Estufa Solar - India - Hawkeye Solar Stove

7/31/2019 Estufa Solar - India - Hawkeye Solar Stove

http://slidepdf.com/reader/full/estufa-solar-india-hawkeye-solar-stove 1/37

THEHAWKEYESOLAR

COOKER

presentedbyTheUniversityofIowaCollegeofEngineeringinconjunction

withTheUniversityofCalifornia,BerkeleyandClimateHealers

Mechanical

EngineeringSenior

DesignProject-

FinalReport



MEDP2011

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TableofContents

Introduction...........................................................................................................................2

Background&Planning..........................................................................................................2

Research.................................................................................................................................5

Constraints.............................................................................................................................5

ConceptualDesigns................................................................................................................6

PreliminaryDesign.................................................................................................................8

Collector...............................................................................................................................11

Design................................................................................................................................................11

Fabrication&Assembly.....................................................................................................................12

Recommendations.............................................................................................................................13

Storage.................................................................................................................................13

Medium.............................................................................................................................................. 13

Insulation...........................................................................................................................................13

InnerStorageBoxes...........................................................................................................................14

OuterStorageBox..............................................................................................................................15

CanArrays..........................................................................................................................................16

Delivery..............................................................................................................................................18

LightFunnel.......................................................................................................................................19


Mechanics............................................................................................................................22Design................................................................................................................................................22

Fabrication&Assembly.....................................................................................................................22


Modeling..............................................................................................................................25

Considerations...................................................................................................................................25

ProjectedPerformance......................................................................................................................29

FinalRecommendations.......................................................................................................33

Acknowledgements..............................................................................................................34

WorksCited..........................................................................................................................36



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TheHawkeyeSolarCooker

Introduction

Forthepastthreemonths,studentsattheUniversityofIowaCollegeofEngineeringhavebeen

workingtowardprovidingthenativevillagersofRajasthanIndiawiththemeanstocookfoodwithout

theuseoffirewood.Approximately2billionpeopleworldwideburn1.2billiontonsofwoodannually.

Theecologicalandsociologicalimpactsofthisstatisticgrowevenmoreapparentasoncefertileforests

swiftlyprogresstowardbarrenwastelands(ClimateHealers).

Figure1:BarrenhillsideinKarech,2002

TheHawkeyeSolarCookeristhefirststeptowardprovidingaviablerenewablemeansof

cooking,notjustinRajasthan,butinconsistentlywarmregionsaroundtheworld.Thebenefitsofsuch

adevicearemanyandtranscendthetechnicalachievementtoprovidehealth,social,andecological

benefitstoend-users.InRajasthan,wherecollectingfirewoodtraditionallyfallsonthematriarch,the

abilitytocookwithoutfirewoodcanpotentiallysavehoursofdailylaboroncedevotedtowood

harvesting.Asfamiliesoftencookindoors,smokeinhalationanditsrelatedmedicalconcernscanbe

avoidedandreforestationofaregioncanbegin(Rao).

Background&Planning

InDecemberof2010,nineUniversityofIowastudentsalongwithProf.H.S.Udaykumar

embarkedonatriptotheKarechandMewarregionsofRajasthan,India.Theirgoalwastocollect

culturalinformationregardingtheRajasthanivillagersaswellastoobservethecurrentimplementation



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ofsolarcookerspreviouslyprovidedbythenon-governmentalorganizations,ClimateHealersandthe

FoundationforEcologicalSecurity .

Theexistingsolarcookerswerefoundtobesuccessfulincookingroti(aflatbread)andother

commonIndiandishes.However,theirinabilitytoconformtotraditionalcookingandeatingpractices

haveledtotheirabandonment.Figure2depictsthe NamastesolarcookercurrentlydeployedinRajasthan.

Figure2:Namastesolarcookerbeingusedtocookroti

TheNamastecookerisdesignedtoreachthedesiredcookingtemperaturesduringpeakhours

ofthedaybyconcentratingsolarraysviaconcavereflectorsontothelowerportionofthecooking

surface.TherewereseveralkeyissueswithitsdesigncontributingtoitsfailurewiththeMewarand

Karechvillagers.1)Thecookerrequiredtheusertocookstandingup.Traditionally,mealsarecooked

andservedfromaseatedposition.2)Thesolarcookerpossessesnoformofenergystoragerequiring

theusertotaketimeawayfromtheirdailytaskstomonitorcookingprogress.3)Onasimilarnote,the

lackofstoragepreventsusersfromcookingatthetraditionalmealtimesofabout7:00amand7:00pm,

IndiaStandardTime.

Inadditiontoevaluatingissueswiththesolarcooker,theWinterimstudentsalsoconducted

surveystogainagreaterunderstandingofthecultureandlifestyleofRajasthanivillagers.Basedon

theirobservations,theMechanicalEngineeringDesignProject(MEDP)Teamwasprovidedwithvaluable

informationonwhichtoestablishconstraintsfortheproject.

TwomealsadayareservedinMewarandKarech;eachatthepreviouslymentiontimes.One

mealconsistsofroti(almostdaily),whiletheotheristypicallycomposedofvegetables.Theaverage

familysizeintheregionis6.2withover300familiesbetweenthetwovillages.Eachfamilyharvests

approximately5-10bundlesofwoodeachweek(abundleweightsabout20kg).Whatfirewoodthat



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isn’tusedissoldtomarket;incentivizingthecuttingofadditionalwoodfromthesurroundingforests

(UniversityofIowaIndiaWinterimTeam).

FromaculturalperspectivethevillagersofRajasthansubscribetoamatriarchalfamilysystem.

Thewomenperformnearlyallofthedailytasksincludingcooking,firewoodcollection,andchildcare.

Basedonthethisinformation,itwastheWinterimTeam’sobservationthatsuccessfuldeploymentoffuturesolarcookersintheregionrestsinthefulfillmentofstringentconstraintsimposedbytheprimary

users;thewomenofRajasthan(UniversityofIowaIndiaWinterimTeam).

Forplanningpurposes,thesemesterwasdividedinto2parts:1)adesignphase,and2)abuild

phase.Forthedesignphase,theclasswasdividedintofiveteams,eachwiththeirownteamleader.An

additionalcoordinatingteam,comprisedofteamleadersandthreeexecutiveofficers,wasusedasa

centralhubforcommunicationandcoordinationbetweengroups.Table1highlightstheteam

breakdownandorganizationalstructure.

Table1:MEDPOrganizationalStructure

Asthedesignandbuildprocessesprogressedtheseteamsmorphedtomeettheneedsof

project.WithinStage1,subgroupswereusedfortofacilitatethecreationofconceptualdesigns.Each

ofthese5subgroups(laterdesignated Designs1-5)consistedofmembersfromeachoftheprimary

teamslistedinTable1.Thisensuredthateachaspectofsolarcookerconstructionwaswellrepresented

ineachoftheconceptualdesigns.ThesesubgroupsreducedinnumberuntilthebuilddesignwasfinalizedbyProf.UdaykumarandDr.SaileshRao.

AsExecutiveDirectorofClimateHealers,Dr.Rao,wasoneoftheprimaryinstigatorsofthe

projectandprovidedvaluablefeedbackanddirectionregardingdesigns.Healsodirectedateamfrom

theUniversityofCaliforniaBerkeleychargedwiththecreationofaheatpipethatcouldbeeasily



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integratedintoMEDPsolarcooker.TheBerkeleyTeam’sreportisforthcomingandtheirslide

presentationcanbefoundinthesupplementalinformationprovidedwiththisreport.

