EXAMINATION PAPER:  ACADEMIC S ES S ION 2020/2021

Campus	Medway
Faculty	Engineering & Science
Level	5
Exam Session	May 2021
MODULE CODE	MECH061
MODULE TITLE	THERMODYNAMICS
Exam Type	Online Exam

Original Exam Duration 2 hours (Now 3 hours)

 

 

 Instructions to Candidates

 

Answer AL L questions from PART A  - Moodle Quiz (separate)

Answer AL L questions from PART B  

Answer ALL questions from PART C

 

S team tables and calculators may be used.

Students will be required to achieve an overall grade of 40% to achieve a pass grade

 

Type the answers to all questions attempted in the exam into this document using a computer- based text editing software such as MS Word and for equations the equation editor.  

PartA

ANSWER(Purchase full paper to get all the solution)

1. C
2. Since the fluid does not pass through a cycle, so the internal combustion engine is often referred to as an “open cycle device”
3. A
4. This is because polytropic process is a thermodynamic process that obeys the relation  and it is a reversible process on any open and closed system.
5. C

The working fluid is pushed through the system and undergoes states changes. The refrigerant enters the compressor as a gas under low pressure and having a low temperature.

PART B

Answer AL L questions in Part B

 

Q6.

 

An ideal Rankine cycle has the following operating conditions.  Steam enters the turbine at 50 bar and 500oC and exhausts to the condenser at pressure of 0.1 bar if the turbine output is 12,000 kW

 

1. Sketch the Rankine cycle in a T- s diagram and define the four stages. 
   4. marks]

 

2. Discuss how does the actual Rankine cycle differ from the ideal Rankine cycle.
   4. marks]

 

3. Calculate the quality of steam and the enthalpy at the turbine outlet. 

                                                                                                                                                                                           [8 marks]

 

 

4. Determine the heat input and heat rejected per unit mass.

                                                                                                                                                                                           [6 marks]

 

5. Calculate the thermal efficiency of the Rankine power cycle.
   4. marks]

 

6. Find the mass flow rate of steam in kg/h flowing through the turbine. 
   4. marks]

 [Total 30 marks]

Q7.

A stationary gas- turbine power plant operates on a simple ideal Brayton cycle with air as the working fluid. The air enters the compressor at 100 kPa and 300 K and the turbine at 2000 kPa and 1000 K temperature. Take cp  = 1.005 kJ /kg- K  and  k = 1.4  

 

1. Describe the four process stages of a simple ideal Brayton cycle; include the block or T- s (temperature entropy) diagram. 

                                                                                                                                                                                           [6 marks]

 

2. Describe the meaning the term back- work ratio in gas turbines and provide a value for a back- work ratio typically found in gas- turbine engines. 

                                                                                                                                                                                         [ 4 marks]

 

3. Calculate the network output of the gas turbine (use information provided above Q7) and state clearly all assumptions made for your calculations. 

                                                                                                                                                                                         [10 marks]

 

4. Calculate the thermal efficiency of the Bryton gas turbine cycle using the values from calculation. 

                                                                                                                                                                                           [4 marks]

             

5. S how graphically the differences between an open and a closed Bryton cycle (include the labelling of the stages of the gas turbine cycle) and discuss the differences. 

                                                                                                                                                                                          [ 6 marks]

 [Total 30 marks]

  

PART C

Answer AL L questions in PART C

 

Q8.

Define entropy and enthalpy and state the units (include the difference between the first law of thermodynamics and the second law of thermodynamics) 

                                                                                                                                                                                          [4 marks]

Q9.

Draw a P- v diagram of a simple Otto cycle, label the four stages and describe the states of the process. 

  [4 marks]

Q10.

Draw a block diagram of a simple Refrigeration cycle and indicate at which stage work is added to the system; discuss why energy needs to be added. 

                                                                                                                                                                                          [4 marks]

Q11.

Draw a block diagram of a two stage (high pressure/ low pressure) turbine and explain why this turbine type is more efficient than a single stage turbine.

                                                                                                                                                                                          [4 marks]

Q12.

Draw a process flow diagram of a heat exchanger in counter current flow, indicate the direction of the process streams and discuss why the counter current flow heat exchanger is more efficient than the parallel flow heat exchanger.

                                                                                                                                                                                          [4 marks]

 [Total 30 marks]

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Last updated: Jun 23, 2021 10:59 AM

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