[試題] 101上 陳瑤明 熱力學 期末考
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）︰2013.1.10
考試時限（分鐘）：110分
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
1.Please answer the following questions:
(a)Define entropy and exergy. Give also their physical meaning.
(b)What are the precesses that make up the Carnot, Stirling and Ericsson
cycles? Sketch the T-s and P-v diagrams.
(c)What is an ideal vapor-compression refrigeration cycle? When selecting a
refrigerant for a certain application, what qualities would you look for in
the refrigerant?
(d)Propose methods to increase the efficiency of the Rankine cycle?
2.The thermal efficiency η of a cold air-standard diesel cycle can be
expressed by k
r - 1
1 ┌ c ┐
η=1-───│─────│
k-1 └ k(r - 1) ┘
r c
where r is compression ratio and r is cutoff ratio and k is the specific
heat ratio. Derive this expression.
3.(a)Consider a simple Brayton cycle using air as the working fluid; has a
pressure ratio of 12;has a maximum cycle temperature of 600°C; and
operates the compressor inlet at 90kPa and at 15°C. Which will have the
greatest impact on the back-work ratio:a compressor is isentropic
efficiency of 90% or a turbine isentropic efficiency of 90%? The
properties of air at room temperature are C = 1.005kJ/kg·K and k=1.4
p
(b)Repeat problem (a) using exergy analysis.
Q
↙ in
→ ┌──┐ →
┌──┤ ├──┐
│ └──┘ │
▕╲│ ｜╱︳Turbine
▕ ╲ ╱ ︳ W
Compressor▕ ▕================︳ ╞=→
▕ ／ ╲ ︳
▕／│ ｜╲︳
│ ┌──┐ │↓
└──┤ ├──┘
← └──┘
↙
Q
out
4.A 200 m^3 rigid tank initially contains atmospheric air at 100kPa and 300K
and is to be used as storage vessel for compressed air at 1MPa and 300K.
Compressed air is to be supplied by a compressor that makes in atmospheric
air at P_0 = 100KPa and T_0 = 300K. Determine the minimum work required for
this process. The gas constant of air is R=0.287 kJ/kg·K.
┌──────┐
│ Air │
│ 3 │
│ V=200m │
│ │
│ 100kPa │ Compressor
│ ↓ │ ↙
│ 1MPa ╞═╤═╗
│ │ ║ ║
│ 300K │ ╙═╣
└──────┘ ║
↖100kPa 300K
5.A simple Rankine cycle uses water as the working fluid. The boiler operates
at 6000kPa and the condencer at 50 kPa. At the entrance to the turbine, the
temperature is 450°C. The isentropic efficiency of the turbine is 94%,
pressure and pump losses are negligible, and the water leaving the condencer
is subcooled by 6.3°C. The boiler is sized for a mass flow rate os 20 kg/s.
Determine the rate at which heat is added in the boiler, the power required
to operate the pumps, the net power produced by the cycle, and the thermal
efficiency.
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 140.112.252.203
推
01/12 15:48, , 1F
01/12 15:48, 1F
推
12/25 22:53, , 2F
12/25 22:53, 2F