Stage1:Design

Research

BetweenJanuary21andMarch11,theMEDPstudentsweredevotedtoresearchingsolar

cookersandsolarcookertechnology.Numerouspapers,casestudies,instructionmanuals,and

websiteswereexploredastheteamsworkedtogatherasmuchinformationaspossibleonsolar

cookers.

Inthebeginning,Prof.Udaykumarprovidedtheclasswithseveraldocumentsandresearcharticles

highlightingthebasicsofsolarcaptureandenergystoragemethodsandmaterials.Astheclassbecame

moreautonomousandresearchmoreextensive,designparadigmsandrestrictionsbegantofallinto

place.Throughoutthedesignprocess,therearoseseveralreoccurringquestionsgoverningthe

decisionsmade:

1. Tracking–willthecollectoractivelytrackthesunthroughoutthedayorpassivelycollectlightas

thesunprogressesthroughthesky?

2. CollectorShape–shouldthereflectorbeaparabolictrough,adualparabolictrough,ora

parabolicdish?

3. PhaseChangeMaterialvs.LatentHeatStorage–whichofthesemediumsshouldbeutilizedto

storetheenergycollectedduringtheday.4. DeliverySystems–shouldheatpipesorconductiveheatingbeemployedtodeliverheattothe

cookingsurface?

5. Interface–howwillthecookerinterfacewithRajastanihomes?

Thefinalsolarcookerdesignaddresseseachoftheseitems;though,itshouldbenotedeachdesign

selectionpresenteditsowntradeoffsaccordingtothe“ Cost,Quality,Time” paradigm.

Constraints

BasedontheresearchconductedbytheWinterimandMEDPTeams,thefollowingconstraintswere

imposedfortheproject:

1. Thecookerrequireda$250dollarfinalproductioncost.Forthisprototype,thecostswere

expectedlyhigher.Therefore,itwasdecidedthattheteamshouldevaluatetheirselectionof

materialsbasedonwhatwasconsideredcheapandavailableinRajasthan.Endingcost

projectionsweremadebasedonwhattheclassbelievedthecostwouldbetomassproducethe

cookersinIndia.



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2. Thegoaltemperatureforthecooksurfacewasbetween150-200degreesC.Thisisthecook

surfacetemperatureforthecookingofroti.

3. Thedesignneededtobecapableofstoring6kWhofenergytoaccountforlossesandtomeet

thetemperaturerequirementsatthetraditionalcookingtimes.

4. Thecookershouldbebuiltusinglocalbuildingmaterials.

5. Thedesignshouldberelativelylowmaintenance.Thevillagershouldbeabletosetthecooker

totheappropriateangleandleaveittocollectenergythroughouttheday.

6. Traditionalcookingpractices,suchasseatedcookingandcookingtimes(7:00amand7:00pm),

neededtobepreservedbythedesign.

7. Safetywasheldparamountwhendesigningacookermeanttooperateathightemperatures.

Itshouldbenotedthatwhilesizewasnotoriginallyofmajorconcern,itdidpresentitselfasthekey

flawinthefinaldesign.Theendingdimensionswerebasedontheassessmentofthemodelingteam

regardinghowmuchmaterialwouldberequiredtomeettheenergyneedsforcooking.Thisrequires

addressinginfuturedesigniterations.

ConceptualDesigns

Afteranappropriateamountofknowledgewasgained,itwasdecidedthattheclassshould

partakeinacharettetobeginpoolingdesignideasandsolutions.Fivedesignswereinitiallyconsidered.

Fromthesefivedesigns,3uniqueconceptualdesignsemerged.

Thefirstofthethreeconceptualdesignswasthe SchefflerSolarCooker .Thisdesigndrawsits

inspirationfromtheSchefflerSolarKitchensfoundthroughoutvariouspartsofIndiaandtheMiddle

East.FirstdevisedbyWolfgangScheffler,the SchefflerSolarCooker hasbeenproventostorebetween2

and4kWhofenergybyfocusinglightviaparabolicdishontoacollectorplatetypicallyplaced10–15

feetaway.

Figure3depictsthebasicpositioningandoverallconceptfortheSchefflercooker.Theprimary

issueswiththisdesignlayinitsmanufactureandassembly.Thetolerancesassociatedwiththe

constructionofthedishposedmanytechnicaldifficulties.Thedishneededtobeconstructedwith

extremeaccuracytoensuremaximumconcentrationoflightonthecollectorsurface.Itwas

questionablewhetherornotthestudentshadtheproperresources,training,andtimetocompletesuch

atask.Thestoragemethodwasalsodeemedextremelycostly.TheSchefflercookeruseslatentheat

forstorageintheformoffour100kilogramsteelcylinderssurroundedbyfiberglassinsulationwithina

steeldrum.Steelinthatamountcouldpotentiallycostbetween$500-$1000dollarsdependingonbulk

pricingandthetypeofsteelused.Thedesignalsoaddressestrackingthroughagearsystemthatadjusts

thereflector’spositionthroughouttheday.Itishighlyrecommendedthatadesignofthisnaturebe

revisitedinfutureiterations.



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Figure3:BasicSchefflerSolarKitchenConcept

Thesecondofthethreeconceptualdesignswasthe“RoseBud”solarcooker.Aptlynamedfor

itsshape(seeFigure4),thiscookeremployeesaseriesofflatreflectiveplatespositionedtocomposea

dish,thusincreasingtheamountoffocusedlight.Alensisusedatthebaseofthecookertofurther

focuslighttoapointandtosealtheinteriorfromheatlosses.Atthefocalpoint,temperatureshave

beenfoundtoreachupwardsof800degreesCinsomestudies.Thestoragemediumutilizedbythis

designwaslatentheat,thoughaparticularmaterialwasneverfullyinvestigated.Thecollectordishalso

restsonatrackthatallowsitrotatetofollowthesunthroughouttheday.

Figure4:"RoseBud"SolarCooker



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Thelastofconceptualdesignswastheparabolictrough.Thisdesigncanbeapproached

multipleways.Figure5showsareceiverpipefilledwithafluidthatisheatedbythereflectedlightrays.

Atroughsimilartothiswasutilizedinthefinaldesign.Thepreliminarydesignutilizesasecondary

reflectortofurtherconcentratelight,furtherdemonstratingthemanyvariationsoftroughdesign.

Figure5:ParabolicTroughDesignOverview

Theparabolictroughprovidesfortrackingitsorientation.Whenpositionedinaneastwestmanor,thetroughcollectslightthroughoutthedayasthesunmovesacrossthesky.Efficiencies,as

result,arelowerinthemorningandnightandpeakduringthedaywhenthemaximumlight

concentrationisachieved.Thisisapassivemethodofsolarcollection.

Anumberofstoragemediumscanbeutilizedwhenemployingtheparabolictrough.The

collectionmethodisprimarilywhatsetthisdesignapartfromthepreviouslymentioneddesigns.

PreliminaryDesign

Afterreviewingtheconceptualdesigns,Prof.UdaykumarandDr.Raodeterminedthatthefinal

solarcookerprototypeshouldincorporatethebestaspectsfromeachoftheconcepts.Intheinterestof

time,theconceptdesignswerecombinedintoapreliminarydesignbytheclasssupervisors.Thegoal

wastoquicklyselectadirectioninwhichtheclassshouldproceed.Preliminarydesignaspectswere

selectedbasedonwhatthesupervisorsbelievedtheclasscouldfeasiblycompletegiventhetimeand

resourcesremaininginthesemester.



