Efficiency of a Heat Engine
A heat engine is a device which is used to convert heat into work. Efficiency of a heat engine is defined as the ratio of its work output and heat input.
Efficiency of a Heat Engine = Work output/ Heat input
η = (Q1-Q2)/Q1 = 1 – (Q2/Q1)
For a reversible heat engine:
Q2/Q1 = T2/T1
For understanding above relation refer: Absolute thermodynamic scale of temperature
Hence for a reversible heat engine
ηREV = 1- (T2/T1)
Coefficient of Performance (COP) of Heat pump and Refrigerator
When we use this device to remove heat then it is called a refrigerator and when we use this device to obtain heat then it is called a heat pump.
Coefficient of Performance (COP) is defined as the ratio of desired effect to work input.
COP = Desired effect/ Work input
In case of heat pump this desired effect is heating and in case of refrigerator this desired effect is cooling.
- COP of a Heat Pump
COPHP = Q1/Q1-Q2
COP for a reversible Heat Pump
COPHP REV = T1/T1-T2
- COP of a Refrigerator
COPREF = Q2/Q1-Q2
COP for a reversible Refrigerator
COPREF REV = T2/T1-T2
By comparing COPs of Heat pump and Refrigerator we can easily observe that
COPHP = 1 + COPREF