課程名稱︰熱力學
課程性質︰系定必修
課程教師︰蘇金佳
開課學院：工學院
開課系所︰機械系
考試日期（年月日）︰98.01.14
考試時限（分鐘）：openbook 50min / closebook 1hr
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
openbook部分 (50min)
1. Steam enters a turbine with a pressure of 30 bars, a temperature of 420℃
and a velocity of 150 m/s. Saturated vapor at 100℃ exits with a velocity
of 90 m/s. At steady state, the turbine develops work equal 550 kJ per kg
of steam flowing through the turbine. Heat transfer between the turbine
and its surroundings occurs at an average outer surface temperature of 500K.
Determine the rate at which entropy is produced within the turbine,in
kJ/kg K. Neglect the change in potential energy between inlet and exit.
(15%)
2. An air compressor operating at steady state receives air at P1 = 1 bar and
T1 = 22℃. The ratio of the pressure at the exit to that at the inlet is 6.
Neglect heat transfer between the compressor and its surroundings, and
kinetic and potential energy changes between the inlet and the exit. If the
isentropic compressor efficiency is 80%, determine the temperature of the
air at the compressor exit. Use the ideal gas model for air. (15%)
3. Two kilograms of water undergo a process from an initial state where the
water is saturated vapor at 100℃, the velocity is 30 m/s, and the elevation
is 6 m to a final state where the water is saturated liquid at 10℃, the
velocity is 26 m/s, and the elevation is 3 m. Determine the change in
exergy. (15%)
closebook部分 (1hr)
4. Write down the Clausius and Kelvin-Planck statements of the second law of
thermodynamics and discuss the equivalence of these two statements. (10%)
5. Will the work requirement of an actual compression process be greater or
less than that of an isentropic one for the same initial and final
pressures? Explain the result with the help of a T-s diagram. (10%)
6. (a) Schematically draw the T-s and P-v diagrams of Otto cycle and explain
the processes of the cycle. (10%)
(b) Under the same compression ratio the efficiency of Otto cycle is higher
than that of Diesel cycle. Explain the situation with the help of a T-s
or h-s diagram. (10%)_
7. Explain the physical meanings of the following terms: (a) exergy, (b) Joule-
Thomson coefficient, and (c) isentropic efficiency. (5% @, 15% total)
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