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Figure6highlightstheoverallpreliminarydesignfortheHawkeyeSolarCooker.Aparabolic

troughdesignwaschosenforit'ssimpleconstructionandabilitytotrackwithlittletonoeffortonthe

partoftheuser.Thepreliminarydesignalsoutilizesasecondaryreflector,however,thisdesignaspect

waslaterscrappedinanattempttoreducetheoverallweightandcomplexityoftheassembly.

Figure6:PreliminaryDesignCADAssembly

Analuminumfinarraysurroundedbysandwasdecideduponforthestoragemedium.

Aluminumisreadilyavailableintheformofpopcansthatcanbecutandfashionedintofinarrays.Sand

isalsoreadilyavailablegiventheproximityofdesertsand.Togetherthesematerialspossessedthedesiredthermalpropertiesforsolarcooking.Theforeseeableissueinusingsandandaluminumstems

fromthequantityrequiredforsuccessfulenergystorage.

Figure7showsacross-sectionalviewoftheproposedassembly.Thecollectorrestsandrotates

aboutitsownframeworkwhilethestorageboxrestuponarailsystemdesignedtomovethecooking

apparatustoandfromthehome.Inordertotrackthesunyearroundusingatroughdesign,abi-weekly

adjustmentwasproposedandbuiltintothecollectorframework.Thepreliminarydesignalsoutilizeda

heatpipetobemanufacturedbytheBerkeleyTeamforheatdeliverytothecookingsurface.

Figure8showsacloserviewoffunnelassemblydesignedtopreventlightraysfromescaping

oncetheyhavebeendirectedtowardtheabsorberplate.Aglasslens/platewasusedtopreventthe

lossofradiativeheatoutoftheabsorberarea.Theabsorberplateisattachedtothefinarraytoaidin

thespreadingofheatthroughoutthestoragebox.



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Figure7:SideViewPreliminaryDesignOverview

Figure8:PreliminaryDesignInteriorOverview



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Stage2:FinalDesign&Construction

ThefollowingsectionshavebeencompiledbytheStage2buildteams(Table1)andhighlight

theirworkandrecommendationsmovingforward.Additionalsupplementalinformationisforthcoming

andcanbeacquiredbyaccessingtheMEDPGoogleGmail/GoogleDocsaccountwiththeusername

medp.uiowaandpasswordslowcooker .TheOrganizationalTeamisintheprocessofcompiling

informationcollectedoverthecourseofthesemester.

Collector

Design

Thedesignoftheoutwardfacingtroughsolarconcentratorincorporatedacompoundparabola

toallowfora16degreeacceptanceangle.Theshapeofthecollectorwasselectedtoreducethefocal

planeasclosetothestorageabsorberplateaspossiblewhileusingaslittlematerialaspossible.Fromthemodelingteam,itwasdeterminedthattheremustbeanapertureareaofapproximately2square

meterstoobtainthenecessaryamountofenergy.Thestorageteamalsoneededtohaveasshortofa

collectionlengthaspossiblesothattheenergycouldbeconcentratedtothecenterstorageboxes.With

theseconsiderations,theteamdeterminedthefollowingparametersoftheparabola:

y=ax^2+bx+c

Eq. 1

witha=0.035,b=0.3,c=1.7

Figure9:CollectorShapeCalculation



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Oncetheshapeoftheparabolawasdetermined,theteamimportedthepointsinto Autodesk

Inventor tocreatea3-Dmodel.Theparabolawasextrudedandmirroredtoobtaintwosides.Eachside

wasthenmoved7inchestowardsthecenterandrotatedinward8degrees.Thiscreatedafocalplane

justbelowthebottomopeningoftheparabola.

Fabrication&Assembly

Theteambeganbyacquiringthree4'x8'sheets,Mother’sPolishingCompound ,polishingpads,

andanindustrialpolisher.Thesheetswerepolishedbysandingwith600,1000andfinally2000grit

sandpaperinorderfromcoursetofineandthenusingthepolishingcompoundtoobtainafinalshine.

Forfuturereference,thismethodprovedtobeslowanddidn'tprovidethedesiredshine.Theteam

experimentedwithseveraldifferentpolishingoptionsusingthepolisherandanglegrinder.Thebest

combinationfoundwastousetheindustrialpolisherwithaclothfoampadstucktotheVelcro

attachment.

Thenextstepwastostartontheframingfortheparabola.Toaccomplishthis,thegroup

createdatemplateoutof1/4"plywood.Thetemplatewasmadebyplacingreferencepointsalongthe

plywoodsheetaccordingtotheparaboliccurvepreviouslyestablished.Afinishingnailwasputateach

referencepointandanaluminumdrywallrulerwasbentalongthereferencepointsestablishingthe

curve.Thecurvewasmarkedandcutoutwithajigsaw.Thistemplatewasthenusedtomarkallsix

verticalribs.Eachoftheverticalribswerecutwiththebandsaw.Thehorizontalribsweremeasured

fromtheassemblyCADdrawings(attachedinthesupplementalmaterial)andcutwithamitersaw.The

assemblywasputtogetherusing3"screws.

Thegroupthencreatedbracketsfortheinterfacepiecethatmaintainsareflectivesurfacealong

thedistancebetweencollectionandstorage.Thebracketswereconstructedfromsquarealuminumtubing.First,theteamcutoneendoffofthetubingusingabandsaw.Second,thebracketswerecutto

8"witha45degreecutononeendtoallowforrotation.Ahingewasmountedthetopofthebracket

using1/4-20nutsandbolts.Finally,asheetofpolishedaluminumwasadheredtothetopinterface

sectionusinganindustrialtape.Thebottomsectionwastheninstalledintothecavityofthetwo

channels.Stopswereusedateachendtocontainthebottominterfacesection.Similarly,anindustrial

tapewasusedtofastenthepolishedaluminumtothefrontofthesub-assembly.

Thecollectorframingwasconstructedusing2”x4”woodboards.Theoveralldimensionsofthe

framewere6’widex8’deepx9’tallwhenthecollectorwasattachedtotheframe.Quickanalysis

concludedthattheoveralldepthoftheframingneededtobeabout7.5feettoenablethecollectorandframingtowithstanda25MPHwindandnotbeblownover.Thisanalysiswasalsoconductedwith

“worstcasescenario”assumptionstoaccountforpotentialgustconditions.

Attachedtotheframingwasadetentplatethatenabledthecollectortobeadjustedfor

seasonalchangesinthesun’salignmentwiththecollector.Thedetentplatewasmadeusingan

aluminumplatewithgrovesfortwospring-actuatedpinstofollowin.Thespring-actuatedpinswere

attachedtothedetentplatesothattheseasonaladjustmentscouldbemadewithlittleeffortfromthe



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user.Everycoupleofweeksonepinwouldberetractedandotherpinwouldsnapintooneoffourteen

1/4“holesallowingforthecollectortobeadjusted3.6degrees.

Recommendations

InthefutureitwouldbeverybeneficialtodeterminehowtoMylarcouldbeeffectivelyusedin

thecollector.ThealuminumwasnotwellpolishedmeaningthereflectivitywasnotnearlythatofMylar.Iftheissuesofairbubblesandtearingcouldbesolved,Mylarwouldprovetobeamuchbetter

materialduetoitshighreflectivity.Also,itwouldbeveryusefultohaveray-tracingsoftwarethatallows

fortheimportingof3-DCADmodels.Thiswouldallowthetestingofmanydifferentreflectorswithout

construction.Finally,therewassomeconcernregardingthedetentplate.Eachangleshouldutilizedual

pinstosecurethecollectorratherthanthesinglepinsystemcurrentlyemployed.

