SHROUDED WIND TURBINE MOBILE CHARGER

B TechMini Project Report2014Done by1. PRAJITH KS ETALEME0662. PRANAV AV ETALEME0673. PRAVEEN PR ETALEME0684. PRAVEEN PRADEEP ETALEME0695. PRAVEEN V PRASAD ETALEME070

Department of Mechanical EngineeringGovernment Engineering CollegeThrissur-680 009

ABSTRACT

This project discusses a novel type of energy converter that uses wind energy to produce electricity. The objective of this project is to harvest energy from low-speed wind flows, available while travelling in trains and buses, in order to power and charge mobile electronic devices like mobile phone. A DC generator and integrated circuit is used in this project to provide constant voltage supply required for charging of mobile devices. DC motor is used as generator in the place of AC generator with a regulator circuit comprising of different components like Voltage regulator IC, Charging pin and capacitors for ripple free voltage supply. The turbine is enclosed in housing instead of more common open turbines, to utilise the venturi effect to generate maximise power. Various designs of the housing were modelled and flow analysis was conducted on each of them in a virtual wind tunnel using simulation software to determine various parameters such as wind velocity, pressure and density during the fluid flow through the housing. Several possible designs of the housing are suggested and best alternative amongst them is determined. The system is able to charge the battery when the wind speed exceeds 36 km/hr.This project could be used as emergency source for charging mobile phone while travelling in a vehicle when charging outlets are not available.

Key words: DC generator, charging, venturi effect, voltage regulator, wind velocity, wind pressure, flow analysis, flow simulation, pressure, velocity, kinetic energy,

ACKNOWLEDGEMENT

The success and final outcome of this project required a lot of guidance and assistance from many people and we are extremely fortunate to have got this all along the completion of our project work. I would not forget to thank them.I respect and thank our project guide Prof. Jayee K. Varghese, for providing me with all the support and guidance I required to complete the project on time. I am extremely grateful to him for providing such a nice support and guidance though he had busy schedule managing.I owe my profound gratitude to our Prof. Abdul Samad, who took keen interest on our project work and guided us all along, till the completion of our project work by providing all the necessary information.I would not forget to remember Mr Kesavan for their unlisted encouragement and more over for their timely support and guidance till the completion of our project work.I heartily thank our head of the department, Prof Varghese Jobs, and our group tutor Prof. Manmohan CV, for the timely information provided to us during the completion of this project work.I am thankful to and fortunate enough to get constant encouragement, support and guidance from all Teaching staffs of Department of Mechanical Engineering which helped us in successfully completing our project work. Also, I would like to extend my sincere regards to all the non-teaching staff of department of computer science for their timely support.

TABLE OF CONTENTS

1. ABSTRACT2. ACKNOWLEDGMENT3. LIST OF TABLES4. LIST OF FIGURES5. LIST OF SYMBOLS6. LIST OF SYMBOLS7. CHAPTER 1 INTRODUCTION8. CHAPTER 2 SIMULATION OF WIND FLOW ANALYSIS9. CHAPTER 3PRESSURE, VELOCITY AND DENSITY ANALYSIS10. CHAPTER 4 CONSTRUCTION11. CHAPTER 5 SCOPE AND CONCLUSION12. REFERENCES

LIST OF TABLES

TABLE1: Parameters fixed for simulationTABLE2: Estimated wind energy harvested by different models

