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Int. J. Mech. Eng. & Rob. Res. 2014 Ayush Khare et al., 2014

ISSN 2278 – 0149 www.ijmerr.com

Vol. 3, No. 4, October, 2014

© 2014 IJMERR. All Rights Reserved

Research Paper

PARABOLIC SOLAR COLLECTOR

Ayush Khare1*, Sachin Saxena1, C H Tyagi1 and Sanjeev Kumar1

*Corresponding Author: Ayush Khare � [email protected]

Solar Energy is a renewable source of energy. Its uses do not contribute to emission ofgreenhouse gases and other pollutants to the environment. It is sustainable since it cannot bedepleted in a time relevant to the human race. In this paper, the potential for a solar- thermalsystem for hot water generation has been studied. A parabolic trough concentrator is made ofan aluminum sheet which is covered by a cloth on which rectangular mirror strips (1.20mx0.05m) are pasted. Two different absorber tubes were taken and the efficiencies of the PTSCwhere compared without glass cover on the absorber tubes. They were designed with principalfocus at 0.3m so that the receiver heat loss was minimized the microstructure and a low amountof defects.

Keywords: Cast aluminum alloys, Heat Treatment, Solution Treatment, Artificial Ageing,Tensile Properties, Plastic Deformation, Microstructure, Modeling

1 Department of Mechanical Engineering, Subharti Institute of Technology & Engineering, Meerut, India.

INTRODUCTION

Recent increase in energy demand andconstraints in supply of energy becomes apriority for the different industry. Very fewresearch attempts have been done toestimate the significance of energy requiredfor the different process. In this experimentalstudy alternative use of solar energy hasbeen studied. Solar energy is a high-temperature, high-exergy radiant energysource, with tremendous advantages overother alternative energy sources. It is areliable, domestic, robust renewable resourcewith large undeveloped potential, and it emitsessentially none of the atmospheric

emissions that are of growing concern. Thedesign and fabrication of parabolic troughsolar water heater for water heating wasexecuted. The procedure employed includesthe design, construction and testing stages.The equipment which is made up of thereflector surface, reflector support, absorberpipe and a stand was fabricated using locallysourced materials. This work presents areproducible parabolic trough solar waterheater as a suitable renewable technologyfor reducing water-heating costs and solarwater heating systems with opticalconcentrating technologies as importantentrants for providing needed bulk solar

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energy. Parabolic trough power plants are theonly types of solar thermal power planttechnology with existing commercialoperating systems.

Parabolic- trough collectors are frequentlyemployed for solar steam-generationbecause temperatures of about 300 can beobtained without any serious degradation inthe collector’s efficiency. The incident solar-radiation falling on the collector is utilized forpipe heating. Inside the pipe, the thermal fluidflows and its temperatureincreases due to theincoming radiation. A vacuum was createdaround the pipe and a thermal insolent wasplaced at its rear. The developed simulationprogram calculates the outlet fluidtemperature and shows the efficiency of theproposed parabolic trough collector as afunction of the outlet temperature, the pipediameter, the intensity of the incoming solarradiation and the active diameter of theparabolic collector.

In spite of efforts to promote and developrenewable sources of energy and other newsources, fossil fuels (coal, oil & natural gas)continue to dominate the energy scene(Duffie John A, and William A Beckman,2006). While the need for alternative sourcesof energy is recognized, no set of alternativeshas emerged which can take over the roleplayed by fossil fuel. In India the energyproblem is very serious. In spite ofdiscoveries of oil and gas off the west coast,the import of crude oil continues to increaseand the price paid for it now dominates allother expenditure. One of the promisingoptions is to make more extensive use ofrenewable sources of energy derived fromthe sun. Solar energy can be used both

directly and indirectly. It can be used directlyin a variety of thermal applications like heatingwater of air, drying, distillation, and cooking.

THE SOLAR OPTION AND

PARABOLIC THROUGH WATER

HEATING

Solar energy is a very large, inexhaustiblesource of energy. The power from the sunintercepted by the earth is approximately 1.8*10^11 mw, which is many thousands of timeslarger than present consumption rate on theearth of all commercial energy sources. Thusis principle solar energy could supply all thepresent and future energy needs of the worldon continuing basis. This makes it one of themost promising of the unconventional energysources. Solar energy has two other factorsin the favor, Firstly unlike fossil fuels andnuclear power, it is environmentally cleansource of energy, secondly, it is free andavailable in adequate quantities in almost allparts of the world parabolic trough solar waterheating is a well-proven technology thatdirectly substitutes renewable energy forconventional energy in water heating.Parabolic trough collectors can also driveabsorption cooling systems or otherequipment that runs off a thermal load.Facilities such as jails, hospitals, thatconsistently use large volumes of hot waterare particularly good candidates. Use ofparabolic trough systems helps federalfacilities comply with executive order 12902’sdirective to reduce energy use by 30% by2005 and advance other efforts to get thefederal government to set a good examplein energy use reduction, such as the 1997million solar roofs initiative. The federaltechnology alert from the federal energy

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management program is one of a seriesonnew energy-efficiency and renewable energytechnologies. It describes the technology ofparabolic trough solar water-heating andabsorption-cooling systems, the situations inwhich parabolic-trough systems are likely tobe cost effective, and considerations inselecting and designing a system.