Storage

Medium

Manythermalstoragemediumswereresearchedandconsideredduringthedesignprocess.

Constraintsonthermalstoragemediumswerecostandavailability.Ultimatelysandwasselected

becauseofitsavailabilityintheregion.Sandwasalsochosenasthethermalstoragemediumbecause

ofitshighenergycapacity,about0.83W/g*K,anditslowthermalconductivity,about.2W/m*K.This

allowssandtostorelargeamountsofheatwithoutlossesfromconduction.

Thetypeofsandusedintheprototypewasplaygroundsandofmediumcoarseness.Theamountof

sandneededtostoretheappropriateenergywascalculatedbasedonvolumeandmass.Theevening

storageunitwastightlypackedwith62.1kgofsandaroundthealuminumarrays(discusseslater).The

morningstorageunitrequired86.8kgofsand.Thetotalamountofsandusedwas148.7kg.Itshouldbe

notedthatthesandwasslightlymoistwhenpackedintothestorageunits,whichhaveaffectedtheperformanceofthestoragedevice.

Insulation

Manyinsulationsolutionswereevaluatedduringthedesignprocess.Ultimately,aninexpensive

insulationthatcoulddrasticallyreduceheatlosswhileresistingheatandflamewasdesired.These

requirementsledtotheselectionofricehullsforinsulationbetweentheinnerandouterboxes.Rice

hullshaveaverylowthermalconductivity(approximately0.07W/m*K)anddonotburninhighheat.

RicehullscouldalsobefoundlocallyinIndiaatverylowcost.TheIowaprototypereceivedtheirrice

hullsforfreethroughadonationfromRiceHarvestersInc.

Evenwithfavorableinsulationproperties,modelingcalculationssuggestedthatalargevolumeofrice

hullswouldstillberequired;anapproximatemassof168.3kgofricehullswasusedinthefinalbuild.

Theinnerstorageboxesweresurroundedby.254mofricehullsonallsixsideswithinthelargerouter

box.Thericehullswerenottightlypackedasitwassuggestedsmallairpocketsthroughouttherice

hullswouldprovidefavorableinsulationproperties.



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InnerStorageBoxes

Theinnerstorageboxesweredesignedtoholdalloftheenergycollectedfromtheabsorber

plateatthebottomofthelightfunnel.Twoinnerstorageboxeswerecreatedtoallowthecookerto

storesufficientenergyforeveningandmorningmeals.Theinnerstorageboxesconsistedofsandand

aluminumforastoragemedium.Thematerialpropertiesoftheseitems,whicharepreviously

mentioned,ideallycreatedahybridmaterialwhichcouldstoreanddeliverheatenergy.Thesizeofthe

morningandeveningstorageboxeswascalculatedbasedonthevolumeofsandandaluminumneeded

tostorethe3.5kWhand2.5kWh,respectively.Therefore,themorningstorageboxwaslargerthanthe

eveningstoragebox.Additionally,thesandtoaluminumratiowithintheboxeswasestimatedbasedon

theenergystoragelengthoftimeandenergydeliveryraterequiredfromeachbox.Themorning

storageboxcontaineda15.5:1sandtoaluminumratio,whiletheeveningboxcontaineda10.4:1ratio.

Figure10andFigure11showthemorningandeveningstorageboxesdimensionsinmm.

Figure10:InternalStorageBox,MorningCooking



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Figure11:InternalStorageBox,NightCookering

Theboxeswereconstructedoutof0.0127[m]thickcementboardandaluminumbrackets.

Durable,heatresistantcinderblockswereusedtosupporttheinternalstoragestructureswithinthe

outerstoragebox.

OuterStorageBox

Theouterbox,whichcontainsallofthecomponentsofthestoragedesign,wasconstructed

using0.0127mthickplywoodwith2”x4”woodforsupportframing.Theextraframingsupportwas

crucialbecauseofthestorageunit’smass.Woodwaschosenasthebuildingmaterialbecauseofits

considerabledurability,lowcost,availability,andmachinability.Thefinaldimensions(inmm)ofthe

outerboxareshowninFigure12.Theouterstorageboxwasalsopaintedblackwithweatherresistant

paint,thepurposeofthiscolorwastocollectasmuchradiantheataspossiblefromthesun.



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Figure12:OuterStorageBoxAssemblyDrawing

CanArrays

Twoseparatealuminumarrayswereconstructedandplacedwithinthesandheatstorage

mediumtoincreaseheattransferfromthecollectionplatetotheheatpipeconnectedtothecook

surface.Onearraydesignwasbuiltfornightstorageandaseparatedesignwasusedforthemorning

storage.Thenightstoragearraywasdesignedtoallowmaximumheattransfertothecooksurfaceby

usingamoreconcentratedaluminummatrixwhilethemorningarraywasdesignedtotransferheat

moreconservativelyinordertoreduceheatlossesfromtherelativelylongtermstoragebox.Thearrays

variedintheamountofaluminumused,theiroverallgeometry,andhowtheywerepositionedwithinthecementboardsandstorageboxes.Becauseofthedifficultyofmathematicallymodelingthe

complexgeometryrequiredforthearrays,twoarraydesignswerechosentobebuiltfortheprototype.

Botharraydesignsconsistoftwo1/4”thickaluminumplatesbentinsuchawaythatthereis

directcontactwiththeanodizedaluminumcollectorsurfacealongtheentirelengthofthestoragebox.

Countersunkboltspressfittheplatesintothecollectorsurfacetoensureproperthermalcontact.The

1/4”platesextendfromthecollectorsurfacetothebottomofthestoragebox.Aholewasdrilledinthe

centerofeachplatesothatalongboltcouldconnecttheplatestotherestofthearray.Thearrays

consistof4”x8”piecesofaluminumsheetingstackedalongthelongboltinsuchawaythatthe

aluminumwouldcreateasand-metalmatrixwithinthesand.Thismatrixallowsheatcollectedfromthe

collectionplatetobeconductedsufficientlytotheentirevolumeofsandinordertomaximizeheat

storagecapability.Theboltrunsacrosstheboxandconnectstoanotheraluminumplatewhichmates

withtheheatpipeusedfortransferringheattothecooksurface.Washerswereaffixedtoeachendof

thelongboltandtightenedsothatthearraywaspressurefittoreducethermalresistancesasheatis

transferredthroughthearray.



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Thearrayfornightstorageconsistsofacrossdesign.One4”x8”sheetwaspositionedvertically

andanotherhorizontallyformingacross.Aholewasdrilledinthecenterofthesheets,andtheywere

slidontothelongconnectingbolt.Betweeneachcross,a1”diameter,1/2”thickaluminumrodspacer

wasslidontothebolt.Thespacerprovidesadequatemeansforheattotransferhorizontallythrough

thearray,whilethecrossesprovideamethodofheattransferintheothertwodimensions.An

illustrationofthenightstoragearraycanbeseeninFigure13.Thisdesignconsistsofarobustamountof

aluminumtoreadilytransferheattothecooksurface.Duetothefactthatthenightstorageboxonly

needstostoreheatforashortamountoftime,heatlossescausedbytheadditionofthisarraywasn’t

aninhibitorinthedesign.

