1. 1
SOLAR COOLER
Dissertation submitted in partial fulfillment of the requirement for The
award of the degree for
BACHELOR OF ENGINEERING
IN
MECHANICAL (PRODUCTION) ENGINEERING
SUBMITTED BY
S.HARI KRISHNA
ROLL NO: 160110738026
K.SAIDEEP
ROLL NO:160110738048
B.VISHNU REDDY.
ROLL NO: 160110738060
MECHANICAL ENGINEERING DEPARTMENT
CHAITANYA BHARATHI INSTITUTE OF TECHNOLOGY
HYDERABAD – 500 075
2014
2. 2
MECHANICAL ENGINEERING DEPARTMENT
CHAINTANYA BHARATHI INSTITUTE OF TECHNOLOGY
HYDERABAD – 500 075
CERTIFICATE
This is to certify that the dissertation titled “COST EFFECTIVE SOLAR
COOLER” being submitted by S.HARI KRISHNA, K.SAIDEEP, B.VISHNU
REDDY in partial fulfillment for the award of the degree of BACHELOR
OF ENGINEERING IN MECHANICAL (PRODUCTION) ENGINEERING of
CHAITANYA BHARATHI INSTITUTE OF TECHNOLOGY
is a record of bonafide work carried out by them under my guidance and
supervision.
The results submitted in this dissertation have not been submitted to any
other University or Institution for the award of any other Degree or Diploma.
Dr. P.PRABHAKAR REDDY Dr. P.V.R.RAVINDRA REDDY
M.E, PhD M.Tech,PhD
Professor Professor
Mechanical Engineering Department Mechanical Engineering Department
Chaitanya Bharathi Institute of
Technology
Chaitanya Bharathi Institute of
Technology
Hyderabad Hyderabad
Dr. P. Ravinder Reddy
PhD
Professor & Head
Mechanical Engineering
Department Chaitanya Bharathi
Institute of Technology Hyderabad
3. 3
ACKNOWLEDGEMENTS
We express our gratitude to Dr.P.Prabhakar Reddy, Professor,
Mechanical Engineering Department, Chaitanya Bharathi Institute of
Technology, Hyderabad for his guidance, valuable suggestions and
encouragement throughout the project course. He motivated us to
work harder and at the same time smarter as well to present this
dissertation successfully.
We are grateful to Dr. P. Ravinder Reddy, Professor & Head,
Mechanical Engineering Department, Chaitanya Bharathi Institute of
Technology, Hyderabad for granting us the permission to undertake
this project towards fulfilling the requirements for the award of B.E
degree. We also thank all the faculty members of Mechanical
Engineering Department for their encouragement and support.
Our sincere thanks to Dr. P.V.R.Ravindra Reddy, Professor,
Mechanical Engineering Department, Chaitanya Bharathi Institute of
Technology, Hyderabad for guiding us for the project seminar. We also
thank all our friends who have supported and encouraged us
throughout the project course.
At the very outset, we express our hearty acknowledgments to our
parents for their unflinching co-operation without which the project
would have not been possible.
S.HARI KRISHNA, K.SAIDEEP, B.VISHNU REDDY
4. 4
ABSTRACT
Our basic motive is to regulate the operating power in solar cooler. This project
presents the results of an experimental investigation carried out to minimize the power
consumption of a solar cooler running at various speeds. The experiments have been
carried out for a total of three speeds that is low, medium and high. We carried out
speed control by minimizing the input current at multiple speeds with the help of
resistors. For high speed, we have connected a couple of resistors in series whereas
for medium speed a couple of resistors were connected in parallel and for low speed a
single resistor was used.
We have replaced DC motor which is traditional coolers with Permanent Magnet DC
motor. PM DC motor is highly efficient since no electrical energy is used or losses
incurred for developing or maintaining motor’s magnetic field. Its size is more
compact and a better dynamic performance can be expected due to higher magnetic
flux density in air gap.PM DC motor has an essentially simplified construction and it
is maintenance free.
We even tried to replace the concept of pump by including cotton to the cooler setup.
Water is made to flow from a higher potential to lower potential making the grass and
cotton wet. Even if the potential of water becomes lower, it does not create any
hindrance to the function of cooler. Elimination of pump reduces the expenses in
addition to lowering the overheads caused while lifting the water.
