““Start with the name of Allah Almighty Start with the name of Allah Almighty who is the Most Beneficent and Most who is the Most Beneficent and Most

Merciful.”Merciful.”

Ihsan Ali WassanIhsan Ali WassanRoll No:Roll No:

14CH1814CH18Discipline:Discipline:

Chemical Engineering Chemical Engineering

Subject:Subject:Chemical Engineering Thermodynamics-IIChemical Engineering Thermodynamics-II

Quaid-e-Awam University Of Engineering, Quaid-e-Awam University Of Engineering, Science and Technology, Nawabshah, Sindh Science and Technology, Nawabshah, Sindh

Pakistan Pakistan

Reversed Carnot Reversed Carnot CycleCycle

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.

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)

Schematic of a Carnot Refrigerator and T-S diagram of Reversed Carnot Cycle

Reversed Carnot CycleReversed Carnot CycleConsists of 4 processes 1. Adiabatic Compression2. Isothermal Compression3. Adiabatic Expansion4. Isothermal Expansion

(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

AdiabaticComp

Adiabatic Exp

IsothermalComp

IsothermalExp

Q1

Q2

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.

COP of Refrigerator COP of Refrigerator Heat absorbed Q2 = T2dsHeat 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

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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