Figure13:NightStorageAluminumArray

Thearrayformorningstorageconsistsofafanneddesigninwhichastackofthe4”x8”sheets

werepressfittogetherinthecenterandthenfannedoutalongthelongsidetocreateafannedeffect

sothatifviewedfromtheside,itlookslikethespokesofawheel.Thisdesignconsistsoflessaluminum

inalessconcentratedhelpeliminateheatlossesandincreaseheatstoragepotential.Figuresofthe

morningstoragearraycanbeseeninFigure14.



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Figure14:MorningCookingAluminumArray

Delivery

TheHawkeyeSolarcookerwasfabricatedfortheeventualinsertionoftheheatpipesfromthe

teamatCaliforniaBerkeley.Becausesemesterschedulesbetweenthetwoteamsdidnotcoincide,the

MEDPTeamdidnotreceivethefinishedheatpipesintime.Theteamdecidedtousea1”solidaluminumrodtoconducttheheatuptothecookingsurfacethroughconvection.Onboththenighttime

andmorningaluminumconductingrods,an8”inchdiametercooktopwasattached.Theteamdecided

togowithan8”cooktoptotryandstayconsistentwiththesizethattheyareusedtocookingonin

ruralIndia.ThisisintendedtobeatemporaryfixuntiltheheatpipesarereceivedfromCalifornia

Berkeley.Atthetopoftheboxalargerthan1”diametersquarewascutoutsothehotaluminumrod

wouldnotcomeincontactwiththebox.Apieceoftilewascutandplacedaroundtherodtoensure

thatthealuminumwouldnotcomeincontactwiththewoodoftheouterbox.Thesolarcookerwas

fabricatedwithtwolidstocoverthecooksurfaceswhentheyarenotinuse.Theeveningcooklidwas

madesmallerthanthemorningcooklidbecauseitdidnotneedtoinsulateaswell.Itwasmadesmaller

tocutcostsandminimizeweight.Themorningcooklidwaslargerandhadmorericehusksinsideofittoinsulatebetter.Thelidswereattachedbyhingestothemainboxtoeasewithopeningandclosingof

them.Themorninglidwouldcoverthecookplateontherightwithmoreinsulation.Howeverthese

lidswereunnecessarybecausetheHawkeyeSolarCookerdidnotworkasplannedandthecooktops

nevergothot.



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LightFunnel

Thefunneldesignwasoneofthemorecomplicatedprocessespresentedtothestorageteam.

Thebeamoflighthadtotravelalongthefunnelwithoutincurringtomanylosesalongtheway.Someof

themainlosesthatwouldoccurwouldbeforthelighttobereflectedbackoutsidethefunnelsystem

intotheatmosphere.Fromtheonsetofthefinaldesignitwasdecidedthatthesolarreflectorwouldbe

thesamelengthasthetotalstoragebox.Thestorageboxwouldhavealloftheinsulation,morningand

eveningstorageunitsinside.Ideallytheapproachwouldbetofunnelthelightfromthefocuslinetothe

absorberplatesasiftheywereonecontinuousplate.Howevermorecomplexgeometrywas

introduced.

Figure15showsthegeometryfromasideprospectiveofthefunnelsystem.Thesolarcollector

andmodelingteamsfoundthattheidealangleofdeclinationwastobe27degreesfromthehorizontal

plane.ThiswasduetothelatitudeinRajasthan.Thiswasthebasepointforthefunnelsystembecause

theabsorberplatewastobeorientatedatthe27degreeinclination.Thiswouldbeidealforspringand

falldeclinationangles.Ideallytheabsorberwouldbeadjustedtothesameangletothatofthecollector

butthiswasjustnotfeasible.Themodelingteamdecidedthatanidealfunnelangletobeat75degreeanglefromtheabsorberplatetoavoidscatteringeffects.Howeverthissettheopeningofthecollector

tobesetat30.4cmwidethatneededtobeabsorbedatonly3.84cm.

Figure15:LIghtFunnelConstructionBlueprint

Withthesetwoanglessettheoptimaldistancefortheopeningofthecollectorcouldbe

determined.ItshouldbenotedthatFigure6isfromthesideprospectiveoftheentiresystem.The

dimensionswerecommunicatedbacktothecollectorteamsothattheadditionalspacecouldbe

accountedforinthedesignoftheinterfacesystem.Thedistancebetweenthestorageboxtothe



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collectorwasaround23.0cm.Ifthestorageboxdidnothavetwoseparateabsorberplatesthenthis

wouldhavebeentheonlyanglesthatwouldhavebeennecessary.Theabsorberplateshadlengthsof

53.4and37.4cmforthemorningandeveningstoragesrespectively.Thismeantthatonly55%ofthe

beamwouldbereflectedinanidealstatereflectedinthesideview.

Figure16showsthefocusbeamsastheyreachedthefunnelsystem.Noticehowthebeamsatthetwoendsoftheboxdonotmakeittothestoragedeviceatall.Thiswasduetothelengthofthe

absorberplatesbeingshorterthanlengthofthefocusbeam.Thenextconundrumwastryingtocollect

asmuchasthefocuslengthaspossible.Thismeantfortheanglesgoingouttowardsthesideofthebox

theangleswouldbelessthantheideal75degrees.Thepaththatwasdecideduponwastoaccept

thoselosesandgeometricallylinktheendsoftheabsorberplatesandlinkthemtotheendofthe

collector.Thiswassetforroughly45degrees

Figure16:LightFunnelwithFocalBeamsShown

Thenextproblemwastodecideonthefunnelanglesbetweenthetwostorageboxes.Theideal

storageinsulationdimensionsweretosetthedistancesbetweenthestorageboxesat14cmtoprevent

thermallosses.Thisinturncreatedanotherlevelofdifficultytoconnectthetwofunnelsystemto

acceptthefocusline.Figure17showsthedimensionsofthelargemorningfunnelpart.Noticethatthe

anglesatbothendsarenotthesame.Essentialtheangleattheleftsideofthemorningfunnelwould

matchthatoftherightsideofevenings.Howeverbotheroftheseanglesarestillnotattheideal75

degreedeclination.

FocalLines



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Figure17:MorningFunnelDimensions

Ingeneral,mostofthedistancesandanglesforthemorningstoragesystemwerealreadyset

becauseofothercorrespondingdimensions.Thislimitedanefficientdesignofthefunnelsystemfor

boththemorningandtheeveningsystems.Dimensionswerenottheonlyproblemforthefunnel

system.Designingformanufacturabilityprovedtobeahardertask.Originallyitwasthoughtthatthere

wouldbemorethanenoughofthepolishedaluminumforthefunnels.Budgetconstraintsandtime

overrodethedecisiontousealuminum,soaglassmirrorsystemwastobeused.Attachingthemirrors

tothesystemprovedtobemostdifficultbecausetherewerenotreadilyavailablebracketingsystemfor

attachingeverythinggiventhecomplexgeometry.

Recommendations

Muchwaslearnedthoughtheplanningandconstructionoftheinternalstorageboxes,light

funnelsystem,insulation,andexternalstoragebox.Thesizeandweightofthestoragesystemsmustbe

changedinfuturedesigns.Withthecurrentprototype,awomanwouldnotbeabletoeasilymaneuver

thestorageunitinandoutofthehousetwotimesaday.Therearecurrently148.9kgofsand,172kgof

ricehulls,andadditionalweightofaluminumandplywood.Infuturedesigns,changingthestorage

materialwoulddecreasetheweightandsizeoftheoverallunit.

