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Unformatted text preview: Problem 1 (20 points): A sparkignition automobile engine can be modeled as an Otto cycle, with compression
ratio l/l/Vz = 9. For operation at full throttle the following conditions are found: P, = 100 kPa, T; = 320 K, T3 = 2400 K. Assume that the effective constant speciﬁc heat ratio is k = 4/3 and that the heating value ofthe fuel is FHV=
43 000 kJ/kg—fuel. The combustion process is modeled as an equivalent input ofheat given by QH = m FHV. I Determine the constant pressure speciﬁc heagp, the pressure after the compression stroke, P2, and the air to
fuel ratio AF @na/mf.
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n . Problem 2 §20 points): Consider the steady—state operation ofthe ideal vapor compression cycle shown in the
schematic below. Theworking ﬂuid is R—l34a. ' .
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(A) Derive anlexpression for the coefﬁcient ofperformance, COPL, in terms ofonly the variables M, 172, and 173.
(B) Calculate the speciﬁc heat loss in the condenser il‘P; = 800 kPa and T2 = 60°C. ___Jit;; 12 1
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below. The working ﬂuid is water with a mass ﬂow rate ofm = l kg/s. The following operating conditions are
known: P1: 10 kPa, P2 =15000kP‘a I72: 206 9 kJ/kcy g, s; —— 0 6492 kJ/kg K T3 = 600 °C W (13 l Calculate the amount ofheat transferred to the ﬂuid 1n the boiler, QH the exit quality X4,c and the amount of
enti‘aopy Oenei‘ation across the boiler and turbine SW71 2 4. ii the boile1 1eceives heat from a constant temperatme 1‘ese1‘voi1‘at 900 0c. 9 LC) (/1 ’" Ti?” ~ \ \
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$391 3M4 ' Vi“ T a) T15} Problem 4 (20 p, oints): An air—breathing turbojet engine operating in steadystate is shown in the schematic
below. The work generated by the turbine is just sufﬁcient to drive the compressor. in addition to, m = 70 kg/s,
175 = 85. %. I77‘= 85 %, rm = 95 %, 0p = L292 l<.l/l<g~l,<. and k = 9/7, the following conditions are known: P, = 50 kPa, ‘7} = 1200 K, :0 = 900 K, P4 = 400 kPa, W 93" CC? on Determine WC, P3, and the exit velocity, V_,. 7;=5841<, ‘ 0.
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V]: nose “/5 Problem 5 (20 points): An ideal Brayton cycle with reheat is shown in the schematic belowhAssume that the
air—standard model is valid and that the following operating conditions are known: 3", = 300 K T3: 550 K, 73 = l lSO K, [35/136 = 3, m = l kg/s ‘
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Determine the compression ratio, PZ/Pl, the required compressor work, WC, and the temperature To. Plot the
cycle on the T—S coordinates provided. Clearly label each state and darken the process line between each state. . t w .. , 
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 Spring '08
 Chung

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