5. 5
TABLE OF CONTENTS
Chapter Topic Page
no
1 Introduction 8
2.1 Objective 9
2.2 Parts of Solar cooler 9
3.1 Solar Panel
3.1.1 Introduction 9
3.1.2 Construction 10
3.1.3 Efficiencies 10
3.1.4 Electrical characteristics 11
3.2 Battery
3.2.1 Introduction 13
3.2.2 Working 14
3.2.3 Electron Flow 14
3.2.4 The “dry cell” battery mechanism 15
3.3 Charge controller
3.3.1 Introduction 17
3.3.2 Specifications 18
3.3.3 Connections 19
6. 6
3.3.4 Wiring diagram 21
3.4 PMDC Motor
3.4.1 Introduction 22
3.4.2 Construction 22
3.4.3 Characteristics 23
3.4.4 Maintenance 23
3.4.5 Applications 24
3.4.6 Advantages over DC motor 24
3.5 Centrifugal Pump
3.5.1 Introduction 31
3.5.2 History 31
3.5.3 Working 31
3.5.4 Problems of using a pump 32
3.6 Cooler Body 34
4.1 Resistors
4.1.1 Introduction to resistors 34
4.2.2 Units of resistor and its symbols 35
4.2.3 Theory of operation of resistor 37
4.2 Power consumption at various speeds by resistors
4.2.1 Power consumption at high speed 41
4.2.2 Power consumption at med. Speed 41
7. 7
4.2.3 Power consumption at low speed 42
4.3 Advantage of using resistors for speed control 42
5.1 Calculation of Payback 44
6.1 Cost effectiveness by elimination of Pump 45
7.1 Limitations 46
8.1 Conclusions 46
9.1 References 46
LIST OF FIGURES
S.NO TOPIC PAGE NO
1. Block diagram of solar cooler 8
2. Solar panel 13
3. Battery 16
4. Wiring diagram 21
5. PMDC overview 25
6. DC motor operation 26
7. Current in DC motor 27
8. Magnetic field in DC motor 28
9. Force in DC motor 29
10. Torque in DC motor 30
11. Centrifugal pump 33
12. Circuit for power consumption 43
8. 8
1.INTRODUCTION:
Our project “Solar Cooler” is based on the concept of harvesting solar energy.
It is easily interpretable from the name of the project that it is based on the solar
energy for satisfying its need of power source. The functionality of Solar
Cooler is dissimilar as that of the traditional coolers. The solar energy is
harvested and stored in a battery. This battery is in turn connected to the solar
cooler for the power source.
The concept of solar cooler sounds good and economical hence almost every
class of our society can bear its expenses. The best part is that, it can be used
even in rural areas where there will be no supply of electricity.
LINE DIAGRAM OF SOLAR COOLER
SOLARPANEL
WIRES
CHARGING SYSTEM
COOLER BODY
BATTERY
9. 9
2.1 OBJECTIVE
Saving power and electricity
Minimizing season wise servicing
Varying power consumption at various speeds
To enable people of those rural areas which do not have electricity supply to
have cool air during summer.
Reduce the maintenance cost by replacing the concept of pump
2.2 COMPONENT LIST OF A SOLAR COOLER
Solar panel
Battery
Charge controller
PM DC motor
Centrifugal DC pump
Cooler body
3.1 SOLAR PANEL
3.1.1 INTRODUCTION
A solar panel is a set of solar photovoltaic modules electrically connected and mounted
on a supporting structure. A photovoltaic module is a packaged, connected assembly of
solar cells. The solar panel can be used as a component of a larger photovoltaic system to
generate and supply electricity in commercial and residential applications. Each module
is rated by its DC output power under standard test conditions (STC), and typically
ranges from 100 to 320 watts. The efficiency of a module determines the area of a
module given the same rated output - an 8% efficient 230 watt module will have twice
the area of a 16% efficient 230 watt module. A single solar module can produce only a
limited amount of power; most installations contain multiple modules. A photovoltaic
system typically includes a panel or an array of solar modules, an inverter, and sometimes
a battery and/or solar tracker and interconnection wiring.
10. 10
3.1.2 CONSTRUCTION
Solar modules use light energy (photons) from the sun to generate electricity through the
photovoltaic effect. The majority of modules use wafer-based crystalline silicon cells or
thin-film cells based on cadmium telluride or silicon. The structural (load carrying)
member of a module can either be the top layer or the back layer. Cells must also be
protected from mechanical damage and moisture. Most solar modules are rigid, but semi-
flexible ones are available, based on thin-film cells. These early solar modules were first
used in space in 1958.
Electrical connections are made in series to achieve a desired output voltage and/or in
parallel to provide a desired current capability. The conducting wires that take the current
off the modules may contain silver, copper or other non-magnetic conductive transition
metals. The cells must be connected electrically to one another and to the rest of the
system. Externally, popular terrestrial usage photovoltaic modules use MC3 (older) or
MC4 connectors to facilitate easy weatherproof connections to the rest of the system.
Bypass diodes may be incorporated or used externally, in case of partial module shading,
to maximize the output of module sections still illuminated.
Some recent solar module designs include concentrators in which light is focused by
lenses or mirrors onto an array of smaller cells. This enables the use of cells with a high
cost per unit area (such as gallium arsenide) in a cost-effective way
3.1.3 EFFICIENCIES
Depending on construction, photovoltaic modules can produce electricity from a range of
frequencies of light, but usually cannot cover the entire solar range (specifically,
ultraviolet, infrared and low or diffused light). Hence much of the incident sunlight
energy is wasted by solar modules, and they can give far higher efficiencies if illuminated
with monochromatic light. Therefore, another design concept is to split the light into
different wavelength ranges and direct the beams onto different cells tuned to those
ranges. This has been projected to be capable of raising efficiency by 50%.
