4. (a) Draw a P-V diagram of a real refrigerator that uses 1 kgof HFC-134a as the working fluid.
Identify the compressor. condenser. throttle and the evaporatorstages of the cycle and indicate
where heat Qc, is extracted from the cold refrigerator and where.Qa is released to the
environment. Also indicate where the refrigerant is in liquid. gas.or a mixed phase.
(b) Show that the COP = Qc(Qh -Qc) can be expressed in terms ofthe enthalpies at three points of the
cycle, explaining all steps of the derivation.
