thermo_hw2_assign - H2.2 A rnass of 15 kg of air in a...

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MAE 110A Winter 2010 HW #2 Due: Friday, .Ianuarl' 29 (beginriing c,f class 12:00 noon) Note: Draw T -'L:. p - u diagrams wherever possible. Text Problems: 3..12 a), b), d), h). Flandout Problems: H2.1 A vertictrl piston-cylinder clevic'e contaius 1 kg of H2O in nrr eqrrilibriutri statc at 20"C (sce Figurer H2.1). Thc initial volurric of tlic -nvatcr is 0.12 nrJ. hiitiallr'tlie piston rcsts on somc stops with the top surface open tci ther atrnosphere such that a prcssrlrc of 30() kPn (HzO) is recluirecl to lift it. 'Ihc rvater is tlien heatccl to saturate<l r'apor. 'l'hc proccss rnav bc consirle'recl quasicclrrilibriuni riitlr rregligible kirretic arrd polelrlial errcrgr"effccls. Dcl e'rrrrirrc: a. ske'tch c'ntire process on 7 - l' arrcl p - 't' cliagrarns b. final tempcrature of H2O, 'C c. rvork, kJ (indicate magnitr-ide arrd direction) d. lieat transfer. kJ (indicate rnagnituclc and dircction)
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Unformatted text preview: H2.2 A rnass of 15 kg of air in a piston-cvlindcr dcvice is heated fronr 25 tct 77"C by passing current through a resistarlce heater inside the cylindcr. The pressure irr the cylinder is hcld corlstant at 300 kPa during the process. and a licat ioss of 60 kJ occurs. Deterrnine the electric energ)' suppliecl. in K\Vh. Assurne idcal gas behavior arrd a. variable specific lieats b. corrstarit spccific hcats Corrrparc solrrtions from a. unci b. a,rrd corrrrrterrt. FI2.3 A gzrllon of rnilk at 68'F is place in a relrigerirtor. It thc ratc of hea,t trarrsfer fioui thc niilk is constarit at 0.08 Btu/s. hou, krng lvill it take (rriinutcs) fbr thc rnilk to cool to,10'F''l Assunre rrrilk behaves as arr irrcorripressiblc substancc u,ith specific heat aricl clcrrsitv vilhres oi 0.9"1 Iltu/lbn'R and 64 lbrn/ft3. respcctivclv. i" ld Y Figrrre II2.1...
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