11. 11
Currently the best achieved sunlight conversion rate (solar module efficiency) is around
21.5% in new commercial products typically lower than the efficiencies of their cells in
isolation. The most efficient mass-produced solar modules have energy density values of
up to 175 W/m2 (16.22 W/ft2). A research by Imperial College, London has shown that
the efficiency of a solar panel can be improved by studding the light-receiving
semiconductor surface with aluminum nanocylinders similar to the ridges on Lego
blocks. The scattered light then travels along a longer path in the semiconductor which
meant that more photons could be absorbed and converted into current. Although these
nanocylinders were used previously in which aluminum was preceded by gold and silver,
the light scattering occurred in the near infrared region and visible light was absorbed
strongly. Aluminum was found to have absorbed ultraviolet part of the spectrum and the
visible and near infrared parts of the spectrum were found to be scattered by the
aluminum surface. This, the research argued, could bring down the cost significantly and
improve the efficiency as aluminum is more abundant and less costly than gold and
silver. The research also noted that the increase in current makes thinner film solar panels
technically feasible without "compromising power conversion efficiencies, thus reducing
material consumption".
Micro-inverted solar panels are wired in parallel which produces more output than
normal panels which are wired in series with the output of the series determined by the
lowest performing panel (this is known as the "Christmas light effect"). Micro-inverters
work independently so each panel contributes its maximum possible output given the
available sunlight.
3.1.4 ELECTRICAL CHARACTERISTICS
Electrical characteristics include nominal power (PMAX, measured in W), open circuit
voltage (VOC), short circuit current (ISC, measured in amperes), maximum power
voltage (VMPP), maximum power current (IMPP), peak power, Wp, and module
efficiency (%).
PMAX = 75W
VOC = 21V
14. 14
3.2 BATTERY ( 12 V 7.2 AH)
3.2.1 INTRODUCTION
The common battery (dry cell) is a device that changes chemical energy to electrical
energy. Dry cells are widely used in toys, flashlights, portable radios, cameras,
hearing aids, and other devices in common use. A battery consists of an outer case
made of zinc (the negative electrode), a carbon rod in the center of the cell (the
positive electrode), and the space between them is filled with an electrolyte paste. In
operation the electrolyte, consisting of ground carbon, Manganese dioxide, Sal
ammoniac, and zinc chloride, causes the electrons to flow and produce electricity.
3.2.2 WORKING
Electricity is the flow of electrons through a circuit or conductive path like a wire
.Batteries have three parts, an anode (-), a cathode (+), and the electrolyte. The
cathode and anode (the positive and negative sides at either end of a smaller battery)
are hooked up to an electrical circuit.
3.2.3 ELECTRON FLOW
The chemical reaction in the battery causes a buildup of electrons at the anode. This
results in an electrical difference between the anode and the cathode. You can think of
this difference as an unstable build-up of the electrons. The electrons want to
rearrange themselves to get rid of this difference. But they do this in a certain way.
Electrons repel each other and try to go to a place with fewer electrons.
In a battery, the only place to go is to the cathode. But, the electrolyte keeps the
electrons from going straight from the anode to the cathode within the battery. When
the circuit is closed (a wire connects the cathode and the anode) the electrons will be
able to get to the cathode. In this example, the electrons go through the wire, lighting
the light bulb along the way. This is one way of describing how electrical potential
causes electrons to flow through the circuit. However, these electrochemical processes
change the chemicals in anode and cathode to make them stop supplying electrons. So
there is a limited amount of power available in a battery. When a battery is recharged,
the direction of the flow of electrons is changed, the electrochemical processes
15. 15
happen in reverse, and the anode and cathode are restored to their original state and
can again provide full power.
Batteries are used in many places such as in flashlights, cars, PCs, laptops, portable
MP3 players and cell phones. A battery is essentially a can full of chemicals that
cause chemical reactions that produce electrons. Looking at any battery, there are
generally two terminals. One terminal is marked (+), or positive, while the other is
marked (-), or negative. In an AA, C or D cell (normal flashlight batteries), the ends
of the battery are the terminals. In a large car battery, there are two heavy lead posts
that act as the terminals. Electrons collect on the negative terminal of the battery. If a
wire is connected between the negative and positive terminals, the electrons will flow
from the negative to the positive terminal as fast as it can wear out the battery quickly
and possibly cause an explosion.
Inside the battery, a chemical reaction produces the electrons. The speed of electron
production by this chemical reaction (the battery's internal resistance) controls how
many electrons can flow between the terminals. Electrons flow from the battery into a
wire, and must travel from the negative to the positive terminal for the chemical
reaction to take place. That is why a battery can sit on a shelf for a year and still have
plenty of power - unless electrons are flowing from the negative to the positive
terminal, the chemical reaction does not take place.
3.2.4 THE “DRY CELL” BATTERY MECHANISM
The most common type of battery used today is the "dry cell" battery. There are many
different types of batteries ranging from the relatively large "flashlight" batteries to
the miniaturized versions used for wristwatches or calculators. Although they vary
widely in composition and form, they all work on the sample principle. A "dry-cell"
battery is essentially comprised of a metal electrode or graphite rod (elemental
carbon) surrounded by a moist electrolyte paste enclosed in a metal cylinder as shown
below.
