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2009Midterm2_solution

# 2009Midterm2_solution - "'~ II Ill z MAE110A Midterm...

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Unformatted text preview: "\ _.-'~ II; Ill. z,- \ .;_ MAE110A Midterm Exam 2, November 23, 2009, 90 minutes open book and calculator only no portable electronic devices, cameras, homeworks, notes, solutions etc 1. (30 points) An air compressor operates at steady state with air entering at p1 = 15 Ibf/inz, T1 = 60°F. The air undergoes a polytropic process and exits at p; = 75 lbf/inz, T2 = 294°F (hint: h; = 180.63 BTU/lb). Assume the ideal gas model for air and neglect changes in kinetic and potential energy. (3) Evaluate the work and heat transfer, each in Btu per lb of air flowing. Hint: the unit conversion factor is 1.986 BTU / (28.97 lb °R) (b) Qualitatively, sketch the process on p-v and T-s diagrams and associate areas on the diagrams with work and heat transfer, respectively. 2. (50 points) Consider a Carnot vapor power cycle. Saturated liquid water enters the boiler at a pressure of 10 MPa, and saturated water vapor enters the turbine. The condenser pressure is 6 kPa. Hint: Do not interpolate tables, but choose closest value. Determine 3. Thermal efficiency. b. Would the thermal efficiency of an ideal Rankine cycle at the same pressures be larger or smaller? Why is the Rankine cycle chosen in practice over the Carnot cycle? c. Heat transfer to the working fluid per unit mass passing through the boiler, in kJ/kg. cl. Now consider irreversibilities in the adiabatic expansion and compression processes. If the states at the turbine and pump inlets remain unchanged, repeat a) with _ isentropic efficiencies of ﬁt = 0.80 for the turbine and 1],, = 1 for the pump. 3. (20 points) Air enters an insulated turbine operating at steady state at 6.5 bar, 687°C (hint: h = 1000.55 kJ/kg) and exits at 1 bar, 327°C. Neglecting kinetic and potential energy changes and assuming the ideal gas model, determine a. The work developed in kJ / kg of air flowing through the turbine. b. Whether the expansion is internally reversible, irreversible, or impossible. l r I _g_M/LE. uQA____.E Migicm L 1 \$olu-Hov15 "6 iTW’ob'tggn l 5 €50 P+s. J _T\ v _ ' . ‘ A :, 4*» Am wrcasar :5 opera-f1 6d” 'é'hzmly Bi-vdﬂ ; NHL! 1119.— 3ivm Eqkf v- ouHa Vajws: (D . I"~ @1210" ‘ 'P.= is 1LVa“: 'Pb=‘76 "ﬁr w ‘ 112,- (smswﬂh 1' z | T,=Lpo'r-' ; 71,: L‘W'F | “‘5 ﬁd—prms ;: “Poly-Hap; => Pvn“: Cami? 593,1‘NodgL: 5) 435%“, (1-5“ 33 M ‘id-EAI 0G b) “rm—“Prams: is ad— 51’1541 88ft“. a) Negkcf "PE-1be e. c‘fs i £95555 : APPN'VQ ﬁe. 5.1243, b-qulm: I ' . L . g :3}? = Q - w + :mm 32537;) — can»: (h+%+3%3 +2. ‘ kﬂdwiﬂs afg=o gmﬂia ﬁat!“ wk! =n5L:M 5mg! ﬂu . EB Earn-LES “(1:35 , ’ o= rig—{N +n31(‘).—lnz,)=—7 g, = 13% + (aghb + hi can be (warm; Wﬂscz 4.72213: la. 2/3427 BTU/rs 63 work M b: dd-cr-ur'hei “FEM: - +2 %=:_ﬂfﬂ U; are. “n” OLA bu oLd-uminei 'FIUM‘ ! n_’ i - -1 1 P1”: Cong'f' => l :3 a) r175" } I PI 5207/ ‘6' i lo (L95) n-t ' .:> _3___ = .._._ => : ' +3 ‘- post 5 ) n _.__L: O , 1:1 I _ (/.5)K(1::n\ h um vuiaggkwe I) H "a (.5 —( h" 3 2,23%? / - W 3% (ED : 60—},E‘ﬂ _‘3F_’rc->ble:n_ 2— pesarlemn; A Came-E— \Mkfcr cycle. 3'13: : 10 Ha . PL 9 1: -. (0 LR. Q :5 Sq‘f‘um'kd V010“: Sink ® .‘3 517‘mk1 lifU-‘d- Eng, Mach‘: N0 in. +ulbfnt a! ‘F-lelO. Ne L» ‘,W{[c’_{ 3‘35?- |. 55:1? ﬂIIEiS‘. 6Q Thorn/«Al 5144mm“, 4:" am. Edin‘ cami— cyc‘k mu Enema Y‘ , T 65 "Zal- .7:- => Tar-Twhwwq - 309.3: K "I; Tafﬂmqg MR3 = 5813.3 K 3°13! 584.13 ») :15?- O.?70Ca. ~ ‘27 2. E? .b.) The, Emma would 9L.mgg._.e£-gegk ﬁéwc-v/er, :74 ES 007‘ US'QOL 'w- ?m-Ha_. bumme— ?nétu._; chalk. la +Y\[ik3 +- <?u-.P 0L. +£1.10 7545;. Mgr-farm 72mm 1424 CG += ﬂu lower. #50, lass “or? is exfmkol-Homf'mbus-Hon +71 when burnihj fuel in 41M. hmlzr +u vaor.'km wd‘L-(ﬁjflui . C3 To Freed, a" beam ﬁnk“! += m mimic; od" each orﬁ {m 7%- mm mm; = "J .5 - 5.02M V39 A“! 2’7Mé/‘3, I [gilt .'- AIL: I” @ h?" at (P ‘OWKJ :3 I14— /‘707 (1 (“S/é :r? r? 57: 5,5370 '54? K s —sﬁn M S =- __ 7 s. 3 ® 5 C9. 5 \$7 3 ﬁg 55f (u 3 k5: 20277 /6 + ( 1305 5%) To save 42v m 1401+- mmw Myaykm 4%,: Ewing, 1m. 51:.- D I 40 4.0 %r @->/+’ﬁ(aﬂ¥-lﬂl)+ V‘Th ' _, T/%v_€f‘; 6; 2.. v. . ® :5 53.7.: hl_hf = (5724.7 ~ #31010, &\ ﬁr m '1?=Io t.) hfrl’lﬁ = Holt; Mia 43* W {WEN-'1 :0'3 a 11.41; '47? 2,721.? - 24.. '5 h h " "uni-:7sz m: mm 921 _\$r59e; '3 “H's _ _ mm: 4h “4&1!th forbML exfme war-L. 1%“ air. 421x94:- ?.-—- (9-5 6“ T,= {937 L madam ‘éj; 1):," Adv 55,7 [—1 I ’ I WV.“ .\\ -.'® 533. Mad-9J5 nejud T954 K5 ’(fSSOM-Q «Si—Cad? 4W ES Edm/ S. MJV‘QM {vvbfmﬁ—‘f‘ a 2'0 C) o ﬁgﬂw “HI-“w WM) 0 0 4» '. 6) _ .U/@ J, M 0 g: {miszm- 2M?) ‘me {In-2,2 8 “f 1 %—=Z42—Z.QL - /n ((75) 8007M Puma"; L7 wrewrsJD/i' E+Z,5 ...
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