S11_test1

S11_test1 - MAE251 Test 1 Spring 2010 Closed book — time:...

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Unformatted text preview: MAE251 Test 1 Spring 2010 Closed book — time: 55 min — grading: 10+10 Remember to solve the problems symbolically first: method! Also remember that there will be very little partial credit for execution errors (signs, numbers, units, etc.) 1. A cycle using an unspecified substance takes place in a piston/cylinder device. State 1 is characterized by p1 = lOOkPa and V1 = lm3/kg, state 2 by V2 = v1 and p2 = 3p1, state 3 by p3 = p2 and V3 :‘= 3V1. During l-2, there is an increase in specific internal energy of 100 kJ/kg; During 3-1, the pressure varies linearly with specific volume, and there is heat transfer out of the system in the amount of SOkJ/kg. Show this cycle on a thermodynamic diagram of your choice. Knowing that the cycle's efficiency is 0.4 and that q31 < 0, determine all heat exchanges per kg of substance. 2. A closed system consisting of 2.5 lbm of refrigerant R—22 is compressed from saturated vapor at 32 psi to saturated liquid at 70 psi. Sketch this process on p—v and T-v diagrams, clearly labeled. Knowing that the compression is polytropic, determine the heat exchange. Conversion factors: 1 bar = 100 kPa 1 Btu = 778 1bf.ft 1 psi = 1 lbf/in2 go = 32.2 lbm.ft/lbf.s2 K=°C+273 OR =°F+460 Tables in English Units 0.01220 0.01229 0.01237 0.01246 0.01255 ..,39 7< Mé/e 4—75 Properties of Saturated efrigerant 22 (Liuid—Vapor): Temperature Table Specific Volume Internal Energy Enthalpy Entropy ft3/lb Btu/lb Btu/lb Btu/1b - °R Sat. Sat. Sat. Sat. Sat. Sat. Sat. Sat. Temp. Press. Liquid Vapor Liquid Vapor Liquid Evap. Vapor Liquid Vapor “F lbf/in.2 U; I) u hf hf h 70 #136118 190.27 W 80.11 110.42 0.0634 0.2147 878 Tables in English Units 7515/6 A-XE Properties of Satura d Refrigerant 22 ‘ uid—Vapor): Pressure Table Specific Volume ntemal Energy Enthalpy Entropy ft3/1b Btu/1b Btu/lb Btu/lb - °R Sat. Sat. Sat. Sat. Sat. Sat. Sat. Sat. Press. Temp. Liquid Vapor Liquid Vapor Liquid Evap. Vapor Liquid Vapor Press. lbf/in.2 °F vf 118 u; ug hf hm its S, SE ibf/in.2 0.01178 0.01189 0.01198 0.01207 0.01216 Temp. \ (ooLP& ngr‘ 3 Earth; 55 “MB/kg "‘55 61:03 03:30\ LL 9— L—3 $4? :0 —-—¢ _—~ (0 [Q3 “5””: : C113 “£23 EL; 0 L; - A - pu‘u3 = (1% ‘ 3‘ F20); UL) _ BF‘ 26‘ N @wt—U/éf 9.:atm La Latina Fgfioy— 3) s 4m til/5o f O : QM +5123 +33. ~wwx OWL/0.2 N]: -—~=> an : 2—“.ng : §©Q(LU/kao (Q ~ 0 :: aha-{— €2$WLQ>© (\OD/ g0 [23 » L‘f .0 Wok 33‘ : ~%OQ . I29 t) L T L @ u 2 3332 SEWAwa refit/flaw , 3 ._ "(34% :——28,(9%£M. ...
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S11_test1 - MAE251 Test 1 Spring 2010 Closed book — time:...

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