Theglasselementsofthestorageunitcanberedesignedtoprovidegreaterstructuralstrength.

Thecurrentdesignofthelightfunnelwasnotsturdyenoughtosurvivethetransportationfromthe

constructionareatothetestinggrounds.Byusingastronger,thickerglassandintroducingback

supportswouldincreasethedurabilityofthelightfunnel.Withmoreaccuratecutsandpropertooling,

theywouldallowformoreprecisecutsandbetterconstruction.

` Computersoftwareshouldbeasignificantpartinthedesignofthestorageunit.Withthelackof

knowledgeofcomputeraidedengineeringanalysissoftware,thecurrentcanarraysanddeliverysystem



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havenotbeentestedormodeled.Withincreasedknowledgeofsuchcomputersoftware,thesesystems

couldbemodeledproperlyandmodifiedtomaximizeoutput.Withmoreefficientdesigns,theweight

issuewouldcontinuetobeaddressed,hopefullydecreasingthetotalweightandsizeoftheunit.From

thedatacollectedforthecomputeranalysis,fewerprototypeswouldhavetobeconstructedandthe

numberoftestswoulddecreaseallowingforquickerimplementationofthedevicetoIndiaandother

developingregions.

Mechanics

Design

Giventhatthecombinationofmaterialsforthecollectionandstoragedevicetotals

approximately800lbs,thetaskofthemechanicsgroupwastodevelopafeasiblewaytotransportthe

device,asawhole,betweentheindoorcookingandoutdoorcollectingpositions.Themostcostefficient

methodofmovingthecookerwastorestthecollectorandstoragedeviceonametalframewithfour

castors.Handleswerethenattachedtothesidesofthestorageassemblytoaidinthemovementofthecooker.Duetotimeconstraints,itwasdecidedthattheframesectionswouldbejoinedthrough

welding.AsteeltrackwasalsodesignedtomovethestoragecontainerintothehomesinIndiathough

duetobudgetconcernsthispiecewasneverfabricated.Thetrackutilizestworailsapproximately60½”

apartwithanopenC-channeldesigntopreventdebrisfrombuildingupinthechannel.Theoverall

lengthofthetrackisdependentonthedistancebetweenthecollectionsiteandthecookingsite,which

willvaryfromhometohome.

Fabrication&Assembly Theinitialdesignofthecookerassemblywasexpectedtototalapproximately600lbs,although

aftercontinuedoptimization,thefinalweightrosetoapproximately800lbs.Consideringthepossibility

offurtherincreasesinweight,thecartfortheassemblywasdesignedtowithstandapproximately1200

lbsofforce.Towithstandthisforce,2”x2”x3/16”steelangleironwasusedintheconstructionofthe

bottomframe.Thedimensionsoftheframeweredependentuponthefinalmeasurementsofthe

bottomofthestoragebox.Oncetheboxwasconstructed,themeasurementswerefoundtobe64¼”x

33¼”.Toprovideenoughclearanceforthecollector,thecartwasbuilttobe64½”x33½”withtwo

additional33½”angleironrunnersinthemiddletofurthersupporttheassembly.

Theouterpiecesofangleironwerefirstmeasuredtospecificationandthencutona45degree

angletocreateamiteredjoint.Thesemitercutsallowforeasierweldingandcleanerjoiningofthe

separatepieces.Atungsteninertgas(TIG)welderwasusedtojointhepiecesofangleirontogether.

WeldswereplacedontheinsidehorizontalandverticallengthsofthejointasseeninFigure18.



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Figure18:Miterwelds

Thetwocentersupportlengthsofangleironwerethenmeasuredtorunwidthwiseinsideofthe

outerframeactingasadditionalsupportforthecenterofthestoragecontainer.Thesesupportsensurethattheweightoftheinternalstoragecomponentsdonotwarptheboxthusweakeningtheplywood

exterior.Additionally,thesecenterrunnershelptorelieveaportionoftheweightontheperimeter

framethusreducingdeflectioninthesteel.Sinceangleironwasusedintheconstructionofthecenter

supportingbeams,partoftheverticalsectionoftheangleironwascuttoproducenotchjoints,allowing

thebeamstobejoinedtotheexistingframe.Additionalweldswereusedtojointhebeamstothe

frameasdepictedinFigure19.

Figure19:Centersupportwelds



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Steelcastorswereprocuredfortheframe.Uponfurtherinspectionofthecasters,itwasfound

thatthetopplateswerecomposedofgalvanizedsteel.Originally,itwasthoughtthatthecastorswould

beweldeddirectlytotheframe.Atthetemperaturesrequiredtoweldthecastorstotheframe,thezinc

inthegalvanizedprotectivecoatingwouldhavevaporizedthusposingaserioushealthrisk.To

circumventthishazardandstilleffectivelyjointhecastorstotheframe,intermediateplateswereused.

Four3”x5”steelplateswereweldedtothefourcornersoftheframe.Four5/16”holesweredrilledin

theseconnectingplates.Figure20illustratestheconnectingplatesweldedtotheprimarysupport

frame.

Figure20:Weldedcasterattachmentplate

Aftertheplateswereweldedtotheframe,adrillwasusedtoborethroughthesteelframe,

allowingthecastorstobesecuredusing5/16”bolts.Onceconnected,theboltswerefileddownonthe

twoswivelcastorstoallowforfullrotationofthewheels.Itisimportantheretonotetheswivelcasters

wereusedforprototypepurposesandwillreplacedwithstraightcastersinthefinaldesign.



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Figure21:Completedframewithcasters

Recommendations

Forshippingpurposes,itisrecommendedthattheframeberedesignedwithoutwelds.Ideally

theframewouldbolttogethermakingiteasiertoshipandeasiertoassembleinRajasthan.

Assumingthatthenewframereliesonboltconnectionsratherthanwelds,itwouldalsobe

prudenttogalvanizethesteel.Despitethefactthattheclimateinquestionissemi-arid,itisstill

importanttoensurethattheprimarysourceofmobilityintheassemblywillnotsuccumbtodegradation

viarust.Ifgalvanizedsteelisnotused,thenperiodiccheckupswillbenecessarybyindividuals

knowledgeableabouttheoperationofthedevice.

Modeling

Considerations

Thefirststepincreatinga0-Dmodelwastodevelopanequationthatwouldbestsimulatethe

solarcookerinitsprojectedworkingenvironment.Thestorageteamstartedwiththeoverallenergy

equation.Thisequationthenhadtobemodifiedtoincorporatethetotalenergystoredinthemorning

andnightcookingboxes.Equation2belowdepictstheresultofthemodifiedtotalenergyequation.

!!!

!"

!"= !!

!′′ !!"− !" !! − !

!−

!!

!!

Eq. 2



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Ontherightsideoftheequation,thefirsttermevaluatedwasthetotalsolarenergyentering

thethermalstoragebox;dependentonthesolarflux,thecollectorplatearea,andanefficiencyfactor.

Thenexttermaccountsforanylossesthroughthewallsofthestoragebox.Thiswasaccomplishedby

findingtheoverallheattransfercoefficient,orU,throughthewallsofthebox.Thelasttermrepresents

theenergyusedincookingwhichwasassumedtobeextractedoveratwohourtimeperiodpermeal,

twomealsaday.Intheequation,misthemassofthestoragebox,C pisthespecificheatofthestorage

box,!"

