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1、为了适应公司新战略的发展，保障停车场安保新项目的正常、顺利开展，特制定安保从业人员的业务技能及个人素质的培训计划郝士明教授材料热力学配套的材料热力学习题与解答Theproblemsofthefirstlaw1.aleadbulletisfiredatafrigidsurface.Atwhatspeedmustittraveltomeltonimpact,ifitsinitialtemperatureis25andheatingoftherigidsurfaceoftherigidsurfaceisneglected?Themeltingpointofleadis327.Themolarheat
2、offusionoftheleadis/mol.ThemolarheatcapacityCPofleadmaybetakenas/(molK)()Qabsorb?Qincrease?Qmelt?n(Cp?T?Hmelting)121mv?nMv222Solution:Qabsorb?WW?n?(327?25)?103?V?(m/s)2.whatistheaveragepowerproductioninwattsofapersonwhoburns2500kcaloffoodinaday?Estimatetheaverageadditionalpowderproductionof75Kgmanwh
3、oisclimbingamountainatehrateof20m/min()QBurning?2500?103?(J)SolutionP?W/t?QBurning/t?Pincreasing?121(J/S)24?60?60?h20?mg?75?245(J/S)t603Onecubicdecimeter(1dm3)ofwaterisbrokenintodropletshavingadiameterofonemicrometer(1um)at20.()(a)whatisthetotalareaofthedroplets?(b)Calculatetheminimumworkrequiredtop
4、roducethedroplets.Assumethatthedropletsarerest(havezerovelocity)Waterhaveasurfacetensionofdyn/cmat20(NOTES:thetermsurfaceenergy(ene/cm2)isalsousedforsurfacetensiondyn/cm)Solution4?(1?10?6)33W?S?10?5?2?(3?103?6?10?2)?(J)Stotal?nSSingle?(1?10?1)3?4?(1?10?6)2?3?103(m2)heliumistobeusedtoquenchahotpieceo
5、fmetal.Theheliumisinstorageinaninsulatedtankwithavolumeof50Landatemperatureof25,thepressureis10atm.Assumethatheliumisanidealgas.(a)whenthevalveisopenedandthegasescapesintothequenchchamber(pressure=1atm),whatwillbethetemperatureofthefirstgastohitthespecimen?(b)Astheheliumflows,thepressureinthetankdro
6、ps.Whatwillbethetemperatureoftheheliumenteringthequenchchamberwhenthepressureinthetankhasfallento1atm?()(a)AdiabaticTP?()R/CPT0P0Solution:T?298?()?118(K)10(b)W1?(500?5)?10?3?T?118(K)?3nCp10?50?10?298T?T0?T?298?118?180(K)5Anevacuated(P=0),insultedtankissurroundedbyaverylargevolume(assumeinfinitevolum
7、e)ofanidealgasatatemperatureT0.Thevalveonthetankisopenedandthesurroundinggasisallowedtoflowquicklyintothetankuntilthepressureinsidethetankisequalsthepressureoutside.Assumethatnoheatflowtakesplace.Whatisthefinaltempetureofthegasinthetank?Theheatcapacityofthegas,CpandCveachmaybeassumedtobeconstantover
8、thetemperaturerangspannedbytheexperiment.YouanswermaybeleftintermsofCpandCvhint:onewaytoapproachtheproblemistodefinethesystemasthegasendsupinthetank.()AdiabaticTP?()R/CPsolutionT0P0T?T0(P0?0R/CP)?T0P06.Calculatetheheatofreactionofmethanewithoxygenat298K,assumingthattheproductsofreactionareCO2andCH4(
9、gas)ThisheatofreactionisalsocalledthelowcalorificpowerofmethaneconverttheanswerintounitesofBtu/1000SCFofmethane.SCFmeansstandardcubicfeet,takenat298and1atmNOTE:thisvalueisagoodapproximationforthelowcalorificpowderofnaturalgas()FORDATA:0?H298Kcal/g?molCH4(g)CO2(g)H2O(g)?solutionCH4?2O2?CO2?2H2O?H298?
10、(?HCO2?2?HH2O?HCH4)?(?2?)?1031?(Kcal/g?mol)?(Btu/1000SCF)310?103?252?1037.Methaneisdeliveredat298Ktoaglassfactory,whichoperatesameltingfurnaceat1600K.Thefuelismixedwithaquantityofair,alsoat298K,whichis10%inexcessoftheamounttheoreticallyneededforcompletecombustion(airisapproximately21%O2and79%N2)()(a
11、)Assumingcompletecombustion,whatisthecompositionofthefluegas(thegasfollowingcombustion)?(b)Whatisthetemperatureofthegas,assumingnoheatloss?(c)ThefurnaceprocessesXXkgofglasshourly,anditsheatlossestothesurroundingsaveragekJ/h.calculatethefuelconsumptionatSTP(inm3/h)assumingthatforgasH1600-H298=1200KJ/
12、KG(d)Aheatexchangerisinstalledtotransfersomeofthesensibleheatofthefluegastothecombustionair.Calculatethedecreaseinfuelconsumptionifthecombustionairisheatedto800KDATASTPmeansT=298K,P=1atmforCH4CO2H2ON2O2SolutionCP(cal/mol?C)(a)CH4?2O2?CO2?2H2OCO2%?1?%793?2?2?(?1)21H2O%?2CO2%?%N2%?%O2%?%(b)Cp,p?Cp,iXi
13、?(?)?(cal/mol?C)T?T0?T?298?1000?2104(K)?(C)P?1200?XX?(KJ/h)VConsuming(d)Cp,r?Cp,iXi?16?100/?(cal/mol?C)?103?3214(m3/h)?1000?(1600?298)1(?)?H?H298?(?Cp,p,ini?Cp,r,ini)dT?1000?(?)?)(800?298)?(cal/g?mol)VConsuming?103?1644(m3/h)?(1600?800)1(?)aninvestigationofthethermodynamicpropertiesofa-manganese,the
14、followingheatcontentsweredetermined:H700-H298=12113J/(gatom)H1000-H298=22803J/(gatom)FindasuitableequationforHT-H298andalsoforCPasafunctionoftemperatureintheform(a+bT)Assumethatnostructuretransformationtakesplaceinthegiventempeturerang.()b?H?CPdT?a?bTdT?aT?T2T2982ba(700?298)?(7002?2982)?ba(1000?298)
15、?(10002?2982)?Solutiona?b?CP?T?H298?(T?298)?(T2?2982)fuelgascontaining40%CO,10%CO2,andtherestN2(byvolume)isburntcompletelywithairinafurnace.Theincomingandongoingtemperaturesofthegasesinthefurnaceare773Kand1250K,respectively.Calculate(a)themaximumflametemperatureand(b)heatsuppliedtothefurnacepercu.ftofexhaustgas()?f,298,CO?J/mol?0