THE SOLAR OPTION AND

SOLAR COLLECTOR

solar energy is a very large, inexhaustible ofenergy, the power from the sun interceptedby the earth Is approximately 1.8* 10^11 mw,which is many thousands of times larger thanpresent consumption rate on the earth of acommercial energy source. Solar radiationenergy to internal energy of transportmedium. Solar collector is a device whichabsorbs the transport medium. Solar collectoris a device which absorbs the incoming solarradiation, converts it into heat, and transferthis heat to a fluid (usually air, water) flowingthrough the collector.

PARABOLIC TROUGH COLLE-

CTORS ENERGY SAVING

MECHANISM

In order to deliver high temperature with goodefficiency a high performance solar collectoris required. Systems with light structures andlow cost technology for process heatapplication up to 400 8c could be obtainedwith parabolic through collectors.

Parabolic-trough collectors are typicallyused in active, indirect water heatingsystems. Such systems use pumps tocirculate an antifreeze solution between thecollectors and the storage tank, where a heat

exchanger transfers heat from the circulatingfluid to water in the thermal storage tank.

DESCRIPTION OF PARABOLIC

TROUGH CONCENTRATOR

A parabolic trough concentrator consists ofa reflecting surface mounted on a reflectorsupport structure having the profile of aparabola. A receiver assembly comprising acircular absorber tube with suitable selectivecoating and enclosed in a concentric glassenvelope is centered along the reflector focalline. Maintain focusing of solar radiation onthe receiver assembly. The incident energyis absorbed by a working fluid circulatingthrough the absorber tube.

Figure 1: Parabolic Trough Concentrator

METHODOLOGY

For this research, a different integratedapproach are used, different theory areintegrated by experimental study.

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DESIGN PARAMETERS

The design parameter of a parabolictrough collector can be classified asgeometric and functional. The geometricparameters of a PTC are its aperture widthand length, rim angle, focal length, diameterof the receiver diameter of the glass envelopeand the concentration ratio.

The functional parameters of a PTC areoptical efficiency, instantaneous and all daythermal efficiency and receiver thermallosses. These parameters are largelyinfluenced by the absorptive of the absorber.

DESIGN ANALYSIS

The initial plan for a solar concentrator wasto use semi-spherical surface covered withmany small sections of mirror to form asegmented, spherical concentrator. Referringto the optics section of a University Physicstextbook it was found that the focal point of aspherical mirror would be located at adistance of half of the radius of the sphericalsection, directly above the vertex of thesphere. Quite some time was spent on tryingto find a way to orient the small mirrorsections at the proper angles about the innersurface of the sphere. The initial thought wasto take the derivative of a circular equationto find the proper incline at different pointsalong the sphere’s inner surface. Theseinclines would then be rotated about theorigin. This was a difficult problemconsidering the limited resources. A differentapproach was taken. After conducting moreresearch on solar energy and solar collection,the decision was made to attempt to build aparabolic trough solar concentrator. In aparabola all of the incoming rays from a light

source (in this case the sun) are reflectedback to the focal point of the parabola. If thesaid parabola is extended along an axis(becoming a trough) the solar rays areconcentrated along a line through the focalpoint of the trough. The focal point of aparabola is located at 1/4a , if the equationof the parabola is y = ax2The instantaneousefficiency of a PTC ( ) can be calculated froman energy balance on the receiver tube. Theinstantaneous efficiency is defined as the rateat which useful energy is delivered to theworking fluid per unit aperture area dividedby the beam solar flux (at the collectoraperture plane.

COMPILATION OF THERMAL

TRANSFER FACTORS FOR

SOLAR PLATE COLLECTORS

The properties mentioned are compiled inTable.

Table 1: Compilation of Factors to Takeinto Account When Calculating

Conduction and Convection

Property

Young’smodulus

(GPa)

Poisson’sratio (-)

Glass

69

0.23

Copper

118

0.30

Aluminium

70

0.30

MECHANICAL PROPERTIES

As can be seen in Table 2, the model in Marcalso needed the mechanical properties forthe parts.

These are the some mechanical proper-ties and thermal transfer factor for itscomplicance which estimate its analyticaldescription.

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Table 2: Properties of Materialsin Solar Collector

Property

Conductivity

Nusselt Number

Rayleigh number

Prandtl number

Grash of number

Density

Plate spacing

Viscosity

Lowering thermaltransfer by

Decrease

Decrease

Decrease

Decrease

Decrease

Decrease

Increase(conduction)

Decrease(convection)

Increase

N.B.

material property

material property

material property

material property

WATER CIRCULATION ANDWATER HEATING SYSTEMSDIRECT CIRCULATIONSYSTEMS (ACTIVE)

• In direct circulation systems a pump isused to circulate potable water fromstorage to the collectors when there isenough available solar energy toincrease its temperature and then returnthe heated water to the storage tankuntil it is needed.

