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[物理学]

题目序号题型归类

第1题中心主旨题型

第2题段落（间）关系题型

第3题审题定位与反推题型

第4题归纳推导题型

第5题审题定位与段落（间）关系题型

Theuseofheatpumpshasbeenheldbacklargelybyskepticismaboutadvertisers’claimsthatheatpumpscanprovideasmanyastwounitsofthermalenergyforeachunitofelectricalenergyused,thusapparentlycontradictingtheprincipleofenergyconservation.

Heatpumpscirculateafluidrefrigerantthatcyclesalternativelyfromitsliquidphasetoitsvaporphaseinaclosedloop.Therefrigerant,startingasalow-temperature,low-pressurevapor,entersacompressordrivenbyanelectricmotor.Therefrigerantleavesthecompressorasahot,densevaporandflowsthroughaheatexchangercalledthecondenser,whichtransfersheatfromtherefrigeranttoabodyofair.Nowtherefrigerant,asahigh-pressure,cooledliquid,confrontsaflowrestrictionwhichcausesthepressuretodrop.Asthepressurefalls,therefrigerantexpandsandpartiallyvaporizes,becomingchilled.Itthenpassesthroughasecondheatexchanger,theevaporator,whichtransfersheatfromtheairtotherefrigerant,reducingthetemperatureofthissecondbodyofair.Ofthetwoheatexchangers,oneislocatedinside,andtheotheroneoutsidethehouse,soeachisincontactwithadifferentbodyofair:roomairandoutsideair,respectively.

Theflowdirectionofrefrigerantthroughaheatpumpiscontrolledbyvalves.Whentherefrigerantflowisreversed,theheatexchangersswitchfunction.Thisflow-reversalcapabilityallowsheatpumpseithertoheatorcoolroomair.

Now,ifundercertainconditionsaheatpumpputsoutmorethermalenergythanitconsumesinelectricalenergy,hasthelawofenergyconservationbeenchallenged?No,notevenremotely:theadditionalinputofthermalenergyintothecirculatingrefrigerantviatheevaporatoraccountsforthedifferenceintheenergyequation.

Unfortunatelythereisonerealproblem.Theheatingcapacityofaheatpumpdecreasesastheoutdoortemperaturefalls.Thedropincapacityiscausedbythelesseningamountofrefrigerantmassmovedthroughthecompressoratonetime.Theheatingcapacityisproportionaltothismassflowrate:thelessthemassofrefrigerantbeingcompressed,thelessthethermalloaditcantransferthroughtheheat-pumpcycle.Thevolumeflowrateofrefrigerantvaporthroughthesingle-speedrotarycompressorusedinheatpumpsisapproximatelyconstant.Butcoldrefrigerantvaporenteringacompressorisatlowerpressurethanwarmervapor.Therefore,themassofcoldrefrigerant—andthusthethermalenergyitcarries—islessthaniftherefrigerantvaporwerewarmerbeforecompression.

Here,then,liesagenuinedrawbackofheatpumps:inextremelycoldclimates—wherethemostheatisneeded—heatpumpsareleastabletosupplyenoughheat.

1.Theprimarypurposeofthetextisto

[A]explainthedifferencesintheworkingofaheatpumpwhentheoutdoortemperaturechanges.

[B]contrasttheheatingandthecoolingmodesofheatpumps.

[C]describeheatpumps,theiruse,andfactorsaffectingtheiruse.

[D]advocatethemorewidespreaduseofheatpumps.

2.Theauthorresolvesthequestionofwhetherheatpumpsruncountertotheprincipleofenergyconservationby

[A]carefullyqualifyingthemeaningofthatprinciple.

[B]pointingoutafactualeffortinthestatementthatgivesrisetothisquestion.

[C]supplyingadditionalrelevantfacts.

[D]denyingtherelevanceofthatprincipletoheatpumps.

3.Itcanbeinferredfromthetextthat,inthecourseofaheatingseason,theheatingcapacityofaheatpumpisgreatestwhen

[A]heatingisleastessential.

[B]electricityratesarelowest.

[C]itscompressorrunsthefastest.

[D]outdoortemperaturesholdsteady.

4.Iftheauthor’sassessmentoftheuseofheatpumps(lines1-4)iscorrect,whichofthefollowingbestexpressesthelessonthatadvertisersshouldlearnfromthiscase?

[A]Donotmakeexaggeratedclaimsabouttheproductsyouaretryingtopromote.

[B]Focusyouradvertisingcampaignonvagueanalogiesandveiledimplicationsinsteadofonfacts.

[C]Donotusefactsinyouradvertisingthatwillstraintheprospectiveclient’sabilitytobelieve.

[D]Donotassumeinyouradvertisingthattheprospectiveclientsknoweventhemostelementaryscientificprinciples.

5.Thetextsuggeststhatheatpumpswouldbeusedmorewidelyif

[A]theycouldalsobeusedasairconditioners.

[B]theycouldbemovedaroundtosupplyheatwhereitismostneeded.

[C]theirheatoutputcouldbethermostaticallycontrolled.

[D]peopleappreciatedtheroleoftheevaporatorintheenergyequation.