Semester Two 2020
Assessment Notice
Faculty of Engineering
ASSESSMENT DETAILS
Unit code(s)
MEC2405
Title of assessment
THERMODYNAMICS I
Assessment type
Take-Home Examination
Assessment duration
3 hours and 10 minutes
Materials required
Hardware/software to submit written or typed answers as a single PDF file for submission
ACADEMIC INTEGRITY
Intentional plagiarism or collusion amounts to cheating under Monash University Council Regulations (Part 7).
Plagiarism: Plagiarism means to take and use another person’s ideas and or manner of expressing them and to pass these off as one’s own by failing
to give appropriate acknowledgement, including the use of material from any source, staff, students or the internet, published and unpublished works.
Collusion: Collusion means unauthorised collaboration on assessable written, oral or practical work with another person. Where there are reasonable
grounds for believing that intentional plagiarism or collusion has occurred, this will be reported to the Associate Dean (Education) or nominee, who may
disallow the work concerned by prohibiting assessment or refer the matter to the Faculty Discipline Panel for a hearing.
During an assessment, you must not have access to any item/material that has not been listed in the materials required section above.
Student Statement:
● I have read the university’s Student Academic Integrity Policy and Procedures.
● I understand the consequences of engaging in plagiarism and collusion as described in Part 7 of the Monash University (Council)Regulations
(academic misconduct).
● I have taken proper care to safeguard this work and made all reasonable efforts to ensure it could not be copied. No part of this assessment
has been previously submitted as part of another unit/course.
● I acknowledge and agree that the assessor of this assessment may for the purposes of assessment, reproduce the assessment and:
i. provide to another member of faculty and any external marker; and/or
ii. submit it to a text matching/originality checking software; and/or
iii. submit it to a text matching/originality checking software which may then retain a copy of the assignment on its database for the purpose
of future plagiarism checking.
● I certify that in completing this assessment I have not plagiarised the work of others, participated in unauthorised collaboration or otherwise
breached the academic integrity requirements in the Student Academic Integrity Policy.
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In completing this assessment task you agree to the statements above. If you do not agree to the Student Statement, please submit directly to your
Unit Coordinator by the due date, providing a written explanation of which aspect of the Student Statement you do not agree with and why.
Instructions:
1. This assessment contains four (4) questions. You must attempt all four (4) questions – 100 marks are full
marks for the assessment.
2. This is an open book final assessment. To complete the questions, you may need to refer to property tables,
which can be found in the prescribed text book and are also available through the MEC2405 M oodle page,
as well as mathematical tables and any other resources that you choose to use such as Matlab, Mathematica,
python, etc. for analysis and to create any required graphs.
NOTE: You must reference all equations, properties, material, results and methods drawn from other
sources.
3. To gain full marks, you must include:
a. a problem statement
b. a fully annotated diagram and process diagram (if applicable)
c. list of assumptions
d. property values
e. governing equations/principles
f. show all your analytical working clearly
g. comment on your solution.
4. Write your answers in pen on plain or ruled A4 paper in a single-column format using legible writing.
5. Number and initial the top right corner of each page.
6. Scan or photograph your work in portrait format, ensuring the text is legible. Use the flash and a white
background if using a camera.
7. IMPORTANT: name your PDF file <Your Student Id Number>.pdf.
8. Upload your work as ONE SINGLE PDF FILE in portrait format to Moodle before the due time.
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Question 1 [25 marks]
Two rigid tanks A and B as shown in Fig. 1(a) are filled with H2O at different states and separated by a closed valve
as shown in Fig. 1(a) and denoted as State 1. The valve is now opened, and mixing is allowed between the H2O in
tank A and tank B. The temperature in both tanks is monitored during the mixing. Once the two temperatures in both
tanks no longer change and are equal to the temperature shown in Fig. 1(b) denoted as State 2, determine the
pressure of the H2O in the tanks and the heat transferred to the surroundings during the mixing process.
Fig. 1
Note: Showing final results or answers without detailed analytical work and explanations will receive no
marks. You must reference all equations, properties and other material drawn from other sources.
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Question 2 [25 marks]
(a) The Carnot heat engine gives the maximum possible efficiency of a heat engine working between two
reservoirs, TH and TL. With respect to the Carnot heat engine schematic shown in Fig. 2, show that the total
entropy change, ∆𝑆 for the Carnot heat engine is equal to zero.
State all assumptions and appropriate laws/principles clearly.
High temperature
reservoir, TH
Carnot
Heat
Engine
Wnet,out
Low temperature
reservoir, TL
Fig. 2
(b) The Carnot heat engine above with TH = 600 K and TL = 400 K, is used to drive a Carnot refrigerator. If the
same source energy, Q is provided for both the Carnot heat engine and Carnot refrigerator, determine the
maximum COP of refrigerator achievable.
Note: Showing final results or answers without detailed analytical work and explanations will receive no
marks. You must reference all equations, properties and other material drawn from other sources.
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Question 3 [25 marks]
Heat pumps are often used to heat households during winter, where heat losses can reach up to 50,000 kJ/hr. In the
heat pump, R-134a enters the compressor at 200 kPa and −10℃, and leaves at 1.2 MPa and 90℃ with the refrigerant
leaving the condenser at 28℃.
(a) Determine the power input to the heat pump (in kW).
(b) The actual compression process involves friction, and as such, a fan is used to force air over the
compressor to enable heat release to the ambient surroundings at 16 oC. Determine the specific heat
transfer (in kJ/kg), which is just enough to ensure an isentropic compression process of the compressor.
(c) To further improve the heat pump efficiency, the fan is now placed to blow air over the condenser instead,
resulting in an additional 20,000 kJ/hr heat release by the condenser. Determine the increase in COP
performance of the heat pump.
(d) Is the Clausius statement violated with the improvements made in part (d)? Explain briefly.
If the cost of electricity is $200/kW, determine the savings made using this heat pump in replacement to
using an electric resistance heater.
Note: Showing final results or answers without detailed analytical work and explanations will receive no
marks. You must reference all equations, properties and other material drawn from other sources.
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Question 4 [25 marks]
A feasibility study is being conducted to ascertain the characteristics of a solar thermal power plant in the Northern
Territory, which receives more than 2000 kWh/ annually in solar radiation. The planned solar thermal power
plant will have a 30 m central tower with a solar collector field of heliostats as shown in Fig. 3 yielding the heating
for a 500kW power system operating on a simple steam Rankine cycle. Each heliostat of the planned solar thermal
power plant has a solar collector surface of 9 .
The planned Rankine power cycle will use water pumped to 3.5 MPa before being heated by the concentrated
solar energy to superheated steam at 650 . The superheated steam will be expanded in the turbine to 41 kPa
before being cooled in the condenser to saturated water. If an efficiency of 70% is assumed for the effectiveness of
the solar heat transfer to heat the water, how many heliostats are required for the heliostat field? What is the
efficiency of the cycle and the heat rejection in the condenser? Comment on your proposal.
Fig 3. A typical solar thermal power plant arrangement showing the heliostats surrounding the solar collecting
tower that collects the solar radiation that is focussed towards the top of the tower.
Note: Showing final results or answers without detailed analytical work and explanations will receive no
marks. You must reference all equations, properties and other material drawn from other sources.
END OF EXAM
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