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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 .
Course Hero
w throttling_dev
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
valve is an adiabatic throttling process; the compressor is
adiabatic and reversible. The evaporator is a heat exchanger.
The following states are given
1: saturated liquid at T, = 39.3 .C
3: saturated vapour at T3 = -10 C
(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.
(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
1, Phillip J.

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