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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.% ;_ masAN 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£30378
(it; .= ‘50 W 9") GM: 2 war3° 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
”wavex : 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 VanniX7
: 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 pistoncylinder assembly undergoes a
constantpressure 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 "tugsgs)
\oo»%()
= Nice. gems/v.3
K ~ \t, 3\ . 0H .r 33 ~86 \ @519. as .. may all)
Wow$9 =. \L'ss. an \AT/M 18. A twophase mixture has u = 144.58 kJ/kg. The following properties
from the tables are at the pressure of the mixture:
uf = 58.77 kJ/kg. ug = 230.38 kJ/kg. hf = 59.35 kJ/kg. hg = 253.99 kJ/kg.
What is the quality of the mixture and what is the specific enthalpy at thatstate?
1 ; \x— «5 .. “‘“L§3“5$'77
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t) 19. A wellinsulated 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.“ await45‘” 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 pistoncylinder assembly undergoes two processes in series
from p1 = 0.5 MPa, T1 = 227 0C.
12 Constant temperature expansion V2 = 2 V1. Find a) p2
23 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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