代写CENG0004 Thermodynamics代写Java编程

CENG0004

CENG0004A4UA

Thermodynamics

24 April 2019

Answer ALL questions.

Make sure to include units in your answers

Each question carries marks distributed as shown

Data:

R = 8.314 J mor1 K1

1. a) Consider two piston-cylinder arrangements containing a gas at the same initial temperature and pressure. The gas is compressed to a final pressure either isothermally (A) or adiabatically (B).State which of the two compression paths will result in a higher final gas temperature? Explain your answer briefly.

b) Air in a piston-cylinder is initially at 25 °C and 5 bar. The piston, which weighs 2 kg, is initially locked in place. When the locks are removed, the piston moves until the pressure is 2 bar. The final temperature is 25 °C. Is there heat transfer in this process? Explain your answer briefly.

c) Two piston-cylinder arrangements are at the same pressure. Cylinder 1 contains saturated liquid water and cylinder 2 contains the same mass of saturated water vapour. 1 kJ of heat is very slowly removed from each container at constant pressure. It is proposed that the entropy of water in cylinder 2 decreases more than the entropy of water in cylinder 1. Is this correct? Explain your answer briefly.

d) Consider an adiabatic steam turbine operating at steady state. Will the temperature of steam passing through the turbine increase or decrease during the process?

Explain your answer briefly.

2. Steam at 450 bar and 400 °C is adiabatically and reversibly expanded to 1 bar through a turbine in a steady-state process.

a) What will be the temperature of the steam after expansion?

b) What will be the fraction of vapour at the exit stream?

c) If steam was replaced by a diatomic ideal gas, what would be the exit temperature?

You may use the steam tables provided.

3. a) Starting from the energy balance for an open system, show that the outlet temperature, T2, of an ideal gas undergoing adiabatic and reversible expansion or compression can be related to its inlet temperature, T1, inlet pressure, P1, and outlet pressure, P2, according to the following expression:

where c; is the specific heat capacity of the ideal gas and R is the universal gas constant. State your assumptions clearly.

b) Argon, which is a monoatomic gas, is expanded adiabatically and reversibly from 400 K and 40 bar to 2 bar in a steady-state turbine. Assuming Argon is an ideal gas, calculate:

i) the outlet temperature of Argon

and

ii) the work done per mole by the turbine.

4. a) Using the fundamental principles of thermodynamics, show that it is not possible to construct a device that:

i) operates in a cycle and whose sole effect is to transfer heat from a cold object to another hotter object as shown in Figure Q.4a.

Figure Q.4a: A schematic representation of the Clausius device which operates in a cycle to transfer heat from a cold object to another hotter object.

(T is temperature and Q is heat transferred.)

and

ii) operates in a cycle which results in no effect other than the production of work by transferring heat from a single body as shown in Figure Q.4b.

Figure Q.4b: A schematic representation of the Kelvin-Planck device which operates in a cycle that results in no effect other than the production of work by transferring heat from a single body. (Q is heat transferred, W is work and T is temperature.)

b) 300 kJs·1 of heat is supplied at a constant temperature of280 °C to a heat engine. The heat rejection takes place at 9 °C. What would be the heat rejection rate if the heat engine were to operate reversibly?

5. Methane is to be compressed from 0.2 MPa and 200 K to 10 MPa in a two stage compressor which operates adiabatically and reversibly. In between the two compression stages, a heat exchanger returns the methane back to its initial temperature. The intermediate pressure is 2 MPa.

a) What is the work required in the first stage compressor?

b) What is the temperature at the exit of the first compressor?

c) What is the cooling duty of the interstage cooler?

d) What is the final temperature of methane?

Use the Pressure-Enthalpy diagram for methane provided ( on the final page of the exam paper), and clearly indicate the thermodynamic trajectories you have followed to perform. your calculations. Make sure to hand in your entire exam paper with your answer booklet.