課程名稱︰熱力學
課程性質︰必修
課程教師︰陳瑤明
開課學院：工學院
開課系所︰機械系
考試日期（年月日）︰2014/1/9
考試時限（分鐘）：120min
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
(附Table:saturated refrigerant-134a-Pressure + Superheated refrigerant-134a )
(配分每大題20%)
1.Please answer the following questions:
(1)What are the Kelvin-Planck and Clausius expressions of the second law
of thermodynamics?
(2)What's entropy? What's its physical significance?
(3)What's exergy? How is it defined?
(4)What's Rankine cycle? How can you improve its thermal efficiency?
(5)How can you select the right refrigerant for a vapor-compression
refrigeration cycle?
2.Air is compresses steadily by a reversible compressor from an inlet state
of 100 kPa and 300K to an exit pressure of 900kPa. Determine the compressor
work per unit mass for (1)isentropic compression with k=1.4
(2)polytropic compression with n=1.3
(3)isothermal compression, and ideal two-stage compression with intercooling
with a polytropic exponent of 1.3.
Ideal gas with constant specific heats can be assumed. The properties of air
at room temperature are:Cp=1.005kL/kgK, Cv=0.718kJ/kgK, R=0.287kJ/kgK, k=1.4
3.What is a Carnot cycle? Illustrate on a P-Vdiagram and an S-Tdiagram. Derive
the efficiency of an engine using the Carnot cycle. (You can assume the
cycle is reversible and the gas used is an ideal gas.)
4.An ideal Diesel cycle has a compression ratio of 20 and a cutoff ratio of
1.3. Determine the maximum temperature of the air and the rate of heat
addition to this cycle when it produces 250kW of power and the state of the
air at the beginning of the compression is 90kPa and 15*C. Use constant
specific heats at room temperature. The properties of air at room
temperature are:(as the end of question 2 provided.)
5.A refrigerator operating on the vapor-compression refrigeration cycle using
refrigerant-134a as the refrigerant is considered. The temperature of the
cooled space and the ambient air are at-13*C and 27*C, respectively. R-134a
enters the compressor at 140kPa as a saturated vapor and leaves at 1MPa and
70*C. The refrigerant leaves the condenser as a saturates liquid. The rate
of cooling provided by the system is 13kW. Determine (1)the mass flow rate
of R-134a and the COP, (2)the exergy destruction in each component of the
cycle and the exergy efficiency of the compressor, and (3)the second-law
efficiency of the cycle.
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