16. 16
In the most common type of dry cell battery, the cathode is composed of a form of
elemental carbon called graphite, which serves as a solid support for the reduction
half-reaction. In an acidic dry cell, the reduction reaction occurs within the moist
paste comprised of ammonium chloride (NH4Cl) and manganese dioxide (MnO2):
2 NH4
+ + 2 MnO2 + 2e- ------> Mn2O3 + 2 NH3 + H2O
A thin zinc cylinder serves as the anode and it undergoes oxidation:
Zn (s) ---------------> Zn+2 + 2e-
This dry cell "couple" produces about 1.5 volts. (These "dry cells" can also be linked
in series to boost the voltage produced). In the alkaline version or "alkaline
17. 17
battery", the ammonium chloride is replaced by KOH or NaOH and the half-cell
reactions are:
Zn + 2 OH- -------> ZnO + H2O + 2e-
2 MnO2 + 2e- + H2O -------> Mn2O3 + 2 OH-
The alkaline dry cell lasts much longer as the zinc anode corrodes less rapidly under
basic conditions than under acidic conditions.
Other types of dry cell batteries are the silver battery in which silver metal serves as
an inert cathode to support the reduction of silver oxide (Ag2O) and the oxidation of
zinc (anode) in a basic medium. The type of battery commonly used for calculators is
the mercury cell. In this type of battery, HgO serves as the oxidizing agent (cathode)
in a basic medium, while zinc metal serves as the anode. Another type of battery is the
nickel/cadmium battery, in which cadmium metal serves as the anode and nickel
oxide serves as the cathode in an alkaline medium. Unlike the other types of dry cells
described above, the nickel/cadmium cell can be recharged like the lead-acid battery.
3.3 CHARGE CONTROLLER
3.3.1 INRODUCTION
A charge controller, charge regulator or battery regulator limits the rate at which
electric current is added to or drawn from electric batteries. It prevents overcharging
and may protect against overvoltage, which can reduce battery performance or
lifespan, and may pose a safety risk. It may also prevent completely draining ("deep
discharging") a battery, or perform controlled discharges, depending on the battery
technology, to protect battery life. The terms "charge controller" or "charge regulator"
may refer to either a stand-alone device, or to control circuitry integrated within a
battery pack, battery-powered device, or battery recharger.
3.3.2 SPECIFICATIONS
19. 19
3.3.3 CONNECTIONS
Connections to the solar controller are made via the positive (+) and negative (-)
screw terminals at the base of the solar controller. These terminals are illustrated for
easy identification as shown in the table to the left.
Note: Ensure connections are made to the correct terminals and polarity +/-.Incorrect
installation may cause damage to the battery, solar panel or appliances.
STEP 1 – CONNECT THE BATTERY
Use suitable cable to connect the battery to the solar controller’s BATTERY terminals
.It is recommended to install a fuse close to the battery positive (+) terminal. When
correctly connected, the SC330 will turn on. The SC330 will automatically detect if
the battery is 12V or 24V and adjust its output accordingly.
STEP 2 – CONNECT THE SOLAR PANEL
Use suitable cable (refer to solar panel manufacturer’s specifications) to connect the
solar panel to the solar controller’s SOLAR PANEL terminals. Ensure the solar panel
is of the same voltage as the battery connected in STEP 1. To check the solar panel
iscorrectly connected scroll through the settings to view the solar panel input voltage.
When correctly connected the voltage displayed should be above 3.5V.
20. 20
CAUTION: Solar panels always generate energy when exposed to a light source, even
if they are disconnected. Accidental ‘shorting’ of the terminals or wiring can result in
sparks, which may cause personal injury, and create a fire hazard. It is recommended
that the user cover the front face of the panel(s) with a soft cloth to block incoming
light during installation.
STEP 3 – CONNECT THE LOAD/APPLIANCE
Connect the load or appliance to the solar controller’s LOAD terminals
3.3.4 WIRING DIAGRAM (Refer next page)
22. 22
3.4 PMDC MOTOR (35W-> 30 W for fan + 5 W for pump)
3.4.1 INTRODUCTION
Permanent magnet (PM) DC motors were introduced in the 19th century but did not
earn widespread acceptance due to the poor quality of magnetic materials (e.g., steel
and tungsten steel) that were then available. So, early motor designers turned to
electromagnetic field excitation, which became the standard until recently. Advances
in magnetic technology, such as rare earth magnets, demonstrated improvements in a
PM motor’s steady state performance and power density. As a result, the permanent
magnet DC motor has seen broad adoption in today’s global marketplace. PM motors
are used by vendors of computer peripherals, office equipment, medical instruments
etc.
3.4.2 CONSTRUCTION
Permanent magnet DC motors are much more efficient, lighter and compact than
comparably sized wound DC motors because the permanent magnets replace the field
windings of wound DC motors. PM DC motors are constructed in two broad
categories: brushed/commutator and brushless. The PM DC commutator motor uses a
rotating armature winding with a stationary field of permanent magnets; a PM DC
brushless motor has a reverse construction: a rotating field of permanent magnets and
a stationary armature winding that is externally commutated by an electronic control.
(Sales of permanent magnet DC commutator motors are steadily decreasing while
sales of PM DC brushless motors are increasing due to the absence of brushes and the
associated maintenance of the brushes and commutator. Subsequent discussion in this
article will refer to the PM DC brushless motor.)
