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 0752014

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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 TECHNOLOGYis 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,PhDProfessor ProfessorMechanical Engineering Department Mechanical Engineering DepartmentChaitanya Bharathi Institute of Technology

Chaitanya Bharathi Institute of Technology

Hyderabad Hyderabad

Dr. P. Ravinder Reddy PhD

Professor & HeadMechanical Engineering Department

Chaitanya Bharathi Institute of Technology Hyderabad

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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

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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.

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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

3.3.4 Wiring diagram 21

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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

4.2.3 Power consumption at low speed 42

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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

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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

SOLAR PANEL

WIRES

CHARGING SYSTEM

COOLER BODY

BATTERY

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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.

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 9

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%.

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

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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

VMP = 17.4/16.2 V

ISC = 4.3 AMPS

IMP = 3.8 AMPS

Module efficiency = 2%

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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

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electrochemical processes 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.

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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

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to boost the voltage produced). In the alkaline version or "alkaline 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

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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.

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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)

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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 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,

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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.

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

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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

PMDC MOTOR OVERVIEW:

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OPERATION OF THE MOTOR:24

25

CURRENT IN THE MOTOR:

26

MAGNETIC FIELD IN THE MOTOR:

27

FORCE IN THE MOTOR:

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TORQUE IN THE MOTOR :

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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.

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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

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CENTRIFUGAL PUMP

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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 INTRODUCTION TO 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 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 33

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 SYMBOLSThe 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.

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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 parallel resistors

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 the network. Thus the equivalent resistance

(Req) of the network can be computed:

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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) + R3However, 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 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

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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 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. 38

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.

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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

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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.

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CIRCUIT FOR POWER CONSUMPTION

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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.

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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).

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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

http://en.wikipedia.org/wiki/Solar_panel

http://en.wikipedia.org/wiki/Resistor

http://en.wikipedia.org/wiki/Charge_controller 45

http://www.equestriancollections.com/storeitems.asp?department=Horses&cc=713

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