《工程热力学》课程考试模拟试卷英文版

工程热力学试卷(120 minutes)

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Section A: Please select true (fill T in the blank) or false (fill F in the blank) of the following statements. (6×3)

( ) 1. Heat can be transferred from a lower temperature body to a higher one.

( ) 2. From state 1 to state 2, a system undergoes a reversible process and a irreversible process separately. The entropy change from 1

to 2 in the irreversible process must be larger than that in the

reversible process.

( ) 3. During a simple heating process of atmospheric air, the specific humidity of air will keep no change.

( ) 4. Absolute pressure and vacuum pressure can not be used as the properties of a system.

( ) 5. The efficiency of an reversible cycle must be higher than that of a irreversible cycle.

( ) 6. It’s impossible for a system to output work in a constant volume process.

Section B: Answer the following questions (8×5)

1)Please state out the following formula’s condit ion:

δ

q+

=

du

)

(pv

d

2)An ideal motor steadily drives a fan. Take the motor as thermodynamics

system. Please point out whether the heat and work of the motor is positive, negative or zero.

3)What is the main difference between quasi-equilibrium process and

reversible process?

4)Please use diagrams to illustrate the influence of inlet temperature and

inlet pressure on the efficiency of a Rankine cycle.

5)An isolated rigid tank is divided into two parts by a board. The right part

is filled with high pressure ideal gas and the left part is vacuum. If the board is taken away, the gas will fill the whole tank. What will happen to the temperature of the gas? Why?

6)Please state out the harmfulness of the clearance volume to a

reciprocating compressor.

7)Could a divergent tube be used as nozzle? Why?

8)If the maximum temperature at the inlet of gas turbine is limited, what

will happen to a Bryton cycle while the pressure ratio increased? Section C: Drawing

1.( 8 ) Please show an absorbtion refrigeration system in a sketch and point

out the name of each equipment.

2. ( 6 ) Please draw a vapor compressing refrigeration cycle on a h-s chart. Section D: Calculation

(10) An ideal gas power cycle. The air is compressed adiabatically from state

1 (p1＝1.01bar、t1 =15℃、V l＝0.014m3) to state

2 (V2=0.0028m3). After this,

heated at constant volume to state 3 (p3=18.5bar). Then expand adiabatically to state 4 (p4=1.01bar). Finally, the air back to state 1 at constant pressure. Please calculate:

(1) The net work of this cycle.

(2) The efficiency of this cycle.

(R=287 J/kg.K k=1.4 take c p, c v as constant)

(8) Please use the second law of thermodynamics to demonstrate it is

impossible for two isentropic lines cross each other.

(10) There is a two-stage regenerative Rankine cycle. The enthalpy of each

point has been marked out. If the pump work can be neglected, please calculate the efficiency of this cycle.