ 41.6 Γ (13.1 Γ 10β3))
ππππ‘ = 3.42πΊ
(4.33)
Resistance of the external load:
The external load used was bulb that came along with the dynamo
package. The bulb was rated 2.5W, 0.3A.
π ππ ππ π‘ππππ ππ π‘βπ ππππ =πππ€ππ πππ‘πππ
ππ’πππππ‘ πππ‘πππ2= π/πΌ2
π ππππ =2.5
0.32= 27.8πΊ
(4.34)
Voltage output from the dynamo is as shown in the meter reading below,
it having been alternating means that it was fluctuating but stabilised around
13V.
91
Figure 31 Electrical Operation.
4.2.7 Circuit diagram
The circuit diagram will thus have two resistors, one for the internal
resistance of the coil and the resistance of the load which in this case was the
load used. The other component of the circuit is the inductance of the coil. It is a
series ac circuit which will appear as the depiction below indicates:
92
Circuit diagram with values plugged in:
The circuit is further condensed to the one shown below:
93
The resultant circuit is an R-L series circuit.
For a purely resistive circuit, the ac voltage is in phase with the current
while the current lags the voltage by 900 in a purely inductive circuit thus the
combined phasor diagram will be:
The resultant voltage V is thus going to be given by:
ππ ππ’πππ2 = ππππ ππ π‘ππ
2 + πππππ’ππ‘ππ2
(πΌπ)2 = (πΌπ )2 + (πΌππΏ)2
π2 = π 2 + ππΏ2
(4.35)
Thus the impedance developed in the circuit will be:
π = βπ 2 + ππΏ2
π = β35.32 + 3.422
π = 35.5πΊ
(4.36)
94
Current developed in the circuit:
πΌ =π
π=
13.08
35.5= 0.368π΄
(4.37)
Phase angle between the supply voltage and the current.
π = π‘ππβ1(ππΏ
π )
π = π‘ππβ1 ((3.42)
35.3) = 5.530πππππππ
(4.38)
Power output and power factor.
πππ€ππ ππ’π‘ππ’π‘ = π = ππΌπππ π
π = 13.08 Γ 0.368 Γ πΆππ 5.53
π = 4.79πππ‘π‘π
πππ€ππ ππππ‘ππ = πππ π = πππ 5.53 = 0.995
(4.39)
Power output /power rating ratio.
The rated power output of the dynamo that was used is 5.5w. Thus the
ratio of the actual power output to the rated power output;
ππ’π‘ππ’π‘ πππ‘ππ =4.79
5.5= 0.87
(4.40)
95
4.3 Discussion of Results
At this stage, the researcher wishes to make it known that the results
obtained during this study especially those which could have been more
accurately determined by the use of costly instruments are very open to
adjustment and thus the researcher does not claim infallibility of such results.
Examples of such results are listed in the table below and the appropriate
instrument which ought to have been used.
Table 14 Instrumentation devices used 2.
RESULT THAT MAY
BE SUBJECT TO
QUESTION
APPROPRIATE
INSTRUMENT
INSTRUMENT USED
Rotational speed of
screw
tachometer stopwatch
Screwβs torque Load cell with hall effect
circuitry
Inductance of the coil LCR meter Tape/calculation
The performance of the turbine is best assessed from its efficiency. As
already established the mechanical efficiency which is the most important aspect
is 78.6%. Typical efficiencies of Archimedes turbine are known to be in the
range of 69% to 90%.
96
CHAPTER 5. CONCLUSION, RECOMMENDATIONS
AND FUTURE WORKS
5.1 Conclusion.
The two questions the researcher sought to answer in carrying out this
research as earlier stated are;
Does Zambia have the skill set and facilities necessary to design and
construct an Archimedes turbine? Design and construct a simplistic and cost-
effective Archimedes turbine that can be used for rural lighting?
Clearly the answer to the first question is an emphatic yes. The design
process merely requires someone with an engineering background capable of
understanding fluid mechanics, dynamics of machines, basic electrical
engineering principles and a basic understanding of the usage of a computer
aided design software such Solid Works. When it comes to the availability of the
skills and facilities necessary to carry out the design produced by the engineer,
the researcher has come to a conclusion that there is no shortage of such in
Zambia. To determine if the second objective had been met consider the cost
incurred towards the construction of the turbine and mobilisation of resources
necessary to reproduce a complete installation of the turbine;
97
Table 15 Project Budget 2.
ITEM COST (US$)
Shaft/galvanised steel pipe 10
3mm thick mild steel sheet 67.5
Labour cost for turbine construction 100
Stainless steel stock for pulley construction and labour for
construction
90
Trough construction 30
Stainless steel members 20
Machining the stainless-steel members to the shaft 25
Fan belt 3.5
Bicycle dynamo 5
Construction of a wooden support for the dynamo 5
Transportation of the turbine to the site 15
Labour arranged during installation of the turbine 5
TOTAL COST USD 376
Since the country already has a body charged with the reasonability to
undertake the electrification of rural areas. Funds of that magnitude would not be
so difficult to come by. In fact some of the resources used in this project can be
accessed at no cost such as the pipe shaft which most of the mines in the country
can eagerly freely make available the same applies to the steel sheet.
98
5.2 Recommendation
A bicycle dynamo is a generator installed on bicycles to generate
electricity used to light up the bicycle lamp during the night, with some
improvements to the circuit, the bicycle dynamo can even be used to charge
phones and other devices while cycling.