LIST OF FIGURESFigure 1: Cylindrical closed pipe constructed for analysing the flow Figure 2.a: Cut plot of X component of velocity of wind through Actual modelFigure 2.b: Cut plot of X component of velocity of wind through Test model 1Figure 2.c: Cut plot of X component of velocity of wind through Test model 2Figure 2.d: Cut plot of X component of velocity of wind through Test model 3Figure 3.a: Cut plot of Total velocity of wind flowing through Actual modelFigure 3.b: Cut plot of Total velocity of wind flowing through Test model 1Figure 3.c: Cut plot of Total velocity of wind flowing through Test model 2Figure 3.d: Cut plot of Total velocity of wind flowing through Test model 3Figure 4.a: Cut plot of pressure of wind flowing through Actual modelFigure 4.b: Cut plot of pressure of wind flowing through test model 1Figure 4.c: Cut plot of pressure of wind flowing through test model 2 Figure 4.d: Cut plot of pressure of wind flowing through test model 3Figure 5.a: Cut plot of density of wind flowing through Actual modelFigure 5.b: Cut plot of density of wind flowing through Test model 1Figure 5.c: Cut plot of density of wind flowing through Test model 2Figure 5.d: Cut plot of density of wind flowing through Test model 3Figure 6: Shrouded wind turbine mobile chargerFigure 7: TurbineFigure8: 20V DC GeneratorFigure 9: IC 7806Figure 10: Circuit DiagramLIST OF SYMBOLS

E - E.m.f generated across the coil of generatorEext - E.m.f required across external circuitEmax - Peak voltage of generator outputf - Frequency of generator output - Density of air flowing through the housingV -velocity of flow of the airA -area of cross section

CHAPTER 1INTRODUCTION

With rapid developments in the technology availability of mobile electronic devices has only shown a rising trend. This tremendous increase in usage of these devices has brought up an important problem of charging these devices on the move. Many times circumstances arise when we are unable to charge our daily use gadgets like mobile phones when we have to travel to a different place. But this problem can be tackled by using energy resources charging pins powered automobile battery and alternators, using solar panels or through hand operated dynamo through a combination of many gears are used for charging mobile phones. But a problem occurs when there is no sunlight or the light is not in a proper amount. Also the person might be using a public transport system or the automobile battery is not in a condition to charge the device. Also the use of hand operated geared charging unit is very laborious to use and also not effective for long. In such circumstances in order to overcome charging limitations, exploration has been carried out with mobile phone charger based on wind energy and at present we have come with a solution of maintaining sustainability of energy stored in the phone battery by Wind Driven Mobile Battery Charger .This concept utilises wind generated electrical energy to charge the mobile phones battery.

1.1 WIND TURBINEAwind turbineis a device that convertskinetic energyfrom thewind into electrical power. A wind turbine used for charging batteries may be referred to as awind charger. The result of over a millennium of windmill development and modern engineering, today's wind turbines are manufactured in a wide range of vertical and horizontal axis types. The smallestturbinesare used for applications such as battery charging for auxiliary power for boats orcaravansor to power traffic warning signs. Slightly larger turbines can be used for making small contributions to a domestic power supply while selling unused power back to the utility supplier via theelectrical grid. Arrays of large turbines, known aswind farms, are becoming an increasingly important source ofrenewable energyand are used by many countries as part of a strategy to reduce their reliance onfossil fuels.

1.2 TYPES OF WIND TURBINES

1.2.1 HORIZONTAL AXIS WIND TURBINE (HAWT)Horizontal-axis wind turbines (HAWT) have the mainrotorshaft andelectrical generatorat the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simplewind vane, while large turbines generally use a wind sensor coupled with aservo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator. 1.2.2 VERTICAL AXIS WIND TURBINE (VAWT)Vertical-axis wind turbines(or VAWTs) have the main rotor shaft arranged vertically. One advantage of this arrangement is that the turbine does not need to be pointed into the wind to be effective, which is an advantage on a site where the wind direction is highly variable, for example when the turbine is integrated into a building. Also, the generator and gearbox can be placed near the ground, using a direct drive from the rotor assembly to the ground-based gearbox, improving accessibility for maintenance.The key disadvantages include the relatively low rotational speed with the consequential highertorqueand hence higher cost of the drive train, the inherently lowerpower coefficient, the 360 degree rotation of the aerofoil within the wind flow during each cycle and hence the highly dynamic loading on the blade, the pulsating torque generated by some rotor designs on the drive train, and the difficulty of modelling the wind flow accurately and hence the challenges of analysing and designing the rotor prior to fabricating a prototype.

