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# exam 1 - ME 300 —D Thermodynamics Midterm Examination...

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Unformatted text preview: ME 300 —D Thermodynamics Midterm Examination —I Fall 2008 YOUR NAME: K E \I Answer all questions. Please do not consult any text book, class notes, home works or neighbor students. Strict penalties for violations will be imposed according to University rules. The first ten problems will be graded for 5 points each, and the next 15 for 10 points each. 1. 90 degrees F is greater than 30 degrees G.or False? 0 00 a“; F : @Q_31§% C : 331.2(5- The wind chill temperature in Chicago in cold January days can be around -25°C. Can the temperature be negative? How much is this in 0F? W55 ‘» «25°C. =_ -15 avg +32 la : —\\5*39~:”\3F Superman weighs 2500 N on Krypton where gravitational acceleration is 20 m/sz. He is reluctant to come to earth because he will appear lighter. If earth’s gravity is 9.8 m/sz, what is his weight on earth? H m _ QSoo _ \‘15 \43 0.3 . __ q.% ;_ mas-AN The specific volume of water vapor at 0.3 MPa, 160°C is 0.651 m3/kg. Water has a molecular weight of 18 kg/kmol. What is the mass in kmol inavolume of 3mg? KNAbuA mow, \a mo\ m; 3 m3 ) \l ., a ; cost km h = M “ M M'U‘ l\%)(o.esxy A thermodynamic process occurs according to the relation pV 1'8 = constant. The initial state of the gas is p1 = 2bars, V1 = 2 mg. The final pressure is 3 bars. What is the final volume? Nb \‘ 3 \>\\I‘ :- \DaVa ' .5— Va -. (Vi) K 33:) \'% n! (=0 l 32';ka = rsw. m3 A object whose mass is 2 kg is accelerated from a velocity of ZOOm/s to a velocity of 500 m/s by applying a force F. If there are no other energy gains, what is the work done by the force? AVE- = NMV 343$. b?) 4°, m , 2 z : V5 \ (“>LV3‘AAZB ,_ US} K2.” £560 ~ﬁso) : 1x0 \sTS 10. A refrigeration cycle operates by extracting heat from a room at the rate of 2000 Btu/hr. and dumping heat to outside at the rate of 3000 Btu/hr. What is its coefficient of performance? 0 Qt?“ : "9.000 Btu/m ; “3000 B’m/‘nr éou’c ' B’r‘u k V! = QM ... am; a ‘°°° / Y Cb? : (inn/Q : loco/loot) 7'" 1 A power plant is rated to generate 30MW of electricity. It burns oil and provides heat to the steam generator at the rate of 80MW. What is the heat rejected to the cooling pond, and what is the efficiency of the cycle? (A: "some ﬂ33£30-378 (it; .= ‘50 W 9") GM: 2 war-3° 1‘ 5° “W4 A heat pump cycle has a coefficient of performance of 2.5. It supplies a dwelling with an output of 20 kW. What is the work input to the dwelling? élm’c 1:. :20 law cm; MM- : a 1.5 \‘A V“ = 3.2. a no . I! i A closed rigid container has initially 5 kg of saturated water. Upon heat addition, 2kg. of water evaporate. What is the quality of the mixture? ”mew =5l‘8 at; Law no.3 ”wave-x : 2 K5 5 11. A manometer attached to a tank reads an absolute pressure of 104.0 kPa. If the atmospheric pressure is 101.0 kPa, what is the gage pressure? If the fluid is mercury with a density of 13,600 kg/m3, g = 9.81 m/sz, what is the reading on the manometer? ‘33“59 3 UO‘A‘O ... \0\.o3 \dot _; Ekea ; 3 csh R“ m WM 3 9mm" Sawx‘A‘lascsm (@390) 1%? l) 12. It is speculated that an asteroid with a diameter of 1000 km, spherical in shape (V = 4/3 7: R3) and density of 8000 kg/m3, may hit earth some time in distant future. What is the kinetic energy of impact, if it is travelling at 5000 km/second? Write your answer as aa.bb x 10nn Joules. (DO NOT GIVE ANSWERS IN A LOT OF ZEROES) w» aw” Hlmtmm 3“. 13. You are driving your Ferrari on |-57 at 100 km/hour. The aerodynamic drag coefficient (CD) for Ferrari is about 0.15. The drag force is given by FD = (co) (1/2 p v2) A Where p = 1.1 kg/mg, V = speed of the vehicle, A = frontal area = 2 m2. What is the power required to overcome the drag? Power = rate of work done. hwm T. F )g Vanni-X7 : cpk%§\1lﬁ\)\l: (0W M>£\\>L\m::;20 o M59 3‘ kidkmoacw WM) 2 BSB’TW '2. > 14. 2 kg of a gas contained in a piston-cylinder assembly undergoes a constant-pressure process at 5 bar beginning at v1 = 0.2 m3/kg. The work performed by the gas = -15 kJ. Determine the final specific volume. Is this a compression or expansion? \Ns: \PAV \l —\5 m = (s so m3) 0’33“”) \fg 3. “‘5 + O‘Df O‘gjm$00 . VS a o.