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ENGINEERING THERMODYNAMICS
SCEE08006
Please read full instructions before commencing writing
Exam paper information
• This exam paper consists of THREE questions.
• Candidates should attempt ALL THREE questions.
• Students are permitted to bring the following textbook: Borgnakke and
Sonntag: Fundamentals of Thermodynamics & an ETO Exam Copy of the
Thermodynamics Tables & 1 x A4 sheet of paper with notes (front and back).
Special instructions
• Students should assume reasonable values for any data not given in a
question nor available on a datasheet, and should make any such assumptions
clear on their script.
• Students in any doubt as to the interpretation of the wording of a question,
should make their own decision, and should state it clearly on their script.
• Please write your name in the space indicated at the right hand side on the
front cover of the answer book. Also enter your examination number in the
appropriate space on the front cover.
• Write ONLY your examination number on any extra sheets or worksheets used
and firmly attach these to the answer book(s).
• This examination will be marked anonymously.
Special items
• None
Question 1
A cylinder is divided into two compartments by a frictionless piston as shown in Figure Q1.
Compartment A initially contains 0.1 kg air at P1A = 100 kPa, T1A = 300 K. Compartment B
initially contains water as a saturated liquid and the piston is in equilibrium. Heat is added to
the water in compartment B. As the piston moves, the air pressure increases linearly with the
displaced volume (i.e. P = C∙V). Heat is added until the water reaches a saturated vapor at
which point the air reaches P2A = 700 kPa, T2A = 350 K as the piston is in equilibrium.
Assume that the air behaves as an ideal gas with constant specific heats CV = 0.717 kJ/kgK
and R = 0.287 kJ/kgK.
a) Draw this process for the water on the P-V diagram. Please include the
saturated liquid-vapor dome. (4)
b) Determine the work performed (in kJ) on the air. (4)
c) Determine the mass of the water (in kg) in compartment B. (4)
d) Determine the heat added to the water (in kJ). (4)
e) Is there any heat transfer between the air and the surroundings? If so,
determine Qair (in kJ). (4)
Figure Q1
Please Turn Over
SCEE08006 Engineering Thermodynamics 2 – May 2018
Question 2
A laboratory requires compressed air at 500 kPa with a maximum temperature of 30oC to
operate experiments. This air is to be supplied by installing a compressor and chiller unit as
shown in Figure Q2. Air is drawn into the compressor at local ambient conditions of 100 kPa
and 20oC. After compression the air enters a chiller unit where it is cooled down to 30oC while
maintaining constant pressure. The compressor is adiabatic and reversible. Air can be
treated as an ideal gas with constant specific heats: CP = 1.004 kJ/kgK, R = 0.287 kJ/kgK,
and k = 1.4.
a) Determine the mass flow rate of air (in kg/s) if the electrical work
delivered to the compressor is 140 kW. (4)
b) Determine the rate of heat rejection (in kW) at this mass flow rate. (4)
c) If the heat from the chiller is given off to the outside air at 20oC,
determine the rate of entropy generation (in kW/K) associated with the
chiller unit. (4)
d) Now assume that the compressor has an isentropic efficiency of 85%.
If the air mass flow rate and heat rejection in the chiller are
unchanged, determine the temperature of the air delivered to the
laboratory due to this isentropic efficiency. (4)
e) Due to this isentropic efficiency, will the heat rejection from the chiller
need to increase or decrease in order to deliver the laboratory air at
30oC? (4)
Figure Q2
Please Turn Over
SCEE08006 Engineering Thermodynamics 2 – May 2018
Question 3
Consider an Atkinson cycle, a current topic of research, which is similar to the Otto cycle with
minor modifications. Instead of the piston starting the compression process at its bottom-most
position, the intake valves remain open as the piston moves upwards such that the
compression process does not take place over the entire piston displacement. This provides
a higher expansion ratio (v4/v3) than compression ratio (v1/v2). The higher expansion ratio
allows more work to be extracted such that the efficiency is higher than the Otto cycle.
The processes associated with the ideal Atkinson cycle are described below. The Atkinson
cycle is shown schematically in Figure Q3a and the P-v diagram is show in Figure Q3b.
Process 1-2: Isentropic compression: compression begins mid-way through the piston’s travel
(i.e. v1 < vmax).
Process 2-3: Constant volume, heat addition: fuel adds in heat energy (q23) into the system at
constant volume (i.e. same as Otto cycle).
Process 3-4: Isentropic expansion: expansion occurs between the entire piston displacement
(vmax – vmin).
Process 4-1: Constant pressure, heat rejection: heat is rejected at constant pressure as the
piston moves from v4 to v1.
Assume an Aktinson cycle with P1 = 100 kPa, T1 = 300K. The cycle has a compression ratio
(v1/v2) of 9 and fuel adds heat release of q23 = 1000 kJ/kg. Assume air as the working fluid
with constant specific heats (Cv = 0.717 kJ/kgK, CP = 1.004 kJ/kgK, R = 0.287 kJ/kgK,
k = 1.4).
a) Determine the maximum temperature within the cycle. (4)
b) Determine the maximum pressure within the cycle. (4)
c) Determine the expansion ratio (v4/v3). (4)
d) Determine the cycle efficiency. (6)
e) List one irreversibility that would reduce the efficiency of Atkinson cycle
from the ideal cycle described above.