• As a pump circulates the water, thecollectors can be mounted either aboveor below the storage tank.

Figure 2: Direct Circulation System

DRAIN DOWN

Figure 3: Drain-Down System

DIRECT OR FORCED CIRCULA-TION TYPE DOMESTIC SWH

• In this system only the solar panels arevisible on the roof.

• The hot water storage tank is locatedindoors in a plant room.

• The system is completed with piping,pump and a differential thermostat.

• This type of system is more appealingmainly due to architectural and aes-thetic reasons but also more expensive.

FORCE CIRCULATION SYS-TEM-1

Figure 4: Forced Circulation System-1

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FORCE CIRCULATION SYS-

TEM-2

Figure 5: Force Circulation System-2

THERMO SYPHON SYSTEMS(PASSIVE)

• Thermosyphon systems heat potablewater or heat transfer fluid and use natu-ral convection to transport it from thecollector to storage.

• The water in the collector expands be-coming less dense as the sun heats itand rises through the collector into thetop of the storage tank.

• There it is replaced by the cooler waterthat has sunk to the bottom of the tank,from which it flows down the collector.

• The circulation continuous as long asthere is sunshine.

• Since the driving force is only a smalldensity difference larger than normalpipe sizes must be used to minimisepipe friction.

• Connecting lines must be well insulatedto prevent heat losses and sloped toprevent formation of air pockets whichwould stop circulation.

TYPICAL THERMOSYPHON SO-LAR WATER HEATER

Figure 6: ThermosyphonSolar Water Heater

INDIRECT WATER HEATINGSYSTEMS (ACTIVE)

• Indirect water heating systems circulatea heat transfer fluid through the closedcollector loop to a heat exchanger,where its heat is transferred to thepotable water.

• The most commonly used heat transferfluids are water/ethylene glycolsolutions, although other heat transferfluids such as silicone oils andrefrigerants can also be used.

• The heat exchanger can be locatedinside the storage tank, around thestorage tank (tank mantle) or can beexternal.

• It should be noted that the collector loopis closed and therefore an expansiontank and a pressure relief valve arerequired.

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Figure 7: Indirect Water Heating System

Figure 8: Drain-Back System

CENTRAL RECEIVER SYSTEM

Figure 9: Central Receiver System

WHERE TO APPLY

the technology is best applied at:

1. Hospitals

2. Other large health care facilities suchas large clinics

3. Military

4. Food preparation

5. Laundries

WANT TO AVOID

If purchasing a system or seeking an projectone should be aware of certain consider-ations. No one of these situations would aproject, but be sure to inform staff about:

1. Areas with unusually high dust or dirtloads in air

2. Facilities possible closure or R e d u c -tion on hot-water or air C o n d i -tioning.

LIMITATIONS

1. Concentration systems collect little dif-fuse radiation depending on theconcentrationratio.

2. Some form of tracking system is re-quired so as to enable the collector

Tofollowthesun.

3. Non uniform flux on the absorberwhereas flux in flat plate collector Uni-form.

4. High initial cost.

CONCLUSION

Dramatic technology break through to makeparabolic-trough solar water heating eco-nomically attractive in areas with less sun orfor facilities the have low cost conventional

DRAIN-BACK SYSTEM

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energy available are unlikely, incrementalimprovements in mirror and absorber coast-ing , however, are quite likely, and will makeparabolic through increasingly efficient for thesituations where the already are attractive.Any major cost reductions would come fromeconomies of scale associated with substan-tially, or an increase in conventional energyprices. Climate change gas emission reduc-tion the outlook is quite good the technologyis more limited geographically to areas of highsolar resources and to larger facilities thanare other solar water heating technologies,but the economics are better.

REFERENCES

1. Bergman and Theodore L (2011), “Intro-duction to Heat Transfer”, 6th ed.Hoboken: Wiley, 2011. Print.

2. Duffie John A and William A (2006),“Beckman”, Solar Engineering of Ther-mal Processes. 3rd ed. Hoboken: Wiley,2006. Print.

3. Eames P C (1999), “Modelling Line-AxisSolar Concentrators in the Medium Tem-perature Range”, Renewable Energy 16(1999): 743-48. Elsevier.Web.

4. Feuermann, Daniel and Jeffrey M Gor-don (1999), “Solar Fiber Optic MiniDishes”, Solar Energy, Vol. 65, No. 3,pp. 159-70.

5. Powell Kody M and Thomas F Edgar(2011), “Modeling and Control of a SolarThermal Power Plant with Thermal En-ergy Storage”, Chemical EngineeringScience, Vol. 71, pp. 138-45.

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