The field PM magnets have two configurations: surface-mounted or interior-mounted.
Surface-mounted magnets are less expensive but are not suited to high speeds.
Interior-mounted, also called flux concentrating machines, overcome the shortcoming
of surfaced mounted machines in terms of air gap flux density, harmonics shielding
and, in some cases, structural integrity.
In the 19th century, magnets were made of iron but it was known that 12 alloys of
23. 23
copper, silver and gold made superior magnets. In 1932, Alnico (alloy of AL, CU, Fe
NI and Co) was developed and reawakened interest in permanent magnet field
excitation. In the past 20 years, other magnetic materials have been developed: rare
earth magnets, which are samarium-cobalt alloys and are the highest performing
magnetic materials. Rare earth magnets are expensive but their price is decreasing.
Another material is neodymium-iron-boron alloy, which performs 30 % better than
samarium cobalt alloys. The only drawback of neodymium is its poor corrosion
resistance; however, protective coatings have been developed to overcome this
deficiency.
Ceramic (barium ferrite and strontium ferrite) magnet motors are widely used in the
world today. They have much higher coercive forces than alnico and are better able
to resist demagnetization.
3.4.3 CHARACTERISTICS
Permanent magnet DC motors have similar characteristics to DC shunt wound motors
in terms of torque, speed, reversing and regenerative braking
characteristics. However, PM DC motors have starting torque several times that of
shunt motors and their speed load characteristics are more linear and
predictable. Torque varies a lot with speed, ranging from maximum (stall torque at
zero speed) to zero torque at maximum (no load speed). An increase in torque
requires a decrease in angular velocity and vice versa.
3.4.4 MAINTENANCE:
Reduced maintenance is one of the primary advantages of permanent magnet DC
motors over wound DC motors. Since the commutator and brush assemblies of
wound motors are not used in PM DC motors, all the maintenance and related-costs
associated to servicing these motor components is eliminated. The maintenance
amounts to cleaning, ensuring clear ventilation pathways and bearing replacements, as
appropriate.
24. 24
3.4.5 APPLICATIONS
Permanent magnet DC motors have been used in power ranges from the milliwatts
(mW) to megawatts (MW), but are primarily known for fractional horsepower
applications. Brushless DC motors are gaining the most market share. This is the
result of advances in control electronics as well as PM quality. The automotive
industry uses a large number of PM DC commutator motors, which can vary from a
few in an inexpensive car to about 100 in a luxury car. PM brushless DC motors are
now recognized as the best propulsion motor for electric hybrid road vehicles. For
industrial applications, permanent magnet DC motors are seeing market adoption in
applications, such as pumps, fans, blowers, compressors, centrifuges, mills, hoists,
handling systems, machine tools, servo drives, elevators, light railways, missiles,
radar, satellites, dentist drills, electric wheel chairs, artificial heart motors and power
tools.
3.4.5 ADVANTAGES OVER DC MOTOR
The benefits 4 of PM field-excited motors over electromagnetically-excited motors
include:
Higher efficiency since no electrical energy is used or losses incurred for
developing or maintaining the motor’s magnetic field.
Higher torque and power density.
Linear torque speed charcteristics. 5 that are more predictable.
Better dynamic performance due to higher magnetic flux density in air gap.
Simplified construction and essentially maintenance-free.
More compact size
31. 31
3.5 CENTRIFUGAL DC PUMP
3.5.1 INTRODUCTION
Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing
turbomachinery. Centrifugal pumps are used to transport fluids by the conversion of
rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational
energy typically comes from an engine or electric motor. The fluid enters the pump
impeller along or near to the rotating axis and is accelerated by the impeller, flowing
radially outward into a diffuser or volute chamber (casing), from where it exits.
Common uses include water, sewage, petroleum and petrochemical pumping. The
reverse function of the centrifugal pump is a water turbine converting potential energy
of water pressure into mechanical rotational energy.
3.5.2 HISTORY
According to Reti, the first machine that could be characterized as a centrifugal pump
was a mud lifting machine which appeared as early as 1475 in a treatise by the Italian
Renaissance engineer Francesco di Giorgio Martini. True centrifugal pumps were not
developed until the late 17th century, when Denis Papin built one using straight
vanes. The curved vane was introduced by British inventor John Appold in 1851.
3.5.3 WORKING
Like most pumps, a centrifugal pump converts mechanical energy from a motor to
energy of a moving fluid. A portion of the energy goes into kinetic energy of the fluid
motion, and some into potential energy, represented by fluid pressure (hydraulic head)
or by lifting the fluid, against gravity, to a higher altitude.
The transfer of energy from the mechanical rotation of the impeller to the motion and
pressure of the fluid is usually described in terms of centrifugal force, especially in
older sources written before the modern concept of centrifugal force as a fictitious
force in a rotating reference frame was well articulated. The concept of centrifugal
force is not actually required to describe the action of the centrifugal pump.
