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B Chap 4 - Prob Sugg
C 5. (15 Marks Total) A.
B) Exemples d'examen f
B) Final Fall 2013 - MCG.
: Final Fall 2013 - Solut .
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A
8 December 2013
Page 2 of 6
4. (17 marks total) The sketch shows a standard
refrigeration cycle using R134a as the working fluid. The
QH
valve is an adiabatic throttling process; the compressor is
adiabatic and reversible. The evaporator is a heat exchanger.
condenser
The following states are given
expansion
W
valve
1: saturated liquid at T, = 39.3 .C
3: saturated vapour at T3 = -10 C
evaporator
compressor
3
(a) (2 mark) State the pressures at point 2 and 4 and sketch
I Qc
the processes for the valve, evaporator and compressor on
a T-s diagram.
(b) (3 marks) Calculate the state (temperature or quality, whichever is appropriate) at the outlet of
the expansion valve, point 2.
(c) (2 marks) Calculate the heat transfer in the evaporator in kJ/kg.
(d) (5 marks) Determine the compressor work in kJ/kg and the compressor outlet temperature T4.
(e) (3 marks) Calculate the coefficient of performance of the cycle and compare it to that of a Carnot
cycle working between a hot reservoir at TH = T, and a cold reservoir at Tc = T3 .
(f) (2 marks) If the the refrigerant mass flow is 0.1 kg/s, determine the diameter of pipe required at
point 3 if the flow velocity entering the compressor is to be V, = 10 m/s.
5. (6 marks total) Steam in a cylinder fitted with a frictionless piston expands in a reversible
isothermal process from an initial state of P, = 1000 kPa with a quality x, = 0.95 to a final pressure
of 300 kPa. Calculate the work done and the heat transfer in kJ/kg.
6. (12 marks total) An insulated container holds two volumes of air
separated by a partition. Volume A initially contains 0.1 m' at PAI =
300 kPa and TAI = 120 C, while volume B initially contains 0.1 m3
at PBI = 100 kPa and TB1 = 150 C. The partition is then removed and
the two volumes mix until a uniform state is achieved.
B
(a) (6 marks) Determine the final temperature and pressure.
(b) (6 marks) Determine the change in the entropy of the system and
of the surroundings, assuming that the surroundings are at 20 C.
+
What does this change indicate about the process?
You may assume that air is an ideal gas with constant specific heats.
Total marks for this paper: 60
. Reflect in ePortfolio
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1, Phillip J.
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