This document discusses the reversed Carnot cycle, which is used in Carnot refrigerators and heat pumps. It consists of four processes: 1) adiabatic compression, 2) isothermal compression, 3) adiabatic expansion, and 4) isothermal expansion. This cycle operates in the counterclockwise direction on a temperature-entropy diagram. It is the most efficient refrigeration cycle possible between two temperature levels, as it achieves the highest theoretical coefficient of performance. However, it cannot be practically implemented due to the different speeds required for the adiabatic and isothermal processes.

1. ““Start with the name of Allah Almighty who is the MostStart with the name of Allah Almighty who is the Most
Beneficent and Most Merciful.”Beneficent and Most Merciful.”

2. Ihsan Ali WassanIhsan Ali Wassan
Roll No:Roll No:
14CH1814CH18
Discipline:Discipline:
Chemical EngineeringChemical Engineering
Subject:Subject:
Chemical Engineering Thermodynamics-IIChemical Engineering Thermodynamics-II
Quaid-e-Awam University Of Engineering, Science andQuaid-e-Awam University Of Engineering, Science and
Technology, Nawabshah, Sindh PakistanTechnology, Nawabshah, Sindh Pakistan

4. Reversed Carnot CycleReversed Carnot Cycle
 Reversing the Carnot cycle does reverse the directions of
heat and work interactions.
 A refrigerator or heat pump that operates on the
reversed Carnot cycle is called a Carnot refrigerator or a
Carnot heat pump.
The reversed Carnot cycle is the most efficient
refrigeration cycle operating between two specified
temperature levels.
 It sets the highest theoretical COP.

5. Schematic of a Carnot Refrigerator
 (1-2) refrigerant absorbs heat
isothermally from a low temperature
source at TL in the amount of QL.
(2-3) refrigerant compressed to
state 3 (temperature rises to TH)
 (3-4) refrigerant reject heat to high
temperature at TH in the amount QH.
Refrigerant changes from saturated
vapor state to a saturated liquid state in
the condenser .
 (4-1) refrigerant expands adiabatically
to state 1(temperature drops to TL)

6. Schematic of a Carnot Refrigerator andT-S diagram of Reversed Carnot Cycle

7. Reversed Carnot CycleReversed Carnot Cycle
Consists of 4 processes
1. Adiabatic Compression
2. Isothermal Compression
3. Adiabatic Expansion
4. Isothermal Expansion

8.  (1-2) Adiabatic compression of
the working fluid with the aid of
external work.The temperature
of the fluid rises from T2 to T1.
 (2-3) Isothermal compression of
the working fluid during which
heat is rejected at constant high
temperature T1.
 (3-4) Adiabatic expansion of the
working fluid. The temperature of
the working fluid falls from T2 to
T1.
 (4-1) Isothermal expansion of air
where heat is absorbed at low
temperature T2 from the space
being cooled.
Reversed Carnot CycleReversed Carnot Cycle
Q1
Q2
T1
T2
Adiabatic
Comp
Adiabatic
Exp
Isothermal
Comp
Isothermal
Exp
Q1
Q2

9. Reversed Carnot CycleReversed Carnot Cycle
 The result is a cycle
that operates in the
counterclockwise
direction on T-S
diagram, which is
called the Reversed
Carnot Cycle.

10. COP of RefrigeratorCOP of Refrigerator
Heat absorbed Q2 = T2ds
Heat rejected Q1 = T1ds
Work input = Heat Rejected – Heat Absorbed
= Q1- Q2 = T1ds - T2ds =(T1-T2)ds
COPR = cooling effect = QL = Q2 = T2ds
work input Wnet.in Q1- Q2 (T1-T2)ds

11. Point to remember ….!Point to remember ….!
Practically, the reversed Carnot cycle cannot
be used for refrigeration purpose as the
adiabatic process requires very high speed
operation, whereas the isothermal process
requires very low speed operation.

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