32. 32
The outlet pressure is a reflection of the pressure that applies the centripetal force that
curves the path of the water to move circularly inside the pump. On the other hand,
the statement that the "outward force generated within the wheel is to be understood
as being produced entirely by the medium of centrifugal force" is best understood in
terms of centrifugal force as a fictional force in the frame of reference of the rotating
impeller; the actual forces on the water are inward, or centripetal, since that is the
direction of force needed to make the water move in circles. This force is supplied by
a pressure gradient that is set up by the rotation, where the pressure at the outside, at
the wall of the volute, can be taken as a reactive centrifugal force. This was typical of
nineteenth and early twentieth century writings, mixing the concepts of centrifugal
force in informal descriptions of effects, such as those in the centrifugal pump.
Differing concepts and explanations of how centrifugal pumps work have long
engendered controversy and criticism. For example, the American Expert
Commission sent to the Vienna Exposition in 1873 issued a report that included
observations that "they are misnamed centrifugal, because they do not operate by
centrifugal force at all; they operate by pressure the same as a turbine water wheel;
when people understand their method of operating we may expect much
improvement." John Richards, editor of the San Francisco-based journal Industry, also
downplayed the significance of centrifugal force in his essay.
3.5.4 PROBLEMS OF USING A PUMP
Cavitation
Wear of the impeller
Corrosion inside the pump
Overheating due to low flow
Leakage along rotating shaft
surge
34. 34
3.6 COOLER BODY
Cooler body is made up of plastic
Plastic avoids corrosion and is durable
Cooler body includes fan , water storage tank and aspen pads
Aspen pads are soaked in the water making the air cooler
4.1 RESISTORS
4.1.1 INTRODUCTIONTO RESISTOR
A resistor is a passive two-terminal electrical component that implements electrical
resistance as a circuit element. Resistors act to reduce current flow, and, at the same
time, act to lower voltage levels within circuits. Resistors may have fixed resistances
or variable resistances, such as those found in thermistors, varistors, trimmers,
photoresistors and potentiometers.
The current through a resistor is in direct proportion to the voltage across the resistor's
terminals. This relationship is represented by Ohm's law:
I = {V over R}
where I is the current through the conductor in units of amperes, V is the potential
difference measured across the conductor in units of volts, and R is the resistance of
the conductor in units of ohms (symbol: Ω).
The ratio of the voltage applied across a resistor's terminals to the intensity of current
in the circuit is called its resistance, and this can be assumed to be a constant
(independent of the voltage) for ordinary resistors working within their ratings.
Resistors are common elements of electrical networks and electronic circuits and are
ubiquitous in electronic equipment. Practical resistors can be composed of various
compounds and films, as well as resistance wires (wire made of a high-resistivity
alloy, such as nickel-chrome). Resistors are also implemented within integrated
circuits, particularly analog devices, and can also be integrated into hybrid and printed
circuits.
The electrical functionality of a resistor is specified by its resistance: common
commercial resistors are manufactured over a range of more than nine orders of
magnitude. When specifying that resistance in an electronic design, the required
precision of the resistance may require attention to the manufacturing tolerance of the
chosen resistor, according to its specific application. The temperature coefficient of
35. 35
the resistance may also be of concern in some precision applications. Practical
resistors are also specified as having a maximum power rating which must exceed the
anticipated power dissipation of that resistor in a particular circuit: this is mainly of
concern in power electronics applications. Resistors with higher power ratings are
physically larger and may require heat sinks. In a high-voltage circuit, attention must
sometimes be paid to the rated maximum working voltage of the resistor. While there
is no minimum working voltage for a given resistor, failure to account for a resistor's
maximum rating may cause the resistor to incinerate when current is run through it.
Practical resistors have a series inductance and a small parallel capacitance; these
specifications can be important in high-frequency applications. In a low-noise
amplifier or pre-amp, the noise characteristics of a resistor may be an issue. The
unwanted inductance, excess noise, and temperature coefficient are mainly dependent
on the technology used in manufacturing the resistor. They are not normally specified
individually for a particular family of resistors manufactured using a particular
technology. A family of discrete resistors is also characterized according to its form
factor, that is, the size of the device and the position of its leads (or terminals) which
is relevant in the practical manufacturing of circuits using them.
4.1.2 UNITS OF RESISTOR AND ITS SYMBOLS
The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon
Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and
manufactured over a very large range of values, the derived units of milliohm (1 mΩ
= 10−3 Ω), kilohm (1 kΩ = 103 Ω), and megohm (1 MΩ = 106 Ω) are also in
common usage.
The reciprocal of resistance R is called conductance G = 1/R and is measured in
siemens (SI unit), sometimes referred to as a mho. Hence, siemens is the reciprocal of
an ohm: S = Omega^{-1}. Although the concept of conductance is often used in
circuit analysis, practical resistors are always specified in terms of their resistance
(ohms) rather than conductance.
37. 37
4.1.3 THEORY OF OPERATION OF RESISTOR
Ohm's law
The behavior of an ideal resistor is dictated by the relationship specified by Ohm's law
V=I cdot R.
Ohm's law states that the voltage (V) across a resistor is proportional to the current (I),
where the constant of proportionality is the resistance (R).
Equivalently, Ohm's law can be stated:
I = frac{V}{R}.