\$‘5‘m3/lé.3 .! CQmYW\On I5 15. 15 Ibm of C02 undergoes heating in a 2 ft3 closed rigid cylinder. What is the work done by the gas, if the heat added is 5 Btu? Does the pressure increase or decrease? Assume ideal gas behavior, MCoz = 44 may. L‘s—w Av :: 0 vi 1&0 ‘ M \f; eow¥o-¢3 MM VV: MET .) ”i. V; J 16.The enthalpy of saturated liquid ammonia at 40°F is 86.33 Btu/Ibm, and of sat vapor is 622.30 Btu/Ibm. if a mixture has a quality of 0.39, what is the enthalpy of the mixture? \I I 2 "IV ‘7' {.‘u'xv v8" mx 3 :- 03.qu (Swab) New“) (was) 3: asset. Mix/ﬁr» 17. The properties of superheated ammonia at 5.5 bars (Tsat — 6. 79 0C) read as: 0C u kJ/kg h kJ/kg 60 1427.13 1583.60 80 1463.85 1631.04 100 1500.36 1678.05 What are the specific internal energy and specific enthalpy at 83°C at this pressure? ’1 “My: 6\ 83:9 Chm ‘0‘ 7’ “H9385 ..,. 86-»80 L\SDO "tugs-gs) \oo»%() = Nice. gems/v.3 K ~ \t, 3\ . 0H .r 33 ~86 \ @519. as .. may all) Wow-$9 =. \L'ss. an \AT/M 18. A two-phase mixture has u = 144.58 kJ/kg. The following properties from the tables are at the pressure of the mixture: uf = 58.77 kJ/kg. ug = 230.38 kJ/kg. hf = 59.35 kJ/kg. hg = 253.99 kJ/kg. What is the quality of the mixture and what is the specific enthalpy at thatstate? 1 ; \x— «5 -.-. “‘“L§3“5$'77 “3 w“% “36 ~33 ”'58 :7“) ; Q.5 'Qn :2. 5&5 ac- ’7 K’Q‘%”&%> H 61 5.. 6" .J / P Li 1: t) 19. A well-insulated closed rigid tank has a volume of 10 fts. And contains saturated water vapor at 212°F. The water is rapidly stirred until the pressure is 20 |bf./in2. What is the work done by the stirrer during this process, and the final temperature? Data given in the Tables AZE and A4E. v = "U ad: a»: F .. 3 WM m - W/ala‘N ,$é '\>‘ $0 a \f" 1.0 M)\‘~m s 15W ’ 3 '1 “No- gay/‘5’“ “vagrant :. \cx. 5b may «WWW u" \ we mk“2”“l3 Lt —- MSJ - “8“5 “"‘ “‘6" ‘ \0 \5‘9 M W .: \\le' “’” use — as.“ await-45‘” 3:30 M31145) 20. A gallon of milk at 68°F is placed in a refrigerator. Energy is removed from the milk at the rate of 0.08 Btu/s. How long will it take in minutes for the milk to cool to 40°F. The specific heat for the milk = 0.94 Btu/lbm. °R and density is 64 lbm/ft3. Q = m CV A T c: In .. lo. 3:33 cg) kWHOA‘k) Ah - m \l ” . Q\o% ﬁhWk-‘Bb .: Hb‘q N“ H 21. A tank contains 1 m3 of air at -93 °C and gage pressure of 1.4 MPa. The atmospheric pressure is 101 kPa. The corresponding 2 factor is 0.67 and air has a specific gas constant of 0.287 kJ/kg.K. Determine the mass in the tank. 22. Hydrogen gas (Mol. Wt = 2) initially at 2 bars (1 bar = 105 Pa) and 200K undergoes a poiytropic process with n = 1.2 to a final pressure of 14 bars. Determine the work for the process in kJ/kg. Assume ideal gas behavior. 1‘“ '1» v - RT in v : (”him :00} — “‘5... \3‘ \ \ ‘ 9‘ kayo) Ma W5 3.. M")... \ 1 p‘ \'2 a”? a ta"; " "V; a “V. “$75. 3...... "i7": = (”A \KL M email W3/“5 o 82.0 W - \FQVQ. “\fcv" = (“‘5 KW > ( 51‘) M .9 WW w- LQ:QBS>(~H \ m \un MMM M M MMMWm. —O\Q 23. Consider a rigid tank that has a partition. One side of the partition initially contains Nitrogen gas at p1 = 3 bar, T1 = 400K and Volume = 0.2 m3. Suddenly the partition is broken and the gas occupies Ehae entire tank. The final volume is 2 V1, p2 = % p1. Taking cv = 0.75, calculate T2 and heat transfer. W \VV 2“- mg”? m ‘ \lm . .. - l’zv'l :3. 2- \P\ " W , T9. _ Tl V 4 T" Ta i». i "" I; :: IDOK . 9N g» 5’ Cu Lian“ 3 : LOWIS) (saw) :1 ”\50 \$43; to y“); 24. 1 kg of air in a piston-cylinder assembly undergoes two processes in series from p1 = 0.5 MPa, T1 = 227 0C. 1-2 Constant temperature expansion V2 = 2 V1. Find a) p2 2-3 Constant volume heating, p3 = p1 = 0.5 MPa. Find b) T3 l“? \f : \f .. RT :1 '9‘an W... in \ K 9. ~ x? . A... toasmra V1 “to '1\H U ‘51. 7’ m "-‘-~ \ 7. V2. (3,3) \] -;. Wk 3, ‘9be a; ‘Favﬁ. ', \15 3’- Va... R73 R”7'2... ”Y3 “-‘- EEIEW :2. L13 Lie.» 2. ‘F’a. moo Vs. 25. The enthalpy of a fluid is given by: h = u + pv. Using the definitions of the specific heats, show that cp = cv + R, where R is the specific gas constant. ': Q‘r‘RT ...
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exam 1 - ME 300 —D Thermodynamics Midterm Examination...

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