課程名稱︰熱力學
課程性質︰必修
課程教師︰黃美嬌
開課學院：工學院
開課系所︰機械系
考試日期（年月日）︰11/11
考試時限（分鐘）：2hr(有延長但不確定延多久)
是否需發放獎勵金：是 謝謝
（如未明確表示，則不予發放）
試題 :
Q1. (15%) Explain in CHINESE and your own words the physical meanings of
(a) an intensive property, (b) the quality of a vapor-liquid mixture,
(c) a stationary simple compressible system, (d) a quasi-equilibrium
process, and (e) a path function.
Q2. (15%) Answer the following questions in CHINESE and your own words.
(a) Why do people compress the refrigerant in a refrigeration cycle
before it enters the condenser?
(b) What makes the difference between the specific heat at constant
volume from that at constant pressure?
(c) What is the so-called flow work?
Q3. (30%) A piston-cylinder device contains 40 kg of water at 3MPa and
350℃. The spring has a spring constant of 100 kN/m and is initially
compressed to certain extent. The piston has an area of 0.2m^2. Heat is
released from the system to its surrounding and the piston moves down.
When the volume decreases by an amount of 0.2m^3, the piston detaches
the linear spring. More heat is released until the piston hits a set of
stops at which point the cylinder contains saturated mixture with a
quality, (b) the total boundary work, and (c) the total heat transfer.
Make clear all your assumptions and the tables you use.
Q4. (20%) Air enters a turbine steadily at 650kPa, 1127℃, and a flow
rate of 40kg/s. After leaving the turbine at 877℃, air enters into a
nozzle and leaves it at a velocity of 1km/s. Estimate the heat loss from
the turbine and the air temperature at the nozzle exit if the efficiency
of the turbine is 0.75 and the heat lost of the nozzle is 65kW. Assume
the air is an ideal gas and use Table A-17. Make clear all your other
assumptions.
Q5. (20%) An insulated mixing chamber receives 2.2 kg/s R-134a at 1MPa,
80℃ in a line (state-4). Another line brings R-134a as saturated
mixture with a quality 0.1 at 70℃ (state-1), which is throttled to a
pressure of 1 MPa (state-2) before its liquid part (state-3) enters the
mixing chamber. At the exit (state-5) the temperature is 50℃. Determine
the mass flow rate passing through the throttling valve.
┬─┐ inlet ◢ ◣
︴ │ ↓◢ ◣
│ ︴ │ ◢air ◣
╞═╧═╡ turbine┌─nozzle →exit
│ │ ◥ │ ◤
╞ ╡ ◥ │ ◤
└─┼─┘ ◥ │ ◤ Q4.
↓Q └┘
Q3.
throttling ┌─→─
valve │vapor
１ ２ ┌┴┐
→─┼─⊕─┼→─┤ │
├─┤
└┬┘
liquid│３ ┌────┐
４ └┼→─┤ mixing │ ５
─→─┼────→───┤chamber ├─┼→
└────┘
Q5.
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