This formulation states that the current (I) is proportional to the voltage (V) and
inversely proportional to the resistance (R). This is directly used in practical
computations. For example, if a 300 ohm resistor is attached across the terminals of a
12 volt battery, then a current of 12 / 300 = 0.04 amperes (or 40 milliamperes) flows
through that resistor.
Series and parallelresistors
In a series configuration, the current through all of the resistors is the same, but the
voltage across each resistor will be in proportion to its resistance. The potential
difference (voltage) seen across the network is the sum of those voltages, thus the
total resistance can be found as the sum of those resistances:
As a special case, the resistance of N resistors connected in series, each of the
same resistance R, is given by NR. Thus, if a 100K ohm resistor and a 22K
ohm resistor are connected in series, their combined resistance will be 122K
ohm— they will function in a circuit as though they were a single resistor
with a resistance value of 122K ohm; three 22K ohm resistors (N=3, R=22K)
will produce a resistance of 3x22K=66K ohms.
Resistors in a parallel configuration are each subject to the same potential
difference (voltage), however the currents through them add.
The conductances of the resistors then add to determine the conductance of
38. 38
the network. Thus the equivalent resistance (Req) of the network can be
computed:
So, for example, a 10 ohm resistor connected in parallel with a 5 ohm resistor
and a 15 ohm resistor will produce the inverse of 1/10+1/5+1/15 ohms of
resistance, or 1/(.1+.2+.067)=2.725 ohms. The greater the number of resistors
in parallel, the less overall resistance they will collectively generate, and the
resistance will never be higher than that of the resistor with the lowest
resistance in the group (in the case above, the resistor with the least resistance
is the 5 ohm resistor, therefore the combined resistance of all resistors attached
to it in parallel will never be greater than 5 ohms).
The parallel equivalent resistance can be represented in equations by two
vertical lines "||" (as in geometry) as a simplified notation. Occasionally two
slashes "//" are used instead of "||", in case the keyboard or font lacks the
vertical line symbol. For the case of two resistors in parallel, this can be
calculated using:
R eq = R1R2/(R1+R2)
A resistor network that is a combination of parallel and series connections can
be broken up into smaller parts that are either one or the other. For instance,
A diagram of three resistors, two in parallel, which are in series with the other
R eq = (R1//R2) + R3 = R1R2/(R1+R2) + R3
However, some complex networks of resistors cannot be resolved in this
manner, requiring more sophisticated circuit analysis. For instance, consider a
cube, each edge of which has been replaced by a resistor. What then is the
resistance that would be measured between two opposite vertices? In the case
of 12 equivalent resistors, it can be shown that the corner-to-corner resistance
is 5⁄6 of the individual resistance. More generally, the Y-Δ transform, or
39. 39
matrix methods can be used to solve such a problem.
One practical application of these relationships is that a non-standard value of
resistance can generally be synthesized by connecting a number of standard
values in series or parallel. This can also be used to obtain a resistance with a
higher power rating than that of the individual resistors used. In the special
case of N identical resistors all connected in series or all connected in parallel,
the power rating of the composite resistor is N times the power rating of the
individual resistors.
Power dissipation
At any instant of time, the power P consumed by a resistor of resistance R (ohms) is
calculated as: where V(volts) is the voltage across the
resistor and I (amps) is the current flowing through it. The first form is a restatement
of Joule's first law. Using Ohm's law, the two other forms can be derived. This power
is converted into heat which must be dissipated by the resistor's package.
The total amount of heat energy released over a period of time can be determined
from the integral of the power over that period of time:
Therefore one could write the average power dissipated over that particular time
period as:
If the time interval t1 - t2 is chosen to be one complete cycle of a periodic
waveform (or an integer number of cycles), then this result is equal to the
long-term average power generated as heat which will be dissipated
continuously. With a periodic waveform (such as, but not limited to, a sine
wave), then this average over complete cycles (or over the long term) is
conveniently given by
where Irms and Vrms are the root mean square values of the current and
voltage. In any case, that heat generated in the resistor must be dissipated
before its temperature rises excessively.
Resistors are rated according to their maximum power dissipation. Most
discrete resistors in solid-state electronic systems absorb much less than a
40. 40
watt of electrical power and require no attention to their power rating. Such
resistors in their discrete form, including most of the packages detailed below,
are typically rated as 1/10, 1/8, or 1/4 watt.
Resistors required to dissipate substantial amounts of power, particularly used in
power supplies, power conversion circuits, and power amplifiers, are generally
referred to as power resistors; this designation is loosely applied to resistors with
power ratings of 1 watt or greater. Power resistors are physically larger and may not
use the preferred values, color codes, and external packages described below.
If the average power dissipated by a resistor is more than its power rating, damage to
the resistor may occur, permanently altering its resistance; this is distinct from the
reversible change in resistance due to its temperature coefficient when it warms.
Excessive power dissipation may raise the temperature of the resistor to a point where
it can burn the circuit board or adjacent components, or even cause a fire. There are
flameproof resistors that fail (open circuit) before they overheat dangerously.
Since poor air circulation, high altitude, or high operating temperatures may occur,
resistors may be specified with higher rated dissipation than will be experienced in
service.
Some types and ratings of resistors may also have a maximum voltage rating; this
may limit available power dissipation for higher resistance values.
