MAE119W2018FINALEXAMPROF.G.R..TYNAN

PartI:MULTIPLECHOICESECTION–2POINTSEACH

1. Whichbestdescribestheworkingdefinitionofenergyusedinclass:a. Energycanbetransformedandindoingsocanbeusedtoperformwork.b. Energyisgraduallyconsumedinproportiontotheamountofworkperformed.c. Energyisthetimerateofchangeofpower.d. Noneoftheabove.

2. Whichphrasebestcapturesthefirstlawofthermodynamics?a. Energycannotbestoredeffectivelyasitgraduallyislostfromasystem.b. Powerisgivenbythetime-rate-of-changeofenergyc. Energycanbeconvertedfromoneformtoanotherbutisalwaysconservedd. Thedegreeofdisorderinasystemgraduallyincreases.

3. Primaryformsofenergyinclude:a. Petroleum,NaturalGas,FissileMaterialb. Coal,Gas,andRefinedpetroleumproductsc. Electricityd. Alltheabove

4. Whichofthesearecommonenergyenduses:a. ElectricityGenerationb. Transportationfuelsc. Heatingd. Alltheabove

5. Adequateaccesstoenergyservicesislinkedtoa. EnergyIntensityb. Humanqualityoflifec. Increasedpopulationgrowthrated. Reducedcarbonintensity

6. TheKayaIdentityisusedtoconnectcarbonemissionratestowhichofthefollowing?a. Humanpopulationb. EnergyandCarbonIntensityc. Per-capitaeconomicactivityd. Alltheabove.

7. About how long does CO2 emitted from fossil fuel combustion reside in the Earth’satmosphere?

a. 10yearsb. Aboutonehumangenerationc. Several100sofyears.d. Itstaysforever.

8. Whichofthefollowingstronglyabsorbinfra-redradiationintheEarth’satmosphere?a. NitrogenandOxygenb. WaterVaporc. MethaneandCarbonDioxided. BothBandCe. A,BandCareallstrongIRabsorbers.

9. Ifall formsofenergyuseareincluded,therateofenergyconsumptionbyhumanbeingstodayisabout

a. 100millionbarrelsofoil/dayb. 15TWc. About10xtherateoftoday’srenewableenergyproductiond. Noneoftheabove.

10. Thecapacityfactorofanelectricalpowergenerationtechniqueisdefinedasa. Therelativefractionoftheelectricalpowerdemandthatitcanprovideb. Itisanotherphraseusedtodescribetheefficiencyc. Ittellshowoftenthetechnologyisavailableforused. It is the ratioof theaveragepowerproduceddividedby the system’speak rated

power.11. Themaximumtheoreticalefficiencyofawindturbineis

a. about60%b. dependsonthedetailsoftheturbinedesignc. canapproach100%ifthewindblowsallthetimed. noneoftheabove

12. Whatconsiderationsimpacthowmuchwindpowercanbeextractedfromalargearrayofwindturbines?

a. Interactionsbetweentheturbinesinthearraylimithowclosetheycanbespacedb. The turbine arraywill slow down thewind in the lower region of the boundary

layerc. Theaveragewindspeedandthevariationofthewindspeedmatterd. Alltheabove

13. Theintermittencyofrenewableenergyresourcescanbereducedbya. UsingsolarPV,windand/orsolarthermalsourcesspreadoutofalargegeographic

areab. Usingbackupconventionalfossilfueledsystemsc. Usingpumpedhydroorbatteriestostoreexcessenergyd. Alltheabove

14. Whichoftheseresourcescanbeexpectedtomeetasignificantfractionofhumanenergydemandfortheforeseeablefuture?

a. Wind,nuclearfission,fossilfuelsb. Wave,tidal,oceanthermalandoceancurrentsc. Conventionalgeothermalpowerd. Noneoftheabove.