The one disadvantage the use of a bicycle dynamo offers for this kind of
project is its low power rating and thus power output. The mechanical power
output of the system is 358W but because the rating of the dynamo is just 5.5W
the system cannot generate more than that.
The advantages and disadvantages of using a bicycle dynamo as
generator are described below;
Table 16 Bicycle dynamo pros and cons.
ADVANTAGES DISADVANTAGES
Cheap Low power output.
Produces an AC output voltage which may
be stepped up using a transformer.
Cannot handle bigger loads.
Easy to find
To that end the researcher would recommend the following options as
optimal devices that could be used as generators.
99
5.3 Future Works
Brushed DC Motor
Brushed DC motors can be found in such house hold devices as washing
machines. The major advantage of using brushed DC motors as generators is that
they are ready made generators. This is made possible due to the presence of
permanent magnets within the motor. Thus when a torque is applied to the shaft
of the motor an AC current is generated, but because a DC motor contains
brushes and a commutator, this combination acts as a mechanical rectifier and as
such a DC output is what is obtained. (Electrical and electronic principles and
Technology 2nd ed, John Bird 2003).
Figure 32 Brushed DC Motor.
This means that by merely rotating the shaft of the motor a DC voltage
output can be obtained. The only thing needed would be to attach a pulley with
groove dimensions similar to those of the pulley attached to the turbine.
100
Perhaps the only disadvantage this approach has is the generation of a DC
voltage which cannot be stepped up to 220v.
Single phase induction motors
The induction motor develops its torque by the interaction of axial
currents on the rotor and a radial magnetic field produced by the stator. The
torque-producing currents in the rotor of the induction motor are induced by
electromagnetic induction and hence the name induction motors. (Electric
Motors and Drives, Austin Hughes 2006).
The induction motor consists of two parts from an electrical standpoint
these are; a fixed wound stator core on the outside and a rotor that rotates in the
centre. The stator winding consists of coils of insulated copper wire fixed into
slots in the core to form a distributed winding. The rotor is usually constructed
from steel and as such there are no permanent magnets in an induction motor.
Thus for an induction motor to be used as a generator the source for magnetizing
current has to be available, capacitors are used to serve this purpose. It is
necessary to determine the correct value of capacitance needed to excite the rotor
if it is to be used as a generator. (Motors as Generators for Micro-Hydro. Nigel
Smith 1994).
For small scale projects a single phase induction motor from a ceiling fan
is the best alternative. This is best done by retrofitting the fan in such way that it
does not rely on the capacitor in order to be magnetized. The ceiling fan is best
suited for small projects in that it can operate at both low and high speeds given
the different pole windings within it. The retrofitting process is achieved by
inserting permanent magnets around the rotor.
101
Figure 33 Single Phase Induction Generator.
This kind of arrangement enables the enables the motor to act as
generator capable of generating at any rotational speed. The output is single
phase alternating voltage which may be stepped by using a transformer to suit
the needs of the user. Though it is very true that PV is becoming cheap, it is
worth noting that PV is significantly more expensive in that it requires a battery
and would need replacing after every two years.
102
REFERENCES
[1] Chris Rorres, Optimal Design of an Archimedes screw pp 1β9.2000.
[2] Christos Charisiadis, An introductory presentation to the βArchimedean
screwβ as a low head hydropower.pp 12-33.20140
[3] S.Ganeshan, CFD of A screw blade for standalone micro generator.pp
12β19.
[4] M.Amjad, Performance Investigation of a Screw Turbine Operating
Under Low Head and Less Flow Rate Requirement. PP 1β5.2015.
[5] W.Lubtiz, Archimedes Screws for Micro Hydro power generation. PP 1β
8.July 2013.
[6] M.Dada, Performance Investigation of a Screw Turbine Operating Under
Low Head and Less Flow Rate Requirement. Research Journal in
Engineering and Applied Sciences .PP 1β5.2014.
[7] N.Smith, Motors as generators for Micro-Hydro Power. ITDG publishing
London.PP 13β22.
[8] R.Suhalka, International Journal of recent research and review.
Generation of electrical using bicycle pedal.PP 1β5.JUNE 2014.
[9] E.Fiardi, Journal of Ocean, Mechanical and Aerospace. Preliminary
Design of Archimedean screw Turbine Prototype for Remote Area Power
Supply. PP 1β4. March 2014.
103
[10] Kyung Chun Kim, Experimental and Numerical Study of the
Aerodynamic Characteristics of an Archimedes Spiral Wind Turbine
Blade. PP 8β12.July 2014.
[11] W.Lubtiz, Gap Flow in Archimedes Screws. PP 1β6. June 2014.
[12] G, Nagel, Archimedean screw pump handbook. RITZ pumpenfabrik
OHG 1968. PP 16-30.
[13] G.Muller, Journal of Hydraulic Research Vol. 47, Simplified theory of
Archimedean screws. PP 1β4.
[14] Z.Kraybill, Structural Analysis of an Archimedes Screw and a Kinetic
Hydro Turbine. PP 13β31.
[15] A.Tessarolo, Hydro-Power. PP 1β20.
[16] M.William, Lab Testing and Modeling of Archimedes Screw Turbines.
PP 38-96. December 2014.
[17] Q.H. Nagpurwala, Hydraulic turbines. PP 11β44.
[18] A.Hughes, Electric motors and drives, fundamentals, types and
applications. Elsevier Ltd. 3rd edition 2006. PP 2β58.
[19] https://www.internationalrivers.org/environmental-impacts-of-dams
[20] www.epa.gov/ghgemission