1.2.3 COMPACT WIND ACCELERATION TURBINECompact Wind Acceleration Turbines (CWATs)are a class ofwind turbinethat uses structures to accelerate wind before it enters the power-generating element.The concept of these structures has been around for decades but has not gained wide acceptance in the marketplace. 1.3 SUBTYPES OF VERTICALAXIS WINDTURBINE 1.3.1 DARRIEUS WIND TURBINEDarrieus turbines were named after the French inventor, Georges Darrieus.They have good efficiency, but produce large torque ripple and cyclical stress on the tower, which contributes to poor reliability. They also generally require some external power source, or an additional Savonius rotor to start turning, because the starting torque is very low. The torque ripple is reduced by using three or more blades which results in greater solidity of the rotor. Solidity is measured by blade area divided by the rotor area. Newer Darrieus type turbines are not held up byguy-wiresbut have an external superstructure connected to the top bearing.

1.3.2 SAVONIUS WIND TURBINEThese are drag-type devices with two (or more) scoops that are used in anemometers, and in some high-reliability low-efficiency power turbines. They are always self-starting if there are at least three scoops.

1.3.3 TWISTED SAVONIUSTwisted Savonius is a modified savonius, with long helical scoops to provide smooth torque. This is often used as a rooftop wind turbine and has even beenadapted for ships.

Not all the energy of blowing wind can be harvested, since conservation of mass requires that as much mass of air exits the turbine as enters it.Betz' lawgives the maximal achievable extraction of wind power by a wind turbine as 59% of the total kinetic energy of the air flowing through the turbine.Further inefficiencies, such as rotor bladefrictionanddrag, gearbox losses, generator and converter losses, reduce the power delivered by a wind turbine. Commercial utility-connected turbines deliver about 75% of the Betz limit of power extractable from the wind, at rated operating speed.

CHAPTER 2SIMULATION OF WIND FLOW

Study of flow through the proposed model of the wind turbine is required for determining the best design solution for the housing of the turbine. The design of the housing must enhance the amount of kinetic energy available at the throat of the housing. This would improve the wind energy density available at cross sectional area of the throat. Thus proper design of the housing can improve the energy extracted from wind. Here we conducted simulation studies on four possible types of designs of housing. 1. Actual model2. Test model 13. Test model 24. Test model 3One of these models (actual model) was designed to be virtual replica of the constructed model. We used the flow simulation add on available in SolidWorks, a commercial simulation software to conduct the study. For the purpose of comparison we analysed the flow by choosing a cylindrical computational domain 132cm long. One face of the cylinder was chosen for the inlet boundary condition representing steady wind flow velocity of 10m/s (36km/hr).The boundary condition on the other face was selected as the pressure equal to atmospheric pressure. The throat area and length of the convergent and divergent parts of the housing were made to be the same for each of the four models. Also the type of material, roughness of surface, very suitable selected but the same for all models.

PARAMETERS FIXEDVALUE

Total length of housing32cm

Length of computational domain132cm

Roughness of surface10 micron

Inlet and outlet diameter17cm

Throat diameter9cm

Boss diameter3cm

Free stream velocity10m/s

Table 1: Parameters fixed for simulation

Figure 1: Cylindrical closed pipe constructed for analysing the flow

Figure1 shows the modelling done for conducting the flow simulation. Each of the four models were modelled in the same manner by enclosing them in similar cylindrical closed pipe. Meshes were later created by computer for solving the various flow parameters such as total velocity component of velocity, pressure and density. The flow through the housing were analysed without introducing the turbine blades. This was done because of three reasons. One, the flow of the air through the housing with turbine is highly turbulent and therefore the cut plots will have large variations according to the selection of planes. Two, the maximum wind energy available at throat occurs when there is no obstruction to flow of wind through the housing. This value obtained from each of the four models could be compared easily without considering the complicated design of the turbine. Third, the mass rotational speed of turbine is required to simulate the flow through turbine. Since the speed of turbine varies with mass of blades and frictional torque of the generator it becomes cumbersome to incorporate the effect on wind flow in the housing after the introduction of the turbine.