!"isthechangeintemperaturebetweentheinsideandtheoutsideoftheboxwithrespecttotime,

ηistheefficiencyofthecollector,q s’’isthesolarfluxfromthesun,A cristheareaofthecollector,Uis

theoverallheattransfercoefficientthroughthewallsofthebox,Aistheareaofthestoragebox

collector,Tsisthetemperatureofthestoragebox,T ∞isthetemperatureoftheambientairsurrounding

thebox,qcistheenergyusedtocook,andη cisthecookingefficiency.

The0-Dequation,afterestablishingallofitsnecessarycomponents,wasintegratedwith

respecttotimeandtemperaturetofindtheinternalstoragetemperatureatsixminutetimesteps.The

finalintegratedsolutionwasthentransferredintoMicrosoftExceltosolveoverthespecifiedtime

intervals.Thefirststepincalculatingtheenergyandtemperaturesavailableforcookingafteraperiodof

storagewastofindthesolarinfluxduringthecollectiontimeperiod.Thisinvolvedfindingtheanglesof

incidentlightfromthesunwhichchangesdailywiththeEarth'srotationandannuallywiththe

revolutionaroundthesun.Thetotaloffsetwascalculatedtobe23.44degreesbetweentheEarth's

rotationalaxisanditsorbitalplane(Wikipedia).Theangleandcompassorientationofthecollector

surfacealsohadtobetakenintoaccountaswellasthelatitudeofthedevice.Thesolarflux,orsolar

powerreceivedperarea,canbecalculatedbytakingthesolarconstantjustabovetheearth’s

atmosphereandthensubtractingofftheefficiencylossesduetoatmosphericeffects,whichispartiallya

functionofcookeraltitude,butisalsodependentuponlocalatmosphericeffectssuchassmog.Asmall

amountofbackgroundskyradiationalsoaddstothetotalsolarflux.Thistermwasnotcalculatedbut

rathertakenfromknownengineeringstandardstables.Thetotalenergyintotheapertureofthe

collectorwasthenreducedbyanefficiencyfactortoaccountforthescatteringoflightandtheoverall

designofthecollection,transfer,andabsorptioncomponents.

Forsimplicity,aNationalOceanicandAtmosphericAdmiration(NOAA)calculatorwas

downloadedofftheNOAAwebsiteandinserteddirectlyintotheExcelspreadsheetsusedforthe0-D

model.Thiscalculatorallowedtheusertoenterthedate,latitude,longitude,andtimezoneofinterest

andsubsequentlybeprovidedspecificsolarpositiondataonasix-minutetimebasisforagiven24-hour

period.Ofparticularinterestforthisprojectwerethehourangle,sundeclination,solarelevation

(correctedforatmosphericrefraction),andthesolarazimuthangleateachsix-minuteincrement.

Figure22showsapartialpictureoftheExcelspreadsheetusedtodeterminethesevalues.Withthis

informationthesolarpositioncouldbedeterminedtowithinareasonabledegreeofaccuracy.Solar

positionwasusedinconjunctionwithcollectororientationandtiltanglestocalculatetheangleof

incidencebetweenthesunandthecollector.



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Figure22:NOAASolarCalculator(partialview)displayingvariousrelevantsolar

anglesonasixminutetime-stepbasedon:latitude,longitude,time-zone,

anddate.

Thenextpieceofinformationrequiredwasthesolarfluxforthelocationatwhichthesolar

cookerwouldbeused.Ratherthancalculatethisfigurebasedonestimations,experimentaldatawas

sought.TheANSI/ASHRAEStandard93-2003wasusedtoacquiredataforboth27degreesnorthlatitude(Rajasthan,India)and40degreesnorthlatitude(IowaCity).The27degreesnorthdata,convertedto

metricequivalentsandshownbelowinFigure23matchedupwellwiththelocationsofinterestin

Rajasthan.IowaCityisactuallycloserto42degreesnorthratherthan40degreesnorth.Thedifference

wassmallenoughtonotcreatesignificanterrorsinthepreliminarymodel.Theinformationfoundin

thesestandardsshowedhourlyaveragesforthesolarfluxtoaflatsurfacenormaltotheincominglight

onamonthbymonthbasis(ANSI/ASHRAE).Inordertomakethisdatacompatiblewiththesixminute

incrementsusedforthesolarangledata,asixthdegreepolynomialapproximationwascreatedforeach

monthwhichgavethesolarfluxonacontinuouscurvewithintheperiodofsun-uptosun-down,an

exampleofwhichisgivenforthemonthofMayat40degreesnorthlatitude(Figure24).

Thetimeofdaycouldthenbeenteredintotheseequationstoprovidethesolarfluxforanytenthofan

hourpointoverthecourseofadayforanymonthoftheyear.Itisimportanttonotethatwhilethese

polynomialscorrectedfordailysteppinginthedata,thefluxusedinthefinalmodelwasstillbasedonly

onmonthlyaverages.Inotherwords,themodelfalselyshowssolarinsolationvaryingsignificantlyfrom

the30ththe1

stofeverymonth.Sincethefinaloutputofthismodelwasdesignedtolookmostlyatyear-



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longtrends,thiswasdeemedavalidapproach.Caremustbetakenwhendeterminingdatathatspan

betweentwomonths;mid-monthfindingsareconsideredtobemostaccurate.

Figure23:Clearskysolarinsolation[W/m^2]atdifferenttimesoftheyearfor27degreesN.latitude

Figure24:ANSI/ASHRAEcurveforMaysolarinsolationat40degreesN.latitude(orange)andthesixthdegreepolynomial

approximation(black)

Theangleofinsolationwilllessentheintensityoftheincominglightrays.Forexample,aone

metersquareareathatisreceivingperpendiculartothesunhavingafluxof500wattspersquaremeter

willhaveaninsolationof500watts.However,ifthatareais60degreesfromtheperpendicular,itsview

factorissuchthattheprojectedareanormaltotheincominglightwillbeonlyhalfofitsfullarea.This



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resultsinaninsolationvalueofonly250watts.Thusthemodelwassetuptoaccountfortheseangles

andreducetheincomingsolarfluxintothecollectorbasedontheaforementionedsolarangulardata

andthecollectororientationandtilt.Theorientationwasassumedtobeduesouth,andthetiltwas

modeledwithastepequationthatadjustedthecollectortiltby3.6degreeseverytwoweeksinorderto

compensateforseasonalshiftsinsolardeclination.

Withtheenergyintothecollectorinhand,inefficienciesfromthecollectoritselfcouldbeused

tofindfinalenergyintothestoragedevice.First,thereflectivityofthepolishedaluminumsurfaceswas

assumedtobe96%;therestwaslosttoscattering.Multiplyingtheinsolationdatabythereflectivity

raisedtothepowerofthenumberofaveragebounceslightraysmakeontheirwaytotheabsorption

plategavethetotalefficiencyofthecollector.Additionally,lossesduetotheglasscontainmentbarrier

andtheabsorberplateabsorptivitywerealsoconsidered.However,basedonalargenumberof

unknowns,especiallyconcerningtheraypathsthroughthedevice,aroughestimateof60%efficiency

wasusedinanattempttoaccountforadditionallosses.Thus,thefinalenergyintothedevicewasfound

bymultiplyingthesolarinsolationbytheapertureareaofthecollectorandbythe60%efficiency

estimateforeachtime-stepconsidered.