15. Theefficiencyofasolarcellcanbeincreasedbya. Increasingtheband-gapenergyofthematerialb. Increasingtheminoritychargecarrierlifetimeinthematerialc. Reducingtherateofminoritycarrierlossesduetodefectsd. BothBandCarecorrect.e. A,BandCareallcorrect.

MAE119W2018FINALEXAMPROF.G.R..TYNAN

PartII:ONESHEETOFNOTESANDCALCULATORSAREPERMITTED.NOOTHER

ELECTRONICDEVICESAREPERMITTED.15pointseach.1. Light fromastarshinesonaplanetwith intensityI,andallof it isabsorbedonthesurface.ThesurfacethenheatsuptoatemperatureT>0.a.Ifthereisnoatmosphere,findanexpressionforthesurfacetemperature.10points.b.Supposethereisnowanatmospherethatisperfectlytransparenttothesolarradiation,andperfectlyabsorbingtotheradiationemittedfromtheplanet’ssurface.Theatmospherewarmsupaswell,andradiates50%ofitsheattowardstheplanet’ssurface,andhalftospace.Whatisthenewsurfacetemperature?10points.

2.Supposehumanbeingsinstantaneouslyinjectamass,M,ofCO2intotheEarth’satmosphereattimet=0.Usingourcarbonbalancemodeldevelopedinclass,howdoesthetransientinthemassofCO2intheatmosphererespondfort>0?20points.3. A solar thermal power plant collects solar radiation with a DNI of 1000 W/m2 andconcentratesthisbyafactorof1000ontothehottargetoftheplant.a.Coolantcirculatingthroughthetargetremoves50%ofthisheatfluxanddeliversittoaheat

engine.Whatistheresultingtargettemperatureifconvectiveheatlossestotheatmospherecanbeneglected?10points.

b. If the coolant achieves a temperature that is 50%of the target temperature, and the coldreservoirhasatemperatureof400K,howmuchpowercananidealheatengineproduceperunittargetarea?10points.

c. Acloudlayerthatis1kmthickcontainingsmallparticleswithacross-sectionalareaof10-8cm2andadensityof1000particles/cm3andlargerparticleswithacross-sectionalareaof10-9cm2atadensityof10,000particles/cm3.ByhowmuchdoestheDNIchange?10points.

4.AsolarPVcellexposedto1kW/m2ofsolarradiationhasashort-circuitcurrentof30mA/cm2andanopencircuitvoltageof1V.a. DrawtheI-Vcharacteristicforthisdevice, labelingtheshortcircuitcurrent,opencircuit

voltage,andpointofmaximumpoweroperation.10points.b.IftheFormFactorforthiscellis0.66,whatisthecell’sefficiency?5points.c.Supposeyoudoubletheminoritycarrierlifetimeinthecell.WhathappenstotheI-Vcurve

andtheefficiency?5points.d.Nametwowaysyoucouldincreasethecarrierlifetimeofthecell.5points.

5. Awindturbine isplacedatasitewhere thewindhasaequalprobabilityofhavingaspeedanywherebetween0and10m/sec. Theturbineisdesignedtoproducemaximumpowerforawindspeedof10m/sec,andthewindneverblowsataspeedabove10m/sec.a.Whatistheaveragewindspeed,Vave?5points.b.Whatisthecorrespondingaveragewindpowerdensity(W/m2)?10points.

c.Compareyouranswertopartaandpartb.Whyisn’ttheanswertopartbequalto 12ρVave

3 ?

10points.d.Whatisthecapacityfactorofaturbineplacedatsuchasite?5points.6. Suppose that two species of greenhouse gases are injected into the atmosphere and areuniformlymixedsuchthattherearen1molecules/volumeforspecies1andn2molecules/volumeforspecies2.Theinfra-redradiationabsorptioncross-sectionforthetwospeciesisgivenass1ands2.

a. Derive an ordinary differential equation governing the variation of unabsorbed IRradiationwithpositioninthisatmosphere.10points.

b.Solvetheequationfrompartatofindthetransmissioncoefficientthroughanatmosphereofthicknessd?10points.