CHAPTER 3VEELOCITY, PRESSURE AND DENSITY STUDY

VELOCITY STUDYVelocity of wind flowing through the housing is an important parameter which determines the kinetic energy available for harvesting. Increase in velocity of wind increases the kinetic energy of the wind. By principle of continuity rate of mass flowing into a flow element should be equal to rate of mass flow out of the element. Mathematically, A V = constant Equation 1So reduction in area increases the velocity of wind flow through the reduced section. This is called venturi effect there is a limitation as to how much the area of throat can be reduced. When the velocity of flow approaches 0.3 mach the flow starts becoming compressible. When this happens the velocity of flow doesnt increase even if inlet flow rate is increased. Figure 1.1 a, b, c, d (next page) shows the cut plots for the X component of velocity of wind in the X-Y plane within the preset computational domain. The cut plots show variation in the x component of wind velocity by using a false colour image with a colour scale. It may be noted that the colour scale varies with the each model. It can be observed that in the actual model peak x-velocity at throat is only 13.56 m/s. It is also to be noted that major region of the flow outside the actual model consists of high velocity wind which cannot be harvested since turbine is placed inside the housing. There is major restriction to wind flow as the velocity at inlet is only 6m/s while the free stream velocity is 10m/s. This shows that the design of actual model has to be improved for more efficient housings. The Test models show better x-velocity profile. The velocity of flow outside the Test models never exceeds the x-velocity at the throat. The throat x-velocity of Test model 1 is especially promising at 18.94 m/s. Peak throat x-velocity for Test models 1 and 2 are 18.05m/s and 17.18m/s. Negative x-Velocity occurs on outer side of housings. This indicates the formation of turbulent vortices.

Resultant velocity or total velocity profile shown in figure 3.a, b, c and d also shows similar trends. However there are no negative velocities since on magnitudes are considered. The peak throat velocity for actual model is 14.95m/s and for Test models 1, 2 and 3, the peak throat velocities are 19.13m/s, 18.18m/s and17.18m/s.The net kinetic energy available per second from wind flowing at the throat can be calculated using the formulaKE=1/2 AV3 Equation 2

ModelTotal available KE at throat

WKE at throat after AccommodatingBethz limit of 59%WAssuming 50% turbine and electrical lossesPossible output power

W

Actual model11.346.693.34

Test model 123.7514.017.01

Test model 220.3912.036.01

Test model 317.2010.155.08

Table 2: Estimated wind energy harvested by different models

PRESSURE STUDY

Figure shows the cut plot of variation of pressure of air flowing through the different models. Common to all pressure cut plots there is a low pressure region generated at the throat of the housing. This indicates a drop in pressure energy .This drop in pressure energy is converted to kinetic energy of air. Comparing the figure 3.a, b, c and d and figure 4.a, b, c and d shows an overlap between regions of high velocity and regions of low pressure.In the inlet portion of each model there is a sudden increase in pressure before it lowers as it reaches the throat of the housings. This is due to sudden obstruction offered to the free wind stream at the inlet.

DENSITY STUDY

Figure 5.a, b, c and d show us the cut plots of variation of density of air flowing through the different models. The respective colour scale show that the variation of density of air is of the order of 10-3 when the colour changes from red to blue. This indicates that the flow is incompressible. This observation was expected as the velocity of air should exceed threshold limit of 0.3 mach for the flow to be compressible. The velocity of wind never exceeds 0.06 mach (20m/s).

CHAPTER 4CONSTRUCTIONThe constructed model consists of four main components that is the turbine, DC generator, chip integrated on PCB for voltage regulation, and mobile set charging pin.