Next,thetotalcookingtimeforRotiwasdetermined.Atthebeginningitwasassumedthat

cookingrequired1000wattsofenergyfor2hoursatatime.Thiswasassumedforbothmorningand

nightcooking.ThisportionofthemodelwaslaterrefinedtoreflectBerkeley’sexperimentalresultson

roticooking.Throughtesting,BerkeleywasabletoprovidetheIowateamwithdatasuggesting550

wattsofenergyisusedtocookoneroti.Thisvaluewasthenimportedintoourmodeltoprovideuswith

evenmoreaccurateresults.

Materialpropertieswerealsoincorporatedintothemathematicalmodel.Storage,Collector,

andMechanicsteamsprovidedtheModelingteamwithmaterialdataandsizingforuseinthemodel.

OnceimportedtoExcel,theequationsprovidedanextremelydynamicsolver,allowingchangestoeasily

bemadetothevariousdesignparameters.Afterallvariableswereaccountedfor,Excelwasableto

produceweeklyandyearlygraphsoftemperatureandenergyinboththemorningandeveningcooking

storageboxes.

ProjectedPerformance

ThefollowingfiguresshowgraphsfortemperatureandtotalenergystoredforbothIndiaandIowa.



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Figure25:NightHeatEnergyStored,India

Figure26:MorningCookingTemperatures,India



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Figure27:Morningheatenergystored,India

Figure28:Nightcookingtemperatures,India



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Figure29:Weeklymorningtemperatures,Iowa

Figure30:Weeklynighttemperatures,Iowa

AfterviewingtheheatandtemperaturegraphsforIndia,itwasnotedthatthereissufficient

energystoredwithwhichtocookroti.Themorningcookinghadaslightlylowercooktemperaturedue

toheatlossesthroughoutthenight.Amorecompletepictureofhowthemodelprojectstemperatures

inthecookercanbefoundintheweeklyIowagraphs(Figure29andFigure30).Thesegraphsshowthat

a1-2daychargingperiodisrequiredbeforethecookerisreadyfordailyuse.Extractionofenergydueto

cookingcanbeseeninthesharptemperaturedropsfoundintheeveningandagainintheearlymorning

timeperiods.Theslowermoreexponentialdropsintemperaturearefromtheheatlossestothe

surroundings.



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Conclusions

FinalRecommendations

Ultimately,theclasswassuccessfulinbringingthefinaldesigntoprototype.However,thereismuch

worktobecompleted.FutureMEDPclassesshouldbetaskedtocorrectsomeofthefollowingissues

whileimprovinguponthebuildqualityofseveralkeycomponents.Theprimaryrecommendation

regardingthesolarcookerinclude:

1. Calibrationandconfirmationofthethermocoupleresults-Theinitialtestresultsyieldedvery

littleinformationandafullcalibrationofthethermocoupleswasnotperformedpriortothe

assemblyofthecooker.Beforeadditionaldataisgathered,calibrationofthethermocouples

mustbeperformed.

2. Isolationoftheinteriorlightfunnelfromtheexternalassembly-Theprimaryhousingandlight

funnelneedstobeassembledseparatelytopreventcrackingthatcanbecausedduringthemovingofthecooker.

3. Asetofexperimentalevaluationcriteriashouldbeestablished-severalsuggestionsforfuture

workinclude:

a. Gatherdataondifferentintervalstoobtainamorecomprehensivesetofperformance

curves

b. Gatherdataatseveralcollectoranglestoevaluateperformancelossbetweenangle

adjustments.

c. Preparehourlynote/evaluationsforcookerperformance.Whilethismightseem

excessive,notinglittlenuancesregardingshadowlocationandlightconcentration

throughoutthedaywillgoalongwaytoaidintheoptimizationofthecooker.

4. Determinetheoptimumreflectorcurvatureforpracticaluse.

5. ObtaintheheatpipefromtheBerkeleyTeamandincorporateitintothefinalsolarcooker

design.

6. Reducetheoverallweightofthesolarcookerthroughouttheoptimizationprocess.

Themajorissuesatthispointintheevaluationprocessdealwiththesolarcooker’sabilitytodirect

andfunnellighttoafocalpoint.Itwasnotedduringthetwo-daytestperiodthatlightconcentrations

wereoffcenterontheabsorberplate.Additionally,thereflectorsurfacesrequireadditionalpolishingto

increasereflectivity.

ItistheOrganizationTeam’ssuggestionthattestsberunoneachofthesubcomponentsseparately.

Buildingandtestingtheindividualpartsfirstwillshedmorelightonproperconstructionpracticesand

actualperformancevaluespriortofutureintegrationbetweencomponents.Inotherwords,theMEDP

groupsshouldgeteachofthecookercomponentsworkingseparatelypriortotryingtogetthemto

worktogether.



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Itisalsorecommendthattheclassbesplitintotwoteamtodividetheworkandprovidemore

studentswithdeeperinvolvement.Thirtystudentsononeprojectprovedtobeabitofalogistical

problemattimeswhenopinionsgotthebetterofengineeringreason.Additionally,thereweretimes

whensomestudentswerewaitingonothergroupstocompletework,whichshouldbeavoidedto

preventteamsfromloosinginterestintheproject.

Acknowledgements

TheMechanicalEngineeringDesignProjectTeamwouldliketogiveaspecialthankstoSailesh

RaoandH.S.Udaykumarforinspiringtheclasstoachievesomuchinsuchashorttime.Thedesign

processwaslongandarduous.InthewordsofProf.Udaykumar,"designismessy;thatisjustthenature

oftheprocess."Movingforward,thereismuchworktobedone.Futuregroupswillneedtostay

focusedandthinkoutsideoftheboxtosucceed.Thisproblemwon’tbesolvedovernight.Makeita

goaltostepforwardeachsemesterandeventuallywewillfindthesolution.

Thankyouallforyourcontributiontoourproject…

SteveStruckman UIEngineeringShopkeeper–Machining&

constructionaid

MargretEvans MIEDepartmentStaff–Budgetaid

JenniferRumping MIEDepartmentStaff–Clericalandofficeaid

RichHarden MIEDepartmentStaff–DasyLabaid

Dr.GaniGanapathi NASAEngineer–Insulationadvisor

ClimateHealers InformationandpublicityEngineeringforChange Informationandpublicity

UCBerkeleyTeam Advisementandheatpipedesign/construction

DFMLabTA’s Machiningandconstructionaid

TheMill Foodandmeetingroomrental

RiceHarvestersInc. Donationofthericehulls



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Andaveryspecialthankstothestudentsforstickingwithitthroughoutthesemester…



MEDP2011

WorksCited

1. UniversityofIowaIndiaWinterimTeam."IndiaWinterimReport."ClassProject.Universityof

Iowa,2011.

2. Wikipedia."Declination."10052011.10052011<http://en.wikipedia.org/wiki/Declination>.

3. ANSI/ASHRAE."TableE.1-E.8:SolarPositionandInsolationValues."Standard93-2003(2003).

4. ClimateHealers.152011<http://www.climatehealers.org/olddump/home.html>.

5. Rao,Dr.Sailesh.ClimateHealers:SolarCookersforRajasthanMechanicalEngineeringDesign

ProjectTeam.IowaCity,1122011.

***Additionalinformationwillbeprovidedintheforthcomingcoursepacketwhichwillincludeaddition

researcharticle,presentation,andthemasterExcelfileusedinproj ectcalculations.

Estufa Solar - India - Hawkeye Solar Stove

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