41. 41
4.2 POWER CONSUMPTION AT VARIOUS SPEEDS
Speed control can be carried out by introducing resistors between the input
and the motor
The speed can be varied by varying the input current by connecting the
resistors in different ways.
4.2.1 POWER CONSUMTION AT HIGH SPEED (330 RPM)
The incoming voltage is constant at 12v
2 resistors of resistances 1 ohm and 1 ohm are connected in seies
Equivalent resistance R= R1+R2=> 1+1= 2Ohms
Value of current obtained from ammeter = 2.58 amps
Power P= V*I=> 2.58*12= 30.96 W
4.2.2 POWER CONSUMTION AT MEDIUM SPEED (250 RPM)
The incoming voltage is constant at 12v
2 resistors of resistances 5 ohms and 10 ohm are connected in parallel
Equivalent resistance R= R1*R2/(R1+R2)=> 10*5/ (10+5)= 3.3 Ohms
Value of current obtained from ammeter = 1.96 amps
Power P= V*I=> 1.96*12= 23.52 W
42. 42
4.2.3 POWER CONSUMTION AT LOW SPEED (204 RPM)
The incoming voltage is constant at 12v
A single resistor of resistance 5 ohms is used
Equivalent resistance R= 5 ohms
Value of current obtained from ammeter = 1.60 amps
Power P= V*I=> 1.60*12= 19.2 W
4.3 ADVNATAGES OF USING RESISTORS FOR SPEED
CONTROL
Circuits are less complicated
Cost is less
The values obtained are precise.
Significant decrease in power consumption is observed with decrease in speed.
44. 44
5.1 CALCULATION OF PAYBACK
Payback is defined as the amount of time in which our product becomes free
We have replaced the input power source with a solar panel
The solar panel that we used is of capacity 75 Pw
Cost per watt =Rs 65. So, the total cost of solar panel is Rs 4850
1000 watts= 1unit of power
The amount charged for 1 unit of power is Rs 6
For a panel of 75w capacity, 1 unit is charged for an usage of 13.3 hours (since
1000/75=13.3)
After using the cooler for 1075 days at an average usage of 10 hours per day,
we can expect a return of investment.
So, the payback period is approximately 2 years 343 days.
45. 45
6.1 COST EFFECTIVENESS BY ELIMINATION OF
PUMP.
Earlier in the traditional cooler, pump was used to lift the water up but in our
concept of solar cooler the water flows down from the higher potential to
downwards making the cotton and cooler grass wet. Thus this wet grass and
cotton makes the air cool; even if the potential of water get lowers it does not
create any kind of hindrance in the smooth working of the solar cooler.
Cotton works on the principle of capillary tube (Meniscus height).
Height of a meniscus
The height h of a liquid column is given by:
where is the liquid-air surface tension (force/unit length), θ is the contact
angle, ρ is the density of liquid (mass/volume), g is local gravitational field
strength (force/unit mass), and r is radius of tube (length).
For a water-filled glass tube in air at standard laboratory conditions, γ =
0.0728 N/m at 20 °C, θ = 20° (0.35rad), ρ is 1000 kg/m3, and g = 9.8 m/s2.
For these values, the height of the water column is
Thus for a 4 m (13 ft) diameter tube (radius 2 m (6.6 ft)), the water would rise
an unnoticeable 0.007 mm (0.00028 in). However, for a 4 cm (1.6 in) diameter
tube (radius 2 cm (0.79 in)), the water would rise 0.7 mm (0.028 in), and for a
0.4 mm (0.016 in) diameter tube (radius 0.2 mm (0.0079 in)), the water would
rise 70 mm (2.8 in).
46. 46
7.1 LIMITATIONS
1. The main limitation is that the intensity of solar radiation is weather
dependent. On cloudy day, the intensity of radiation is very low which is
further affected by the dust, fog and smoke. There for it cannot work properly
in cloudy days
2. It covers only small area.
3. The initial cost of the system is quite high
CONCLUSIONS AND FUTURE SCOPE
In traditional coolers a chopper is used for reduction of speed whereas
in our cooler we have used resistors which reduce the power consumed
along with the variation in speed
The DC motor has been replaced with the highly efficient PMDC
motor, which is maintenance free and simplified in construction.
Though our intent to replace the concept of pump was unsuccessful, it
leaves a lot of scope for future batches to find out a way for
eliminating the defects of pump’s usage by using an alternative that
works in a better way than the cotton.
9.1 REFERENCES
Gieras, Jacek F. and Wing, Mitchell. Permanent magnet motor technology:
design and applications. Marcel Dekker, Inc. 2002.
C. Elanchezhan, G. Shanmuga Sundar and et al. Computer Aided
Manufacturing. 2nd ed. Laxmi Publications 2007.
G. K. Dubey. Fundamentals of electrical drives. 2nd ed. Alpha Science
International. 2001
Sivanagaraju, S and et al. Power Semiconductor Drives. PHI Private
Learning Ltd. 2009
. Non-Conventional Energy Sources - By G.D. RAI
Nonconventional Energy – By Ashok V. Desai
Renewable energy sources and conversion technology – By Bansal
Keemann