Figure 6: Shrouded wind turbine mobile charger

Turbine Aturbineis a rotary mechanical device that extractsenergyfrom afluidflow and converts it into usefulwork. A turbine is aturbo machinewith at least one moving part called a rotor assembly, which is a shaft or drum withbladesattached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. The turbine used in the model has 7 blades. In a wind turbine as number of blades increases, for a given mass, its efficiency increases. Wind turbinesuse anairfoilto generate a reactionliftfrom the moving fluid and impart it to the rotor. Wind turbines also gain some energy from the impulse of the wind, by deflecting it at an angle.

Figure 7: Turbine20 volt D.C Generator A simple D.C generator is preferred over the A.C generator so as to avoid the use of rectifier circuit and to make the circuit cheap and compact and also to avoid extra cost. The main difference in the A.C and D.C generator lies in the manner in which the rotating coil is connected to the external circuit connecting the load.

Figure8: 20V DC Generator

In an A.C generator both end of the coil is connected to the external circuit via brushes. In this manner, the e.m.f Eext in the external circuit is always the same as the e.m.f E generated around the rotating coil. In a D.C generator the two ends of the coil are attached to the different halves of a single split ring which co-rotates with the coil. The split ring is connected to the external circuit by means of metal brushes. The combination of split rings and the stationary metal brushes is called a commutator. The purpose of the commutator is to ensure that the e.m.f Eext in the external circuit is equal to the e.m.f E generated around the rotating coil for half the rotating period, but is equal and opposite of polarity of this e.m.f for the other half. In the special case as theoretical, the e.m.f seen in the external circuit is simply.

Eext = E =Emax sin (2ft) Equation -3

If Eext is plotted as a function of time according to the formula, the variation of the voltage with respect to time is very similar to that of an A.C generator, except that when the negative polarity of an A.C generator is reversed to the positive one by the commutator. So, as to avoid the use of diodes in the A.C generator D.C generator is preferred. So, as a result a bumpy DC which rises and fall but never changes the direction is achieved at the output terminals of the generator.

I.C 7806

I.C. 7806 voltage regulator employ built in current limiting, thermal shutdown, and safe area protection which make them virtually immune to damage from output overload. With adequate heat sinking it can deliver in excess of 0.5 A of current. The most prominent voltage for charging the mobile phones is 5 Volts. So, I.C 7806 is used as a regulator. A diode is connected in series to the output to prevent current flowing in the reverse direction. 0.5V is dropped across the diode. So the output voltage is regulated to about 5.5V.The Figure 9 shows the circuit diagram of the voltage regulator.

Figure 9: IC 7806

Figure 10: Circuit Diagram

CHAPTER 5SCOPE AND CONCLUSION

A portable wind powered charging unit of great relevance in the current scenario. As observed from velocity and pressure cut plots test model 1 is suitable design for efficient wind power harvesting. High voltage dc brushless generators could improve the efficiency of the system so that power output could be stepped up to 10 watts. The size of the turbine is one of the limitations of the model.Smaller turbines could be designed at the expense of lowered power rating for the charger. Designing smaller, lightweight and efficient turbines can help in improved efficiency. The turbine could be designed as easy to knock down unit to enhance portability. The design of the housing could be extended to large scale power generation since this size of the turbine could be reduced.Further simulation studies could be conducted involving various other parameters such as lengths of convergent and divergent part of the housing. This could further enhance the efficiency the turbine.

REFERENCESDouglas, Fluid Mechanics, Pearson EducationR.K. Bansal, Fluid Mechanics and Hydraulic MachinesD. S. Kumar, Fluid Mechanics, S K Kataria & SonsF. M. White, Fluid Mechanics, 5th Edition, McGraw HillYuji Ohya, Takashi, Karasudani , Xing Zhang, Shrouded Wind Turbine

Department of ME, GEC, Thrissur